Merge branch 'master' of github.com:grpc/grpc into compression-accept-encoding

53 files changed, 1640 insertions, 500 deletions

diff --git a/src/csharp/Grpc.Core/AsyncClientStreamingCall.cs b/src/csharp/Grpc.Core/AsyncClientStreamingCall.cs
index bf020cd627..dbaa3085c5 100644
--- a/src/csharp/Grpc.Core/AsyncClientStreamingCall.cs
+++ b/src/csharp/Grpc.Core/AsyncClientStreamingCall.cs
@@ -44,14 +44,16 @@ namespace Grpc.Core
     {
         readonly IClientStreamWriter<TRequest> requestStream;
         readonly Task<TResponse> responseAsync;
+        readonly Task<Metadata> responseHeadersAsync;
         readonly Func<Status> getStatusFunc;
         readonly Func<Metadata> getTrailersFunc;
         readonly Action disposeAction;
 
-        public AsyncClientStreamingCall(IClientStreamWriter<TRequest> requestStream, Task<TResponse> responseAsync, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
+        public AsyncClientStreamingCall(IClientStreamWriter<TRequest> requestStream, Task<TResponse> responseAsync, Task<Metadata> responseHeadersAsync, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
         {
             this.requestStream = requestStream;
             this.responseAsync = responseAsync;
+            this.responseHeadersAsync = responseHeadersAsync;
             this.getStatusFunc = getStatusFunc;
             this.getTrailersFunc = getTrailersFunc;
             this.disposeAction = disposeAction;
@@ -69,6 +71,17 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// Asynchronous access to response headers.
+        /// </summary>
+        public Task<Metadata> ResponseHeadersAsync
+        {
+            get
+            {
+                return this.responseHeadersAsync;
+            }
+        }
+
+        /// <summary>
         /// Async stream to send streaming requests.
         /// </summary>
         public IClientStreamWriter<TRequest> RequestStream
@@ -89,6 +102,24 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// Gets the call status if the call has already finished.
+        /// Throws InvalidOperationException otherwise.
+        /// </summary>
+        public Status GetStatus()
+        {
+            return getStatusFunc();
+        }
+
+        /// <summary>
+        /// Gets the call trailing metadata if the call has already finished.
+        /// Throws InvalidOperationException otherwise.
+        /// </summary>
+        public Metadata GetTrailers()
+        {
+            return getTrailersFunc();
+        }
+
+        /// <summary>
         /// Provides means to cleanup after the call.
         /// If the call has already finished normally (request stream has been completed and call result has been received), doesn't do anything.
         /// Otherwise, requests cancellation of the call which should terminate all pending async operations associated with the call.
diff --git a/src/csharp/Grpc.Core/AsyncDuplexStreamingCall.cs b/src/csharp/Grpc.Core/AsyncDuplexStreamingCall.cs
index 0979de606f..ee7ba29695 100644
--- a/src/csharp/Grpc.Core/AsyncDuplexStreamingCall.cs
+++ b/src/csharp/Grpc.Core/AsyncDuplexStreamingCall.cs
@@ -32,7 +32,6 @@
 #endregion
 
 using System;
-using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
 
 namespace Grpc.Core
@@ -44,14 +43,16 @@ namespace Grpc.Core
     {
         readonly IClientStreamWriter<TRequest> requestStream;
         readonly IAsyncStreamReader<TResponse> responseStream;
+        readonly Task<Metadata> responseHeadersAsync;
         readonly Func<Status> getStatusFunc;
         readonly Func<Metadata> getTrailersFunc;
         readonly Action disposeAction;
 
-        public AsyncDuplexStreamingCall(IClientStreamWriter<TRequest> requestStream, IAsyncStreamReader<TResponse> responseStream, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
+        public AsyncDuplexStreamingCall(IClientStreamWriter<TRequest> requestStream, IAsyncStreamReader<TResponse> responseStream, Task<Metadata> responseHeadersAsync, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
         {
             this.requestStream = requestStream;
             this.responseStream = responseStream;
+            this.responseHeadersAsync = responseHeadersAsync;
             this.getStatusFunc = getStatusFunc;
             this.getTrailersFunc = getTrailersFunc;
             this.disposeAction = disposeAction;
@@ -80,6 +81,17 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// Asynchronous access to response headers.
+        /// </summary>
+        public Task<Metadata> ResponseHeadersAsync
+        {
+            get
+            {
+                return this.responseHeadersAsync;
+            }
+        }
+
+        /// <summary>
         /// Gets the call status if the call has already finished.
         /// Throws InvalidOperationException otherwise.
         /// </summary>
diff --git a/src/csharp/Grpc.Core/AsyncServerStreamingCall.cs b/src/csharp/Grpc.Core/AsyncServerStreamingCall.cs
index 380efcdb0e..2853a79ce6 100644
--- a/src/csharp/Grpc.Core/AsyncServerStreamingCall.cs
+++ b/src/csharp/Grpc.Core/AsyncServerStreamingCall.cs
@@ -32,7 +32,6 @@
 #endregion
 
 using System;
-using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
 
 namespace Grpc.Core
@@ -43,13 +42,15 @@ namespace Grpc.Core
     public sealed class AsyncServerStreamingCall<TResponse> : IDisposable
     {
         readonly IAsyncStreamReader<TResponse> responseStream;
+        readonly Task<Metadata> responseHeadersAsync;
         readonly Func<Status> getStatusFunc;
         readonly Func<Metadata> getTrailersFunc;
         readonly Action disposeAction;
 
-        public AsyncServerStreamingCall(IAsyncStreamReader<TResponse> responseStream, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
+        public AsyncServerStreamingCall(IAsyncStreamReader<TResponse> responseStream, Task<Metadata> responseHeadersAsync, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
         {
             this.responseStream = responseStream;
+            this.responseHeadersAsync = responseHeadersAsync;
             this.getStatusFunc = getStatusFunc;
             this.getTrailersFunc = getTrailersFunc;
             this.disposeAction = disposeAction;
@@ -67,6 +68,17 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// Asynchronous access to response headers.
+        /// </summary>
+        public Task<Metadata> ResponseHeadersAsync
+        {
+            get
+            {
+                return this.responseHeadersAsync;
+            }
+        }
+
+        /// <summary>
         /// Gets the call status if the call has already finished.
         /// Throws InvalidOperationException otherwise.
         /// </summary>
diff --git a/src/csharp/Grpc.Core/AsyncUnaryCall.cs b/src/csharp/Grpc.Core/AsyncUnaryCall.cs
index 224e343916..154a17a33e 100644
--- a/src/csharp/Grpc.Core/AsyncUnaryCall.cs
+++ b/src/csharp/Grpc.Core/AsyncUnaryCall.cs
@@ -43,13 +43,15 @@ namespace Grpc.Core
     public sealed class AsyncUnaryCall<TResponse> : IDisposable
     {
         readonly Task<TResponse> responseAsync;
+        readonly Task<Metadata> responseHeadersAsync;
         readonly Func<Status> getStatusFunc;
         readonly Func<Metadata> getTrailersFunc;
         readonly Action disposeAction;
 
-        public AsyncUnaryCall(Task<TResponse> responseAsync, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
+        public AsyncUnaryCall(Task<TResponse> responseAsync, Task<Metadata> responseHeadersAsync, Func<Status> getStatusFunc, Func<Metadata> getTrailersFunc, Action disposeAction)
         {
             this.responseAsync = responseAsync;
+            this.responseHeadersAsync = responseHeadersAsync;
             this.getStatusFunc = getStatusFunc;
             this.getTrailersFunc = getTrailersFunc;
             this.disposeAction = disposeAction;
@@ -67,6 +69,17 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// Asynchronous access to response headers.
+        /// </summary>
+        public Task<Metadata> ResponseHeadersAsync
+        {
+            get
+            {
+                return this.responseHeadersAsync;
+            }
+        }
+
+        /// <summary>
         /// Allows awaiting this object directly.
         /// </summary>
         public TaskAwaiter<TResponse> GetAwaiter()
diff --git a/src/csharp/Grpc.Core/CallInvocationDetails.cs b/src/csharp/Grpc.Core/CallInvocationDetails.cs
index eb23a3a209..6565073fc5 100644
--- a/src/csharp/Grpc.Core/CallInvocationDetails.cs
+++ b/src/csharp/Grpc.Core/CallInvocationDetails.cs
@@ -40,30 +40,60 @@ namespace Grpc.Core
     /// <summary>
     /// Details about a client-side call to be invoked.
     /// </summary>
-    public class CallInvocationDetails<TRequest, TResponse>
+    public struct CallInvocationDetails<TRequest, TResponse>
     {
         readonly Channel channel;
         readonly string method;
         readonly string host;
         readonly Marshaller<TRequest> requestMarshaller;
         readonly Marshaller<TResponse> responseMarshaller;
-        readonly CallOptions options;
+        CallOptions options;
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Grpc.Core.CallInvocationDetails`2"/> struct.
+        /// </summary>
+        /// <param name="channel">Channel to use for this call.</param>
+        /// <param name="method">Method to call.</param>
+        /// <param name="options">Call options.</param>
         public CallInvocationDetails(Channel channel, Method<TRequest, TResponse> method, CallOptions options) :
-            this(channel, method.FullName, null, method.RequestMarshaller, method.ResponseMarshaller, options)
+            this(channel, method, null, options)
         {
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Grpc.Core.CallInvocationDetails`2"/> struct.
+        /// </summary>
+        /// <param name="channel">Channel to use for this call.</param>
+        /// <param name="method">Method to call.</param>
+        /// <param name="host">Host that contains the method. if <c>null</c>, default host will be used.</param>
+        /// <param name="options">Call options.</param>
+        public CallInvocationDetails(Channel channel, Method<TRequest, TResponse> method, string host, CallOptions options) :
+            this(channel, method.FullName, host, method.RequestMarshaller, method.ResponseMarshaller, options)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Grpc.Core.CallInvocationDetails`2"/> struct.
+        /// </summary>
+        /// <param name="channel">Channel to use for this call.</param>
+        /// <param name="method">Qualified method name.</param>
+        /// <param name="host">Host that contains the method.</param>
+        /// <param name="requestMarshaller">Request marshaller.</param>
+        /// <param name="responseMarshaller">Response marshaller.</param>
+        /// <param name="options">Call options.</param>
         public CallInvocationDetails(Channel channel, string method, string host, Marshaller<TRequest> requestMarshaller, Marshaller<TResponse> responseMarshaller, CallOptions options)
         {
-            this.channel = Preconditions.CheckNotNull(channel);
-            this.method = Preconditions.CheckNotNull(method);
+            this.channel = Preconditions.CheckNotNull(channel, "channel");
+            this.method = Preconditions.CheckNotNull(method, "method");
             this.host = host;
-            this.requestMarshaller = Preconditions.CheckNotNull(requestMarshaller);
-            this.responseMarshaller = Preconditions.CheckNotNull(responseMarshaller);
-            this.options = Preconditions.CheckNotNull(options);
+            this.requestMarshaller = Preconditions.CheckNotNull(requestMarshaller, "requestMarshaller");
+            this.responseMarshaller = Preconditions.CheckNotNull(responseMarshaller, "responseMarshaller");
+            this.options = options;
         }
 
+        /// <summary>
+        /// Get channel associated with this call.
+        /// </summary>
         public Channel Channel
         {
             get
@@ -72,6 +102,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets name of method to be called.
+        /// </summary>
         public string Method
         {
             get
@@ -80,6 +113,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Get name of host.
+        /// </summary>
         public string Host
         {
             get
@@ -88,6 +124,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets marshaller used to serialize requests.
+        /// </summary>
         public Marshaller<TRequest> RequestMarshaller
         {
             get
@@ -96,6 +135,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets marshaller used to deserialized responses.
+        /// </summary>
         public Marshaller<TResponse> ResponseMarshaller
         {
             get
@@ -104,6 +146,9 @@ namespace Grpc.Core
             }
         }
             
+        /// <summary>
+        /// Gets the call options.
+        /// </summary>
         public CallOptions Options
         {
             get
@@ -111,5 +156,16 @@ namespace Grpc.Core
                 return options;
             }
         }
+
+        /// <summary>
+        /// Returns new instance of <see cref="CallInvocationDetails"/> with
+        /// <c>Options</c> set to the value provided. Values of all other fields are preserved.
+        /// </summary>
+        public CallInvocationDetails<TRequest, TResponse> WithOptions(CallOptions options)
+        {
+            var newDetails = this;
+            newDetails.options = options;
+            return newDetails;
+        }
     }
 }
diff --git a/src/csharp/Grpc.Core/CallOptions.cs b/src/csharp/Grpc.Core/CallOptions.cs
index 8e9739335f..3dfe80b48c 100644
--- a/src/csharp/Grpc.Core/CallOptions.cs
+++ b/src/csharp/Grpc.Core/CallOptions.cs
@@ -42,24 +42,30 @@ namespace Grpc.Core
     /// <summary>
     /// Options for calls made by client.
     /// </summary>
-    public class CallOptions
+    public struct CallOptions
     {
-        readonly Metadata headers;
-        readonly DateTime deadline;
-        readonly CancellationToken cancellationToken;
+        Metadata headers;
+        DateTime? deadline;
+        CancellationToken cancellationToken;
+        WriteOptions writeOptions;
+        ContextPropagationToken propagationToken;
 
         /// <summary>
-        /// Creates a new instance of <c>CallOptions</c>.
+        /// Creates a new instance of <c>CallOptions</c> struct.
         /// </summary>
         /// <param name="headers">Headers to be sent with the call.</param>
         /// <param name="deadline">Deadline for the call to finish. null means no deadline.</param>
         /// <param name="cancellationToken">Can be used to request cancellation of the call.</param>
-        public CallOptions(Metadata headers = null, DateTime? deadline = null, CancellationToken cancellationToken = default(CancellationToken))
+        /// <param name="writeOptions">Write options that will be used for this call.</param>
+        /// <param name="propagationToken">Context propagation token obtained from <see cref="ServerCallContext"/>.</param>
+        public CallOptions(Metadata headers = null, DateTime? deadline = null, CancellationToken cancellationToken = default(CancellationToken),
+                           WriteOptions writeOptions = null, ContextPropagationToken propagationToken = null)
         {
-            // TODO(jtattermusch): consider only creating metadata object once it's really needed.
-            this.headers = headers != null ? headers : new Metadata();
-            this.deadline = deadline.HasValue ? deadline.Value : DateTime.MaxValue;
+            this.headers = headers;
+            this.deadline = deadline;
             this.cancellationToken = cancellationToken;
+            this.writeOptions = writeOptions;
+            this.propagationToken = propagationToken;
         }
 
         /// <summary>
@@ -73,7 +79,7 @@ namespace Grpc.Core
         /// <summary>
         /// Call deadline.
         /// </summary>
-        public DateTime Deadline
+        public DateTime? Deadline
         {
             get { return deadline; }
         }
@@ -85,5 +91,88 @@ namespace Grpc.Core
         {
             get { return cancellationToken; }
         }
+
+        /// <summary>
+        /// Write options that will be used for this call.
+        /// </summary>
+        public WriteOptions WriteOptions
+        {
+            get
+            {
+                return this.writeOptions;
+            }
+        }
+
+        /// <summary>
+        /// Token for propagating parent call context.
+        /// </summary>
+        public ContextPropagationToken PropagationToken
+        {
+            get
+            {
+                return this.propagationToken;
+            }
+        }
+
+        /// <summary>
+        /// Returns new instance of <see cref="CallOptions"/> with
+        /// <c>Headers</c> set to the value provided. Values of all other fields are preserved.
+        /// </summary>
+        public CallOptions WithHeaders(Metadata headers)
+        {
+            var newOptions = this;
+            newOptions.headers = headers;
+            return newOptions;
+        }
+
+        /// <summary>
+        /// Returns new instance of <see cref="CallOptions"/> with
+        /// <c>Deadline</c> set to the value provided. Values of all other fields are preserved.
+        /// </summary>
+        public CallOptions WithDeadline(DateTime deadline)
+        {
+            var newOptions = this;
+            newOptions.deadline = deadline;
+            return newOptions;
+        }
+
+        /// <summary>
+        /// Returns new instance of <see cref="CallOptions"/> with
+        /// <c>CancellationToken</c> set to the value provided. Values of all other fields are preserved.
+        /// </summary>
+        public CallOptions WithCancellationToken(CancellationToken cancellationToken)
+        {
+            var newOptions = this;
+            newOptions.cancellationToken = cancellationToken;
+            return newOptions;
+        }
+
+        /// <summary>
+        /// Returns a new instance of <see cref="CallOptions"/> with 
+        /// all previously unset values set to their defaults and deadline and cancellation
+        /// token propagated when appropriate.
+        /// </summary>
+        internal CallOptions Normalize()
+        {
+            var newOptions = this;
+            if (propagationToken != null)
+            {
+                if (propagationToken.Options.IsPropagateDeadline)
+                {
+                    Preconditions.CheckArgument(!newOptions.deadline.HasValue,
+                        "Cannot propagate deadline from parent call. The deadline has already been set explicitly.");
+                    newOptions.deadline = propagationToken.ParentDeadline;
+                }
+                if (propagationToken.Options.IsPropagateCancellation)
+                {
+                    Preconditions.CheckArgument(!newOptions.cancellationToken.CanBeCanceled,
+                        "Cannot propagate cancellation token from parent call. The cancellation token has already been set to a non-default value.");
+                }
+            }
+                
+            newOptions.headers = newOptions.headers ?? Metadata.Empty;
+            newOptions.deadline = newOptions.deadline ?? DateTime.MaxValue;
+            return newOptions;
+        }
     }
 }
diff --git a/src/csharp/Grpc.Core/Calls.cs b/src/csharp/Grpc.Core/Calls.cs
index 00a8cabf82..e57ac89db3 100644
--- a/src/csharp/Grpc.Core/Calls.cs
+++ b/src/csharp/Grpc.Core/Calls.cs
@@ -31,8 +31,6 @@
 
 #endregion
 
-using System;
-using System.Threading;
 using System.Threading.Tasks;
 using Grpc.Core.Internal;
 
@@ -40,9 +38,20 @@ namespace Grpc.Core
 {
     /// <summary>
     /// Helper methods for generated clients to make RPC calls.
+    /// Most users will use this class only indirectly and will be 
+    /// making calls using client object generated from protocol
+    /// buffer definition files.
     /// </summary>
     public static class Calls
     {
+        /// <summary>
+        /// Invokes a simple remote call in a blocking fashion.
+        /// </summary>
+        /// <returns>The response.</returns>
+        /// <param name="call">The call defintion.</param>
+        /// <param name="req">Request message.</param>
+        /// <typeparam name="TRequest">Type of request message.</typeparam>
+        /// <typeparam name="TResponse">The of response message.</typeparam>
         public static TResponse BlockingUnaryCall<TRequest, TResponse>(CallInvocationDetails<TRequest, TResponse> call, TRequest req)
             where TRequest : class
             where TResponse : class
@@ -51,15 +60,32 @@ namespace Grpc.Core
             return asyncCall.UnaryCall(req);
         }
 
+        /// <summary>
+        /// Invokes a simple remote call asynchronously.
+        /// </summary>
+        /// <returns>An awaitable call object providing access to the response.</returns>
+        /// <param name="call">The call defintion.</param>
+        /// <param name="req">Request message.</param>
+        /// <typeparam name="TRequest">Type of request message.</typeparam>
+        /// <typeparam name="TResponse">The of response message.</typeparam>
         public static AsyncUnaryCall<TResponse> AsyncUnaryCall<TRequest, TResponse>(CallInvocationDetails<TRequest, TResponse> call, TRequest req)
             where TRequest : class
             where TResponse : class
         {
             var asyncCall = new AsyncCall<TRequest, TResponse>(call);
             var asyncResult = asyncCall.UnaryCallAsync(req);
-            return new AsyncUnaryCall<TResponse>(asyncResult, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
+            return new AsyncUnaryCall<TResponse>(asyncResult, asyncCall.ResponseHeadersAsync, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
         }
 
+        /// <summary>
+        /// Invokes a server streaming call asynchronously.
+        /// In server streaming scenario, client sends on request and server responds with a stream of responses.
+        /// </summary>
+        /// <returns>A call object providing access to the asynchronous response stream.</returns>
+        /// <param name="call">The call defintion.</param>
+        /// <param name="req">Request message.</param>
+        /// <typeparam name="TRequest">Type of request message.</typeparam>
+        /// <typeparam name="TResponse">The of response messages.</typeparam>
         public static AsyncServerStreamingCall<TResponse> AsyncServerStreamingCall<TRequest, TResponse>(CallInvocationDetails<TRequest, TResponse> call, TRequest req)
             where TRequest : class
             where TResponse : class
@@ -67,9 +93,16 @@ namespace Grpc.Core
             var asyncCall = new AsyncCall<TRequest, TResponse>(call);
             asyncCall.StartServerStreamingCall(req);
             var responseStream = new ClientResponseStream<TRequest, TResponse>(asyncCall);
-            return new AsyncServerStreamingCall<TResponse>(responseStream, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
+            return new AsyncServerStreamingCall<TResponse>(responseStream, asyncCall.ResponseHeadersAsync, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
         }
 
+        /// <summary>
+        /// Invokes a client streaming call asynchronously.
+        /// In client streaming scenario, client sends a stream of requests and server responds with a single response.
+        /// </summary>
+        /// <returns>An awaitable call object providing access to the response.</returns>
+        /// <typeparam name="TRequest">Type of request messages.</typeparam>
+        /// <typeparam name="TResponse">The of response message.</typeparam>
         public static AsyncClientStreamingCall<TRequest, TResponse> AsyncClientStreamingCall<TRequest, TResponse>(CallInvocationDetails<TRequest, TResponse> call)
             where TRequest : class
             where TResponse : class
@@ -77,9 +110,18 @@ namespace Grpc.Core
             var asyncCall = new AsyncCall<TRequest, TResponse>(call);
             var resultTask = asyncCall.ClientStreamingCallAsync();
             var requestStream = new ClientRequestStream<TRequest, TResponse>(asyncCall);
-            return new AsyncClientStreamingCall<TRequest, TResponse>(requestStream, resultTask, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
+            return new AsyncClientStreamingCall<TRequest, TResponse>(requestStream, resultTask, asyncCall.ResponseHeadersAsync, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
         }
 
+        /// <summary>
+        /// Invokes a duplex streaming call asynchronously.
+        /// In duplex streaming scenario, client sends a stream of requests and server responds with a stream of responses.
+        /// The response stream is completely independent and both side can be sending messages at the same time.
+        /// </summary>
+        /// <returns>A call object providing access to the asynchronous request and response streams.</returns>
+        /// <param name="call">The call definition.</param>
+        /// <typeparam name="TRequest">Type of request messages.</typeparam>
+        /// <typeparam name="TResponse">Type of reponse messages.</typeparam>
         public static AsyncDuplexStreamingCall<TRequest, TResponse> AsyncDuplexStreamingCall<TRequest, TResponse>(CallInvocationDetails<TRequest, TResponse> call)
             where TRequest : class
             where TResponse : class
@@ -88,7 +130,7 @@ namespace Grpc.Core
             asyncCall.StartDuplexStreamingCall();
             var requestStream = new ClientRequestStream<TRequest, TResponse>(asyncCall);
             var responseStream = new ClientResponseStream<TRequest, TResponse>(asyncCall);
-            return new AsyncDuplexStreamingCall<TRequest, TResponse>(requestStream, responseStream, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
+            return new AsyncDuplexStreamingCall<TRequest, TResponse>(requestStream, responseStream, asyncCall.ResponseHeadersAsync, asyncCall.GetStatus, asyncCall.GetTrailers, asyncCall.Cancel);
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/Channel.cs b/src/csharp/Grpc.Core/Channel.cs
index 9273ea4582..c11b320a64 100644
--- a/src/csharp/Grpc.Core/Channel.cs
+++ b/src/csharp/Grpc.Core/Channel.cs
@@ -45,26 +45,31 @@ namespace Grpc.Core
     /// <summary>
     /// gRPC Channel
     /// </summary>
-    public class Channel : IDisposable
+    public class Channel
     {
         static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<Channel>();
 
+        readonly object myLock = new object();
+        readonly AtomicCounter activeCallCounter = new AtomicCounter();
+
+        readonly string target;
         readonly GrpcEnvironment environment;
         readonly ChannelSafeHandle handle;
         readonly List<ChannelOption> options;
-        bool disposed;
+
+        bool shutdownRequested;
 
         /// <summary>
         /// Creates a channel that connects to a specific host.
         /// Port will default to 80 for an unsecure channel and to 443 for a secure channel.
         /// </summary>
-        /// <param name="host">The name or IP address of the host.</param>
+        /// <param name="target">Target of the channel.</param>
         /// <param name="credentials">Credentials to secure the channel.</param>
         /// <param name="options">Channel options.</param>
-        public Channel(string host, Credentials credentials, IEnumerable<ChannelOption> options = null)
+        public Channel(string target, Credentials credentials, IEnumerable<ChannelOption> options = null)
         {
-            Preconditions.CheckNotNull(host);
-            this.environment = GrpcEnvironment.GetInstance();
+            this.target = Preconditions.CheckNotNull(target, "target");
+            this.environment = GrpcEnvironment.AddRef();
             this.options = options != null ? new List<ChannelOption>(options) : new List<ChannelOption>();
 
             EnsureUserAgentChannelOption(this.options);
@@ -73,11 +78,11 @@ namespace Grpc.Core
             {
                 if (nativeCredentials != null)
                 {
-                    this.handle = ChannelSafeHandle.CreateSecure(nativeCredentials, host, nativeChannelArgs);
+                    this.handle = ChannelSafeHandle.CreateSecure(nativeCredentials, target, nativeChannelArgs);
                 }
                 else
                 {
-                    this.handle = ChannelSafeHandle.CreateInsecure(host, nativeChannelArgs);
+                    this.handle = ChannelSafeHandle.CreateInsecure(target, nativeChannelArgs);
                 }
             }
         }
@@ -131,8 +136,8 @@ namespace Grpc.Core
             return tcs.Task;
         }
 
-        /// <summary> Address of the remote endpoint in URI format.</summary>
-        public string Target
+        /// <summary>Resolved address of the remote endpoint in URI format.</summary>
+        public string ResolvedTarget
         {
             get
             {
@@ -140,6 +145,15 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>The original target used to create the channel.</summary>
+        public string Target
+        {
+            get
+            {
+                return this.target;
+            }
+        }
+
         /// <summary>
         /// Allows explicitly requesting channel to connect without starting an RPC.
         /// Returned task completes once state Ready was seen. If the deadline is reached,
@@ -162,12 +176,26 @@ namespace Grpc.Core
         }
 
         /// <summary>
-        /// Destroys the underlying channel.
+        /// Waits until there are no more active calls for this channel and then cleans up
+        /// resources used by this channel.
         /// </summary>
-        public void Dispose()
+        public async Task ShutdownAsync()
         {
-            Dispose(true);
-            GC.SuppressFinalize(this);
+            lock (myLock)
+            {
+                Preconditions.CheckState(!shutdownRequested);
+                shutdownRequested = true;
+            }
+
+            var activeCallCount = activeCallCounter.Count;
+            if (activeCallCount > 0)
+            {
+                Logger.Warning("Channel shutdown was called but there are still {0} active calls for that channel.", activeCallCount);
+            }
+
+            handle.Dispose();
+
+            await Task.Run(() => GrpcEnvironment.Release());
         }
 
         internal ChannelSafeHandle Handle
@@ -186,13 +214,20 @@ namespace Grpc.Core
             }
         }
 
-        protected virtual void Dispose(bool disposing)
+        internal void AddCallReference(object call)
         {
-            if (disposing && handle != null && !disposed)
-            {
-                disposed = true;
-                handle.Dispose();
-            }
+            activeCallCounter.Increment();
+
+            bool success = false;
+            handle.DangerousAddRef(ref success);
+            Preconditions.CheckState(success);
+        }
+
+        internal void RemoveCallReference(object call)
+        {
+            handle.DangerousRelease();
+
+            activeCallCounter.Decrement();
         }
 
         private static void EnsureUserAgentChannelOption(List<ChannelOption> options)
diff --git a/src/csharp/Grpc.Core/ChannelOptions.cs b/src/csharp/Grpc.Core/ChannelOptions.cs
index 1e0f90287a..ad54b46ad5 100644
--- a/src/csharp/Grpc.Core/ChannelOptions.cs
+++ b/src/csharp/Grpc.Core/ChannelOptions.cs
@@ -63,19 +63,19 @@ namespace Grpc.Core
         public ChannelOption(string name, string stringValue)
         {
             this.type = OptionType.String;
-            this.name = Preconditions.CheckNotNull(name);
-            this.stringValue = Preconditions.CheckNotNull(stringValue);
+            this.name = Preconditions.CheckNotNull(name, "name");
+            this.stringValue = Preconditions.CheckNotNull(stringValue, "stringValue");
         }
 
         /// <summary>
         /// Creates a channel option with an integer value.
         /// </summary>
         /// <param name="name">Name.</param>
-        /// <param name="stringValue">String value.</param>
+        /// <param name="intValue">Integer value.</param>
         public ChannelOption(string name, int intValue)
         {
             this.type = OptionType.Integer;
-            this.name = Preconditions.CheckNotNull(name);
+            this.name = Preconditions.CheckNotNull(name, "name");
             this.intValue = intValue;
         }
 
diff --git a/src/csharp/Grpc.Core/ClientBase.cs b/src/csharp/Grpc.Core/ClientBase.cs
index 88494bb4ac..903449439b 100644
--- a/src/csharp/Grpc.Core/ClientBase.cs
+++ b/src/csharp/Grpc.Core/ClientBase.cs
@@ -32,31 +32,50 @@
 #endregion
 
 using System;
-using System.Collections.Generic;
-
-using Grpc.Core.Internal;
+using System.Text.RegularExpressions;
+using System.Threading.Tasks;
 
 namespace Grpc.Core
 {
-    public delegate void MetadataInterceptorDelegate(Metadata metadata);
+    /// <summary>
+    /// Interceptor for call headers.
+    /// </summary>
+    public delegate void HeaderInterceptor(IMethod method, string authUri, Metadata metadata);
 
     /// <summary>
     /// Base class for client-side stubs.
     /// </summary>
     public abstract class ClientBase
     {
+        // Regex for removal of the optional DNS scheme, trailing port, and trailing backslash
+        static readonly Regex ChannelTargetPattern = new Regex(@"^(dns:\/{3})?([^:\/]+)(:\d+)?\/?$");
+
         readonly Channel channel;
+        readonly string authUriBase;
 
         public ClientBase(Channel channel)
         {
             this.channel = channel;
+            this.authUriBase = GetAuthUriBase(channel.Target);
+        }
+
+        /// <summary>
+        /// Can be used to register a custom header (request metadata) interceptor.
+        /// The interceptor is invoked each time a new call on this client is started.
+        /// </summary>
+        public HeaderInterceptor HeaderInterceptor
+        {
+            get;
+            set;
         }
 
         /// <summary>
-        /// Can be used to register a custom header (initial metadata) interceptor.
-        /// The delegate each time before a new call on this client is started.
+        /// gRPC supports multiple "hosts" being served by a single server. 
+        /// This property can be used to set the target host explicitly.
+        /// By default, this will be set to <c>null</c> with the meaning
+        /// "use default host".
         /// </summary>
-        public MetadataInterceptorDelegate HeaderInterceptor
+        public string Host
         {
             get;
             set;
@@ -83,10 +102,28 @@ namespace Grpc.Core
             var interceptor = HeaderInterceptor;
             if (interceptor != null)
             {
-                interceptor(options.Headers);
-                options.Headers.Freeze();
+                if (options.Headers == null)
+                {
+                    options = options.WithHeaders(new Metadata());
+                }
+                var authUri = authUriBase != null ? authUriBase + method.ServiceName : null;
+                interceptor(method, authUri, options.Headers);
+            }
+            return new CallInvocationDetails<TRequest, TResponse>(channel, method, Host, options);
+        }
+
+        /// <summary>
+        /// Creates Auth URI base from channel's target (the one passed at channel creation).
+        /// Fully-qualified service name is to be appended to this.
+        /// </summary>
+        internal static string GetAuthUriBase(string target)
+        {
+            var match = ChannelTargetPattern.Match(target);
+            if (!match.Success)
+            {
+                return null;
             }
-            return new CallInvocationDetails<TRequest, TResponse>(channel, method, options);
+            return "https://" + match.Groups[2].Value + "/";
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/OperationFailedException.cs b/src/csharp/Grpc.Core/CompressionLevel.cs
index 9b1c24d0c1..399652b85e 100644
--- a/src/csharp/Grpc.Core/OperationFailedException.cs
+++ b/src/csharp/Grpc.Core/CompressionLevel.cs
@@ -36,12 +36,28 @@ using System;
 namespace Grpc.Core
 {
     /// <summary>
-    /// Thrown when gRPC operation fails.
+    /// Compression level based on grpc_compression_level from grpc/compression.h
     /// </summary>
-    public class OperationFailedException : Exception
+    public enum CompressionLevel
     {
-        public OperationFailedException(string message) : base(message)
-        {
-        }
+        /// <summary>
+        /// No compression.
+        /// </summary>
+        None = 0,
+
+        /// <summary>
+        /// Low compression.
+        /// </summary>
+        Low,
+
+        /// <summary>
+        /// Medium compression.
+        /// </summary>
+        Medium,
+
+        /// <summary>
+        /// High compression.
+        /// </summary>
+        High,
     }
 }
diff --git a/src/csharp/Grpc.Core/ContextPropagationToken.cs b/src/csharp/Grpc.Core/ContextPropagationToken.cs
new file mode 100644
index 0000000000..a5bf1b5a70
--- /dev/null
+++ b/src/csharp/Grpc.Core/ContextPropagationToken.cs
@@ -0,0 +1,170 @@
+#region Copyright notice and license
+
+// Copyright 2015, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#endregion
+
+using System;
+using System.Threading;
+
+using Grpc.Core.Internal;
+using Grpc.Core.Utils;
+
+namespace Grpc.Core
+{
+    /// <summary>
+    /// Token for propagating context of server side handlers to child calls.
+    /// In situations when a backend is making calls to another backend,
+    /// it makes sense to propagate properties like deadline and cancellation 
+    /// token of the server call to the child call.
+    /// C core provides some other contexts (like tracing context) that
+    /// are not accessible to C# layer, but this token still allows propagating them.
+    /// </summary>
+    public class ContextPropagationToken
+    {
+        /// <summary>
+        /// Default propagation mask used by C core.
+        /// </summary>
+        private const ContextPropagationFlags DefaultCoreMask = (ContextPropagationFlags)0xffff;
+
+        /// <summary>
+        /// Default propagation mask used by C# - we want to propagate deadline 
+        /// and cancellation token by our own means.
+        /// </summary>
+        internal const ContextPropagationFlags DefaultMask = DefaultCoreMask
+            & ~ContextPropagationFlags.Deadline & ~ContextPropagationFlags.Cancellation;
+
+        readonly CallSafeHandle parentCall;
+        readonly DateTime deadline;
+        readonly CancellationToken cancellationToken;
+        readonly ContextPropagationOptions options;
+
+        internal ContextPropagationToken(CallSafeHandle parentCall, DateTime deadline, CancellationToken cancellationToken, ContextPropagationOptions options)
+        {
+            this.parentCall = Preconditions.CheckNotNull(parentCall);
+            this.deadline = deadline;
+            this.cancellationToken = cancellationToken;
+            this.options = options ?? ContextPropagationOptions.Default;
+        }
+
+        /// <summary>
+        /// Gets the native handle of the parent call.
+        /// </summary>
+        internal CallSafeHandle ParentCall
+        {
+            get
+            {
+                return this.parentCall;
+            }
+        }
+
+        /// <summary>
+        /// Gets the parent call's deadline.
+        /// </summary>
+        internal DateTime ParentDeadline
+        {
+            get
+            {
+                return this.deadline;
+            }
+        }
+
+        /// <summary>
+        /// Gets the parent call's cancellation token.
+        /// </summary>
+        internal CancellationToken ParentCancellationToken
+        {
+            get
+            {
+                return this.cancellationToken;
+            }
+        }
+
+        /// <summary>
+        /// Get the context propagation options.
+        /// </summary>
+        internal ContextPropagationOptions Options
+        {
+            get
+            {
+                return this.options;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Options for <see cref="ContextPropagationToken"/>.
+    /// </summary>
+    public class ContextPropagationOptions
+    {
+        /// <summary>
+        /// The context propagation options that will be used by default.
+        /// </summary>
+        public static readonly ContextPropagationOptions Default = new ContextPropagationOptions();
+
+        bool propagateDeadline;
+        bool propagateCancellation;
+
+        /// <summary>
+        /// Creates new context propagation options.
+        /// </summary>
+        /// <param name="propagateDeadline">If set to <c>true</c> parent call's deadline will be propagated to the child call.</param>
+        /// <param name="propagateCancellation">If set to <c>true</c> parent call's cancellation token will be propagated to the child call.</param>
+        public ContextPropagationOptions(bool propagateDeadline = true, bool propagateCancellation = true)
+        {
+            this.propagateDeadline = propagateDeadline;
+            this.propagateCancellation = propagateCancellation;
+        }
+            
+        /// <value><c>true</c> if parent call's deadline should be propagated to the child call.</value>
+        public bool IsPropagateDeadline
+        {
+            get { return this.propagateDeadline; }
+        }
+
+        /// <value><c>true</c> if parent call's cancellation token should be propagated to the child call.</value>
+        public bool IsPropagateCancellation
+        {
+            get { return this.propagateCancellation; }
+        }
+    }
+
+    /// <summary>
+    /// Context propagation flags from grpc/grpc.h.
+    /// </summary>
+    [Flags]
+    internal enum ContextPropagationFlags
+    {
+        Deadline = 1,
+        CensusStatsContext = 2,
+        CensusTracingContext = 4,
+        Cancellation = 8
+    }
+}
diff --git a/src/csharp/Grpc.Core/Grpc.Core.csproj b/src/csharp/Grpc.Core/Grpc.Core.csproj
index 52defd1965..ad2af17bc7 100644
--- a/src/csharp/Grpc.Core/Grpc.Core.csproj
+++ b/src/csharp/Grpc.Core/Grpc.Core.csproj
@@ -49,6 +49,7 @@
     <Compile Include="AsyncDuplexStreamingCall.cs" />
     <Compile Include="AsyncServerStreamingCall.cs" />
     <Compile Include="IClientStreamWriter.cs" />
+    <Compile Include="Internal\INativeCall.cs" />
     <Compile Include="IServerStreamWriter.cs" />
     <Compile Include="IAsyncStreamWriter.cs" />
     <Compile Include="IAsyncStreamReader.cs" />
@@ -77,14 +78,12 @@
     <Compile Include="ServerServiceDefinition.cs" />
     <Compile Include="Utils\AsyncStreamExtensions.cs" />
     <Compile Include="Utils\BenchmarkUtil.cs" />
-    <Compile Include="Utils\ExceptionHelper.cs" />
     <Compile Include="Internal\CredentialsSafeHandle.cs" />
     <Compile Include="Credentials.cs" />
     <Compile Include="Internal\ChannelArgsSafeHandle.cs" />
     <Compile Include="Internal\AsyncCompletion.cs" />
     <Compile Include="Internal\AsyncCallBase.cs" />
     <Compile Include="Internal\AsyncCallServer.cs" />
-    <Compile Include="OperationFailedException.cs" />
     <Compile Include="Internal\AsyncCall.cs" />
     <Compile Include="Utils\Preconditions.cs" />
     <Compile Include="Internal\ServerCredentialsSafeHandle.cs" />
@@ -115,6 +114,9 @@
     <Compile Include="ChannelState.cs" />
     <Compile Include="CallInvocationDetails.cs" />
     <Compile Include="CallOptions.cs" />
+    <Compile Include="CompressionLevel.cs" />
+    <Compile Include="WriteOptions.cs" />
+    <Compile Include="ContextPropagationToken.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="Grpc.Core.nuspec" />
diff --git a/src/csharp/Grpc.Core/GrpcEnvironment.cs b/src/csharp/Grpc.Core/GrpcEnvironment.cs
index 034a66be3c..e7c04185c2 100644
--- a/src/csharp/Grpc.Core/GrpcEnvironment.cs
+++ b/src/csharp/Grpc.Core/GrpcEnvironment.cs
@@ -53,8 +53,12 @@ namespace Grpc.Core
         [DllImport("grpc_csharp_ext.dll")]
         static extern void grpcsharp_shutdown();
 
+        [DllImport("grpc_csharp_ext.dll")]
+        static extern IntPtr grpcsharp_version_string();  // returns not-owned const char*
+
         static object staticLock = new object();
         static GrpcEnvironment instance;
+        static int refCount;
 
         static ILogger logger = new ConsoleLogger();
 
@@ -64,13 +68,14 @@ namespace Grpc.Core
         bool isClosed;
 
         /// <summary>
-        /// Returns an instance of initialized gRPC environment.
-        /// Subsequent invocations return the same instance unless Shutdown has been called first.
+        /// Returns a reference-counted instance of initialized gRPC environment.
+        /// Subsequent invocations return the same instance unless reference count has dropped to zero previously.
         /// </summary>
-        internal static GrpcEnvironment GetInstance()
+        internal static GrpcEnvironment AddRef()
         {
             lock (staticLock)
             {
+                refCount++;
                 if (instance == null)
                 {
                     instance = new GrpcEnvironment();
@@ -80,14 +85,16 @@ namespace Grpc.Core
         }
 
         /// <summary>
-        /// Shuts down the gRPC environment if it was initialized before.
-        /// Blocks until the environment has been fully shutdown.
+        /// Decrements the reference count for currently active environment and shuts down the gRPC environment if reference count drops to zero.
+        /// (and blocks until the environment has been fully shutdown).
         /// </summary>
-        public static void Shutdown()
+        internal static void Release()
         {
             lock (staticLock)
             {
-                if (instance != null)
+                Preconditions.CheckState(refCount > 0);
+                refCount--;
+                if (refCount == 0)
                 {
                     instance.Close();
                     instance = null;
@@ -95,6 +102,14 @@ namespace Grpc.Core
             }
         }
 
+        internal static int GetRefCount()
+        {
+            lock (staticLock)
+            {
+                return refCount;
+            }
+        }
+
         /// <summary>
         /// Gets application-wide logger used by gRPC.
         /// </summary>
@@ -112,7 +127,7 @@ namespace Grpc.Core
         /// </summary>
         public static void SetLogger(ILogger customLogger)
         {
-            Preconditions.CheckNotNull(customLogger);
+            Preconditions.CheckNotNull(customLogger, "customLogger");
             logger = customLogger;
         }
 
@@ -122,12 +137,10 @@ namespace Grpc.Core
         private GrpcEnvironment()
         {
             NativeLogRedirector.Redirect();
-            grpcsharp_init();
+            GrpcNativeInit();
             completionRegistry = new CompletionRegistry(this);
             threadPool = new GrpcThreadPool(this, THREAD_POOL_SIZE);
             threadPool.Start();
-            // TODO: use proper logging here
-            Logger.Info("gRPC initialized.");
         }
 
         /// <summary>
@@ -164,6 +177,25 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// Gets version of gRPC C core.
+        /// </summary>
+        internal static string GetCoreVersionString()
+        {
+            var ptr = grpcsharp_version_string();  // the pointer is not owned
+            return Marshal.PtrToStringAnsi(ptr);
+        }
+
+        internal static void GrpcNativeInit()
+        {
+            grpcsharp_init();
+        }
+
+        internal static void GrpcNativeShutdown()
+        {
+            grpcsharp_shutdown();
+        }
+
+        /// <summary>
         /// Shuts down this environment.
         /// </summary>
         private void Close()
@@ -173,30 +205,10 @@ namespace Grpc.Core
                 throw new InvalidOperationException("Close has already been called");
             }
             threadPool.Stop();
-            grpcsharp_shutdown();
+            GrpcNativeShutdown();
             isClosed = true;
 
             debugStats.CheckOK();
-
-            Logger.Info("gRPC shutdown.");
-        }
-
-        /// <summary>
-        /// Shuts down this environment asynchronously.
-        /// </summary>
-        private Task CloseAsync()
-        {
-            return Task.Run(() =>
-            {
-                try
-                {
-                    Close();
-                }
-                catch (Exception e)
-                {
-                    Logger.Error(e, "Error occured while shutting down GrpcEnvironment.");
-                }
-            });
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/IAsyncStreamReader.cs b/src/csharp/Grpc.Core/IAsyncStreamReader.cs
index 371fbf27ce..c0a0674e50 100644
--- a/src/csharp/Grpc.Core/IAsyncStreamReader.cs
+++ b/src/csharp/Grpc.Core/IAsyncStreamReader.cs
@@ -43,7 +43,7 @@ namespace Grpc.Core
     /// A stream of messages to be read.
     /// </summary>
     /// <typeparam name="T"></typeparam>
-    public interface IAsyncStreamReader<TResponse> : IAsyncEnumerator<TResponse>
+    public interface IAsyncStreamReader<T> : IAsyncEnumerator<T>
     {
         // TODO(jtattermusch): consider just using IAsyncEnumerator instead of this interface.
     }
diff --git a/src/csharp/Grpc.Core/IAsyncStreamWriter.cs b/src/csharp/Grpc.Core/IAsyncStreamWriter.cs
index 2000210252..4e2acb9c71 100644
--- a/src/csharp/Grpc.Core/IAsyncStreamWriter.cs
+++ b/src/csharp/Grpc.Core/IAsyncStreamWriter.cs
@@ -50,5 +50,13 @@ namespace Grpc.Core
         /// </summary>
         /// <param name="message">the message to be written. Cannot be null.</param>
         Task WriteAsync(T message);
+
+        /// <summary>
+        /// Write options that will be used for the next write.
+        /// If null, default options will be used.
+        /// Once set, this property maintains its value across subsequent
+        /// writes.
+        /// <value>The write options.</value>
+        WriteOptions WriteOptions { get; set; }
     }
 }
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCall.cs b/src/csharp/Grpc.Core/Internal/AsyncCall.cs
index 414b5c4282..be5d611a53 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCall.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCall.cs
@@ -50,20 +50,34 @@ namespace Grpc.Core.Internal
     {
         static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<AsyncCall<TRequest, TResponse>>();
 
-        readonly CallInvocationDetails<TRequest, TResponse> callDetails;
+        readonly CallInvocationDetails<TRequest, TResponse> details;
+        readonly INativeCall injectedNativeCall;  // for testing
 
         // Completion of a pending unary response if not null.
         TaskCompletionSource<TResponse> unaryResponseTcs;
 
+        // Indicates that steaming call has finished.
+        TaskCompletionSource<object> streamingCallFinishedTcs = new TaskCompletionSource<object>();
+
+        // Response headers set here once received.
+        TaskCompletionSource<Metadata> responseHeadersTcs = new TaskCompletionSource<Metadata>();
+
         // Set after status is received. Used for both unary and streaming response calls.
         ClientSideStatus? finishedStatus;
 
-        bool readObserverCompleted;  // True if readObserver has already been completed.
-
         public AsyncCall(CallInvocationDetails<TRequest, TResponse> callDetails)
-            : base(callDetails.RequestMarshaller.Serializer, callDetails.ResponseMarshaller.Deserializer)
+            : base(callDetails.RequestMarshaller.Serializer, callDetails.ResponseMarshaller.Deserializer, callDetails.Channel.Environment)
         {
-            this.callDetails = callDetails;
+            this.details = callDetails.WithOptions(callDetails.Options.Normalize());
+            this.initialMetadataSent = true;  // we always send metadata at the very beginning of the call.
+        }
+
+        /// <summary>
+        /// This constructor should only be used for testing.
+        /// </summary>
+        public AsyncCall(CallInvocationDetails<TRequest, TResponse> callDetails, INativeCall injectedNativeCall) : this(callDetails)
+        {
+            this.injectedNativeCall = injectedNativeCall;
         }
 
         // TODO: this method is not Async, so it shouldn't be in AsyncCall class, but 
@@ -89,17 +103,17 @@ namespace Grpc.Core.Internal
                     readingDone = true;
                 }
 
-                using (var metadataArray = MetadataArraySafeHandle.Create(callDetails.Options.Headers))
+                using (var metadataArray = MetadataArraySafeHandle.Create(details.Options.Headers))
                 {
                     using (var ctx = BatchContextSafeHandle.Create())
                     {
-                        call.StartUnary(payload, ctx, metadataArray);
+                        call.StartUnary(ctx, payload, metadataArray, GetWriteFlagsForCall());
                         var ev = cq.Pluck(ctx.Handle);
 
                         bool success = (ev.success != 0);
                         try
                         {
-                            HandleUnaryResponse(success, ctx);
+                            HandleUnaryResponse(success, ctx.GetReceivedStatusOnClient(), ctx.GetReceivedMessage(), ctx.GetReceivedInitialMetadata());
                         }
                         catch (Exception e)
                         {
@@ -108,15 +122,9 @@ namespace Grpc.Core.Internal
                     }
                 }
 
-                try
-                {
-                    // Once the blocking call returns, the result should be available synchronously.
-                    return unaryResponseTcs.Task.Result;
-                }
-                catch (AggregateException ae)
-                {
-                    throw ExceptionHelper.UnwrapRpcException(ae);
-                }
+                // Once the blocking call returns, the result should be available synchronously.
+                // Note that GetAwaiter().GetResult() doesn't wrap exceptions in AggregateException.
+                return unaryResponseTcs.Task.GetAwaiter().GetResult();
             }
         }
 
@@ -130,7 +138,7 @@ namespace Grpc.Core.Internal
                 Preconditions.CheckState(!started);
                 started = true;
 
-                Initialize(callDetails.Channel.Environment.CompletionQueue);
+                Initialize(environment.CompletionQueue);
 
                 halfcloseRequested = true;
                 readingDone = true;
@@ -138,9 +146,9 @@ namespace Grpc.Core.Internal
                 byte[] payload = UnsafeSerialize(msg);
 
                 unaryResponseTcs = new TaskCompletionSource<TResponse>();
-                using (var metadataArray = MetadataArraySafeHandle.Create(callDetails.Options.Headers))
+                using (var metadataArray = MetadataArraySafeHandle.Create(details.Options.Headers))
                 {
-                    call.StartUnary(payload, HandleUnaryResponse, metadataArray);
+                    call.StartUnary(HandleUnaryResponse, payload, metadataArray, GetWriteFlagsForCall());
                 }
                 return unaryResponseTcs.Task;
             }
@@ -157,12 +165,12 @@ namespace Grpc.Core.Internal
                 Preconditions.CheckState(!started);
                 started = true;
 
-                Initialize(callDetails.Channel.Environment.CompletionQueue);
+                Initialize(environment.CompletionQueue);
 
                 readingDone = true;
 
                 unaryResponseTcs = new TaskCompletionSource<TResponse>();
-                using (var metadataArray = MetadataArraySafeHandle.Create(callDetails.Options.Headers))
+                using (var metadataArray = MetadataArraySafeHandle.Create(details.Options.Headers))
                 {
                     call.StartClientStreaming(HandleUnaryResponse, metadataArray);
                 }
@@ -181,17 +189,17 @@ namespace Grpc.Core.Internal
                 Preconditions.CheckState(!started);
                 started = true;
 
-                Initialize(callDetails.Channel.Environment.CompletionQueue);
+                Initialize(environment.CompletionQueue);
 
                 halfcloseRequested = true;
-                halfclosed = true;  // halfclose not confirmed yet, but it will be once finishedHandler is called.
 
                 byte[] payload = UnsafeSerialize(msg);
 
-                using (var metadataArray = MetadataArraySafeHandle.Create(callDetails.Options.Headers))
+                using (var metadataArray = MetadataArraySafeHandle.Create(details.Options.Headers))
                 {
-                    call.StartServerStreaming(payload, HandleFinished, metadataArray);
+                    call.StartServerStreaming(HandleFinished, payload, metadataArray, GetWriteFlagsForCall());
                 }
+                call.StartReceiveInitialMetadata(HandleReceivedResponseHeaders);
             }
         }
 
@@ -206,12 +214,13 @@ namespace Grpc.Core.Internal
                 Preconditions.CheckState(!started);
                 started = true;
 
-                Initialize(callDetails.Channel.Environment.CompletionQueue);
+                Initialize(environment.CompletionQueue);
 
-                using (var metadataArray = MetadataArraySafeHandle.Create(callDetails.Options.Headers))
+                using (var metadataArray = MetadataArraySafeHandle.Create(details.Options.Headers))
                 {
                     call.StartDuplexStreaming(HandleFinished, metadataArray);
                 }
+                call.StartReceiveInitialMetadata(HandleReceivedResponseHeaders);
             }
         }
 
@@ -219,9 +228,9 @@ namespace Grpc.Core.Internal
         /// Sends a streaming request. Only one pending send action is allowed at any given time.
         /// completionDelegate is called when the operation finishes.
         /// </summary>
-        public void StartSendMessage(TRequest msg, AsyncCompletionDelegate<object> completionDelegate)
+        public void StartSendMessage(TRequest msg, WriteFlags writeFlags, AsyncCompletionDelegate<object> completionDelegate)
         {
-            StartSendMessageInternal(msg, completionDelegate);
+            StartSendMessageInternal(msg, writeFlags, completionDelegate);
         }
 
         /// <summary>
@@ -253,6 +262,28 @@ namespace Grpc.Core.Internal
         }
 
         /// <summary>
+        /// Get the task that completes once if streaming call finishes with ok status and throws RpcException with given status otherwise.
+        /// </summary>
+        public Task StreamingCallFinishedTask
+        {
+            get
+            {
+                return streamingCallFinishedTcs.Task;
+            }
+        }
+
+        /// <summary>
+        /// Get the task that completes once response headers are received.
+        /// </summary>
+        public Task<Metadata> ResponseHeadersAsync
+        {
+            get
+            {
+                return responseHeadersTcs.Task;
+            }
+        }
+
+        /// <summary>
         /// Gets the resulting status if the call has already finished.
         /// Throws InvalidOperationException otherwise.
         /// </summary>
@@ -278,54 +309,45 @@ namespace Grpc.Core.Internal
             }
         }
 
-        /// <summary>
-        /// On client-side, we only fire readCompletionDelegate once all messages have been read 
-        /// and status has been received.
-        /// </summary>
-        protected override void ProcessLastRead(AsyncCompletionDelegate<TResponse> completionDelegate)
+        public CallInvocationDetails<TRequest, TResponse> Details
         {
-            if (completionDelegate != null && readingDone && finishedStatus.HasValue)
+            get
             {
-                bool shouldComplete;
-                lock (myLock)
-                {
-                    shouldComplete = !readObserverCompleted;
-                    readObserverCompleted = true;
-                }
-
-                if (shouldComplete)
-                {
-                    var status = finishedStatus.Value.Status;
-                    if (status.StatusCode != StatusCode.OK)
-                    {
-                        FireCompletion(completionDelegate, default(TResponse), new RpcException(status));
-                    }
-                    else
-                    {
-                        FireCompletion(completionDelegate, default(TResponse), null);
-                    }
-                }
+                return this.details;
             }
         }
 
-        protected override void OnReleaseResources()
+        protected override void OnAfterReleaseResources()
         {
-            callDetails.Channel.Environment.DebugStats.ActiveClientCalls.Decrement();
+            details.Channel.RemoveCallReference(this);
         }
 
         private void Initialize(CompletionQueueSafeHandle cq)
         {
-            var call = callDetails.Channel.Handle.CreateCall(callDetails.Channel.Environment.CompletionRegistry, cq,
-                callDetails.Method, callDetails.Host, Timespec.FromDateTime(callDetails.Options.Deadline));
-            callDetails.Channel.Environment.DebugStats.ActiveClientCalls.Increment();
+            var call = CreateNativeCall(cq);
+            details.Channel.AddCallReference(this);
             InitializeInternal(call);
             RegisterCancellationCallback();
         }
 
+        private INativeCall CreateNativeCall(CompletionQueueSafeHandle cq)
+        {
+            if (injectedNativeCall != null)
+            {
+                return injectedNativeCall;  // allows injecting a mock INativeCall in tests.
+            }
+
+            var parentCall = details.Options.PropagationToken != null ? details.Options.PropagationToken.ParentCall : CallSafeHandle.NullInstance;
+
+            return details.Channel.Handle.CreateCall(environment.CompletionRegistry,
+                parentCall, ContextPropagationToken.DefaultMask, cq,
+                details.Method, details.Host, Timespec.FromDateTime(details.Options.Deadline.Value));
+        }
+
         // Make sure that once cancellationToken for this call is cancelled, Cancel() will be called.
         private void RegisterCancellationCallback()
         {
-            var token = callDetails.Options.CancellationToken;
+            var token = details.Options.CancellationToken;
             if (token.CanBeCanceled)
             {
                 token.Register(() => this.Cancel());
@@ -333,31 +355,40 @@ namespace Grpc.Core.Internal
         }
 
         /// <summary>
-        /// Handler for unary response completion.
+        /// Gets WriteFlags set in callDetails.Options.WriteOptions
+        /// </summary>
+        private WriteFlags GetWriteFlagsForCall()
+        {
+            var writeOptions = details.Options.WriteOptions;
+            return writeOptions != null ? writeOptions.Flags : default(WriteFlags);
+        }
+
+        /// <summary>
+        /// Handles receive status completion for calls with streaming response.
         /// </summary>
-        private void HandleUnaryResponse(bool success, BatchContextSafeHandle ctx)
+        private void HandleReceivedResponseHeaders(bool success, Metadata responseHeaders)
         {
-            var fullStatus = ctx.GetReceivedStatusOnClient();
+            responseHeadersTcs.SetResult(responseHeaders);
+        }
 
+        /// <summary>
+        /// Handler for unary response completion.
+        /// </summary>
+        private void HandleUnaryResponse(bool success, ClientSideStatus receivedStatus, byte[] receivedMessage, Metadata responseHeaders)
+        {
             lock (myLock)
             {
                 finished = true;
-                finishedStatus = fullStatus;
-
-                halfclosed = true;
+                finishedStatus = receivedStatus;
 
                 ReleaseResourcesIfPossible();
             }
 
-            if (!success)
-            {
-                unaryResponseTcs.SetException(new RpcException(new Status(StatusCode.Internal, "Internal error occured.")));
-                return;
-            }
+            responseHeadersTcs.SetResult(responseHeaders);
 
-            var status = fullStatus.Status;
+            var status = receivedStatus.Status;
 
-            if (status.StatusCode != StatusCode.OK)
+            if (!success || status.StatusCode != StatusCode.OK)
             {
                 unaryResponseTcs.SetException(new RpcException(status));
                 return;
@@ -365,7 +396,7 @@ namespace Grpc.Core.Internal
 
             // TODO: handle deserialization error
             TResponse msg;
-            TryDeserialize(ctx.GetReceivedMessage(), out msg);
+            TryDeserialize(receivedMessage, out msg);
 
             unaryResponseTcs.SetResult(msg);
         }
@@ -373,22 +404,25 @@ namespace Grpc.Core.Internal
         /// <summary>
         /// Handles receive status completion for calls with streaming response.
         /// </summary>
-        private void HandleFinished(bool success, BatchContextSafeHandle ctx)
+        private void HandleFinished(bool success, ClientSideStatus receivedStatus)
         {
-            var fullStatus = ctx.GetReceivedStatusOnClient();
-
-            AsyncCompletionDelegate<TResponse> origReadCompletionDelegate = null;
             lock (myLock)
             {
                 finished = true;
-                finishedStatus = fullStatus;
-
-                origReadCompletionDelegate = readCompletionDelegate;
+                finishedStatus = receivedStatus;
 
                 ReleaseResourcesIfPossible();
             }
 
-            ProcessLastRead(origReadCompletionDelegate);
+            var status = receivedStatus.Status;
+
+            if (!success || status.StatusCode != StatusCode.OK)
+            {
+                streamingCallFinishedTcs.SetException(new RpcException(status));
+                return;
+            }
+
+            streamingCallFinishedTcs.SetResult(null);
         }
     }
 }
\ No newline at end of file
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs b/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs
index 38f2a5baeb..4d20394644 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCallBase.cs
@@ -54,27 +54,30 @@ namespace Grpc.Core.Internal
         readonly Func<TWrite, byte[]> serializer;
         readonly Func<byte[], TRead> deserializer;
 
+        protected readonly GrpcEnvironment environment;
         protected readonly object myLock = new object();
 
-        protected CallSafeHandle call;
+        protected INativeCall call;
         protected bool disposed;
 
         protected bool started;
-        protected bool errorOccured;
         protected bool cancelRequested;
 
         protected AsyncCompletionDelegate<object> sendCompletionDelegate;  // Completion of a pending send or sendclose if not null.
         protected AsyncCompletionDelegate<TRead> readCompletionDelegate;  // Completion of a pending send or sendclose if not null.
 
-        protected bool readingDone;
-        protected bool halfcloseRequested;
-        protected bool halfclosed;
+        protected bool readingDone;  // True if last read (i.e. read with null payload) was already received.
+        protected bool halfcloseRequested;  // True if send close have been initiated.
         protected bool finished;  // True if close has been received from the peer.
 
-        public AsyncCallBase(Func<TWrite, byte[]> serializer, Func<byte[], TRead> deserializer)
+        protected bool initialMetadataSent;
+        protected long streamingWritesCounter;  // Number of streaming send operations started so far.
+
+        public AsyncCallBase(Func<TWrite, byte[]> serializer, Func<byte[], TRead> deserializer, GrpcEnvironment environment)
         {
             this.serializer = Preconditions.CheckNotNull(serializer);
             this.deserializer = Preconditions.CheckNotNull(deserializer);
+            this.environment = Preconditions.CheckNotNull(environment);
         }
 
         /// <summary>
@@ -111,7 +114,7 @@ namespace Grpc.Core.Internal
             }
         }
 
-        protected void InitializeInternal(CallSafeHandle call)
+        protected void InitializeInternal(INativeCall call)
         {
             lock (myLock)
             {
@@ -123,7 +126,7 @@ namespace Grpc.Core.Internal
         /// Initiates sending a message. Only one send operation can be active at a time.
         /// completionDelegate is invoked upon completion.
         /// </summary>
-        protected void StartSendMessageInternal(TWrite msg, AsyncCompletionDelegate<object> completionDelegate)
+        protected void StartSendMessageInternal(TWrite msg, WriteFlags writeFlags, AsyncCompletionDelegate<object> completionDelegate)
         {
             byte[] payload = UnsafeSerialize(msg);
 
@@ -132,8 +135,11 @@ namespace Grpc.Core.Internal
                 Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                 CheckSendingAllowed();
 
-                call.StartSendMessage(payload, HandleSendFinished);
+                call.StartSendMessage(HandleSendFinished, payload, writeFlags, !initialMetadataSent);
+
                 sendCompletionDelegate = completionDelegate;
+                initialMetadataSent = true;
+                streamingWritesCounter++;
             }
         }
 
@@ -153,16 +159,6 @@ namespace Grpc.Core.Internal
             }
         }
 
-        // TODO(jtattermusch): find more fitting name for this method.
-        /// <summary>
-        /// Default behavior just completes the read observer, but more sofisticated behavior might be required
-        /// by subclasses.
-        /// </summary>
-        protected virtual void ProcessLastRead(AsyncCompletionDelegate<TRead> completionDelegate)
-        {
-            FireCompletion(completionDelegate, default(TRead), null);
-        }
-
         /// <summary>
         /// If there are no more pending actions and no new actions can be started, releases
         /// the underlying native resources.
@@ -171,7 +167,7 @@ namespace Grpc.Core.Internal
         {
             if (!disposed && call != null)
             {
-                bool noMoreSendCompletions = halfclosed || (cancelRequested && sendCompletionDelegate == null);
+                bool noMoreSendCompletions = sendCompletionDelegate == null && (halfcloseRequested || cancelRequested || finished);
                 if (noMoreSendCompletions && readingDone && finished)
                 {
                     ReleaseResources();
@@ -183,34 +179,33 @@ namespace Grpc.Core.Internal
 
         private void ReleaseResources()
         {
-            OnReleaseResources();
             if (call != null)
             {
                 call.Dispose();
             }
             disposed = true;
+            OnAfterReleaseResources();
         }
 
-        protected virtual void OnReleaseResources()
+        protected virtual void OnAfterReleaseResources()
         {
         }
 
         protected void CheckSendingAllowed()
         {
             Preconditions.CheckState(started);
-            Preconditions.CheckState(!errorOccured);
             CheckNotCancelled();
             Preconditions.CheckState(!disposed);
 
             Preconditions.CheckState(!halfcloseRequested, "Already halfclosed.");
+            Preconditions.CheckState(!finished, "Already finished.");
             Preconditions.CheckState(sendCompletionDelegate == null, "Only one write can be pending at a time");
         }
 
-        protected void CheckReadingAllowed()
+        protected virtual void CheckReadingAllowed()
         {
             Preconditions.CheckState(started);
             Preconditions.CheckState(!disposed);
-            Preconditions.CheckState(!errorOccured);
 
             Preconditions.CheckState(!readingDone, "Stream has already been closed.");
             Preconditions.CheckState(readCompletionDelegate == null, "Only one read can be pending at a time");
@@ -274,7 +269,7 @@ namespace Grpc.Core.Internal
         /// <summary>
         /// Handles send completion.
         /// </summary>
-        protected void HandleSendFinished(bool success, BatchContextSafeHandle ctx)
+        protected void HandleSendFinished(bool success)
         {
             AsyncCompletionDelegate<object> origCompletionDelegate = null;
             lock (myLock)
@@ -287,7 +282,7 @@ namespace Grpc.Core.Internal
 
             if (!success)
             {
-                FireCompletion(origCompletionDelegate, null, new OperationFailedException("Send failed"));
+                FireCompletion(origCompletionDelegate, null, new InvalidOperationException("Send failed"));
             }
             else
             {
@@ -298,12 +293,11 @@ namespace Grpc.Core.Internal
         /// <summary>
         /// Handles halfclose completion.
         /// </summary>
-        protected void HandleHalfclosed(bool success, BatchContextSafeHandle ctx)
+        protected void HandleHalfclosed(bool success)
         {
             AsyncCompletionDelegate<object> origCompletionDelegate = null;
             lock (myLock)
             {
-                halfclosed = true;
                 origCompletionDelegate = sendCompletionDelegate;
                 sendCompletionDelegate = null;
 
@@ -312,7 +306,7 @@ namespace Grpc.Core.Internal
 
             if (!success)
             {
-                FireCompletion(origCompletionDelegate, null, new OperationFailedException("Halfclose failed"));
+                FireCompletion(origCompletionDelegate, null, new InvalidOperationException("Halfclose failed"));
             }
             else
             {
@@ -323,23 +317,17 @@ namespace Grpc.Core.Internal
         /// <summary>
         /// Handles streaming read completion.
         /// </summary>
-        protected void HandleReadFinished(bool success, BatchContextSafeHandle ctx)
+        protected void HandleReadFinished(bool success, byte[] receivedMessage)
         {
-            var payload = ctx.GetReceivedMessage();
-
             AsyncCompletionDelegate<TRead> origCompletionDelegate = null;
             lock (myLock)
             {
                 origCompletionDelegate = readCompletionDelegate;
-                if (payload != null)
-                {
-                    readCompletionDelegate = null;
-                }
-                else
+                readCompletionDelegate = null;
+
+                if (receivedMessage == null)
                 {
-                    // This was the last read. Keeping the readCompletionDelegate
-                    // to be either fired by this handler or by client-side finished
-                    // handler.
+                    // This was the last read.
                     readingDone = true;
                 }
 
@@ -348,17 +336,17 @@ namespace Grpc.Core.Internal
 
             // TODO: handle the case when error occured...
 
-            if (payload != null)
+            if (receivedMessage != null)
             {
                 // TODO: handle deserialization error
                 TRead msg;
-                TryDeserialize(payload, out msg);
+                TryDeserialize(receivedMessage, out msg);
 
                 FireCompletion(origCompletionDelegate, msg, null);
             }
             else
             {
-                ProcessLastRead(origCompletionDelegate);
+                FireCompletion(origCompletionDelegate, default(TRead), null);
             }
         }
     }
diff --git a/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs b/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
index 513902ee36..5c47251030 100644
--- a/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
+++ b/src/csharp/Grpc.Core/Internal/AsyncCallServer.cs
@@ -49,17 +49,18 @@ namespace Grpc.Core.Internal
     {
         readonly TaskCompletionSource<object> finishedServersideTcs = new TaskCompletionSource<object>();
         readonly CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
-        readonly GrpcEnvironment environment;
+        readonly Server server;
 
-        public AsyncCallServer(Func<TResponse, byte[]> serializer, Func<byte[], TRequest> deserializer, GrpcEnvironment environment) : base(serializer, deserializer)
+        public AsyncCallServer(Func<TResponse, byte[]> serializer, Func<byte[], TRequest> deserializer, GrpcEnvironment environment, Server server) : base(serializer, deserializer, environment)
         {
-            this.environment = Preconditions.CheckNotNull(environment);
+            this.server = Preconditions.CheckNotNull(server);
         }
 
         public void Initialize(CallSafeHandle call)
         {
             call.SetCompletionRegistry(environment.CompletionRegistry);
-            environment.DebugStats.ActiveServerCalls.Increment();
+
+            server.AddCallReference(this);
             InitializeInternal(call);
         }
 
@@ -83,9 +84,9 @@ namespace Grpc.Core.Internal
         /// Sends a streaming response. Only one pending send action is allowed at any given time.
         /// completionDelegate is called when the operation finishes.
         /// </summary>
-        public void StartSendMessage(TResponse msg, AsyncCompletionDelegate<object> completionDelegate)
+        public void StartSendMessage(TResponse msg, WriteFlags writeFlags, AsyncCompletionDelegate<object> completionDelegate)
         {
-            StartSendMessageInternal(msg, completionDelegate);
+            StartSendMessageInternal(msg, writeFlags, completionDelegate);
         }
 
         /// <summary>
@@ -98,6 +99,35 @@ namespace Grpc.Core.Internal
         }
 
         /// <summary>
+        /// Initiates sending a initial metadata. 
+        /// Even though C-core allows sending metadata in parallel to sending messages, we will treat sending metadata as a send message operation
+        /// to make things simpler.
+        /// completionDelegate is invoked upon completion.
+        /// </summary>
+        public void StartSendInitialMetadata(Metadata headers, AsyncCompletionDelegate<object> completionDelegate)
+        {
+            lock (myLock)
+            {
+                Preconditions.CheckNotNull(headers, "metadata");
+                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+
+                Preconditions.CheckState(!initialMetadataSent, "Response headers can only be sent once per call.");
+                Preconditions.CheckState(streamingWritesCounter == 0, "Response headers can only be sent before the first write starts.");
+                CheckSendingAllowed();
+
+                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
+
+                using (var metadataArray = MetadataArraySafeHandle.Create(headers))
+                {
+                    call.StartSendInitialMetadata(HandleSendFinished, metadataArray);
+                }
+
+                this.initialMetadataSent = true;
+                sendCompletionDelegate = completionDelegate;
+            }
+        }
+
+        /// <summary>
         /// Sends call result status, also indicating server is done with streaming responses.
         /// Only one pending send action is allowed at any given time.
         /// completionDelegate is called when the operation finishes.
@@ -111,7 +141,7 @@ namespace Grpc.Core.Internal
 
                 using (var metadataArray = MetadataArraySafeHandle.Create(trailers))
                 {
-                    call.StartSendStatusFromServer(status, HandleHalfclosed, metadataArray);
+                    call.StartSendStatusFromServer(HandleHalfclosed, status, metadataArray, !initialMetadataSent);
                 }
                 halfcloseRequested = true;
                 readingDone = true;
@@ -139,18 +169,22 @@ namespace Grpc.Core.Internal
             }
         }
 
-        protected override void OnReleaseResources()
+        protected override void CheckReadingAllowed()
         {
-            environment.DebugStats.ActiveServerCalls.Decrement();
+            base.CheckReadingAllowed();
+            Preconditions.CheckArgument(!cancelRequested);
+        }
+
+        protected override void OnAfterReleaseResources()
+        {
+            server.RemoveCallReference(this);
         }
 
         /// <summary>
         /// Handles the server side close completion.
         /// </summary>
-        private void HandleFinishedServerside(bool success, BatchContextSafeHandle ctx)
+        private void HandleFinishedServerside(bool success, bool cancelled)
         {
-            bool cancelled = ctx.GetReceivedCloseOnServerCancelled();
-
             lock (myLock)
             {
                 finished = true;
diff --git a/src/csharp/Grpc.Core/Internal/BatchContextSafeHandle.cs b/src/csharp/Grpc.Core/Internal/BatchContextSafeHandle.cs
index 6a2add54db..3a96414bea 100644
--- a/src/csharp/Grpc.Core/Internal/BatchContextSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/BatchContextSafeHandle.cs
@@ -134,7 +134,7 @@ namespace Grpc.Core.Internal
         }
 
         // Gets data of server_rpc_new completion.
-        public ServerRpcNew GetServerRpcNew()
+        public ServerRpcNew GetServerRpcNew(Server server)
         {
             var call = grpcsharp_batch_context_server_rpc_new_call(this);
 
@@ -145,7 +145,7 @@ namespace Grpc.Core.Internal
             IntPtr metadataArrayPtr = grpcsharp_batch_context_server_rpc_new_request_metadata(this);
             var metadata = MetadataArraySafeHandle.ReadMetadataFromPtrUnsafe(metadataArrayPtr);
 
-            return new ServerRpcNew(call, method, host, deadline, metadata);
+            return new ServerRpcNew(server, call, method, host, deadline, metadata);
         }
 
         // Gets data of receive_close_on_server completion.
@@ -198,14 +198,16 @@ namespace Grpc.Core.Internal
     /// </summary>
     internal struct ServerRpcNew
     {
+        readonly Server server;
         readonly CallSafeHandle call;
         readonly string method;
         readonly string host;
         readonly Timespec deadline;
         readonly Metadata requestMetadata;
 
-        public ServerRpcNew(CallSafeHandle call, string method, string host, Timespec deadline, Metadata requestMetadata)
+        public ServerRpcNew(Server server, CallSafeHandle call, string method, string host, Timespec deadline, Metadata requestMetadata)
         {
+            this.server = server;
             this.call = call;
             this.method = method;
             this.host = host;
@@ -213,6 +215,14 @@ namespace Grpc.Core.Internal
             this.requestMetadata = requestMetadata;
         }
 
+        public Server Server
+        {
+            get
+            {
+                return this.server;
+            }
+        }
+
         public CallSafeHandle Call
         {
             get
diff --git a/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs b/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs
index 714749b171..0f187529e8 100644
--- a/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs
@@ -40,8 +40,10 @@ namespace Grpc.Core.Internal
     /// <summary>
     /// grpc_call from <grpc/grpc.h>
     /// </summary>
-    internal class CallSafeHandle : SafeHandleZeroIsInvalid
+    internal class CallSafeHandle : SafeHandleZeroIsInvalid, INativeCall
     {
+        public static readonly CallSafeHandle NullInstance = new CallSafeHandle();
+
         const uint GRPC_WRITE_BUFFER_HINT = 1;
         CompletionRegistry completionRegistry;
 
@@ -53,7 +55,7 @@ namespace Grpc.Core.Internal
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_start_unary(CallSafeHandle call,
-            BatchContextSafeHandle ctx, byte[] send_buffer, UIntPtr send_buffer_len, MetadataArraySafeHandle metadataArray);
+            BatchContextSafeHandle ctx, byte[] send_buffer, UIntPtr send_buffer_len, MetadataArraySafeHandle metadataArray, WriteFlags writeFlags);
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_start_client_streaming(CallSafeHandle call,
@@ -62,7 +64,7 @@ namespace Grpc.Core.Internal
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_start_server_streaming(CallSafeHandle call,
             BatchContextSafeHandle ctx, byte[] send_buffer, UIntPtr send_buffer_len,
-            MetadataArraySafeHandle metadataArray);
+            MetadataArraySafeHandle metadataArray, WriteFlags writeFlags);
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_start_duplex_streaming(CallSafeHandle call,
@@ -70,7 +72,7 @@ namespace Grpc.Core.Internal
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_send_message(CallSafeHandle call,
-            BatchContextSafeHandle ctx, byte[] send_buffer, UIntPtr send_buffer_len);
+            BatchContextSafeHandle ctx, byte[] send_buffer, UIntPtr send_buffer_len, WriteFlags writeFlags, bool sendEmptyInitialMetadata);
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_send_close_from_client(CallSafeHandle call,
@@ -78,17 +80,25 @@ namespace Grpc.Core.Internal
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_send_status_from_server(CallSafeHandle call, 
-            BatchContextSafeHandle ctx, StatusCode statusCode, string statusMessage, MetadataArraySafeHandle metadataArray);
+            BatchContextSafeHandle ctx, StatusCode statusCode, string statusMessage, MetadataArraySafeHandle metadataArray, bool sendEmptyInitialMetadata);
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_recv_message(CallSafeHandle call,
             BatchContextSafeHandle ctx);
 
         [DllImport("grpc_csharp_ext.dll")]
+        static extern GRPCCallError grpcsharp_call_recv_initial_metadata(CallSafeHandle call,
+            BatchContextSafeHandle ctx);
+
+        [DllImport("grpc_csharp_ext.dll")]
         static extern GRPCCallError grpcsharp_call_start_serverside(CallSafeHandle call,
             BatchContextSafeHandle ctx);
 
         [DllImport("grpc_csharp_ext.dll")]
+        static extern GRPCCallError grpcsharp_call_send_initial_metadata(CallSafeHandle call,
+            BatchContextSafeHandle ctx, MetadataArraySafeHandle metadataArray);
+
+        [DllImport("grpc_csharp_ext.dll")]
         static extern CStringSafeHandle grpcsharp_call_get_peer(CallSafeHandle call);
 
         [DllImport("grpc_csharp_ext.dll")]
@@ -103,76 +113,90 @@ namespace Grpc.Core.Internal
             this.completionRegistry = completionRegistry;
         }
 
-        public void StartUnary(byte[] payload, BatchCompletionDelegate callback, MetadataArraySafeHandle metadataArray)
+        public void StartUnary(UnaryResponseClientHandler callback, byte[] payload, MetadataArraySafeHandle metadataArray, WriteFlags writeFlags)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
-            grpcsharp_call_start_unary(this, ctx, payload, new UIntPtr((ulong)payload.Length), metadataArray)
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedStatusOnClient(), context.GetReceivedMessage(), context.GetReceivedInitialMetadata()));
+            grpcsharp_call_start_unary(this, ctx, payload, new UIntPtr((ulong)payload.Length), metadataArray, writeFlags)
                 .CheckOk();
         }
 
-        public void StartUnary(byte[] payload, BatchContextSafeHandle ctx, MetadataArraySafeHandle metadataArray)
+        public void StartUnary(BatchContextSafeHandle ctx, byte[] payload, MetadataArraySafeHandle metadataArray, WriteFlags writeFlags)
         {
-            grpcsharp_call_start_unary(this, ctx, payload, new UIntPtr((ulong)payload.Length), metadataArray)
+            grpcsharp_call_start_unary(this, ctx, payload, new UIntPtr((ulong)payload.Length), metadataArray, writeFlags)
                 .CheckOk();
         }
 
-        public void StartClientStreaming(BatchCompletionDelegate callback, MetadataArraySafeHandle metadataArray)
+        public void StartClientStreaming(UnaryResponseClientHandler callback, MetadataArraySafeHandle metadataArray)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedStatusOnClient(), context.GetReceivedMessage(), context.GetReceivedInitialMetadata()));
             grpcsharp_call_start_client_streaming(this, ctx, metadataArray).CheckOk();
         }
 
-        public void StartServerStreaming(byte[] payload, BatchCompletionDelegate callback, MetadataArraySafeHandle metadataArray)
+        public void StartServerStreaming(ReceivedStatusOnClientHandler callback, byte[] payload, MetadataArraySafeHandle metadataArray, WriteFlags writeFlags)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
-            grpcsharp_call_start_server_streaming(this, ctx, payload, new UIntPtr((ulong)payload.Length), metadataArray).CheckOk();
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedStatusOnClient()));
+            grpcsharp_call_start_server_streaming(this, ctx, payload, new UIntPtr((ulong)payload.Length), metadataArray, writeFlags).CheckOk();
         }
 
-        public void StartDuplexStreaming(BatchCompletionDelegate callback, MetadataArraySafeHandle metadataArray)
+        public void StartDuplexStreaming(ReceivedStatusOnClientHandler callback, MetadataArraySafeHandle metadataArray)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedStatusOnClient()));
             grpcsharp_call_start_duplex_streaming(this, ctx, metadataArray).CheckOk();
         }
 
-        public void StartSendMessage(byte[] payload, BatchCompletionDelegate callback)
+        public void StartSendMessage(SendCompletionHandler callback, byte[] payload, WriteFlags writeFlags, bool sendEmptyInitialMetadata)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
-            grpcsharp_call_send_message(this, ctx, payload, new UIntPtr((ulong)payload.Length)).CheckOk();
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success));
+            grpcsharp_call_send_message(this, ctx, payload, new UIntPtr((ulong)payload.Length), writeFlags, sendEmptyInitialMetadata).CheckOk();
         }
 
-        public void StartSendCloseFromClient(BatchCompletionDelegate callback)
+        public void StartSendCloseFromClient(SendCompletionHandler callback)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success));
             grpcsharp_call_send_close_from_client(this, ctx).CheckOk();
         }
 
-        public void StartSendStatusFromServer(Status status, BatchCompletionDelegate callback, MetadataArraySafeHandle metadataArray)
+        public void StartSendStatusFromServer(SendCompletionHandler callback, Status status, MetadataArraySafeHandle metadataArray, bool sendEmptyInitialMetadata)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
-            grpcsharp_call_send_status_from_server(this, ctx, status.StatusCode, status.Detail, metadataArray).CheckOk();
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success));
+            grpcsharp_call_send_status_from_server(this, ctx, status.StatusCode, status.Detail, metadataArray, sendEmptyInitialMetadata).CheckOk();
         }
 
-        public void StartReceiveMessage(BatchCompletionDelegate callback)
+        public void StartReceiveMessage(ReceivedMessageHandler callback)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedMessage()));
             grpcsharp_call_recv_message(this, ctx).CheckOk();
         }
 
-        public void StartServerSide(BatchCompletionDelegate callback)
+        public void StartReceiveInitialMetadata(ReceivedResponseHeadersHandler callback)
         {
             var ctx = BatchContextSafeHandle.Create();
-            completionRegistry.RegisterBatchCompletion(ctx, callback);
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedInitialMetadata()));
+            grpcsharp_call_recv_initial_metadata(this, ctx).CheckOk();
+        }
+
+        public void StartServerSide(ReceivedCloseOnServerHandler callback)
+        {
+            var ctx = BatchContextSafeHandle.Create();
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success, context.GetReceivedCloseOnServerCancelled()));
             grpcsharp_call_start_serverside(this, ctx).CheckOk();
         }
 
+        public void StartSendInitialMetadata(SendCompletionHandler callback, MetadataArraySafeHandle metadataArray)
+        {
+            var ctx = BatchContextSafeHandle.Create();
+            completionRegistry.RegisterBatchCompletion(ctx, (success, context) => callback(success));
+            grpcsharp_call_send_initial_metadata(this, ctx, metadataArray).CheckOk();
+        }
+
         public void Cancel()
         {
             grpcsharp_call_cancel(this).CheckOk();
diff --git a/src/csharp/Grpc.Core/Internal/ChannelSafeHandle.cs b/src/csharp/Grpc.Core/Internal/ChannelSafeHandle.cs
index 7324ebdf57..8cef566c14 100644
--- a/src/csharp/Grpc.Core/Internal/ChannelSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/ChannelSafeHandle.cs
@@ -47,7 +47,7 @@ namespace Grpc.Core.Internal
         static extern ChannelSafeHandle grpcsharp_secure_channel_create(CredentialsSafeHandle credentials, string target, ChannelArgsSafeHandle channelArgs);
 
         [DllImport("grpc_csharp_ext.dll")]
-        static extern CallSafeHandle grpcsharp_channel_create_call(ChannelSafeHandle channel, CompletionQueueSafeHandle cq, string method, string host, Timespec deadline);
+        static extern CallSafeHandle grpcsharp_channel_create_call(ChannelSafeHandle channel, CallSafeHandle parentCall, ContextPropagationFlags propagationMask, CompletionQueueSafeHandle cq, string method, string host, Timespec deadline);
 
         [DllImport("grpc_csharp_ext.dll")]
         static extern ChannelState grpcsharp_channel_check_connectivity_state(ChannelSafeHandle channel, int tryToConnect);
@@ -68,17 +68,23 @@ namespace Grpc.Core.Internal
 
         public static ChannelSafeHandle CreateInsecure(string target, ChannelArgsSafeHandle channelArgs)
         {
+            // Increment reference count for the native gRPC environment to make sure we don't do grpc_shutdown() before destroying the server handle.
+            // Doing so would make object finalizer crash if we end up abandoning the handle.
+            GrpcEnvironment.GrpcNativeInit();
             return grpcsharp_insecure_channel_create(target, channelArgs);
         }
 
         public static ChannelSafeHandle CreateSecure(CredentialsSafeHandle credentials, string target, ChannelArgsSafeHandle channelArgs)
         {
+            // Increment reference count for the native gRPC environment to make sure we don't do grpc_shutdown() before destroying the server handle.
+            // Doing so would make object finalizer crash if we end up abandoning the handle.
+            GrpcEnvironment.GrpcNativeInit();
             return grpcsharp_secure_channel_create(credentials, target, channelArgs);
         }
 
-        public CallSafeHandle CreateCall(CompletionRegistry registry, CompletionQueueSafeHandle cq, string method, string host, Timespec deadline)
+        public CallSafeHandle CreateCall(CompletionRegistry registry, CallSafeHandle parentCall, ContextPropagationFlags propagationMask, CompletionQueueSafeHandle cq, string method, string host, Timespec deadline)
         {
-            var result = grpcsharp_channel_create_call(this, cq, method, host, deadline);
+            var result = grpcsharp_channel_create_call(this, parentCall, propagationMask, cq, method, host, deadline);
             result.SetCompletionRegistry(registry);
             return result;
         }
@@ -107,6 +113,7 @@ namespace Grpc.Core.Internal
         protected override bool ReleaseHandle()
         {
             grpcsharp_channel_destroy(handle);
+            GrpcEnvironment.GrpcNativeShutdown();
             return true;
         }
     }
diff --git a/src/csharp/Grpc.Core/Internal/ClientRequestStream.cs b/src/csharp/Grpc.Core/Internal/ClientRequestStream.cs
index 58f493463b..013f00ff6f 100644
--- a/src/csharp/Grpc.Core/Internal/ClientRequestStream.cs
+++ b/src/csharp/Grpc.Core/Internal/ClientRequestStream.cs
@@ -40,16 +40,18 @@ namespace Grpc.Core.Internal
     internal class ClientRequestStream<TRequest, TResponse> : IClientStreamWriter<TRequest>
     {
         readonly AsyncCall<TRequest, TResponse> call;
+        WriteOptions writeOptions;
 
         public ClientRequestStream(AsyncCall<TRequest, TResponse> call)
         {
             this.call = call;
+            this.writeOptions = call.Details.Options.WriteOptions;
         }
 
         public Task WriteAsync(TRequest message)
         {
             var taskSource = new AsyncCompletionTaskSource<object>();
-            call.StartSendMessage(message, taskSource.CompletionDelegate);
+            call.StartSendMessage(message, GetWriteFlags(), taskSource.CompletionDelegate);
             return taskSource.Task;
         }
 
@@ -59,5 +61,24 @@ namespace Grpc.Core.Internal
             call.StartSendCloseFromClient(taskSource.CompletionDelegate);
             return taskSource.Task;
         }
+
+        public WriteOptions WriteOptions
+        {
+            get
+            {
+                return this.writeOptions;
+            }
+
+            set
+            {
+                writeOptions = value;
+            }
+        }
+
+        private WriteFlags GetWriteFlags()
+        {
+            var options = writeOptions;
+            return options != null ? options.Flags : default(WriteFlags);
+        }
     }
 }
diff --git a/src/csharp/Grpc.Core/Internal/ClientResponseStream.cs b/src/csharp/Grpc.Core/Internal/ClientResponseStream.cs
index 6c44521038..b4a7335c7c 100644
--- a/src/csharp/Grpc.Core/Internal/ClientResponseStream.cs
+++ b/src/csharp/Grpc.Core/Internal/ClientResponseStream.cs
@@ -72,7 +72,13 @@ namespace Grpc.Core.Internal
             call.StartReadMessage(taskSource.CompletionDelegate);
             var result = await taskSource.Task;
             this.current = result;
-            return result != null;
+
+            if (result == null)
+            {
+                await call.StreamingCallFinishedTask;
+                return false;
+            }
+            return true;
         }
 
         public void Dispose()
diff --git a/src/csharp/Grpc.Core/Internal/DebugStats.cs b/src/csharp/Grpc.Core/Internal/DebugStats.cs
index 8793450ff3..1bea1adf9e 100644
--- a/src/csharp/Grpc.Core/Internal/DebugStats.cs
+++ b/src/csharp/Grpc.Core/Internal/DebugStats.cs
@@ -38,10 +38,6 @@ namespace Grpc.Core.Internal
 {
     internal class DebugStats
     {
-        public readonly AtomicCounter ActiveClientCalls = new AtomicCounter();
-
-        public readonly AtomicCounter ActiveServerCalls = new AtomicCounter();
-
         public readonly AtomicCounter PendingBatchCompletions = new AtomicCounter();
 
         /// <summary>
@@ -49,16 +45,6 @@ namespace Grpc.Core.Internal
         /// </summary>
         public void CheckOK()
         {
-            var remainingClientCalls = ActiveClientCalls.Count;
-            if (remainingClientCalls != 0)
-            {                
-                DebugWarning(string.Format("Detected {0} client calls that weren't disposed properly.", remainingClientCalls));
-            }
-            var remainingServerCalls = ActiveServerCalls.Count;
-            if (remainingServerCalls != 0)
-            {
-                DebugWarning(string.Format("Detected {0} server calls that weren't disposed properly.", remainingServerCalls));
-            }
             var pendingBatchCompletions = PendingBatchCompletions.Count;
             if (pendingBatchCompletions != 0)
             {
diff --git a/src/csharp/Grpc.Core/Internal/GrpcThreadPool.cs b/src/csharp/Grpc.Core/Internal/GrpcThreadPool.cs
index cb4c7c821e..4b7124ee74 100644
--- a/src/csharp/Grpc.Core/Internal/GrpcThreadPool.cs
+++ b/src/csharp/Grpc.Core/Internal/GrpcThreadPool.cs
@@ -83,8 +83,6 @@ namespace Grpc.Core.Internal
             lock (myLock)
             {
                 cq.Shutdown();
-
-                Logger.Info("Waiting for GRPC threads to finish.");
                 foreach (var thread in threads)
                 {
                     thread.Join();
@@ -136,7 +134,6 @@ namespace Grpc.Core.Internal
                 }
             }
             while (ev.type != GRPCCompletionType.Shutdown);
-            Logger.Info("Completion queue has shutdown successfully, thread {0} exiting.", Thread.CurrentThread.Name);
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/Internal/INativeCall.cs b/src/csharp/Grpc.Core/Internal/INativeCall.cs
new file mode 100644
index 0000000000..cbef599139
--- /dev/null
+++ b/src/csharp/Grpc.Core/Internal/INativeCall.cs
@@ -0,0 +1,85 @@
+#region Copyright notice and license
+// Copyright 2015, Google Inc.
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+// 
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#endregion
+
+using System;
+
+namespace Grpc.Core.Internal
+{
+    internal delegate void UnaryResponseClientHandler(bool success, ClientSideStatus receivedStatus, byte[] receivedMessage, Metadata responseHeaders);
+
+    // Received status for streaming response calls.
+    internal delegate void ReceivedStatusOnClientHandler(bool success, ClientSideStatus receivedStatus);
+
+    internal delegate void ReceivedMessageHandler(bool success, byte[] receivedMessage);
+
+    internal delegate void ReceivedResponseHeadersHandler(bool success, Metadata responseHeaders);
+
+    internal delegate void SendCompletionHandler(bool success);
+
+    internal delegate void ReceivedCloseOnServerHandler(bool success, bool cancelled);
+
+    /// <summary>
+    /// Abstraction of a native call object.
+    /// </summary>
+    internal interface INativeCall : IDisposable
+    {
+        void Cancel();
+
+        void CancelWithStatus(Grpc.Core.Status status);
+
+        string GetPeer();
+
+        void StartUnary(UnaryResponseClientHandler callback, byte[] payload, MetadataArraySafeHandle metadataArray, Grpc.Core.WriteFlags writeFlags);
+
+        void StartUnary(BatchContextSafeHandle ctx, byte[] payload, MetadataArraySafeHandle metadataArray, Grpc.Core.WriteFlags writeFlags);
+
+        void StartClientStreaming(UnaryResponseClientHandler callback, MetadataArraySafeHandle metadataArray);
+
+        void StartServerStreaming(ReceivedStatusOnClientHandler callback, byte[] payload, MetadataArraySafeHandle metadataArray, Grpc.Core.WriteFlags writeFlags);
+
+        void StartDuplexStreaming(ReceivedStatusOnClientHandler callback, MetadataArraySafeHandle metadataArray);
+
+        void StartReceiveMessage(ReceivedMessageHandler callback);
+
+        void StartReceiveInitialMetadata(ReceivedResponseHeadersHandler callback);
+
+        void StartSendInitialMetadata(SendCompletionHandler callback, MetadataArraySafeHandle metadataArray);
+
+        void StartSendMessage(SendCompletionHandler callback, byte[] payload, Grpc.Core.WriteFlags writeFlags, bool sendEmptyInitialMetadata);
+
+        void StartSendCloseFromClient(SendCompletionHandler callback);
+
+        void StartSendStatusFromServer(SendCompletionHandler callback, Grpc.Core.Status status, MetadataArraySafeHandle metadataArray, bool sendEmptyInitialMetadata);
+
+        void StartServerSide(ReceivedCloseOnServerHandler callback);
+    }
+}
diff --git a/src/csharp/Grpc.Core/Internal/MetadataArraySafeHandle.cs b/src/csharp/Grpc.Core/Internal/MetadataArraySafeHandle.cs
index 427c16fac6..83994f6762 100644
--- a/src/csharp/Grpc.Core/Internal/MetadataArraySafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/MetadataArraySafeHandle.cs
@@ -70,7 +70,8 @@ namespace Grpc.Core.Internal
             var metadataArray = grpcsharp_metadata_array_create(new UIntPtr((ulong)metadata.Count));
             for (int i = 0; i < metadata.Count; i++)
             {
-                grpcsharp_metadata_array_add(metadataArray, metadata[i].Key, metadata[i].ValueBytes, new UIntPtr((ulong)metadata[i].ValueBytes.Length));
+                var valueBytes = metadata[i].GetSerializedValueUnsafe();
+                grpcsharp_metadata_array_add(metadataArray, metadata[i].Key, valueBytes, new UIntPtr((ulong)valueBytes.Length));
             }
             return metadataArray;
         }
@@ -94,7 +95,7 @@ namespace Grpc.Core.Internal
                 string key = Marshal.PtrToStringAnsi(grpcsharp_metadata_array_get_key(metadataArray, index));
                 var bytes = new byte[grpcsharp_metadata_array_get_value_length(metadataArray, index).ToUInt64()];
                 Marshal.Copy(grpcsharp_metadata_array_get_value(metadataArray, index), bytes, 0, bytes.Length);
-                metadata.Add(new Metadata.Entry(key, bytes));
+                metadata.Add(Metadata.Entry.CreateUnsafe(key, bytes));
             }
             return metadata;
         }
diff --git a/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs b/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs
index 19f0e3c57f..59f4c5727c 100644
--- a/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs
+++ b/src/csharp/Grpc.Core/Internal/ServerCallHandler.cs
@@ -67,7 +67,7 @@ namespace Grpc.Core.Internal
             var asyncCall = new AsyncCallServer<TRequest, TResponse>(
                 method.ResponseMarshaller.Serializer,
                 method.RequestMarshaller.Deserializer,
-                environment);
+                environment, newRpc.Server);
 
             asyncCall.Initialize(newRpc.Call);
             var finishedTask = asyncCall.ServerSideCallAsync();
@@ -75,7 +75,7 @@ namespace Grpc.Core.Internal
             var responseStream = new ServerResponseStream<TRequest, TResponse>(asyncCall);
 
             Status status;
-            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, asyncCall.CancellationToken);
+            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, responseStream, asyncCall.CancellationToken);
             try
             {
                 Preconditions.CheckArgument(await requestStream.MoveNext());
@@ -123,7 +123,7 @@ namespace Grpc.Core.Internal
             var asyncCall = new AsyncCallServer<TRequest, TResponse>(
                 method.ResponseMarshaller.Serializer,
                 method.RequestMarshaller.Deserializer,
-                environment);
+                environment, newRpc.Server);
 
             asyncCall.Initialize(newRpc.Call);
             var finishedTask = asyncCall.ServerSideCallAsync();
@@ -131,7 +131,7 @@ namespace Grpc.Core.Internal
             var responseStream = new ServerResponseStream<TRequest, TResponse>(asyncCall);
 
             Status status;
-            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, asyncCall.CancellationToken);
+            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, responseStream, asyncCall.CancellationToken);
             try
             {
                 Preconditions.CheckArgument(await requestStream.MoveNext());
@@ -179,7 +179,7 @@ namespace Grpc.Core.Internal
             var asyncCall = new AsyncCallServer<TRequest, TResponse>(
                 method.ResponseMarshaller.Serializer,
                 method.RequestMarshaller.Deserializer,
-                environment);
+                environment, newRpc.Server);
 
             asyncCall.Initialize(newRpc.Call);
             var finishedTask = asyncCall.ServerSideCallAsync();
@@ -187,7 +187,7 @@ namespace Grpc.Core.Internal
             var responseStream = new ServerResponseStream<TRequest, TResponse>(asyncCall);
 
             Status status;
-            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, asyncCall.CancellationToken);
+            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, responseStream, asyncCall.CancellationToken);
             try
             {
                 var result = await handler(requestStream, context);
@@ -239,7 +239,7 @@ namespace Grpc.Core.Internal
             var asyncCall = new AsyncCallServer<TRequest, TResponse>(
                 method.ResponseMarshaller.Serializer,
                 method.RequestMarshaller.Deserializer,
-                environment);
+                environment, newRpc.Server);
 
             asyncCall.Initialize(newRpc.Call);
             var finishedTask = asyncCall.ServerSideCallAsync();
@@ -247,7 +247,7 @@ namespace Grpc.Core.Internal
             var responseStream = new ServerResponseStream<TRequest, TResponse>(asyncCall);
 
             Status status;
-            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, asyncCall.CancellationToken);
+            var context = HandlerUtils.NewContext(newRpc, asyncCall.Peer, responseStream, asyncCall.CancellationToken);
             try
             {
                 await handler(requestStream, responseStream, context);
@@ -278,7 +278,7 @@ namespace Grpc.Core.Internal
         {
             // We don't care about the payload type here.
             var asyncCall = new AsyncCallServer<byte[], byte[]>(
-                (payload) => payload, (payload) => payload, environment);
+                (payload) => payload, (payload) => payload, environment, newRpc.Server);
             
             asyncCall.Initialize(newRpc.Call);
             var finishedTask = asyncCall.ServerSideCallAsync();
@@ -304,13 +304,14 @@ namespace Grpc.Core.Internal
             return new Status(StatusCode.Unknown, "Exception was thrown by handler.");
         }
 
-        public static ServerCallContext NewContext(ServerRpcNew newRpc, string peer, CancellationToken cancellationToken)
+        public static ServerCallContext NewContext<TRequest, TResponse>(ServerRpcNew newRpc, string peer, ServerResponseStream<TRequest, TResponse> serverResponseStream, CancellationToken cancellationToken)
+            where TRequest : class
+            where TResponse : class
         {
             DateTime realtimeDeadline = newRpc.Deadline.ToClockType(GPRClockType.Realtime).ToDateTime();
 
-            return new ServerCallContext(
-                newRpc.Method, newRpc.Host, peer, realtimeDeadline,
-                newRpc.RequestMetadata, cancellationToken);
+            return new ServerCallContext(newRpc.Call, newRpc.Method, newRpc.Host, peer, realtimeDeadline,
+                newRpc.RequestMetadata, cancellationToken, serverResponseStream.WriteResponseHeadersAsync, serverResponseStream);
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/Internal/ServerResponseStream.cs b/src/csharp/Grpc.Core/Internal/ServerResponseStream.cs
index 756dcee87f..03e39efc02 100644
--- a/src/csharp/Grpc.Core/Internal/ServerResponseStream.cs
+++ b/src/csharp/Grpc.Core/Internal/ServerResponseStream.cs
@@ -38,11 +38,12 @@ namespace Grpc.Core.Internal
     /// <summary>
     /// Writes responses asynchronously to an underlying AsyncCallServer object.
     /// </summary>
-    internal class ServerResponseStream<TRequest, TResponse> : IServerStreamWriter<TResponse>
+    internal class ServerResponseStream<TRequest, TResponse> : IServerStreamWriter<TResponse>, IHasWriteOptions
         where TRequest : class
         where TResponse : class
     {
         readonly AsyncCallServer<TRequest, TResponse> call;
+        WriteOptions writeOptions;
 
         public ServerResponseStream(AsyncCallServer<TRequest, TResponse> call)
         {
@@ -52,7 +53,7 @@ namespace Grpc.Core.Internal
         public Task WriteAsync(TResponse message)
         {
             var taskSource = new AsyncCompletionTaskSource<object>();
-            call.StartSendMessage(message, taskSource.CompletionDelegate);
+            call.StartSendMessage(message, GetWriteFlags(), taskSource.CompletionDelegate);
             return taskSource.Task;
         }
 
@@ -62,5 +63,31 @@ namespace Grpc.Core.Internal
             call.StartSendStatusFromServer(status, trailers, taskSource.CompletionDelegate);
             return taskSource.Task;
         }
+
+        public Task WriteResponseHeadersAsync(Metadata responseHeaders)
+        {
+            var taskSource = new AsyncCompletionTaskSource<object>();
+            call.StartSendInitialMetadata(responseHeaders, taskSource.CompletionDelegate);
+            return taskSource.Task;
+        }
+
+        public WriteOptions WriteOptions
+        {
+            get
+            {
+                return writeOptions;
+            }
+
+            set
+            {
+                writeOptions = value;
+            }
+        }
+
+        private WriteFlags GetWriteFlags()
+        {
+            var options = writeOptions;
+            return options != null ? options.Flags : default(WriteFlags);
+        }
     }
 }
diff --git a/src/csharp/Grpc.Core/Internal/ServerSafeHandle.cs b/src/csharp/Grpc.Core/Internal/ServerSafeHandle.cs
index f9b44b1acf..5ee7ac14e8 100644
--- a/src/csharp/Grpc.Core/Internal/ServerSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/ServerSafeHandle.cs
@@ -74,6 +74,9 @@ namespace Grpc.Core.Internal
 
         public static ServerSafeHandle NewServer(CompletionQueueSafeHandle cq, ChannelArgsSafeHandle args)
         {
+            // Increment reference count for the native gRPC environment to make sure we don't do grpc_shutdown() before destroying the server handle.
+            // Doing so would make object finalizer crash if we end up abandoning the handle.
+            GrpcEnvironment.GrpcNativeInit();
             return grpcsharp_server_create(cq, args);
         }
 
@@ -109,6 +112,7 @@ namespace Grpc.Core.Internal
         protected override bool ReleaseHandle()
         {
             grpcsharp_server_destroy(handle);
+            GrpcEnvironment.GrpcNativeShutdown();
             return true;
         }
             
diff --git a/src/csharp/Grpc.Core/Internal/Timespec.cs b/src/csharp/Grpc.Core/Internal/Timespec.cs
index e83d21f4a4..daf85d5f61 100644
--- a/src/csharp/Grpc.Core/Internal/Timespec.cs
+++ b/src/csharp/Grpc.Core/Internal/Timespec.cs
@@ -211,7 +211,7 @@ namespace Grpc.Core.Internal
                 return Timespec.InfPast;
             }
 
-            Preconditions.CheckArgument(dateTime.Kind == DateTimeKind.Utc, "dateTime");
+            Preconditions.CheckArgument(dateTime.Kind == DateTimeKind.Utc, "dateTime needs of kind DateTimeKind.Utc or be equal to DateTime.MaxValue or DateTime.MinValue.");
 
             try
             {
diff --git a/src/csharp/Grpc.Core/KeyCertificatePair.cs b/src/csharp/Grpc.Core/KeyCertificatePair.cs
index 5def15a656..6f691975e9 100644
--- a/src/csharp/Grpc.Core/KeyCertificatePair.cs
+++ b/src/csharp/Grpc.Core/KeyCertificatePair.cs
@@ -54,8 +54,8 @@ namespace Grpc.Core
         /// <param name="privateKey">PEM encoded private key.</param>
         public KeyCertificatePair(string certificateChain, string privateKey)
         {
-            this.certificateChain = Preconditions.CheckNotNull(certificateChain);
-            this.privateKey = Preconditions.CheckNotNull(privateKey);
+            this.certificateChain = Preconditions.CheckNotNull(certificateChain, "certificateChain");
+            this.privateKey = Preconditions.CheckNotNull(privateKey, "privateKey");
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/Logging/ConsoleLogger.cs b/src/csharp/Grpc.Core/Logging/ConsoleLogger.cs
index c67765c78d..35561d25d8 100644
--- a/src/csharp/Grpc.Core/Logging/ConsoleLogger.cs
+++ b/src/csharp/Grpc.Core/Logging/ConsoleLogger.cs
@@ -42,16 +42,33 @@ namespace Grpc.Core.Logging
         readonly Type forType;
         readonly string forTypeString;
 
+        /// <summary>Creates a console logger not associated to any specific type.</summary>
         public ConsoleLogger() : this(null)
         {
         }
 
+        /// <summary>Creates a console logger that logs messsage specific for given type.</summary>
         private ConsoleLogger(Type forType)
         {
             this.forType = forType;
-            this.forTypeString = forType != null ? forType.FullName + " " : "";
+            if (forType != null)
+            {
+                var namespaceStr = forType.Namespace ?? "";
+                if (namespaceStr.Length > 0)
+                {
+                     namespaceStr += ".";
+                }
+                this.forTypeString = namespaceStr + forType.Name + " ";
+            }
+            else
+            {
+                this.forTypeString = "";
+            }
         }
-
+ 
+        /// <summary>
+        /// Returns a logger associated with the specified type.
+        /// </summary>
         public ILogger ForType<T>()
         {
             if (typeof(T) == forType)
@@ -61,31 +78,37 @@ namespace Grpc.Core.Logging
             return new ConsoleLogger(typeof(T));
         }
 
+        /// <summary>Logs a message with severity Debug.</summary>
         public void Debug(string message, params object[] formatArgs)
         {
             Log("D", message, formatArgs);
         }
 
+        /// <summary>Logs a message with severity Info.</summary>
         public void Info(string message, params object[] formatArgs)
         {
             Log("I", message, formatArgs);
         }
 
+        /// <summary>Logs a message with severity Warning.</summary>
         public void Warning(string message, params object[] formatArgs)
         {
             Log("W", message, formatArgs);
         }
 
+        /// <summary>Logs a message and an associated exception with severity Warning.</summary>
         public void Warning(Exception exception, string message, params object[] formatArgs)
         {
             Log("W", message + " " + exception, formatArgs);
         }
 
+        /// <summary>Logs a message with severity Error.</summary>
         public void Error(string message, params object[] formatArgs)
         {
             Log("E", message, formatArgs);
         }
 
+        /// <summary>Logs a message and an associated exception with severity Error.</summary>
         public void Error(Exception exception, string message, params object[] formatArgs)
         {
             Log("E", message + " " + exception, formatArgs);
diff --git a/src/csharp/Grpc.Core/Logging/ILogger.cs b/src/csharp/Grpc.Core/Logging/ILogger.cs
index 0d58f133e3..61e0c91388 100644
--- a/src/csharp/Grpc.Core/Logging/ILogger.cs
+++ b/src/csharp/Grpc.Core/Logging/ILogger.cs
@@ -42,16 +42,22 @@ namespace Grpc.Core.Logging
         /// <summary>Returns a logger associated with the specified type.</summary>
         ILogger ForType<T>();
 
+        /// <summary>Logs a message with severity Debug.</summary>
         void Debug(string message, params object[] formatArgs);
 
+        /// <summary>Logs a message with severity Info.</summary>
         void Info(string message, params object[] formatArgs);
 
+        /// <summary>Logs a message with severity Warning.</summary>
         void Warning(string message, params object[] formatArgs);
 
+        /// <summary>Logs a message and an associated exception with severity Warning.</summary>
         void Warning(Exception exception, string message, params object[] formatArgs);
 
+        /// <summary>Logs a message with severity Error.</summary>
         void Error(string message, params object[] formatArgs);
 
+        /// <summary>Logs a message and an associated exception with severity Error.</summary>
         void Error(Exception exception, string message, params object[] formatArgs);
     }
 }
diff --git a/src/csharp/Grpc.Core/Marshaller.cs b/src/csharp/Grpc.Core/Marshaller.cs
index 8b1a929074..f38cb0863f 100644
--- a/src/csharp/Grpc.Core/Marshaller.cs
+++ b/src/csharp/Grpc.Core/Marshaller.cs
@@ -37,19 +37,27 @@ using Grpc.Core.Utils;
 namespace Grpc.Core
 {
     /// <summary>
-    /// For serializing and deserializing messages.
+    /// Encapsulates the logic for serializing and deserializing messages.
     /// </summary>
     public struct Marshaller<T>
     {
         readonly Func<T, byte[]> serializer;
         readonly Func<byte[], T> deserializer;
 
+        /// <summary>
+        /// Initializes a new marshaller.
+        /// </summary>
+        /// <param name="serializer">Function that will be used to serialize messages.</param>
+        /// <param name="deserializer">Function that will be used to deserialize messages.</param>
         public Marshaller(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
         {
-            this.serializer = Preconditions.CheckNotNull(serializer);
-            this.deserializer = Preconditions.CheckNotNull(deserializer);
+            this.serializer = Preconditions.CheckNotNull(serializer, "serializer");
+            this.deserializer = Preconditions.CheckNotNull(deserializer, "deserializer");
         }
 
+        /// <summary>
+        /// Gets the serializer function.
+        /// </summary>
         public Func<T, byte[]> Serializer
         {
             get
@@ -58,6 +66,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets the deserializer function.
+        /// </summary>
         public Func<byte[], T> Deserializer
         {
             get
@@ -72,11 +83,17 @@ namespace Grpc.Core
     /// </summary>
     public static class Marshallers
     {
+        /// <summary>
+        /// Creates a marshaller from specified serializer and deserializer.
+        /// </summary>
         public static Marshaller<T> Create<T>(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
         {
             return new Marshaller<T>(serializer, deserializer);
         }
 
+        /// <summary>
+        /// Returns a marshaller for <c>string</c> type. This is useful for testing.
+        /// </summary>
         public static Marshaller<string> StringMarshaller
         {
             get
diff --git a/src/csharp/Grpc.Core/Metadata.cs b/src/csharp/Grpc.Core/Metadata.cs
index 6fd0a7109d..a589b50caa 100644
--- a/src/csharp/Grpc.Core/Metadata.cs
+++ b/src/csharp/Grpc.Core/Metadata.cs
@@ -46,6 +46,11 @@ namespace Grpc.Core
     public sealed class Metadata : IList<Metadata.Entry>
     {
         /// <summary>
+        /// All binary headers should have this suffix.
+        /// </summary>
+        public const string BinaryHeaderSuffix = "-bin";
+
+        /// <summary>
         /// An read-only instance of metadata containing no entries.
         /// </summary>
         public static readonly Metadata Empty = new Metadata().Freeze();
@@ -114,6 +119,16 @@ namespace Grpc.Core
             entries.Add(item);
         }
 
+        public void Add(string key, string value)
+        {
+            Add(new Entry(key, value));
+        }
+
+        public void Add(string key, byte[] valueBytes)
+        {
+            Add(new Entry(key, valueBytes));
+        }
+
         public void Clear()
         {
             CheckWriteable();
@@ -171,23 +186,49 @@ namespace Grpc.Core
             private static readonly Encoding Encoding = Encoding.ASCII;
 
             readonly string key;
-            string value;
-            byte[] valueBytes;
+            readonly string value;
+            readonly byte[] valueBytes;
 
+            private Entry(string key, string value, byte[] valueBytes)
+            {
+                this.key = key;
+                this.value = value;
+                this.valueBytes = valueBytes;
+            }
+
+            /// <summary>
+            /// Initializes a new instance of the <see cref="Grpc.Core.Metadata+Entry"/> struct with a binary value.
+            /// </summary>
+            /// <param name="key">Metadata key, needs to have suffix indicating a binary valued metadata entry.</param>
+            /// <param name="valueBytes">Value bytes.</param>
             public Entry(string key, byte[] valueBytes)
             {
-                this.key = Preconditions.CheckNotNull(key);
+                this.key = NormalizeKey(key);
+                Preconditions.CheckArgument(this.key.EndsWith(BinaryHeaderSuffix),
+                    "Key for binary valued metadata entry needs to have suffix indicating binary value.");
                 this.value = null;
-                this.valueBytes = Preconditions.CheckNotNull(valueBytes);
+                Preconditions.CheckNotNull(valueBytes, "valueBytes");
+                this.valueBytes = new byte[valueBytes.Length];
+                Buffer.BlockCopy(valueBytes, 0, this.valueBytes, 0, valueBytes.Length);  // defensive copy to guarantee immutability
             }
 
+            /// <summary>
+            /// Initializes a new instance of the <see cref="Grpc.Core.Metadata+Entry"/> struct holding an ASCII value.
+            /// </summary>
+            /// <param name="key">Metadata key, must not use suffix indicating a binary valued metadata entry.</param>
+            /// <param name="value">Value string. Only ASCII characters are allowed.</param>
             public Entry(string key, string value)
             {
-                this.key = Preconditions.CheckNotNull(key);
-                this.value = Preconditions.CheckNotNull(value);
+                this.key = NormalizeKey(key);
+                Preconditions.CheckArgument(!this.key.EndsWith(BinaryHeaderSuffix),
+                    "Key for ASCII valued metadata entry cannot have suffix indicating binary value.");
+                this.value = Preconditions.CheckNotNull(value, "value");
                 this.valueBytes = null;
             }
 
+            /// <summary>
+            /// Gets the metadata entry key.
+            /// </summary>
             public string Key
             {
                 get
@@ -196,33 +237,86 @@ namespace Grpc.Core
                 }
             }
 
+            /// <summary>
+            /// Gets the binary value of this metadata entry.
+            /// </summary>
             public byte[] ValueBytes
             {
                 get
                 {
                     if (valueBytes == null)
                     {
-                        valueBytes = Encoding.GetBytes(value);
+                        return Encoding.GetBytes(value);
                     }
-                    return valueBytes;
+
+                    // defensive copy to guarantee immutability
+                    var bytes = new byte[valueBytes.Length];
+                    Buffer.BlockCopy(valueBytes, 0, bytes, 0, valueBytes.Length);
+                    return bytes;
                 }
             }
 
+            /// <summary>
+            /// Gets the string value of this metadata entry.
+            /// </summary>
             public string Value
             {
                 get
                 {
-                    if (value == null)
-                    {
-                        value = Encoding.GetString(valueBytes);
-                    }
-                    return value;
+                    Preconditions.CheckState(!IsBinary, "Cannot access string value of a binary metadata entry");
+                    return value ?? Encoding.GetString(valueBytes);
                 }
             }
-                
+
+            /// <summary>
+            /// Returns <c>true</c> if this entry is a binary-value entry.
+            /// </summary>
+            public bool IsBinary
+            {
+                get
+                {
+                    return value == null;
+                }
+            }
+
+            /// <summary>
+            /// Returns a <see cref="System.String"/> that represents the current <see cref="Grpc.Core.Metadata+Entry"/>.
+            /// </summary>
             public override string ToString()
             {
-                return string.Format("[Entry: key={0}, value={1}]", Key, Value);
+                if (IsBinary)
+                {
+                    return string.Format("[Entry: key={0}, valueBytes={1}]", key, valueBytes);
+                }
+                
+                return string.Format("[Entry: key={0}, value={1}]", key, value);
+            }
+
+            /// <summary>
+            /// Gets the serialized value for this entry. For binary metadata entries, this leaks
+            /// the internal <c>valueBytes</c> byte array and caller must not change contents of it.
+            /// </summary>
+            internal byte[] GetSerializedValueUnsafe()
+            {
+                return valueBytes ?? Encoding.GetBytes(value);
+            }
+
+            /// <summary>
+            /// Creates a binary value or ascii value metadata entry from data received from the native layer.
+            /// We trust C core to give us well-formed data, so we don't perform any checks or defensive copying.
+            /// </summary>
+            internal static Entry CreateUnsafe(string key, byte[] valueBytes)
+            {
+                if (key.EndsWith(BinaryHeaderSuffix))
+                {
+                    return new Entry(key, null, valueBytes);
+                }
+                return new Entry(key, Encoding.GetString(valueBytes), null);
+            }
+
+            private static string NormalizeKey(string key)
+            {
+                return Preconditions.CheckNotNull(key, "key").ToLower();
             }
         }
     }
diff --git a/src/csharp/Grpc.Core/Method.cs b/src/csharp/Grpc.Core/Method.cs
index cc047ac9f8..4c53285893 100644
--- a/src/csharp/Grpc.Core/Method.cs
+++ b/src/csharp/Grpc.Core/Method.cs
@@ -41,16 +41,50 @@ namespace Grpc.Core
     /// </summary>
     public enum MethodType
     {
-        Unary,  // Unary request, unary response.
-        ClientStreaming,  // Streaming request, unary response.
-        ServerStreaming,  // Unary request, streaming response.
-        DuplexStreaming  // Streaming request, streaming response.
+        /// <summary>Single request sent from client, single response received from server.</summary>
+        Unary,
+
+        /// <summary>Stream of request sent from client, single response received from server.</summary>
+        ClientStreaming,
+
+        /// <summary>Single request sent from client, stream of responses received from server.</summary>
+        ServerStreaming,
+
+        /// <summary>Both server and client can stream arbitrary number of requests and responses simultaneously.</summary>
+        DuplexStreaming
     }
 
     /// <summary>
-    /// A description of a service method.
+    /// A non-generic representation of a remote method.
     /// </summary>
-    public class Method<TRequest, TResponse>
+    public interface IMethod
+    {
+        /// <summary>
+        /// Gets the type of the method.
+        /// </summary>
+        MethodType Type { get; }
+
+        /// <summary>
+        /// Gets the name of the service to which this method belongs.
+        /// </summary>
+        string ServiceName { get; }
+
+        /// <summary>
+        /// Gets the unqualified name of the method.
+        /// </summary>
+        string Name { get; }
+
+        /// <summary>
+        /// Gets the fully qualified name of the method. On the server side, methods are dispatched
+        /// based on this name.
+        /// </summary>
+        string FullName { get; }
+    }
+
+    /// <summary>
+    /// A description of a remote method.
+    /// </summary>
+    public class Method<TRequest, TResponse> : IMethod
     {
         readonly MethodType type;
         readonly string serviceName;
@@ -59,16 +93,27 @@ namespace Grpc.Core
         readonly Marshaller<TResponse> responseMarshaller;
         readonly string fullName;
 
+        /// <summary>
+        /// Initializes a new instance of the <c>Method</c> class.
+        /// </summary>
+        /// <param name="type">Type of method.</param>
+        /// <param name="serviceName">Name of service this method belongs to.</param>
+        /// <param name="name">Unqualified name of the method.</param>
+        /// <param name="requestMarshaller">Marshaller used for request messages.</param>
+        /// <param name="responseMarshaller">Marshaller used for response messages.</param>
         public Method(MethodType type, string serviceName, string name, Marshaller<TRequest> requestMarshaller, Marshaller<TResponse> responseMarshaller)
         {
             this.type = type;
-            this.serviceName = Preconditions.CheckNotNull(serviceName);
-            this.name = Preconditions.CheckNotNull(name);
-            this.requestMarshaller = Preconditions.CheckNotNull(requestMarshaller);
-            this.responseMarshaller = Preconditions.CheckNotNull(responseMarshaller);
-            this.fullName = GetFullName(serviceName);
+            this.serviceName = Preconditions.CheckNotNull(serviceName, "serviceName");
+            this.name = Preconditions.CheckNotNull(name, "name");
+            this.requestMarshaller = Preconditions.CheckNotNull(requestMarshaller, "requestMarshaller");
+            this.responseMarshaller = Preconditions.CheckNotNull(responseMarshaller, "responseMarshaller");
+            this.fullName = GetFullName(serviceName, name);
         }
 
+        /// <summary>
+        /// Gets the type of the method.
+        /// </summary>
         public MethodType Type
         {
             get
@@ -77,6 +122,9 @@ namespace Grpc.Core
             }
         }
             
+        /// <summary>
+        /// Gets the name of the service to which this method belongs.
+        /// </summary>
         public string ServiceName
         {
             get
@@ -85,6 +133,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets the unqualified name of the method.
+        /// </summary>
         public string Name
         {
             get
@@ -93,6 +144,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets the marshaller used for request messages.
+        /// </summary>
         public Marshaller<TRequest> RequestMarshaller
         {
             get
@@ -101,6 +155,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Gets the marshaller used for response messages.
+        /// </summary>
         public Marshaller<TResponse> ResponseMarshaller
         {
             get
@@ -108,7 +165,11 @@ namespace Grpc.Core
                 return this.responseMarshaller;
             }
         }
-
+            
+        /// <summary>
+        /// Gets the fully qualified name of the method. On the server side, methods are dispatched
+        /// based on this name.
+        /// </summary>
         public string FullName
         {
             get
@@ -120,9 +181,9 @@ namespace Grpc.Core
         /// <summary>
         /// Gets full name of the method including the service name.
         /// </summary>
-        internal string GetFullName(string serviceName)
+        internal static string GetFullName(string serviceName, string methodName)
         {
-            return "/" + Preconditions.CheckNotNull(serviceName) + "/" + this.Name;
+            return "/" + serviceName + "/" + methodName;
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/RpcException.cs b/src/csharp/Grpc.Core/RpcException.cs
index c58578286b..cac417e626 100644
--- a/src/csharp/Grpc.Core/RpcException.cs
+++ b/src/csharp/Grpc.Core/RpcException.cs
@@ -36,22 +36,34 @@ using System;
 namespace Grpc.Core
 {
     /// <summary>
-    /// Thrown when remote procedure call fails.
+    /// Thrown when remote procedure call fails. Every <c>RpcException</c> is associated with a resulting <see cref="Status"/> of the call.
     /// </summary>
     public class RpcException : Exception
     {
         private readonly Status status;
 
+        /// <summary>
+        /// Creates a new <c>RpcException</c> associated with given status.
+        /// </summary>
+        /// <param name="status">Resulting status of a call.</param>
         public RpcException(Status status) : base(status.ToString())
         {
             this.status = status;
         }
 
+        /// <summary>
+        /// Creates a new <c>RpcException</c> associated with given status and message.
+        /// </summary>
+        /// <param name="status">Resulting status of a call.</param>
+        /// <param name="message">The exception message.</param> 
         public RpcException(Status status, string message) : base(message)
         {
             this.status = status;
         }
 
+        /// <summary>
+        /// Resulting status of the call.
+        /// </summary>
         public Status Status
         {
             get
diff --git a/src/csharp/Grpc.Core/Server.cs b/src/csharp/Grpc.Core/Server.cs
index eb5b043d1c..28f1686e20 100644
--- a/src/csharp/Grpc.Core/Server.cs
+++ b/src/csharp/Grpc.Core/Server.cs
@@ -50,6 +50,8 @@ namespace Grpc.Core
     {
         static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<Server>();
 
+        readonly AtomicCounter activeCallCounter = new AtomicCounter();
+
         readonly ServiceDefinitionCollection serviceDefinitions;
         readonly ServerPortCollection ports;
         readonly GrpcEnvironment environment;
@@ -73,7 +75,7 @@ namespace Grpc.Core
         {
             this.serviceDefinitions = new ServiceDefinitionCollection(this);
             this.ports = new ServerPortCollection(this);
-            this.environment = GrpcEnvironment.GetInstance();
+            this.environment = GrpcEnvironment.AddRef();
             this.options = options != null ? new List<ChannelOption>(options) : new List<ChannelOption>();
             using (var channelArgs = ChannelOptions.CreateChannelArgs(this.options))
             {
@@ -106,6 +108,17 @@ namespace Grpc.Core
         }
 
         /// <summary>
+        /// To allow awaiting termination of the server.
+        /// </summary>
+        public Task ShutdownTask
+        {
+            get
+            {
+                return shutdownTcs.Task;
+            }
+        }
+
+        /// <summary>
         /// Starts the server.
         /// </summary>
         public void Start()
@@ -136,18 +149,9 @@ namespace Grpc.Core
 
             handle.ShutdownAndNotify(HandleServerShutdown, environment);
             await shutdownTcs.Task;
-            handle.Dispose();
-        }
+            DisposeHandle();
 
-        /// <summary>
-        /// To allow awaiting termination of the server.
-        /// </summary>
-        public Task ShutdownTask
-        {
-            get
-            {
-                return shutdownTcs.Task;
-            }
+            await Task.Run(() => GrpcEnvironment.Release());
         }
 
         /// <summary>
@@ -166,7 +170,22 @@ namespace Grpc.Core
             handle.ShutdownAndNotify(HandleServerShutdown, environment);
             handle.CancelAllCalls();
             await shutdownTcs.Task;
-            handle.Dispose();
+            DisposeHandle();
+        }
+
+        internal void AddCallReference(object call)
+        {
+            activeCallCounter.Increment();
+
+            bool success = false;
+            handle.DangerousAddRef(ref success);
+            Preconditions.CheckState(success);
+        }
+
+        internal void RemoveCallReference(object call)
+        {
+            handle.DangerousRelease();
+            activeCallCounter.Decrement();
         }
 
         /// <summary>
@@ -192,7 +211,7 @@ namespace Grpc.Core
         {
             lock (myLock)
             {
-                Preconditions.CheckNotNull(serverPort.Credentials);
+                Preconditions.CheckNotNull(serverPort.Credentials, "serverPort");
                 Preconditions.CheckState(!startRequested);
                 var address = string.Format("{0}:{1}", serverPort.Host, serverPort.Port);
                 int boundPort;
@@ -227,6 +246,16 @@ namespace Grpc.Core
             }
         }
 
+        private void DisposeHandle()
+        {
+            var activeCallCount = activeCallCounter.Count;
+            if (activeCallCount > 0)
+            {
+                Logger.Warning("Server shutdown has finished but there are still {0} active calls for that server.", activeCallCount);
+            }
+            handle.Dispose();
+        }
+
         /// <summary>
         /// Selects corresponding handler for given call and handles the call.
         /// </summary>
@@ -254,7 +283,7 @@ namespace Grpc.Core
         {
             if (success)
             {
-                ServerRpcNew newRpc = ctx.GetServerRpcNew();
+                ServerRpcNew newRpc = ctx.GetServerRpcNew(this);
 
                 // after server shutdown, the callback returns with null call
                 if (!newRpc.Call.IsInvalid)
diff --git a/src/csharp/Grpc.Core/ServerCallContext.cs b/src/csharp/Grpc.Core/ServerCallContext.cs
index 032b1390db..75d81c64f3 100644
--- a/src/csharp/Grpc.Core/ServerCallContext.cs
+++ b/src/csharp/Grpc.Core/ServerCallContext.cs
@@ -36,15 +36,16 @@ using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Tasks;
 
+using Grpc.Core.Internal;
+
 namespace Grpc.Core
 {
     /// <summary>
     /// Context for a server-side call.
     /// </summary>
-    public sealed class ServerCallContext
+    public class ServerCallContext
     {
-        // TODO(jtattermusch): expose method to send initial metadata back to client
-
+        private readonly CallSafeHandle callHandle;
         private readonly string method;
         private readonly string host;
         private readonly string peer;
@@ -54,15 +55,34 @@ namespace Grpc.Core
         private readonly Metadata responseTrailers = new Metadata();
 
         private Status status = Status.DefaultSuccess;
+        private Func<Metadata, Task> writeHeadersFunc;
+        private IHasWriteOptions writeOptionsHolder;
 
-        public ServerCallContext(string method, string host, string peer, DateTime deadline, Metadata requestHeaders, CancellationToken cancellationToken)
+        internal ServerCallContext(CallSafeHandle callHandle, string method, string host, string peer, DateTime deadline, Metadata requestHeaders, CancellationToken cancellationToken,
+            Func<Metadata, Task> writeHeadersFunc, IHasWriteOptions writeOptionsHolder)
         {
+            this.callHandle = callHandle;
             this.method = method;
             this.host = host;
             this.peer = peer;
             this.deadline = deadline;
             this.requestHeaders = requestHeaders;
             this.cancellationToken = cancellationToken;
+            this.writeHeadersFunc = writeHeadersFunc;
+            this.writeOptionsHolder = writeOptionsHolder;
+        }
+
+        public Task WriteResponseHeadersAsync(Metadata responseHeaders)
+        {
+            return writeHeadersFunc(responseHeaders);
+        }
+
+        /// <summary>
+        /// Creates a propagation token to be used to propagate call context to a child call.
+        /// </summary>
+        public ContextPropagationToken CreatePropagationToken(ContextPropagationOptions options = null)
+        {
+            return new ContextPropagationToken(callHandle, deadline, cancellationToken, options);
         }
             
         /// <summary>Name of method called in this RPC.</summary>
@@ -110,7 +130,7 @@ namespace Grpc.Core
             }
         }
 
-        ///<summary>Cancellation token signals when call is cancelled.</summary>
+        /// <summary>Cancellation token signals when call is cancelled.</summary>
         public CancellationToken CancellationToken
         {
             get
@@ -141,5 +161,31 @@ namespace Grpc.Core
                 status = value;
             }
         }
+
+        /// <summary>
+        /// Allows setting write options for the following write.
+        /// For streaming response calls, this property is also exposed as on IServerStreamWriter for convenience.
+        /// Both properties are backed by the same underlying value.
+        /// </summary>
+        public WriteOptions WriteOptions
+        {
+            get
+            {
+                return writeOptionsHolder.WriteOptions;
+            }
+
+            set
+            {
+                writeOptionsHolder.WriteOptions = value;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Allows sharing write options between ServerCallContext and other objects.
+    /// </summary>
+    public interface IHasWriteOptions
+    {
+        WriteOptions WriteOptions { get; set; }
     }
 }
diff --git a/src/csharp/Grpc.Core/ServerCredentials.cs b/src/csharp/Grpc.Core/ServerCredentials.cs
index c11a1ede08..3c6703d30e 100644
--- a/src/csharp/Grpc.Core/ServerCredentials.cs
+++ b/src/csharp/Grpc.Core/ServerCredentials.cs
@@ -91,7 +91,7 @@ namespace Grpc.Core
         {
             this.keyCertificatePairs = new List<KeyCertificatePair>(keyCertificatePairs).AsReadOnly();
             Preconditions.CheckArgument(this.keyCertificatePairs.Count > 0,
-                "At least one KeyCertificatePair needs to be provided");
+                "At least one KeyCertificatePair needs to be provided.");
             if (forceClientAuth)
             {
                 Preconditions.CheckNotNull(rootCertificates,
diff --git a/src/csharp/Grpc.Core/ServerMethods.cs b/src/csharp/Grpc.Core/ServerMethods.cs
index d457770203..1f119a80ff 100644
--- a/src/csharp/Grpc.Core/ServerMethods.cs
+++ b/src/csharp/Grpc.Core/ServerMethods.cs
@@ -31,12 +31,8 @@
 
 #endregion
 
-using System;
-using System.Threading;
 using System.Threading.Tasks;
 
-using Grpc.Core.Internal;
-
 namespace Grpc.Core
 {
     /// <summary>
diff --git a/src/csharp/Grpc.Core/ServerPort.cs b/src/csharp/Grpc.Core/ServerPort.cs
index 55e4bd0062..598404d045 100644
--- a/src/csharp/Grpc.Core/ServerPort.cs
+++ b/src/csharp/Grpc.Core/ServerPort.cs
@@ -62,9 +62,9 @@ namespace Grpc.Core
         /// <param name="credentials">credentials to use to secure this port.</param>
         public ServerPort(string host, int port, ServerCredentials credentials)
         {
-            this.host = Preconditions.CheckNotNull(host);
+            this.host = Preconditions.CheckNotNull(host, "host");
             this.port = port;
-            this.credentials = Preconditions.CheckNotNull(credentials);
+            this.credentials = Preconditions.CheckNotNull(credentials, "credentials");
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/ServerServiceDefinition.cs b/src/csharp/Grpc.Core/ServerServiceDefinition.cs
index a00d156e52..94b0a320c3 100644
--- a/src/csharp/Grpc.Core/ServerServiceDefinition.cs
+++ b/src/csharp/Grpc.Core/ServerServiceDefinition.cs
@@ -79,7 +79,7 @@ namespace Grpc.Core
                     where TRequest : class
                     where TResponse : class
             {
-                callHandlers.Add(method.GetFullName(serviceName), ServerCalls.UnaryCall(method, handler));
+                callHandlers.Add(method.FullName, ServerCalls.UnaryCall(method, handler));
                 return this;
             }
 
@@ -89,7 +89,7 @@ namespace Grpc.Core
                     where TRequest : class
                     where TResponse : class
             {
-                callHandlers.Add(method.GetFullName(serviceName), ServerCalls.ClientStreamingCall(method, handler));
+                callHandlers.Add(method.FullName, ServerCalls.ClientStreamingCall(method, handler));
                 return this;
             }
 
@@ -99,7 +99,7 @@ namespace Grpc.Core
                     where TRequest : class
                     where TResponse : class
             {
-                callHandlers.Add(method.GetFullName(serviceName), ServerCalls.ServerStreamingCall(method, handler));
+                callHandlers.Add(method.FullName, ServerCalls.ServerStreamingCall(method, handler));
                 return this;
             }
 
@@ -109,7 +109,7 @@ namespace Grpc.Core
                     where TRequest : class
                     where TResponse : class
             {
-                callHandlers.Add(method.GetFullName(serviceName), ServerCalls.DuplexStreamingCall(method, handler));
+                callHandlers.Add(method.FullName, ServerCalls.DuplexStreamingCall(method, handler));
                 return this;
             }
 
diff --git a/src/csharp/Grpc.Core/Status.cs b/src/csharp/Grpc.Core/Status.cs
index 754f6cb3ca..6bd8dc820b 100644
--- a/src/csharp/Grpc.Core/Status.cs
+++ b/src/csharp/Grpc.Core/Status.cs
@@ -29,13 +29,12 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 
-using System;
-using System.Runtime.InteropServices;
+using Grpc.Core.Utils;
 
 namespace Grpc.Core
 {
     /// <summary>
-    /// Represents RPC result.
+    /// Represents RPC result, which consists of <see cref="StatusCode"/> and an optional detail string. 
     /// </summary>
     public struct Status
     {
@@ -52,6 +51,11 @@ namespace Grpc.Core
         readonly StatusCode statusCode;
         readonly string detail;
 
+        /// <summary>
+        /// Creates a new instance of <c>Status</c>.
+        /// </summary>
+        /// <param name="statusCode">Status code.</param>
+        /// <param name="detail">Detail.</param>
         public Status(StatusCode statusCode, string detail)
         {
             this.statusCode = statusCode;
@@ -80,6 +84,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Returns a <see cref="System.String"/> that represents the current <see cref="Grpc.Core.Status"/>.
+        /// </summary>
         public override string ToString()
         {
             return string.Format("Status(StatusCode={0}, Detail=\"{1}\")", statusCode, detail);
diff --git a/src/csharp/Grpc.Core/StatusCode.cs b/src/csharp/Grpc.Core/StatusCode.cs
index a9696fa469..90606955af 100644
--- a/src/csharp/Grpc.Core/StatusCode.cs
+++ b/src/csharp/Grpc.Core/StatusCode.cs
@@ -31,8 +31,6 @@
 
 #endregion
 
-using System;
-
 namespace Grpc.Core
 {
     /// <summary>
@@ -41,101 +39,101 @@ namespace Grpc.Core
     /// </summary>
     public enum StatusCode
     {
-        /* Not an error; returned on success */
+        /// <summary>Not an error; returned on success.</summary>
         OK = 0,
-        /* The operation was cancelled (typically by the caller). */
+
+        /// <summary>The operation was cancelled (typically by the caller).</summary>
         Cancelled = 1,
-        /* Unknown error.  An example of where this error may be returned is
-     if a Status value received from another address space belongs to
-     an error-space that is not known in this address space.  Also
-     errors raised by APIs that do not return enough error information
-     may be converted to this error. */
+
+        /// <summary>
+        /// Unknown error.  An example of where this error may be returned is
+        /// if a Status value received from another address space belongs to
+        /// an error-space that is not known in this address space.  Also
+        /// errors raised by APIs that do not return enough error information
+        /// may be converted to this error.
+        /// </summary>
         Unknown = 2,
-        /* Client specified an invalid argument.  Note that this differs
-     from FAILED_PRECONDITION.  INVALID_ARGUMENT indicates arguments
-     that are problematic regardless of the state of the system
-     (e.g., a malformed file name). */
+
+        /// <summary>
+        /// Client specified an invalid argument.  Note that this differs
+        /// from FAILED_PRECONDITION.  INVALID_ARGUMENT indicates arguments
+        /// that are problematic regardless of the state of the system
+        /// (e.g., a malformed file name).
+        /// </summary>
         InvalidArgument = 3,
-        /* Deadline expired before operation could complete.  For operations
-     that change the state of the system, this error may be returned
-     even if the operation has completed successfully.  For example, a
-     successful response from a server could have been delayed long
-     enough for the deadline to expire. */
+
+        /// <summary>
+        /// Deadline expired before operation could complete.  For operations
+        /// that change the state of the system, this error may be returned
+        /// even if the operation has completed successfully.  For example, a
+        /// successful response from a server could have been delayed long
+        /// enough for the deadline to expire.
+        /// </summary>
         DeadlineExceeded = 4,
-        /* Some requested entity (e.g., file or directory) was not found. */
+
+        /// <summary>Some requested entity (e.g., file or directory) was not found.</summary>
         NotFound = 5,
-        /* Some entity that we attempted to create (e.g., file or directory)
-     already exists. */
+
+        /// <summary>Some entity that we attempted to create (e.g., file or directory) already exists.</summary>
         AlreadyExists = 6,
-        /* The caller does not have permission to execute the specified
-     operation.  PERMISSION_DENIED must not be used for rejections
-     caused by exhausting some resource (use RESOURCE_EXHAUSTED
-     instead for those errors).  PERMISSION_DENIED must not be
-     used if the caller can not be identified (use UNAUTHENTICATED
-     instead for those errors). */
+
+        /// <summary>
+        /// The caller does not have permission to execute the specified
+        /// operation.  PERMISSION_DENIED must not be used for rejections
+        /// caused by exhausting some resource (use RESOURCE_EXHAUSTED
+        /// instead for those errors).  PERMISSION_DENIED must not be
+        /// used if the caller can not be identified (use UNAUTHENTICATED
+        /// instead for those errors).
+        /// </summary>
         PermissionDenied = 7,
-        /* The request does not have valid authentication credentials for the
-     operation. */
+
+        /// <summary>The request does not have valid authentication credentials for the operation.</summary>
         Unauthenticated = 16,
-        /* Some resource has been exhausted, perhaps a per-user quota, or
-     perhaps the entire file system is out of space. */
+
+        /// <summary>
+        /// Some resource has been exhausted, perhaps a per-user quota, or
+        /// perhaps the entire file system is out of space.
+        /// </summary>
         ResourceExhausted = 8,
-        /* Operation was rejected because the system is not in a state
-     required for the operation's execution.  For example, directory
-     to be deleted may be non-empty, an rmdir operation is applied to
-     a non-directory, etc.
-
-     A litmus test that may help a service implementor in deciding
-     between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE:
-      (a) Use UNAVAILABLE if the client can retry just the failing call.
-      (b) Use ABORTED if the client should retry at a higher-level
-          (e.g., restarting a read-modify-write sequence).
-      (c) Use FAILED_PRECONDITION if the client should not retry until
-          the system state has been explicitly fixed.  E.g., if an "rmdir"
-          fails because the directory is non-empty, FAILED_PRECONDITION
-          should be returned since the client should not retry unless
-          they have first fixed up the directory by deleting files from it.
-      (d) Use FAILED_PRECONDITION if the client performs conditional
-          REST Get/Update/Delete on a resource and the resource on the
-          server does not match the condition. E.g., conflicting
-          read-modify-write on the same resource. */
+
+        /// <summary>
+        /// Operation was rejected because the system is not in a state
+        /// required for the operation's execution.  For example, directory
+        /// to be deleted may be non-empty, an rmdir operation is applied to
+        /// a non-directory, etc.
+        /// </summary>
         FailedPrecondition = 9,
-        /* The operation was aborted, typically due to a concurrency issue
-     like sequencer check failures, transaction aborts, etc.
 
-     See litmus test above for deciding between FAILED_PRECONDITION,
-     ABORTED, and UNAVAILABLE. */
+        /// <summary>
+        /// The operation was aborted, typically due to a concurrency issue
+        /// like sequencer check failures, transaction aborts, etc.
+        /// </summary>
         Aborted = 10,
-        /* Operation was attempted past the valid range.  E.g., seeking or
-     reading past end of file.
-
-     Unlike INVALID_ARGUMENT, this error indicates a problem that may
-     be fixed if the system state changes. For example, a 32-bit file
-     system will generate INVALID_ARGUMENT if asked to read at an
-     offset that is not in the range [0,2^32-1], but it will generate
-     OUT_OF_RANGE if asked to read from an offset past the current
-     file size.
-
-     There is a fair bit of overlap between FAILED_PRECONDITION and
-     OUT_OF_RANGE.  We recommend using OUT_OF_RANGE (the more specific
-     error) when it applies so that callers who are iterating through
-     a space can easily look for an OUT_OF_RANGE error to detect when
-     they are done. */
+
+        /// <summary>
+        /// Operation was attempted past the valid range.  E.g., seeking or
+        /// reading past end of file.
+        /// </summary>
         OutOfRange = 11,
-        /* Operation is not implemented or not supported/enabled in this service. */
+
+        /// <summary>Operation is not implemented or not supported/enabled in this service.</summary>
         Unimplemented = 12,
-        /* Internal errors.  Means some invariants expected by underlying
-     system has been broken.  If you see one of these errors,
-     something is very broken. */
+
+        /// <summary>
+        /// Internal errors.  Means some invariants expected by underlying
+        /// system has been broken.  If you see one of these errors,
+        /// something is very broken.
+        /// </summary>
         Internal = 13,
-        /* The service is currently unavailable.  This is a most likely a
-     transient condition and may be corrected by retrying with
-     a backoff.
 
-     See litmus test above for deciding between FAILED_PRECONDITION,
-     ABORTED, and UNAVAILABLE. */
+        /// <summary>
+        /// The service is currently unavailable.  This is a most likely a
+        /// transient condition and may be corrected by retrying with
+        /// a backoff.
+        /// </summary>
         Unavailable = 14,
-        /* Unrecoverable data loss or corruption. */
+
+        /// <summary>Unrecoverable data loss or corruption.</summary>
         DataLoss = 15
     }
 }
diff --git a/src/csharp/Grpc.Core/Utils/AsyncStreamExtensions.cs b/src/csharp/Grpc.Core/Utils/AsyncStreamExtensions.cs
index 8a748b45a8..cdf1e51026 100644
--- a/src/csharp/Grpc.Core/Utils/AsyncStreamExtensions.cs
+++ b/src/csharp/Grpc.Core/Utils/AsyncStreamExtensions.cs
@@ -33,7 +33,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 
 namespace Grpc.Core.Utils
@@ -46,7 +45,7 @@ namespace Grpc.Core.Utils
         /// <summary>
         /// Reads the entire stream and executes an async action for each element.
         /// </summary>
-        public static async Task ForEach<T>(this IAsyncStreamReader<T> streamReader, Func<T, Task> asyncAction)
+        public static async Task ForEachAsync<T>(this IAsyncStreamReader<T> streamReader, Func<T, Task> asyncAction)
             where T : class
         {
             while (await streamReader.MoveNext())
@@ -58,7 +57,7 @@ namespace Grpc.Core.Utils
         /// <summary>
         /// Reads the entire stream and creates a list containing all the elements read.
         /// </summary>
-        public static async Task<List<T>> ToList<T>(this IAsyncStreamReader<T> streamReader)
+        public static async Task<List<T>> ToListAsync<T>(this IAsyncStreamReader<T> streamReader)
             where T : class
         {
             var result = new List<T>();
@@ -73,7 +72,7 @@ namespace Grpc.Core.Utils
         /// Writes all elements from given enumerable to the stream.
         /// Completes the stream afterwards unless close = false.
         /// </summary>
-        public static async Task WriteAll<T>(this IClientStreamWriter<T> streamWriter, IEnumerable<T> elements, bool complete = true)
+        public static async Task WriteAllAsync<T>(this IClientStreamWriter<T> streamWriter, IEnumerable<T> elements, bool complete = true)
             where T : class
         {
             foreach (var element in elements)
@@ -89,7 +88,7 @@ namespace Grpc.Core.Utils
         /// <summary>
         /// Writes all elements from given enumerable to the stream.
         /// </summary>
-        public static async Task WriteAll<T>(this IServerStreamWriter<T> streamWriter, IEnumerable<T> elements)
+        public static async Task WriteAllAsync<T>(this IServerStreamWriter<T> streamWriter, IEnumerable<T> elements)
             where T : class
         {
             foreach (var element in elements)
diff --git a/src/csharp/Grpc.Core/Utils/BenchmarkUtil.cs b/src/csharp/Grpc.Core/Utils/BenchmarkUtil.cs
index 82653c3a1f..eb3a5b16e3 100644
--- a/src/csharp/Grpc.Core/Utils/BenchmarkUtil.cs
+++ b/src/csharp/Grpc.Core/Utils/BenchmarkUtil.cs
@@ -39,6 +39,9 @@ using System.Threading.Tasks;
 
 namespace Grpc.Core.Utils
 {
+    /// <summary>
+    /// Utility methods to run microbenchmarks.
+    /// </summary>
     public static class BenchmarkUtil
     {
         /// <summary>
diff --git a/src/csharp/Grpc.Core/Utils/Preconditions.cs b/src/csharp/Grpc.Core/Utils/Preconditions.cs
index aeb5d210a7..374262f87a 100644
--- a/src/csharp/Grpc.Core/Utils/Preconditions.cs
+++ b/src/csharp/Grpc.Core/Utils/Preconditions.cs
@@ -32,17 +32,16 @@
 #endregion
 
 using System;
-using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.Diagnostics;
-using System.Threading.Tasks;
 
 namespace Grpc.Core.Utils
 {
+    /// <summary>
+    /// Utility methods to simplify checking preconditions in the code.
+    /// </summary>
     public static class Preconditions
     {
         /// <summary>
-        /// Throws ArgumentException if condition is false.
+        /// Throws <see cref="ArgumentException"/> if condition is false.
         /// </summary>
         public static void CheckArgument(bool condition)
         {
@@ -53,7 +52,7 @@ namespace Grpc.Core.Utils
         }
 
         /// <summary>
-        /// Throws ArgumentException with given message if condition is false.
+        /// Throws <see cref="ArgumentException"/> with given message if condition is false.
         /// </summary>
         public static void CheckArgument(bool condition, string errorMessage)
         {
@@ -64,31 +63,31 @@ namespace Grpc.Core.Utils
         }
 
         /// <summary>
-        /// Throws NullReferenceException if reference is null.
+        /// Throws <see cref="ArgumentNullException"/> if reference is null.
         /// </summary>
         public static T CheckNotNull<T>(T reference)
         {
             if (reference == null)
             {
-                throw new NullReferenceException();
+                throw new ArgumentNullException();
             }
             return reference;
         }
 
         /// <summary>
-        /// Throws NullReferenceException with given message if reference is null.
+        /// Throws <see cref="ArgumentNullException"/> if reference is null.
         /// </summary>
-        public static T CheckNotNull<T>(T reference, string errorMessage)
+        public static T CheckNotNull<T>(T reference, string paramName)
         {
             if (reference == null)
             {
-                throw new NullReferenceException(errorMessage);
+                throw new ArgumentNullException(paramName);
             }
             return reference;
         }
 
         /// <summary>
-        /// Throws InvalidOperationException if condition is false.
+        /// Throws <see cref="InvalidOperationException"/> if condition is false.
         /// </summary>
         public static void CheckState(bool condition)
         {
@@ -99,7 +98,7 @@ namespace Grpc.Core.Utils
         }
 
         /// <summary>
-        /// Throws InvalidOperationException with given message if condition is false.
+        /// Throws <see cref="InvalidOperationException"/> with given message if condition is false.
         /// </summary>
         public static void CheckState(bool condition, string errorMessage)
         {
diff --git a/src/csharp/Grpc.Core/Version.cs b/src/csharp/Grpc.Core/Version.cs
index b5cb652945..d02b301cac 100644
--- a/src/csharp/Grpc.Core/Version.cs
+++ b/src/csharp/Grpc.Core/Version.cs
@@ -1,5 +1,37 @@
+#region Copyright notice and license
+
+// Copyright 2015, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#endregion
+
 using System.Reflection;
-using System.Runtime.CompilerServices;
 
 // The current version of gRPC C#.
-[assembly: AssemblyVersion(Grpc.Core.VersionInfo.CurrentVersion + ".*")]
+[assembly: AssemblyVersion(Grpc.Core.VersionInfo.CurrentVersion + ".0")]
diff --git a/src/csharp/Grpc.Core/VersionInfo.cs b/src/csharp/Grpc.Core/VersionInfo.cs
index 656a3d47bb..b6dbd3b49c 100644
--- a/src/csharp/Grpc.Core/VersionInfo.cs
+++ b/src/csharp/Grpc.Core/VersionInfo.cs
@@ -1,13 +1,46 @@
-using System.Reflection;
-using System.Runtime.CompilerServices;
+#region Copyright notice and license
+
+// Copyright 2015, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#endregion
 
 namespace Grpc.Core
 {
+    /// <summary>
+    /// Provides info about current version of gRPC.
+    /// </summary>
     public static class VersionInfo
     {
         /// <summary>
         /// Current version of gRPC
         /// </summary>
-        public const string CurrentVersion = "0.6.0";
+        public const string CurrentVersion = "0.6.1";
     }
 }
diff --git a/src/csharp/Grpc.Core/Utils/ExceptionHelper.cs b/src/csharp/Grpc.Core/WriteOptions.cs
index c4d6bee058..7ef3189d76 100644
--- a/src/csharp/Grpc.Core/Utils/ExceptionHelper.cs
+++ b/src/csharp/Grpc.Core/WriteOptions.cs
@@ -33,25 +33,50 @@
 
 using System;
 
-namespace Grpc.Core.Utils
+namespace Grpc.Core
 {
-    public static class ExceptionHelper
+    /// <summary>
+    /// Flags for write operations.
+    /// </summary>
+    [Flags]
+    public enum WriteFlags
     {
         /// <summary>
-        /// If inner exceptions contain RpcException, rethrows it.
-        /// Otherwise, rethrows the original aggregate exception.
-        /// Always throws, the exception return type is here only to make the.
+        /// Hint that the write may be buffered and need not go out on the wire immediately.
+        /// gRPC is free to buffer the message until the next non-buffered
+        /// write, or until write stream completion, but it need not buffer completely or at all.
         /// </summary>
-        public static Exception UnwrapRpcException(AggregateException ae)
+        BufferHint = 0x1,
+
+        /// <summary>
+        /// Force compression to be disabled for a particular write.
+        /// </summary>
+        NoCompress = 0x2
+    }
+
+    /// <summary>
+    /// Options for write operations.
+    /// </summary>
+    public class WriteOptions
+    {
+        /// <summary>
+        /// Default write options.
+        /// </summary>
+        public static readonly WriteOptions Default = new WriteOptions();
+            
+        private WriteFlags flags;
+
+        public WriteOptions(WriteFlags flags = default(WriteFlags))
+        {
+            this.flags = flags;
+        }
+
+        public WriteFlags Flags
         {
-            foreach (var e in ae.InnerExceptions)
+            get
             {
-                if (e is RpcException)
-                {
-                    throw e;
-                }
+                return this.flags;
             }
-            throw ae;
         }
     }
 }