echo server是学习网络编程必要的一个入门程序。
本例使用boost::asio提供的网络库实现一个简单的异步的echo server。
技术原理:
1、使用std::shared_ptr管理session对象的生命周期
2、使用继承enabled_shared_from_this来获取当前对象的智能指针。
3、特别注意shared_from_this不能在构造函数和析构函数中调用,因为此时一个是对象没有构造完成,第二个是对象已经部分销毁,不能获取对象的智能指针。
4、在do_read和do_write函数中使用值捕获使智能指针对象的引用计数加1,延长到绑定的回调函数的生命周期后销毁。
5、do_read和do_write相互调用,构成调用链,使得io_service永远存在io事件,io.run函数不会退出。
server端代码,
main.cpp
#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
class session: public std::enable_shared_from_this<session> {
public:
session(tcp::socket socket): socket_(std::move(socket)) {
// 不要在此处调用start, 因为对象还没有构造完成,不能调用
// shared_from_this生成智能指针
}
void start() {do_read(); }
private:
void do_read() {
auto self(shared_from_this());
socket_.async_read_some(
boost::asio::buffer(data, max_length),
[this, self] (boost::system::error_code ec, std::size_t length) {
if(!ec) {
// 实际读取多少字节就写多少字节
do_write(length);
}
}
);
}
void do_write(std::size_t length) {
auto self(shared_from_this());
boost::asio::async_write(socket_,
boost::asio::buffer(data, length),
[self, this](boost::system::error_code ec, std::size_t length) {
if(!ec) {
// 调起回调链
do_read();
}
}
);
}
tcp::socket socket_;
enum {max_length=1024 };
char data[max_length];
};
class server {
public:
server(boost::asio::io_service& io_service, short port)
: acceptor_(io_service, tcp::endpoint(tcp::v4(), port)),
socket_(io_service){
}
void start() {
do_accept();
}
private:
void do_accept() {
acceptor_.async_accept(
socket_,
[this](boost::system::error_code error) {
if(!error) {
auto newSession = std::make_shared<session>(std::move(socket_));
newSession->start();
}
do_accept();
}
);
}
tcp::acceptor acceptor_;
tcp::socket socket_;
};
int main(int argc, char* argv[]) {
try {
if(argc != 2) {
std::cerr << "Usage: async_tcp_echo_server [port] \n";
return 1;
}
boost::asio::io_service io_service;
server s(io_service, std::atoi(argv[1]));
s.start();
io_service.run();
}catch(std::exception& ex) {
std::cerr << ex.what() << std::endl;
}
return 0;
}
CMakeLists.txt
cmake_minimum_required(VERSION 2.6)
project(main)
add_definitions(-std=c++14)
aux_source_directory(. CPP_LIST)
find_package(Boost REQUIRED COMPONENTS
system
filesystem
)
include_directories(${Boost_INCLUDE_DIRS})
add_executable(main ${CPP_LIST})
target_link_libraries(main ${Boost_LIBRARIES})
target_link_libraries(main pthread)
client端,client端是同步模式,
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
enum {max_length=1024 };
int main(int argc, char* argv[]) {
try {
if(argc != 3) {
std::cout << "Usage: main [host] [port]\n";
return 1;
}
boost::asio::io_service io_service;
tcp::socket s(io_service);
tcp::resolver resolver(io_service);
// argv[1], argv[2] 这种写法其实是用 初始化列表方式构造一个 query对象
// resolver.resolve方法是同步的调用方法,非常低效,可能10秒才返回
// 实际应用中尽量使用异步调用方法
boost::asio::connect(s, resolver.resolve({argv[1], argv[2]}));
std::cout << "Enter message:";
char request[max_length];
std::cin.getline(request, max_length);
std::size_t request_len = std::strlen(request);
boost::asio::write(s, boost::asio::buffer(request, request_len));
char reply[max_length];
std::size_t reply_length = boost::asio::read(s, boost::asio::buffer(reply, request_len));
std::cout << "Reply is:";
std::cout.write(reply, reply_length);
std::cout << "\n";
}catch(std::exception& ex) {
std::cerr << ex.what() << std::endl;
}
return 0;
}
CMakeLists.txt
cmake_minimum_required(VERSION 2.6)
project(main)
add_definitions(-std=c++14)
aux_source_directory(. CPP_LIST)
find_package(Boost REQUIRED COMPONENTS
system
filesystem
)
include_directories(${Boost_INCLUDE_DIRS})
add_executable(main ${CPP_LIST})
target_link_libraries(main ${Boost_LIBRARIES})
target_link_libraries(main pthread)
程序输出如下