The qtgrpcgen Tool

The qtgrpcgen tool can be used to generate Qt GRPC service classes from a protobuf schema. The tool is provided by the CMake Qt6::GrpcTools package. It works as an extension to Google's protoc tool.

 find_package(Qt6 COMPONENTS GrpcTools REQUIRED)

Usage

Qt provides CMake functions that ease the use of the qtgrpcgen tool. When using CMake as a build tool you should prefer using the Qt CMake API. For build systems other than CMake, adapt the commands described in Running qtgrpcgen manually.

CMake

The following CMake commands integrate a gRPC service into a Qt project.

Usually qtgrpcgen would be invoked through CMake using the qt_add_grpc macro, as shown in the following example:

 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.

Running qtgrpcgen manually

 protoc --plugin=protoc-gen-qtgrpc=<path/to/bin/>qtgrpcgen \
     --qtgrpc_out="[<options>:]<output_dir>" \
     [--qtgrpc_opt="<options>"] \
     [-I/extra/proto/include/path] \
     <protofile>.proto

The options argument is a semicolon-separated list of Options. It can be passed by prepending the options to the output_dir argument, delimited by a colon, or through a separate argument, --qtgrpc_opt. You also can pass the corresponding keys as the QT_GRPC_OPTIONS environment variable. Keys must be presented as a semicolon-separated list:

 export QT_GRPC_OPTIONS="COPY_COMMENTS;GENERATE_PACKAGE_SUBFOLDERS"

Options

The generator supports options that can be provided to tune generation. Options have direct aliases in the qt_add_grpc function. The following options are supported:

• COPY_COMMENTS copies comments from the .proto files into the generated code.
• GENERATE_PACKAGE_SUBFOLDERS uses the package name specifier from the .proto files to create the folder structure for the generated files. For example, if the package is defined as: package io.qt.test, the generated files will be placed in OUTPUT_DIRECTORY/io/qt/test/.
• EXPORT_MACRO defines the base name for the export macro used in the generated code. The final macro name is constructed as QPB_<EXPORT_MACRO>_EXPORT. If this option is not set, no export macro is generated.

  Since Qt 6.8, the following format is supported: EXPORT_MACRO=macro_name[:macro_output_file[:<true|false>]]. This format allows you to specify the name of the header file containing the export macro and explicitly control whether it is generated.

  Note: If <macro_output_file> is not provided, the option defaults to the previous syntax.

• QML enables the generation of a QML client for the gRPC service.