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十、网络基础

5. socket编程

socket 常见API

// 创建 socket 文件描述符 (TCP/UDP, 客户端 + 服务器)
int socket(int domain, int type, int protocol);// 绑定端口号 (TCP/UDP, 服务器) 
int bind(int socket, const struct sockaddr *address,socklen_t address_len);// 开始监听socket (TCP, 服务器)
int listen(int socket, int backlog);// 接收请求 (TCP, 服务器)
int accept(int socket, struct sockaddr* address,socklen_t* address_len);// 建立连接 (TCP, 客户端)
int connect(int sockfd, const struct sockaddr *addr,socklen_t addrlen);

sockaddr结构

socket API是一层抽象的网络编程接口,适用于各种底层网络协议,如IPv4、IPv6,以及后面要讲的UNIX DomainSocket. 然而, 各种网络协议的地址格式并不相同。

IPv4、IPv6地址类型分别定义为常数AF_INET、AF_INET6. 这样,只要取得某种sockaddr结构体的首地址,不需要知道具体是哪种类型的sockaddr结构体,就可以根据地址类型字段确定结构体中的内容。
我们真正在基于IPv4编程时, 使用的数据结构是sockaddr_in; 这个结构里主要有三部分信息: 地址类型，端口号，IP地址。

简单的UDP网络程序

我们需要我们之前写的日志程序：
Log.hpp：

#pragma once#include <iostream>
#include <fstream>
#include <cstdio>
#include <string>
#include <ctime>
#include <cstdarg>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include "LockGuard.hpp"// 宏定义，用于定义日志格式
#define LOG(level, format, ...) do{LogMessage(__FILE__, __LINE__, gIsSave, level, format, ##__VA_ARGS__);}while (0)
// 将日志输入到文件
#define EnableFile() do{gIsSave = true;}while (0)
// 将日志输出到显示器
#define EnableScreen() do{gIsSave = false;}while (0)bool gIsSave = false;
// 日志文件名
const std::string logname = "log.txt";// 枚举日志级别
enum Level
{DEBUG = 0,INFO,WARNING,ERROR,FATAL
};// 保存日志到文件
void SaveFile(const std::string &filename, const std::string &message)
{std::ofstream out(filename, std::ios::app);if (!out.is_open()){return;}out << message;out.close();
}// 日志级别转字符串
std::string LevelToString(int level)
{switch (level){case DEBUG:return "Debug";case INFO:return "Info";case WARNING:return "Warning";case ERROR:return "Error";case FATAL:return "Fatal";default:return "Unknown";}
}// 获取当前时间字符串
std::string GetTimeString()
{time_t curr_time = time(nullptr);struct tm *format_time = localtime(&curr_time);if (format_time == nullptr)return "None";char time_buffer[1024];snprintf(time_buffer, sizeof(time_buffer), "%d-%d-%d %d:%d:%d",format_time->tm_year + 1900,format_time->tm_mon + 1,format_time->tm_mday,format_time->tm_hour,format_time->tm_min,format_time->tm_sec);return time_buffer;
}// 日志锁，同一时刻只能写一个日志
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;// 日志信息
void LogMessage(std::string filename, int line, bool issave, int level, const char *format, ...)
{// 日志级别std::string levelstr = LevelToString(level);// 时间std::string timestr = GetTimeString();// 进程idpid_t selfid = getpid();// 日志内容char buffer[1024];va_list arg;va_start(arg, format);vsnprintf(buffer, sizeof(buffer), format, arg);va_end(arg);// 日志格式化std::string message = "[" + timestr + "]" + "[" + levelstr + "]" +"[" + std::to_string(selfid) + "]" +"[" + filename + "]" + "[" + std::to_string(line) + "] " + buffer;LockGuard lockguard(&lock);// 输出日志if (!issave){std::cout << message;}else{SaveFile(logname, message);}
}

封装的RAII模式的锁：
LockGuard.hpp：

#ifndef __LOCK_GUARD_HPP__
#define __LOCK_GUARD_HPP__#include <iostream>
#include <pthread.h>class LockGuard
{
public:// 构造函数加锁LockGuard(pthread_mutex_t *mutex):_mutex(mutex){pthread_mutex_lock(_mutex);}// 析构函数解锁~LockGuard(){pthread_mutex_unlock(_mutex);}
private:pthread_mutex_t *_mutex;
};#endif

服务端代码：
UdpServer.hpp：

#pragma once#include <iostream>
#include <string>
#include <cerrno>
#include <cstring>
#include <cstdlib>
#include <strings.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include "Log.hpp"
#include "InetAddr.hpp"enum
{SOCKET_ERROR = 1,BIND_ERROR,USAGE_ERROR
};const static int defaultfd = -1;class UdpServer
{
public:UdpServer(uint16_t port):_sockfd(defaultfd),_port(port),_isrunning(false){}void InitServer(){// 创建 UDP socket 套接字_sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (_sockfd < 0){LOG(FATAL, "socket error, %s, %d\n", strerror(errno), errno);exit(SOCKET_ERROR);}LOG(INFO, "socket create success, sockfd: %d\n", _sockfd);struct sockaddr_in local;bzero(&local, sizeof(local));local.sin_family = AF_INET;// 端口号要经过网络传输，需要转换成网络字节序local.sin_port = htons(_port);local.sin_addr.s_addr = 0;// 绑定本地地址int n = bind(_sockfd, (struct sockaddr*)&local, sizeof(local));if (n < 0){LOG(FATAL, "bind error, %s, %d\n", strerror(errno), errno);exit(BIND_ERROR);}LOG(INFO, "socket bind success\n");}void Start(){// 启动服务器_isrunning = true;while (true){// 接收数据char buffer[1024];struct sockaddr_in peer;socklen_t len = sizeof(peer);ssize_t n = recvfrom(_sockfd, buffer, sizeof(buffer) - 1, 0, (struct sockaddr*)&peer, &len);if (n > 0){// 收到数据，打印buffer[n] = '\0';InetAddr addr(peer);LOG(DEBUG, "get message from [%s:%d]: %s\n", addr.Ip().c_str(), addr.Port(), buffer);sendto(_sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)&peer, len);}// sleep(1);// LOG(DEBUG, "server is running...\n");}_isrunning = false;}~UdpServer(){}
private:int _sockfd;// std::string _ip;// 服务器所用端口号uint16_t _port;bool _isrunning;
};

客户端代码：
UdpClient.hpp：

#include <iostream>
#include <string>
#include <cstring>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <cstdlib>void Usage(std::string proc)
{std::cout << "Usage:\n\t" << proc << " local_ip local_prot\n" << std::endl;
}int main(int argc, char* argv[])
{if (argc != 3){Usage(argv[0]);exit(1);}// 获取本地IP地址和端口号std::string serverip = argv[1];uint16_t serverport = std::stoi(argv[2]);int sockfd = socket(AF_INET, SOCK_DGRAM, 0);if (sockfd < 0){std::cerr << "socket error" << std::endl;}// 构建目标主机的socket信息struct sockaddr_in server;memset(&server, 0, sizeof(server));server.sin_family = AF_INET;server.sin_port = htons(serverport);server.sin_addr.s_addr = inet_addr(serverip.c_str());std::string message;// 循环发送消息while (true){// 输入消息std::cout << "Please Enter# ";std::getline(std::cin, message);sendto(sockfd, message.c_str(), message.size(), 0, (struct sockaddr*)&server, sizeof(server));// 接收消息struct sockaddr_in peer;socklen_t len = sizeof(peer);char buffer[1024];ssize_t n = recvfrom(sockfd, buffer, sizeof(buffer) - 1, 0, (struct sockaddr*)&peer, &len);if (n > 0){std::cout << "server echo# " << buffer <<std::endl;}}return 0;
}

发送者数据：
InetAddr.hpp：

#pragma once#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>class InetAddr
{
private:void GetAddress(std::string *ip, uint16_t *port){*port = ntohs(_addr.sin_port);*ip = inet_ntoa(_addr.sin_addr);}public:InetAddr(const struct sockaddr_in &addr) : _addr(addr){GetAddress(&_ip, &_port);}std::string Ip(){return _ip;}uint16_t Port(){return _port;}~InetAddr(){}
private:struct sockaddr_in _addr;std::string _ip;uint16_t _port;
};

Main.cc：

#include <iostream>
#include <memory>
#include "UdpServer.hpp"void Usage(std::string proc)
{std::cout << "Usage:\n\t" << proc << " local_prot\n" << std::endl;
}int main(int argc, char* argv[])
{if (argc != 2){Usage(argv[0]);exit(USAGE_ERROR);}EnableScreen();// std::string local_ip = argv[1];uint16_t port = std::stoi(argv[1]);std::unique_ptr<UdpServer> usvr(new UdpServer(port));// 初始化服务器usvr->InitServer();// 启动服务器usvr->Start();return 0;
}

Makefile：

.PHONY:all
all:udpserver udpclientudpserver:Main.ccg++ -o $@ $^ -std=c++11
udpclient:UdpClient.ccg++ -o $@ $^ -std=c++11
.PHONY:clean
clean:rm -f udpserver udpclient

结果：
服务端输入：./udpserver 端口号 即可
客户端输入：./udpclient 服务器的ip地址（若是本地互联，输入0即可） 端口号 即可

成功通信！

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未完待续