asio聊天室客户端(C++asio网络库相关）

以下ASIO聊天室客户端例子：
#include “chat_message.h”

//client.cpp
#include <boost/asio.hpp>

#include <deque>
#include <iostream>
#include <thread>

#include <cstdlib>

using boost::asio::ip::tcp;

using chat_message_queue = std::deque<chat_message>;


class chat_client {
public:
  chat_client(boost::asio::io_service &io_service,
              tcp::resolver::iterator endpoint_iterator)
      : io_service_(io_service), socket_(io_service) {
    do_connect(endpoint_iterator);
  }

  void write(const chat_message &msg) {
    io_service_.post([this, msg]() {
      bool write_in_progress = !write_msgs_.empty();
      write_msgs_.push_back(msg);
      if (!write_in_progress) {
        do_write();
      }
    });
  }

  void close() {
    io_service_.post([this]() { socket_.close(); });
  }

private:
  void do_connect(tcp::resolver::iterator endpoint_iterator) {
    boost::asio::async_connect(
        socket_, endpoint_iterator,
        [this](boost::system::error_code ec, tcp::resolver::iterator) {
          if (!ec) {
            do_read_header();
          }
        });
  }

  void do_read_header() {
    boost::asio::async_read(
        socket_,
        boost::asio::buffer(read_msg_.data(), chat_message::header_length),
        [this](boost::system::error_code ec, std::size_t /*length*/) {
          if (!ec && read_msg_.decode_header()) {
            do_read_body();
          } else {
            socket_.close();
          }
        });
  }

  void do_read_body() {
    boost::asio::async_read(
        socket_, boost::asio::buffer(read_msg_.body(), read_msg_.body_length()),
        [this](boost::system::error_code ec, std::size_t /*length*/) {
          if (!ec) {
            std::cout.write(read_msg_.body(), read_msg_.body_length());
            std::cout << "\n";
            do_read_header();
          } else {
            socket_.close();
          }
        });
  }

  void do_write() {
    boost::asio::async_write(
        socket_, boost::asio::buffer(write_msgs_.front().data(),
                                     write_msgs_.front().length()),
        [this](boost::system::error_code ec, std::size_t /*length*/) {
          if (!ec) {
            write_msgs_.pop_front();
            if (!write_msgs_.empty()) {
              do_write();
            }
          } else {
            socket_.close();
          }
        });
  }

private:
  boost::asio::io_service &io_service_;
  tcp::socket socket_;
  chat_message read_msg_;
  chat_message_queue write_msgs_;
};

int main(int argc, char *argv[]) {
  try {
    if (argc != 3) {
      std::cerr << "Usage: chat_client <host> <port>\n";
      return 1;
    }

    boost::asio::io_service io_service;

    tcp::resolver resolver(io_service);
    auto endpoint_iterator = resolver.resolve({argv[1], argv[2]});
    chat_client c(io_service, endpoint_iterator);

    std::thread t([&io_service]() { io_service.run(); });

    char line[chat_message::max_body_length + 1];
		// ctrl-d
    while (std::cin.getline(line, chat_message::max_body_length + 1)) {
      chat_message msg;
      msg.body_length(std::strlen(line));
      std::memcpy(msg.body(), line, msg.body_length());
      msg.encode_header();
      c.write(msg);
    }

    c.close();
    t.join();
  } catch (std::exception &e) {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}

客户端的io_service.run要在子线程中跑因为会阻塞

void write(const chat_message &msg) {
io_service_.post(this, msg {
对msg进行了值的拷贝并用io_service_.post注册了一个事件在io_service的控制中最终在run下执行

在外部调度用c.write注册事件放到t线程中最终在t线程下调用run执行，service能调度在哪个线程下运行防止多个线程并行处理事件出现问题，当前只有t线程

真正调用do_read_header是在run线程下执行的所以可以直接用socket_.close()，同个io_service_跑run下不会有抢资源，死锁之类的问题

用c.close()清空注册事件再t.join才能结束子线程

ctrl+d正常退出客户端，ctrl+c中断信号