7 files changed, 218 insertions, 2 deletions
diff --git a/include/grpcpp/channel.h b/include/grpcpp/channel.h
index f1dba5b8ad..b7c9e354de 100644
--- a/include/grpcpp/channel.h
+++ b/include/grpcpp/channel.h
@@ -24,6 +24,7 @@
 #include <grpc/grpc.h>
 #include <grpcpp/impl/call.h>
 #include <grpcpp/impl/codegen/channel_interface.h>
+#include <grpcpp/impl/codegen/client_interceptor.h>
 #include <grpcpp/impl/codegen/config.h>
 #include <grpcpp/impl/codegen/grpc_library.h>
 
@@ -62,8 +63,14 @@ class Channel final : public ChannelInterface,
   friend class internal::BlockingUnaryCallImpl;
   friend void experimental::ChannelResetConnectionBackoff(Channel* channel);
   friend std::shared_ptr<Channel> CreateChannelInternal(
-      const grpc::string& host, grpc_channel* c_channel);
-  Channel(const grpc::string& host, grpc_channel* c_channel);
+      const grpc::string& host, grpc_channel* c_channel,
+      std::unique_ptr<std::vector<
+          std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+          interceptor_creators);
+  Channel(const grpc::string& host, grpc_channel* c_channel,
+          std::unique_ptr<std::vector<
+              std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+              interceptor_creators);
 
   internal::Call CreateCall(const internal::RpcMethod& method,
                             ClientContext* context,
@@ -91,6 +98,9 @@ class Channel final : public ChannelInterface,
   // It is _not owned_ by the channel; ownership belongs with its internal
   // shutdown callback tag (invoked when the CQ is fully shutdown).
   CompletionQueue* callback_cq_ = nullptr;
+
+  std::vector<std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>
+      interceptor_creators_;
 };
 
 }  // namespace grpc
diff --git a/include/grpcpp/create_channel.h b/include/grpcpp/create_channel.h
index 7a505a7127..43188d09e7 100644
--- a/include/grpcpp/create_channel.h
+++ b/include/grpcpp/create_channel.h
@@ -22,6 +22,7 @@
 #include <memory>
 
 #include <grpcpp/channel.h>
+#include <grpcpp/impl/codegen/client_interceptor.h>
 #include <grpcpp/security/credentials.h>
 #include <grpcpp/support/channel_arguments.h>
 #include <grpcpp/support/config.h>
@@ -53,6 +54,26 @@ std::shared_ptr<Channel> CreateCustomChannel(
     const std::shared_ptr<ChannelCredentials>& creds,
     const ChannelArguments& args);
 
+namespace experimental {
+/// Create a new \em custom \a Channel pointing to \a target with \a
+/// interceptors being invoked per call.
+///
+/// \warning For advanced use and testing ONLY. Override default channel
+/// arguments only if necessary.
+///
+/// \param target The URI of the endpoint to connect to.
+/// \param creds Credentials to use for the created channel. If it does not
+/// hold an object or is invalid, a lame channel (one on which all operations
+/// fail) is returned.
+/// \param args Options for channel creation.
+std::shared_ptr<Channel> CreateCustomChannelWithInterceptors(
+    const grpc::string& target,
+    const std::shared_ptr<ChannelCredentials>& creds,
+    const ChannelArguments& args,
+    std::unique_ptr<std::vector<
+        std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+        interceptor_creators);
+}  // namespace experimental
 }  // namespace grpc
 
 #endif  // GRPCPP_CREATE_CHANNEL_H
diff --git a/include/grpcpp/create_channel_posix.h b/include/grpcpp/create_channel_posix.h
index 9bf5acc45c..808514041b 100644
--- a/include/grpcpp/create_channel_posix.h
+++ b/include/grpcpp/create_channel_posix.h
@@ -45,6 +45,23 @@ std::shared_ptr<Channel> CreateInsecureChannelFromFd(const grpc::string& target,
 std::shared_ptr<Channel> CreateCustomInsecureChannelFromFd(
     const grpc::string& target, int fd, const ChannelArguments& args);
 
+namespace experimental {
+
+/// Create a new \a Channel communicating over given file descriptor with custom
+/// channel arguments.
+///
+/// \param target The name of the target.
+/// \param fd The file descriptor representing a socket.
+/// \param args Options for channel creation.
+/// \param interceptor_creators Vector of interceptor factory objects.
+std::shared_ptr<Channel> CreateCustomInsecureChannelWithInterceptorsFromFd(
+    const grpc::string& target, int fd, const ChannelArguments& args,
+    std::unique_ptr<std::vector<
+        std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+        interceptor_creators);
+
+}  // namespace experimental
+
 #endif  // GPR_SUPPORT_CHANNELS_FROM_FD
 
 }  // namespace grpc
diff --git a/include/grpcpp/impl/codegen/client_interceptor.h b/include/grpcpp/impl/codegen/client_interceptor.h
new file mode 100644
index 0000000000..f460c5ac0c
--- /dev/null
+++ b/include/grpcpp/impl/codegen/client_interceptor.h
@@ -0,0 +1,44 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPCPP_IMPL_CODEGEN_CLIENT_INTERCEPTOR_H
+#define GRPCPP_IMPL_CODEGEN_CLIENT_INTERCEPTOR_H
+
+#include <grpcpp/impl/codegen/interceptor.h>
+
+namespace grpc {
+namespace experimental {
+class ClientInterceptor {
+ public:
+  virtual ~ClientInterceptor() {}
+
+  virtual void Intercept(InterceptorBatchMethods* methods) = 0;
+};
+
+class ClientRpcInfo {};
+
+class ClientInterceptorFactoryInterface {
+ public:
+  virtual ~ClientInterceptorFactoryInterface() {}
+  virtual ClientInterceptor* CreateClientInterceptor(ClientRpcInfo* info) = 0;
+};
+
+}  // namespace experimental
+}  // namespace grpc
+
+#endif  // GRPCPP_IMPL_CODEGEN_CLIENT_INTERCEPTOR_H
diff --git a/include/grpcpp/impl/codegen/interceptor.h b/include/grpcpp/impl/codegen/interceptor.h
new file mode 100644
index 0000000000..6402a3a946
--- /dev/null
+++ b/include/grpcpp/impl/codegen/interceptor.h
@@ -0,0 +1,67 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPCPP_IMPL_CODEGEN_INTERCEPTOR_H
+#define GRPCPP_IMPL_CODEGEN_INTERCEPTOR_H
+
+namespace grpc {
+namespace experimental {
+class InterceptedMessage {
+ public:
+  template <class M>
+  bool Extract(M* msg);  // returns false if definitely invalid extraction
+  template <class M>
+  M* MutableExtract();
+  uint64_t length();  // length on wire
+};
+
+enum class InterceptionHookPoints {
+  /* The first two in this list are for clients and servers */
+  PRE_SEND_INITIAL_METADATA,
+  PRE_SEND_MESSAGE,
+  PRE_SEND_STATUS /* server only */,
+  /* The following three are for hijacked clients only and can only be
+     registered by the global interceptor */
+  PRE_RECV_INITIAL_METADATA,
+  PRE_RECV_MESSAGE,
+  PRE_RECV_STATUS,
+  /* The following two are for all clients and servers */
+  POST_RECV_INITIAL_METADATA,
+  POST_RECV_MESSAGE,
+  POST_RECV_STATUS /* client only */,
+  POST_RECV_CLOSE /* server only */,
+  NUM_INTERCEPTION_HOOKS
+};
+
+class InterceptorBatchMethods {
+ public:
+  virtual ~InterceptorBatchMethods();
+  // Queries to check whether the current batch has an interception hook point
+  // of type \a type
+  virtual bool QueryInterceptionHookPoint(InterceptionHookPoints type) = 0;
+  // Calling this will signal that the interceptor is done intercepting the
+  // current batch of the RPC
+  virtual void Proceed() = 0;
+  // Calling this indicates that the interceptor has hijacked the RPC (only
+  // valid if the batch contains send_initial_metadata on the client side)
+  virtual void Hijack() = 0;
+};
+}  // namespace experimental
+}  // namespace grpc
+
+#endif  // GRPCPP_IMPL_CODEGEN_INTERCEPTOR_H
diff --git a/include/grpcpp/security/credentials.h b/include/grpcpp/security/credentials.h
index bfadc15df5..8dfbdec3e6 100644
--- a/include/grpcpp/security/credentials.h
+++ b/include/grpcpp/security/credentials.h
@@ -24,6 +24,7 @@
 #include <vector>
 
 #include <grpc/grpc_security_constants.h>
+#include <grpcpp/impl/codegen/client_interceptor.h>
 #include <grpcpp/impl/codegen/grpc_library.h>
 #include <grpcpp/security/auth_context.h>
 #include <grpcpp/support/status.h>
@@ -38,6 +39,18 @@ class SecureChannelCredentials;
 class CallCredentials;
 class SecureCallCredentials;
 
+class ChannelCredentials;
+
+namespace experimental {
+std::shared_ptr<Channel> CreateCustomChannelWithInterceptors(
+    const grpc::string& target,
+    const std::shared_ptr<ChannelCredentials>& creds,
+    const ChannelArguments& args,
+    std::unique_ptr<std::vector<
+        std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+        interceptor_creators);
+}  // namespace experimental
+
 /// A channel credentials object encapsulates all the state needed by a client
 /// to authenticate with a server for a given channel.
 /// It can make various assertions, e.g., about the client’s identity, role
@@ -62,8 +75,27 @@ class ChannelCredentials : private GrpcLibraryCodegen {
       const std::shared_ptr<ChannelCredentials>& creds,
       const ChannelArguments& args);
 
+  friend std::shared_ptr<Channel>
+  experimental::CreateCustomChannelWithInterceptors(
+      const grpc::string& target,
+      const std::shared_ptr<ChannelCredentials>& creds,
+      const ChannelArguments& args,
+      std::unique_ptr<std::vector<
+          std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+          interceptor_creators);
+
   virtual std::shared_ptr<Channel> CreateChannel(
       const grpc::string& target, const ChannelArguments& args) = 0;
+
+  // This function should have been a pure virtual function, but it is
+  // implemented as a virtual function so that it does not break API.
+  virtual std::shared_ptr<Channel> CreateChannelWithInterceptors(
+      const grpc::string& target, const ChannelArguments& args,
+      std::unique_ptr<std::vector<
+          std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+          interceptor_creators) {
+    return nullptr;
+  };
 };
 
 /// A call credentials object encapsulates the state needed by a client to
diff --git a/include/grpcpp/server.h b/include/grpcpp/server.h
index 72544c0f0b..8d3e856502 100644
--- a/include/grpcpp/server.h
+++ b/include/grpcpp/server.h
@@ -28,6 +28,7 @@
 #include <grpc/compression.h>
 #include <grpcpp/completion_queue.h>
 #include <grpcpp/impl/call.h>
+#include <grpcpp/impl/codegen/client_interceptor.h>
 #include <grpcpp/impl/codegen/grpc_library.h>
 #include <grpcpp/impl/codegen/server_interface.h>
 #include <grpcpp/impl/rpc_service_method.h>
@@ -99,6 +100,30 @@ class Server : public ServerInterface, private GrpcLibraryCodegen {
   /// Establish a channel for in-process communication
   std::shared_ptr<Channel> InProcessChannel(const ChannelArguments& args);
 
+  /// NOTE: class experimental_type is not part of the public API of this class.
+  /// TODO(yashykt): Integrate into public API when this is no longer
+  /// experimental.
+  class experimental_type {
+   public:
+    explicit experimental_type(Server* server) : server_(server) {}
+
+    /// Establish a channel for in-process communication with client
+    /// interceptors
+    std::shared_ptr<Channel> InProcessChannelWithInterceptors(
+        const ChannelArguments& args,
+        std::unique_ptr<std::vector<
+            std::unique_ptr<experimental::ClientInterceptorFactoryInterface>>>
+            interceptor_creators);
+
+   private:
+    Server* server_;
+  };
+
+  /// NOTE: The function experimental() is not stable public API. It is a view
+  /// to the experimental components of this class. It may be changed or removed
+  /// at any time.
+  experimental_type experimental() { return experimental_type(this); }
+
  protected:
   /// Register a service. This call does not take ownership of the service.
   /// The service must exist for the lifetime of the Server instance.