- Qt 6.6
- Qt GRPC
- Qt 6.6.1 Reference Documentation

# Qt GRPC

The Qt GRPC and Qt Protobuf modules together allow you to define data and messages in `proto` files, and then use the code generators, which generate client code allowing accessors for fields and gRPC services in the Qt framework. The code generated by Qt GRPC enables client code 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.

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`.

Note: if the `.proto` file API contains messages, then the `qt_add_protobuf()` CMake function should be called to generate protobuf message classes for the project.

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

## Class Documentation

- C++ Classes

## CMake API

- CMake Commands in Qt6 GRPC

## 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