6 files changed, 521 insertions, 49 deletions
diff --git a/src/csharp/Grpc.Core/CallInvoker.cs b/src/csharp/Grpc.Core/CallInvoker.cs
new file mode 100644
index 0000000000..39199b1fd5
--- /dev/null
+++ b/src/csharp/Grpc.Core/CallInvoker.cs
@@ -0,0 +1,84 @@
+#region Copyright notice and license
+
+// Copyright 2015-2016, 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.Threading.Tasks;
+using Grpc.Core.Internal;
+
+namespace Grpc.Core
+{
+    /// <summary>
+    /// Abstraction of client-side RPC invocation.
+    /// </summary>
+    /// <seealso cref="Calls"/>
+    public abstract class CallInvoker
+    {
+        /// <summary>
+        /// Invokes a simple remote call in a blocking fashion.
+        /// </summary>
+        public abstract TResponse BlockingUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+            where TRequest : class
+            where TResponse : class;
+
+        /// <summary>
+        /// Invokes a simple remote call asynchronously.
+        /// </summary>
+        public abstract AsyncUnaryCall<TResponse> AsyncUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+            where TRequest : class
+            where TResponse : class;
+
+        /// <summary>
+        /// Invokes a server streaming call asynchronously.
+        /// In server streaming scenario, client sends on request and server responds with a stream of responses.
+        /// </summary>
+        public abstract AsyncServerStreamingCall<TResponse> AsyncServerStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+            where TRequest : class
+            where TResponse : class;
+
+        /// <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>
+        public abstract AsyncClientStreamingCall<TRequest, TResponse> AsyncClientStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+            where TRequest : class
+            where TResponse : class;
+
+        /// <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>
+        public abstract AsyncDuplexStreamingCall<TRequest, TResponse> AsyncDuplexStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+            where TRequest : class
+            where TResponse : class;
+    }
+}
diff --git a/src/csharp/Grpc.Core/ClientBase.cs b/src/csharp/Grpc.Core/ClientBase.cs
index e5b398062b..5517233e3c 100644
--- a/src/csharp/Grpc.Core/ClientBase.cs
+++ b/src/csharp/Grpc.Core/ClientBase.cs
@@ -1,6 +1,6 @@
 #region Copyright notice and license
 
-// Copyright 2015, Google Inc.
+// Copyright 2015-2016, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
@@ -31,93 +31,156 @@
 
 #endregion
 
-using System;
-using System.Text.RegularExpressions;
-using System.Threading.Tasks;
+using Grpc.Core.Internal;
+using Grpc.Core.Utils;
 
 namespace Grpc.Core
 {
     /// <summary>
-    /// Interceptor for call headers.
+    /// Generic base class for client-side stubs.
     /// </summary>
-    /// <remarks>Header interceptor is no longer to recommented way to perform authentication.
-    /// For header (initial metadata) based auth such as OAuth2 or JWT access token, use <see cref="MetadataCredentials"/>.
-    /// </remarks>
-    public delegate void HeaderInterceptor(IMethod method, Metadata metadata);
+    public abstract class ClientBase<T> : ClientBase
+        where T : ClientBase<T>
+    {
+        /// <summary>
+        /// Initializes a new instance of <c>ClientBase</c> class that
+        /// throws <c>NotImplementedException</c> upon invocation of any RPC.
+        /// This constructor is only provided to allow creation of test doubles
+        /// for client classes (e.g. mocking requires a parameterless constructor).
+        /// </summary>
+        protected ClientBase() : base()
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <c>ClientBase</c> class.
+        /// </summary>
+        /// <param name="configuration">The configuration.</param>
+        protected ClientBase(ClientBaseConfiguration configuration) : base(configuration)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <c>ClientBase</c> class.
+        /// </summary>
+        /// <param name="channel">The channel to use for remote call invocation.</param>
+        public ClientBase(Channel channel) : base(channel)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <c>ClientBase</c> class.
+        /// </summary>
+        /// <param name="callInvoker">The <c>CallInvoker</c> for remote call invocation.</param>
+        public ClientBase(CallInvoker callInvoker) : base(callInvoker)
+        {
+        }
+
+        /// <summary>
+        /// Creates a new client that sets host field for calls explicitly.
+        /// gRPC supports multiple "hosts" being served by a single server.
+        /// By default (if a client was not created by calling this method),
+        /// host <c>null</c> with the meaning "use default host" is used.
+        /// </summary>
+        public T WithHost(string host)
+        {
+            var newConfiguration = this.Configuration.WithHost(host);
+            return NewInstance(newConfiguration);
+        }
+
+        /// <summary>
+        /// Creates a new instance of client from given <c>ClientBaseConfiguration</c>.
+        /// </summary>
+        protected abstract T NewInstance(ClientBaseConfiguration configuration);
+    }
 
     /// <summary>
     /// Base class for client-side stubs.
     /// </summary>
     public abstract class ClientBase
     {
-        readonly Channel channel;
+        readonly ClientBaseConfiguration configuration;
+        readonly CallInvoker callInvoker;
+
+        /// <summary>
+        /// Initializes a new instance of <c>ClientBase</c> class that
+        /// throws <c>NotImplementedException</c> upon invocation of any RPC.
+        /// This constructor is only provided to allow creation of test doubles
+        /// for client classes (e.g. mocking requires a parameterless constructor).
+        /// </summary>
+        protected ClientBase() : this(new UnimplementedCallInvoker())
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of <c>ClientBase</c> class.
+        /// </summary>
+        /// <param name="configuration">The configuration.</param>
+        protected ClientBase(ClientBaseConfiguration configuration)
+        {
+            this.configuration = GrpcPreconditions.CheckNotNull(configuration, "configuration");
+            this.callInvoker = configuration.CreateDecoratedCallInvoker();
+        }
 
         /// <summary>
         /// Initializes a new instance of <c>ClientBase</c> class.
         /// </summary>
         /// <param name="channel">The channel to use for remote call invocation.</param>
-        public ClientBase(Channel channel)
+        public ClientBase(Channel channel) : this(new DefaultCallInvoker(channel))
         {
-            this.channel = channel;
         }
 
         /// <summary>
-        /// Can be used to register a custom header interceptor.
-        /// The interceptor is invoked each time a new call on this client is started.
-        /// It is not recommented to use header interceptor to add auth headers to RPC calls.
+        /// Initializes a new instance of <c>ClientBase</c> class.
         /// </summary>
-        /// <seealso cref="HeaderInterceptor"/>
-        public HeaderInterceptor HeaderInterceptor
+        /// <param name="callInvoker">The <c>CallInvoker</c> for remote call invocation.</param>
+        public ClientBase(CallInvoker callInvoker) : this(new ClientBaseConfiguration(callInvoker, null))
         {
-            get;
-            set;
         }
 
         /// <summary>
-        /// 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".
+        /// Gets the call invoker.
         /// </summary>
-        public string Host
+        protected CallInvoker CallInvoker
         {
-            get;
-            set;
+            get { return this.callInvoker; }
         }
 
         /// <summary>
-        /// Channel associated with this client.
+        /// Gets the configuration.
         /// </summary>
-        public Channel Channel
+        internal ClientBaseConfiguration Configuration
         {
-            get
-            {
-                return this.channel;
-            }
+            get { return this.configuration; }
         }
 
         /// <summary>
-        /// Creates a new call to given method.
+        /// Represents configuration of ClientBase. The class itself is visible to
+        /// subclasses, but contents are marked as internal to make the instances opaque.
+        /// The verbose name of this class was chosen to make name clash in generated code 
+        /// less likely.
         /// </summary>
-        /// <param name="method">The method to invoke.</param>
-        /// <param name="options">The call options.</param>
-        /// <typeparam name="TRequest">Request message type.</typeparam>
-        /// <typeparam name="TResponse">Response message type.</typeparam>
-        /// <returns>The call invocation details.</returns>
-        protected CallInvocationDetails<TRequest, TResponse> CreateCall<TRequest, TResponse>(Method<TRequest, TResponse> method, CallOptions options)
-            where TRequest : class
-            where TResponse : class
+        protected internal class ClientBaseConfiguration
         {
-            var interceptor = HeaderInterceptor;
-            if (interceptor != null)
+            readonly CallInvoker undecoratedCallInvoker;
+            readonly string host;
+
+            internal ClientBaseConfiguration(CallInvoker undecoratedCallInvoker, string host)
+            {
+                this.undecoratedCallInvoker = GrpcPreconditions.CheckNotNull(undecoratedCallInvoker);
+                this.host = host;
+            }
+
+            internal CallInvoker CreateDecoratedCallInvoker()
+            {
+                return new InterceptingCallInvoker(undecoratedCallInvoker, hostInterceptor: (h) => host);
+            }
+
+            internal ClientBaseConfiguration WithHost(string host)
             {
-                if (options.Headers == null)
-                {
-                    options = options.WithHeaders(new Metadata());
-                }
-                interceptor(method, options.Headers);
+                GrpcPreconditions.CheckNotNull(host, "host");
+                return new ClientBaseConfiguration(this.undecoratedCallInvoker, host);
             }
-            return new CallInvocationDetails<TRequest, TResponse>(channel, method, Host, options);
         }
     }
 }
diff --git a/src/csharp/Grpc.Core/DefaultCallInvoker.cs b/src/csharp/Grpc.Core/DefaultCallInvoker.cs
new file mode 100644
index 0000000000..1a99e41153
--- /dev/null
+++ b/src/csharp/Grpc.Core/DefaultCallInvoker.cs
@@ -0,0 +1,112 @@
+#region Copyright notice and license
+
+// Copyright 2015-2016, 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.Threading.Tasks;
+using Grpc.Core.Internal;
+using Grpc.Core.Utils;
+
+namespace Grpc.Core
+{
+    /// <summary>
+    /// Invokes client RPCs using <see cref="Calls"/>.
+    /// </summary>
+    public class DefaultCallInvoker : CallInvoker
+    {
+        readonly Channel channel;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Grpc.Core.DefaultCallInvoker"/> class.
+        /// </summary>
+        /// <param name="channel">Channel to use.</param>
+        public DefaultCallInvoker(Channel channel)
+        {
+            this.channel = GrpcPreconditions.CheckNotNull(channel);
+        }
+
+        /// <summary>
+        /// Invokes a simple remote call in a blocking fashion.
+        /// </summary>
+        public override TResponse BlockingUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            var call = CreateCall(method, host, options);
+            return Calls.BlockingUnaryCall(call, request);
+        }
+
+        /// <summary>
+        /// Invokes a simple remote call asynchronously.
+        /// </summary>
+        public override AsyncUnaryCall<TResponse> AsyncUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            var call = CreateCall(method, host, options);
+            return Calls.AsyncUnaryCall(call, request);
+        }
+
+        /// <summary>
+        /// Invokes a server streaming call asynchronously.
+        /// In server streaming scenario, client sends on request and server responds with a stream of responses.
+        /// </summary>
+        public override AsyncServerStreamingCall<TResponse> AsyncServerStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            var call = CreateCall(method, host, options);
+            return Calls.AsyncServerStreamingCall(call, request);
+        }
+
+        /// <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>
+        public override AsyncClientStreamingCall<TRequest, TResponse> AsyncClientStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+        {
+            var call = CreateCall(method, host, options);
+            return Calls.AsyncClientStreamingCall(call);
+        }
+
+        /// <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>
+        public override AsyncDuplexStreamingCall<TRequest, TResponse> AsyncDuplexStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+        {
+            var call = CreateCall(method, host, options);
+            return Calls.AsyncDuplexStreamingCall(call);
+        }
+
+        protected virtual CallInvocationDetails<TRequest, TResponse> CreateCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+                where TRequest : class
+                where TResponse : class
+        {
+            return new CallInvocationDetails<TRequest, TResponse>(channel, method, host, options);
+        }
+    }
+}
diff --git a/src/csharp/Grpc.Core/Grpc.Core.csproj b/src/csharp/Grpc.Core/Grpc.Core.csproj
index 3189835ccd..251a688946 100644
--- a/src/csharp/Grpc.Core/Grpc.Core.csproj
+++ b/src/csharp/Grpc.Core/Grpc.Core.csproj
@@ -129,6 +129,10 @@
     <Compile Include="Profiling\Profilers.cs" />
     <Compile Include="Internal\DefaultSslRootsOverride.cs" />
     <Compile Include="Utils\GrpcPreconditions.cs" />
+    <Compile Include="CallInvoker.cs" />
+    <Compile Include="DefaultCallInvoker.cs" />
+    <Compile Include="Internal\UnimplementedCallInvoker.cs" />
+    <Compile Include="Internal\InterceptingCallInvoker.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="Grpc.Core.nuspec" />
diff --git a/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs b/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs
new file mode 100644
index 0000000000..ef48dc7121
--- /dev/null
+++ b/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs
@@ -0,0 +1,134 @@
+#region Copyright notice and license
+
+// Copyright 2015-2016, 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.Tasks;
+using Grpc.Core;
+using Grpc.Core.Utils;
+
+namespace Grpc.Core.Internal
+{
+    /// <summary>
+    /// Decorates an underlying <c>CallInvoker</c> to intercept call invocations.
+    /// </summary>
+    internal class InterceptingCallInvoker : CallInvoker
+    {
+        readonly CallInvoker callInvoker;
+        readonly Func<string, string> hostInterceptor;
+        readonly Func<CallOptions, CallOptions> callOptionsInterceptor;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Grpc.Core.InterceptingCallInvoker"/> class.
+        /// </summary>
+        public InterceptingCallInvoker(CallInvoker callInvoker,
+            Func<string, string> hostInterceptor = null,
+            Func<CallOptions, CallOptions> callOptionsInterceptor = null)
+        {
+            this.callInvoker = GrpcPreconditions.CheckNotNull(callInvoker);
+            this.hostInterceptor = hostInterceptor;
+            this.callOptionsInterceptor = callOptionsInterceptor;
+        }
+
+        /// <summary>
+        /// Intercepts a unary call.
+        /// </summary>
+        public override TResponse BlockingUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            host = InterceptHost(host);
+            options = InterceptCallOptions(options);
+            return callInvoker.BlockingUnaryCall(method, host, options, request);
+        }
+
+        /// <summary>
+        /// Invokes a simple remote call asynchronously.
+        /// </summary>
+        public override AsyncUnaryCall<TResponse> AsyncUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            host = InterceptHost(host);
+            options = InterceptCallOptions(options);
+            return callInvoker.AsyncUnaryCall(method, host, options, request);
+        }
+
+        /// <summary>
+        /// Invokes a server streaming call asynchronously.
+        /// In server streaming scenario, client sends on request and server responds with a stream of responses.
+        /// </summary>
+        public override AsyncServerStreamingCall<TResponse> AsyncServerStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            host = InterceptHost(host);
+            options = InterceptCallOptions(options);
+            return callInvoker.AsyncServerStreamingCall(method, host, options, request);
+        }
+
+        /// <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>
+        public override AsyncClientStreamingCall<TRequest, TResponse> AsyncClientStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+        {
+            host = InterceptHost(host);
+            options = InterceptCallOptions(options);
+            return callInvoker.AsyncClientStreamingCall(method, host, options);
+        }
+
+        /// <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>
+        public override AsyncDuplexStreamingCall<TRequest, TResponse> AsyncDuplexStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+        {
+            host = InterceptHost(host);
+            options = InterceptCallOptions(options);
+            return callInvoker.AsyncDuplexStreamingCall(method, host, options);
+        }
+
+        private string InterceptHost(string host)
+        {
+            if (hostInterceptor == null)
+            {
+                return host;
+            }
+            return hostInterceptor(host);
+        }
+
+        private CallOptions InterceptCallOptions(CallOptions options)
+        {
+            if (callOptionsInterceptor == null)
+            {
+                return options;
+            }
+            return callOptionsInterceptor(options);
+        }
+    }
+}
diff --git a/src/csharp/Grpc.Core/Internal/UnimplementedCallInvoker.cs b/src/csharp/Grpc.Core/Internal/UnimplementedCallInvoker.cs
new file mode 100644
index 0000000000..0c7340873b
--- /dev/null
+++ b/src/csharp/Grpc.Core/Internal/UnimplementedCallInvoker.cs
@@ -0,0 +1,75 @@
+#region Copyright notice and license
+
+// Copyright 2015-2016, 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.Tasks;
+using Grpc.Core;
+using Grpc.Core.Utils;
+
+namespace Grpc.Core.Internal
+{
+    /// <summary>
+    /// Call invoker that throws <c>NotImplementedException</c> for all requests.
+    /// </summary>
+    internal class UnimplementedCallInvoker : CallInvoker
+    {
+        public UnimplementedCallInvoker()
+        {
+        }
+
+        public override TResponse BlockingUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override AsyncUnaryCall<TResponse> AsyncUnaryCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override AsyncServerStreamingCall<TResponse> AsyncServerStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options, TRequest request)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override AsyncClientStreamingCall<TRequest, TResponse> AsyncClientStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override AsyncDuplexStreamingCall<TRequest, TResponse> AsyncDuplexStreamingCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}