protoc-gen-grpcxx.md

Protobuf compiler plugin

protoc-gen-grpcxx can be used to translate gRPC service definitions from .proto files to C++ code.

Example

Let's take the following proto definitions from helloworld example.

syntax = "proto3";

package helloworld.v1;

service Greeter {
  rpc Hello(GreeterHelloRequest) returns (GreeterHelloResponse) {}
}

message GreeterHelloRequest {
  string name = 1;
}

message GreeterHelloResponse {
  string message = 1;
}

Using protoc and protoc-gen-grpcxx, we can generate the grpcxx::service definitions and stub implementations.

e.g.

❯ protoc --proto_path=. \
  --cpp_out=/path/to/output \
  --grpcxx_out=/path/to/output \
  --plugin=/path/to/protoc-gen-grpcxx \
  helloworld/v1/greeter.proto

The above command will output 3 files.

❯ tree /path/to/output
/path/to/output
└── helloworld
  └── v1
    ├── greeter.grpcxx.pb.h
    ├── greeter.pb.cc
    └── greeter.pb.h

greeter.pb.h and greeter.pb.cc contains the C++ definitions and implementations for protobuf messages. greeter.grpcxx.pb.h containes the grpcxx::service definitions and stub implementations.

greeter.grpcxx.pb.h would look something like this;

// Code generated by protoc-gen-grpcxx.
// Versions:
//   - protoc-gen-grpcxx: v0.1.0
// Source: helloworld/v1/greeter.proto

#pragma once

#include <grpcxx/rpc.h>
#include <grpcxx/service.h>

#include "helloworld/v1/greeter.pb.h"

namespace helloworld {
namespace v1 {
namespace Greeter {
using rpcHello = grpcxx::rpc<"Hello", GreeterHelloRequest, GreeterHelloResponse>;

using Service = grpcxx::service<"helloworld.v1.Greeter", rpcHello>;

struct ServiceImpl {
  template <typename T>
  typename T::result_type call(grpcxx::context &, const typename T::request_type &) {
    return {grpcxx::status::code_t::unimplemented, std::nullopt};
  }
};
} // namespace Greeter
} // namespace v1
} // namespace helloworld

Example (cmake)

While you could manually invoke protoc and protoc-gen-grpcxx to generate code, you could also generate the code as part of your project build process.

Here's a snippet that uses CMake's add_custom_command to generate code as part of the build.

add_custom_command(
  OUTPUT  ${headers} ${sources}
  DEPENDS ${protos}
  COMMAND ${Protobuf_PROTOC_EXECUTABLE}
  ARGS
    --proto_path=${CMAKE_CURRENT_SOURCE_DIR}
    --proto_path=${Protobuf_INCLUDE_DIR}
    --cpp_out=${CMAKE_CURRENT_BINARY_DIR}
    --grpcxx_out=${CMAKE_CURRENT_BINARY_DIR}
    --plugin=protoc-gen-grpcxx=$<TARGET_FILE:libgrpcxx::protoc-gen>
    ${protos}
)

💡 You can find a complete example here.