Magic 8 Ball

Creating a HTTP2 connection between a Qt GRPC client and a C++ gRPC server.

Magic 8 ball shows an answer it receives from a server:

Magic 8 ball has the following components:

magic8ball Qt GRPC client application that includes the qt_add_protobuf() and qt_add_grpc() CMake functions for message and service Qt code generation.
SimpleGrpcServer 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 message = 1;
}

message AnswerResponse {
    string message = 1;
}

service ExampleService {
    rpc answerMethod(AnswerRequest) returns (AnswerResponse) {}
}

The client application binds on the localhost with port 50051:

    QUrl url("http://localhost:50051", QUrl::StrictMode);
    m_client->attachChannel(std::make_shared<QGrpcHttp2Channel>(url,
                                                                QGrpcInsecureChannelCredentials()
                                                                | QGrpcInsecureCallCredentials()));

And sends a request to the server part:

void ClientService::sendRequest()
{
    // clean error on UI before new request
    emit errorRecieved("");

    AnswerRequest request;
    request.setMessage("sleep");

    m_client->answerMethod(request, m_response.get());
}

Click the Ask question button to send the request to the SimpleGrpcServer application.

The SimpleGrpcServer application chooses a random answer from the list of answers and sends the data to the client's port.

Status ExampleServiceServiceImpl::answerMethod(grpc::ServerContext *,
                                               const AnswerRequest *request,
                                               AnswerResponse *response)
{
    if (request->message() == "sleep")
        QThread::msleep(2000);

    response->set_message(std::string(answers[generateRandomIndex()]));
    return Status();
}

After receiving a response the client application shows the answer.

Example project @ code.qt.io

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