flatbuffers_protocol_client.md

中文

Overview

This chapter introduces a client example of the tRPC-Cpp framework using flatbuffers. For the principles and background of flatbuffers, please refer to the documentation flatbuffers_protocol_service.

Example

The example mainly focuses on writing client-side business logic. For steps such as defining flatbuffers IDL files and generating stub code, you can refer to the documentation flatbuffers_protocol_service.

Definition of flatbuffers IDL files and code generation for stubs

Taking forward.fbs as an example, please refer to the documentation Writing an IDL file of flatbuffers and To generate stub code using the fbs code generation tool

Writing client business code based on stub code

• Client stub code

  // ... Omitted code.
  
  namespace trpc {
  namespace test {
  namespace forward {
  // ... Omitted code.
  class FbForwardServiceProxy : public ::trpc::RpcServiceProxy {
   public:
    // Synchronous interface.
    virtual ::trpc::Status Forward(const ::trpc::ClientContextPtr& context, const flatbuffers::trpc::Message<trpc::test::helloworld::FbRequest>* request, flatbuffers::trpc::Message<trpc::test::helloworld::FbReply>* response);
    // Asynchronous interface.
    virtual ::trpc::Future<flatbuffers::trpc::Message<trpc::test::helloworld::FbReply>> AsyncForward(const ::trpc::ClientContextPtr& context, const flatbuffers::trpc::Message<trpc::test::helloworld::FbRequest>* request);
  };
  
  }  // namespace forward
  }  // namespace test
  }  // namespace trpc

  FbForwardServiceProxy is the client proxy class. Users can access the service based on the flatbuffers serialization protocol by calling the Forward or AsyncForward interfaces through objects of this class.

• Writing client business code(source code: client)

  void DoForward(std::shared_ptr<::trpc::test::forward::FbForwardServiceProxy>& proxy) {
    std::string msg("hello world");
  
    ::flatbuffers::trpc::MessageBuilder mb;
    auto name_offset = mb.CreateString(msg);
    auto request_offset = ::trpc::test::helloworld::CreateFbRequest(mb, name_offset);
    mb.Finish(request_offset);
    auto request_msg = mb.ReleaseMessage<::trpc::test::helloworld::FbRequest>();
  
    const ::trpc::test::helloworld::FbRequest* request = request_msg.GetRoot();
  
    std::cout << "request msg: " << request->message()->str() << std::endl;
  
    ::flatbuffers::trpc::Message<::trpc::test::helloworld::FbReply> response_msg;
  
    auto context = trpc::MakeClientContext(proxy);
    context->SetTimeout(1000);
  
    // Accessing backend FlatBuffer service through the client object.
    auto status = proxy->Forward(context, request_msg, &response_msg);
    if (status.OK()) {
      const trpc::test::helloworld::FbReply* response = response_msg.GetRoot();
      std::cout << "response msg: " << response->message()->str() << std::endl;
    } else {
      std::cout << "error: " << status.ErrorMessage() << std::endl;
    }
  }

  The above source code introduces the process of synchronous invocation, mainly including request construction (lines 2-10). The construction of requests and responses in the Building server-side code based on stub code is the same. However, the interface being constructed is changed to trpc::test::helloworld::CreateFbRequest (line 6). Additionally, synchronous interface invocation is used here: proxy->Forward(context, request_msg, &response_msg), where the request is a constant reference of flatbuffers::trpc::Message<::trpc::test::helloworld::FbRequest>, and the response is a pointer form of flatbuffers::trpc::Message<::trpc::test::helloworld::FbReply>.