Provide a generic client-side unary callback API

1 files changed, 92 insertions, 0 deletions

diff --git a/include/grpcpp/impl/codegen/client_callback.h b/include/grpcpp/impl/codegen/client_callback.h
new file mode 100644
index 0000000000..419933f85c
--- /dev/null
+++ b/include/grpcpp/impl/codegen/client_callback.h
@@ -0,0 +1,92 @@
+/*
+ *
+ * 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_CALLBACK_H
+#define GRPCPP_IMPL_CODEGEN_CLIENT_CALLBACK_H
+
+#include <functional>
+
+#include <grpcpp/impl/codegen/call.h>
+#include <grpcpp/impl/codegen/callback_common.h>
+#include <grpcpp/impl/codegen/channel_interface.h>
+#include <grpcpp/impl/codegen/config.h>
+#include <grpcpp/impl/codegen/core_codegen_interface.h>
+#include <grpcpp/impl/codegen/status.h>
+
+namespace grpc {
+
+class Channel;
+class ClientContext;
+class CompletionQueue;
+
+namespace internal {
+class RpcMethod;
+
+/// Perform a callback-based unary call
+/// TODO(vjpai): Combine as much as possible with the blocking unary call code
+template <class InputMessage, class OutputMessage>
+void CallbackUnaryCall(ChannelInterface* channel, const RpcMethod& method,
+                       ClientContext* context, const InputMessage* request,
+                       OutputMessage* result,
+                       std::function<void(Status)> on_completion) {
+  CallbackUnaryCallImpl<InputMessage, OutputMessage> x(
+      channel, method, context, request, result, on_completion);
+}
+
+template <class InputMessage, class OutputMessage>
+class CallbackUnaryCallImpl {
+ public:
+  CallbackUnaryCallImpl(ChannelInterface* channel, const RpcMethod& method,
+                        ClientContext* context, const InputMessage* request,
+                        OutputMessage* result,
+                        std::function<void(Status)> on_completion) {
+    CompletionQueue* cq = channel->CallbackCQ();
+    GPR_CODEGEN_ASSERT(cq != nullptr);
+
+    // TODO(vjpai): Allocate this as part of the tag's arena
+    auto* ops = new CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+                              CallOpRecvInitialMetadata,
+                              CallOpRecvMessage<OutputMessage>,
+                              CallOpClientSendClose, CallOpClientRecvStatus>;
+
+    // TODO(vjpai): Move to using pre-allocated tags rather than new/self-delete
+    auto* tag = new CallbackWithStatusTag(on_completion, true, ops);
+
+    // TODO(vjpai): Unify code with sync API as much as possible
+    Call call(channel->CreateCall(method, context, cq));
+    Status s = ops->SendMessage(*request);
+    if (!s.ok()) {
+      tag->force_run(s);
+      return;
+    }
+    ops->SendInitialMetadata(context->send_initial_metadata_,
+                             context->initial_metadata_flags());
+    ops->RecvInitialMetadata(context);
+    ops->RecvMessage(result);
+    ops->AllowNoMessage();
+    ops->ClientSendClose();
+    ops->ClientRecvStatus(context, tag->status_ptr());
+    ops->set_cq_tag(tag->tag());
+    call.PerformOps(ops);
+  }
+};
+
+}  // namespace internal
+}  // namespace grpc
+
+#endif  // GRPCPP_IMPL_CODEGEN_CLIENT_CALLBACK_H