Qt GRPC

Qt GRPC is the client-side implementation that, together with the Qt Protobuf module, allows the definition of messages and services in .proto files, which then use the provided code generators to generate client code that allows the access for fields and gRPC services in the Qt framework. The code generated by Qt GRPC enables the client-side to communicate with a gRPC server (regardless of whether the server uses Qt) by sending calls or streaming messages.

Overview

gRPC is a cross-platform high performance Remote Procedure Call (RPC) framework, that generates client/server bindings for a lot of languages. Usually, you use it to connect services in a microservices-style architecture or to connect mobile applications and browsers to backend services. The gRPC clients and servers can run and talk to each other in various environments, and you can write in any of gRPC’s supported languages. For more details see gRPC Introduction

Using the Module

Module prerequisites:

• protoc, the Google protocol buffers compiler, must be installed to generate code from .proto specification files. See Protoc Installation.
• If you also install the gRPC libraries, you'll be able to use native gRPC channels. See gRPC for C++ for details.
• OpenSSL Toolkit may be needed.

To start working with the Qt GRPC functionality you should define required services and messages in a .proto file. See the helloworld.proto example:

// The service definition.
service Salutation {
  // Sends a greeting
  rpc SendHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

To add a .proto file to a Qt-based project and generate the required source code, you should use the protoc compiler with the qtgrpcgen and qtprotobufgen Qt plugins.

• The Qt Protobuf plugin generates classes that you can use to serialize and deserialize their associated protobuf messages.
• The Qt GRPC plugin generates gRPC client classes from the proto file.

This processing of proto files into source code can be automated in CMake using the following commands provided by Qt:

• qt_add_protobuf
• qt_add_grpc

As a result, the full example of a CMake project file, that uses Qt GRPC functionality shall be:

cmake_minimum_required(VERSION 3.16...3.22)
project(MyProject)

find_package(Qt6 REQUIRED COMPONENTS Protobuf Grpc)
qt_standard_project_setup()

qt_add_protobuf(MyProtoMessageLib
    PROTO_FILES
        path/to/helloworld.proto
    PROTO_INCLUDES
        path/to/proto/include
)

qt_add_grpc(MyGrpcClient CLIENT
    PROTO_FILES
        path/to/helloworld.proto
    PROTO_INCLUDES
        path/to/proto/include
)

qt_add_executable(MyApp main.cpp)

target_link_libraries(MyApp PRIVATE MyGrpcClient MyProtoMessageLib Qt6::Protobuf)

The example above calls the qt_add_grpc() CMake function to generate a library called MyGrpcClient.

Finally, the example creates a target for an executable called MyApp which links to the MyGrpcClient and MyProtoMessageLib libraries.

QML API

The QML types of the module are available through the QtGrpc import. To use the types, add the following import statement to your .qml file:

import QtGrpc

C++ API

Using a Qt module's C++ API requires linking against the module library, either directly or through other dependencies. Several build tools have dedicated support for this, including CMake and qmake.

Building with CMake

Use the find_package() command to locate the needed module component in the Qt6 package:

find_package(Qt6 REQUIRED COMPONENTS Grpc)
target_link_libraries(mytarget PRIVATE Qt6::Grpc)

For more details, see the Build with CMake overview.

Articles and Guides

• CMake Commands in Qt6 GRPC
• Client Methods of the Qt GRPC Service

References

• Qt GRPC Quick
• C++ Classes

Licenses and Trademarks

Qt GRPC is available under commercial licenses from The Qt Company. In addition, it is available under the GNU General Public License, version 3. See Qt Licensing for further details.

gRPC^® is a registered trademark of The Linux Foundation. Please see https://grpc.io/ for more information.

Examples

• Qt GRPC Examples

Licenses and Attributions

The Qt GRPC module is available under commercial licenses from The Qt Company. In addition, it is available under free software licenses: The GNU General Public License, version 3. See Qt Licensing for further details.

Furthermore, Qt GRPC in Qt 6.8.1 may contain third party modules under the following permissive licenses: