gRPC 基础

1. 安装 gRPC

设置安装地址

export MY_INSTALL_DIR=$HOME/.local
mkdir -p $MY_INSTALL_DIR

安装编译依赖

sudo apt install -y build-essential autoconf libtool pkg-config

下载代码并开始编译

git clone --recurse-submodules -b v1.55.0 --depth 1 --shallow-submodules https://github.com/grpc/grpc

cd grpc
mkdir -p cmake/build
pushd cmake/build
cmake -DgRPC_INSTALL=ON \
      -DgRPC_BUILD_TESTS=OFF \
      -DCMAKE_INSTALL_PREFIX=$MY_INSTALL_DIR \
      ../..
make -j8
make install
popd

2. Demo

hello.proto

protobuf 由 service 和 mssage 这两个基本部分组成，前者相当于函数，由服务端实现，客户端可以直接调用，后者则表示一种数据结构，在 cpp 中则是一个类，里面的就是类的成员变量，可以看到 message 中成员变量后面都有一个数字，在 protobuf 中就是用这个数字来表示这个变量，而不是采用这些变量名。
```
syntax = "proto3";

package hello;

service Greeter{
    rpc SayHello(HelloRequest) returns (HelloReply){}
}

message HelloRequest{
    string name = 1;
}

message HelloReply{
    string message = 1;
}
```

server.cc

server 里面实现对应的 service 需要定义一个类来继承自动生成的代码

#include <string>
#include <iostream>
#include <memory>

#include "absl/strings/str_format.h"
#include "absl/flags/flag.h"
#include "absl/flags/parse.h"

#include <grpcpp/ext/proto_server_reflection_plugin.h>
#include <grpcpp/grpcpp.h>
#include <grpcpp/support/status.h>
#include <grpcpp/health_check_service_interface.h>

#include "grpcpp/health_check_service_interface.h"
#include "grpcpp/security/server_credentials.h"
#include "grpcpp/server_builder.h"
#include "grpcpp/server_context.h"
#include "hello.grpc.pb.h"
#include "hello.pb.h"

ABSL_FLAG(uint16_t, port, 50051, "Server port for the service");

class GreeterServiceTmpl final : public hello::Greeter::Service{
    grpc::Status SayHello(grpc::ServerContext* context, 
        const hello::HelloRequest* request, 
        hello::HelloReply* reply
    ) override {
        std::string prefix("Hello ");

        reply->set_message(prefix + request->name());
        return grpc::Status::OK;
    }
};

void RunServer(uint16_t port){
    std::string server_address = absl::StrFormat("0.0.0.0:%d", port);
    GreeterServiceTmpl service;

    grpc::EnableDefaultHealthCheckService(true);
    grpc::reflection::InitProtoReflectionServerBuilderPlugin();

    grpc::ServerBuilder builder;
    builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
    builder.RegisterService(&service);

    std::unique_ptr<grpc::Server> server(builder.BuildAndStart());
    std::cout << "Server listening on " << server_address << std::endl;

    server->Wait();
}

int main(int argc, char** argv){
    absl::ParseCommandLine(argc, argv);
    RunServer(absl::GetFlag(FLAGS_port));

    return 0;
}

client.cc

#include "absl/flags/flag.h"
#include "absl/flags/parse.h"

#include "grpcpp/channel.h"
#include "grpcpp/client_context.h"
#include "hello.grpc.pb.h"
#include "hello.pb.h"
#include <grpcpp/grpcpp.h>
#include <iterator>
#include <memory>
#include <string>

ABSL_FLAG(std::string, target, "localhost:50051", "Server address");

class GreeterClient{
private:
    std::unique_ptr<hello::Greeter::Stub> stub_;
public:
    GreeterClient(std::shared_ptr<grpc::Channel> channel):stub_(hello::Greeter::NewStub(channel)){}

    std::string SayHello(const std::string& user){
        hello::HelloRequest request;
        request.set_name(user);

        hello::HelloReply reply;
        grpc::ClientContext context;

        grpc::Status status = stub_->SayHello(&context, request, &reply);       // 发起请求

        if(status.ok()){
            return reply.message();
        }else{
            std::cout << status.error_code() << ": " << status.error_message() << std::endl;
            return "RPC failed";
        }
    }
};


int main(int grac, char** argv){
    absl::ParseCommandLine(grac, argv);
    std::string target_str = absl::GetFlag(FLAGS_target);
    GreeterClient greeter(grpc::CreateChannel(target_str, grpc::InsecureChannelCredentials()));

    std::string user("world");
    std::string reply = greeter.SayHello(user);
    std::cout << "Greeter received: " << reply << std::endl;

    return 0;
}

CMakeList.txt

# Copyright 2018 gRPC authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# cmake build file for C++ helloworld example.
# Assumes protobuf and gRPC have been installed using cmake.
# See cmake_externalproject/CMakeLists.txt for all-in-one cmake build
# that automatically builds all the dependencies before building helloworld.

cmake_minimum_required(VERSION 3.8)

project(hello C CXX)

include(common.cmake)


# Proto file
get_filename_component(hw_proto "./hello.proto" ABSOLUTE)
get_filename_component(hw_proto_path "${hw_proto}" PATH)

# Generated sources
set(hw_proto_srcs "${CMAKE_CURRENT_BINARY_DIR}/hello.pb.cc")
set(hw_proto_hdrs "${CMAKE_CURRENT_BINARY_DIR}/hello.pb.h")
set(hw_grpc_srcs "${CMAKE_CURRENT_BINARY_DIR}/hello.grpc.pb.cc")
set(hw_grpc_hdrs "${CMAKE_CURRENT_BINARY_DIR}/hello.grpc.pb.h")
add_custom_command(
      OUTPUT "${hw_proto_srcs}" "${hw_proto_hdrs}" "${hw_grpc_srcs}" "${hw_grpc_hdrs}"
      COMMAND ${_PROTOBUF_PROTOC}
      ARGS --grpc_out "${CMAKE_CURRENT_BINARY_DIR}"
        --cpp_out "${CMAKE_CURRENT_BINARY_DIR}"
        -I "${hw_proto_path}"
        --plugin=protoc-gen-grpc="${_GRPC_CPP_PLUGIN_EXECUTABLE}"
        "${hw_proto}"
      DEPENDS "${hw_proto}")

# Include generated *.pb.h files
include_directories("${CMAKE_CURRENT_BINARY_DIR}")

# hw_grpc_proto
add_library(hw_grpc_proto
  ${hw_grpc_srcs}
  ${hw_grpc_hdrs}
  ${hw_proto_srcs}
  ${hw_proto_hdrs})
target_link_libraries(hw_grpc_proto
  ${_REFLECTION}
  ${_GRPC_GRPCPP}
  ${_PROTOBUF_LIBPROTOBUF})

# Targets greeter_[async_](client|server)
foreach(_target
  server client)
  add_executable(${_target} "${_target}.cc")
  target_link_libraries(${_target}
    hw_grpc_proto
    absl::flags
    absl::flags_parse
    ${_REFLECTION}
    ${_GRPC_GRPCPP}
    ${_PROTOBUF_LIBPROTOBUF})
endforeach()

编译 proto 文件
```
protoc -I . --grpc_out=. --plugin=protoc-gen-grpc=`which grpc_cpp_plugin` hello.proto
protoc -I . --cpp_out=. hello.proto
```
第一行会生成：hello.grpc.pb.h 和 hello.grpc.pb.cc, 前者包含你的消息(message)的声明，后者包含你的消息类的实现

第二行会生成：hello.pb.cc 和 hello.pb.h，前者包含你的服务(service)的声明，后者包含你的服务类的实现

3. 关键概念

stub

On the client side, the client has a stub (referred to as just a client in some languages) that provides the same methods as the server.

这个词不是蛮好翻译，可以理解把他理解为一个接口，通过这个接口调用远程的函数就像调用本地函数一样。
channel

A gRPC channel provides a connection to a gRPC server on a specified host and port. It is used when creating a client stub. Clients can specify channel arguments to modify gRPC’s default behavior, such as switching message compression on or off. A channel has state, including connected and idle.

channel 就是指 server 和 client 之间的连接

4. WireShark 抓包

设置 protobuf 搜索路径，让 WireShark 认识 protobuf

Edit->Preferences > Protocols > Protobuf.
设置 decode，让 WireShark 可以成功的解析 HTTP2 协议

Analyze -> decode as -> add

1. 安装 gRPC

2. Demo

3. 关键概念

4. WireShark 抓包

参考