Global hook for doing something in response to a synchronous server call

include/grpc++/server.h

@@ -56,6 +56,7 @@ class AsyncGenericService;
 class RpcService;
 class RpcServiceMethod;
 class ServerAsyncStreamingInterface;
+class ServerContext;
 class ThreadPoolInterface;
 
 /// Models a gRPC server.
@@ -84,6 +85,17 @@ class Server GRPC_FINAL : public GrpcLibrary, private CallHook {
   /// call \a Shutdown for this function to ever return.
   void Wait();
 
+  /// Global Callbacks
+  ///
+  /// Can be set exactly once per application to install hooks whenever
+  /// a server event occurs
+  class GlobalCallbacks {
+   public:
+    virtual void PreSynchronousRequest(ServerContext* context) = 0;
+    virtual void PostSynchronousRequest(ServerContext* context) = 0;
+  };
+  static void SetGlobalCallbacks(GlobalCallbacks* callbacks);
+
  private:
   friend class AsyncGenericService;
   friend class AsynchronousService;

src/cpp/server/server.cc

@@ -51,6 +51,15 @@
 
 namespace grpc {
 
+class DefaultGlobalCallbacks GRPC_FINAL : public Server::GlobalCallbacks {
+ public:
+  void PreSynchronousRequest(ServerContext* context) GRPC_OVERRIDE {}
+  void PostSynchronousRequest(ServerContext* context) GRPC_OVERRIDE {}
+};
+
+static DefaultGlobalCallbacks g_default_callbacks;
+static Server::GlobalCallbacks* g_callbacks = &g_default_callbacks;
+
 class Server::UnimplementedAsyncRequestContext {
  protected:
   UnimplementedAsyncRequestContext() : generic_stream_(&server_context_) {}
@@ -220,8 +229,10 @@ class Server::SyncRequest GRPC_FINAL : public CompletionQueueTag {
 
     void Run() {
       ctx_.BeginCompletionOp(&call_);
+      g_callbacks->PreSynchronousRequest(&ctx_);
       method_->handler()->RunHandler(MethodHandler::HandlerParameter(
           &call_, &ctx_, request_payload_, call_.max_message_size()));
+      g_callbacks->PostSynchronousRequest(&ctx_);
       request_payload_ = nullptr;
       void* ignored_tag;
       bool ignored_ok;
@@ -304,6 +315,13 @@ Server::~Server() {
   delete sync_methods_;
 }
 
+void Server::SetGlobalCallbacks(GlobalCallbacks* callbacks) {
+  GPR_ASSERT(g_callbacks == &g_default_callbacks);
+  GPR_ASSERT(callbacks != NULL);
+  GPR_ASSERT(callbacks != &g_default_callbacks);
+  g_callbacks = callbacks;
+}
+
 bool Server::RegisterService(const grpc::string* host, RpcService* service) {
   for (int i = 0; i < service->GetMethodCount(); ++i) {
     RpcServiceMethod* method = service->GetMethod(i);