《unix网络编程》（19）使用select的TCP和UDP回射程序

àì夳堔傛蜴生んèń 2022-08-07 14:54 148阅读 0赞

# TCP和UDP服务器端程序    #

注意：信号处理函数可能中断对select的调用，因此要处理EINTR错误

//udpservselect01.c
    
    #include "myheader.h"
    
    void str_echo(int sockfd) {
       ssize_t n;
       char buf[MAXLINE];
    again:
       while (( n = read(sockfd, buf, MAXLINE)) > 0)
          Writen(sockfd, buf, n);
       if (n < 0 && errno == EINTR)
          goto again;
       else if (n < 0) {
          err_exit("str_echo: read error.");   
       }
    }
    
    int main(int argc, char **argv)
    {
      int listenfd, connfd, udpfd, nready, maxfdp1;
      char mesg[MAXLINE];
      pid_t childpid;
      fd_set rset;
      ssize_t n;
      socklen_t len;
      const int on = 1;
      struct sockaddr_in cliaddr, servaddr;
      void onSignalCatch(int);
      
      listenfd = Socket(AF_INET, SOCK_STREAM, 0);
      
      bzero(&servaddr, sizeof(servaddr));
      servaddr.sin_family = AF_INET;
      servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
      servaddr.sin_port = htons(SERV_PORT);
      
      //设置SO_REUSEADDR套接字以防该端口上已经有连接
      Setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
      Bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr));
      Listen(listenfd, LISTENQ);
      
      //以下创建UDP套接字并绑定与TCP套接字相同的端口。这里无须设置SO_REUSEADDR
      //因为TCP端口独立于UDP端口
      udpfd = Socket(AF_INET, SOCK_DGRAM, 0);
      
      bzero(&servaddr, sizeof(servaddr));
      servaddr.sin_family = AF_INET;
      servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
      servaddr.sin_port = htons(SERV_PORT);
      Bind(udpfd, (struct sockaddr*)&servaddr, sizeof(servaddr));
      
      //处理SIGCHLD信号，因为TCP连接由子进程处理
      Signal(SIGCHLD, onSignalCatch);
      
      FD_ZERO(&rset);
      //计算等待的描述符中较大的
      int maxfd = listenfd > udpfd ? listenfd : udpfd;
      maxfdp1 = maxfd + 1;
      
      for( ; ; ) {
        //调用select等待监听TCP或UDP套接字变为可读
        FD_SET(listenfd, &rset);
        FD_SET(udpfd, &rset);
        if ((nready = select(maxfdp1, &rset, NULL, NULL, NULL)) < 0) {
          //信号处理函数可能中断对select的调用，因此要处理EINTR错误
          if (errno == EINTR)
    	continue;
          else
    	err_exit("select error\n");
        }
        
        if (FD_ISSET(udpfd, &rset)) {
          len = sizeof(cliaddr);
          n = Recvfrom(udpfd, mesg, MAXLINE, 0, (struct sockaddr*)&cliaddr, &len);
          Sendto(udpfd, mesg, n, 0, (struct sockaddr*)&cliaddr, len);
        }
        
        if (FD_ISSET(listenfd, &rset)) {
          len = sizeof(cliaddr);
          connfd = Accept(listenfd, (struct sockaddr*)&cliaddr, &len);
          if ((childpid = Fork()) == 0) { //child process
            Close(listenfd);   //close listening socket
    	str_echo(connfd);  //process the request
    	exit(0);
          }
          Close(connfd);  //parent closes connected socket
        }
      }
    }

客户端程序分别使用：tcpcliselect.c 和udpcli01.c

# 程序运行结果 #

服务器端：tcp客户端进程中断了一次

![Center][]

tcp客户端：

![Center 1][]

udp客户端：

![Center 2][]

# 完整源码 #

[http://download.csdn.net/download/u013074465/8602301][http_download.csdn.net_download_u013074465_8602301]

[Center]: /images/20220805/536257f5119942a79519c492974b608f.png
[Center 1]: /images/20220805/2b8795d62236418db779ef6b58fad8c9.png
[Center 2]: /images/20220805/2cfcb76ac5814761b8ca03edc113a1a6.png
[http_download.csdn.net_download_u013074465_8602301]: http://download.csdn.net/download/u013074465/8602301