Magic 8 Ball
Creating a HTTP2 connection between a Qt gRPC client and a C++ gRPC server.
Magic 8 ball sends a question to a server and displays the received answer:
The example code includes the following components:
magic8ball
Qt gRPC client application that uses the qt_add_protobuf() and qt_add_grpc() CMake functions for message and service Qt code generation.server
application that calls C++ gRPC plugin for generating server code and implementing simple server logic.
Note: you need the C++ gRPC plugin installed. Find details here: Module prerequisites
Both components use generated messages from the protobuf schema described in the exampleservice.proto
file:
syntax = "proto3"; package qtgrpc.examples; message AnswerRequest { string question = 1; } message AnswerResponse { string message = 1; } service ExampleService { rpc answerMethod(AnswerRequest) returns (AnswerResponse) {} }
The gRPC client is defined as a QML object which is available after the code is compiled.
ExampleServiceClient { id: grpcClient channel: grpcChannel.channel }
The client service connects to the localhost
with port 50051
, which is specified in the gRPC channel options:
GrpcHttp2Channel { id: grpcChannel hostUri: "http://localhost:50051" // Optionally, you can specify custom channel options here // options: GrpcChannelOptions {} }
And sends a request to the server part:
function requestAnswer(question: string): void { ... root.answerReq.question = question; grpcClient.answerMethod(root.answerReq, finishCallback, errorCallback, grpcCallOptions); }
answerMethod
is a gRPC method that the client calls. It has four parameters: the request object, a finish callback function, an error callback function and a GrpcCallOptions object.
Click the Ask button to send the request to the magic8ball server.
Note: You have to run the server in parallel with the client application.
The server
application chooses a random answer from the list of answers and sends the data to the client's port. It also checks that the request contains a non empty field question
. If the field is empty, it returns a StatusCode::INVALID_ARGUMENT
grpc::Status answerMethod(grpc::ServerContext *, const AnswerRequest *request, AnswerResponse *response) override { if (request->question().empty()) { std::cerr << "Question is empty" << std::endl; return grpc::Status(grpc::StatusCode::INVALID_ARGUMENT, "Question is empty"); } std::cout << "Received question: " << request->question() << std::endl; response->set_message(getRandomAnswer()); return grpc::Status(); };
After receiving a response, the client application shows the answer.
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