UNIX Network Programming Volume 1, Third Edition [Electronic resources] : The Sockets Networking API

5.4 TCP Echo Client: main Function

Figure 5.4 shows the TCP client main function.

Figure 5.3 str_echo function: echoes data on a socket.

lib/str_echo.c

1 #include    "unp.h"
2 void
3 str_echo(int sockfd)
4 {
5     ssize_t n;
6     char    buf[MAXLINE];
7   again:
8     while ( (n = read(sockfd, buf, MAXLINE)) > 0)
9         Writen(sockfd, buf, n);
10     if (n < 0 && errno == EINTR)
11         goto again;
12     else if (n < 0)
13         err_sys("str_echo: read error");
14 }

Figure 5.4 TCP echo client.

tcpcliserv/tcpli01.c

1 #include    "unp.h"
2 int
3 main(int argc, char **argv)
4 {
5     int     sockfd;
6     struct sockaddr_in servaddr;
7     if (argc != 2)
8         err_quit("usage: tcpcli <IPaddress>");
9     sockfd = Socket(AF_INET, SOCK_STREAM, 0);
10     bzero(&servaddr, sizeof(servaddr));
11     servaddr.sin_family = AF_INET;
12     servaddr.sin_port = htons(SERV_PORT);
13     Inet_pton(AF_INET, argv[1], &servaddr.sin_addr);
14     Connect(sockfd, (SA *) &servaddr, sizeof(servaddr));
15     str_cli(stdin, sockfd);     /* do it all */
16     exit(0);
17 }

Create socket, fill in Internet socket address structure

913 A TCP socket is created and an Internet socket address structure is filled in with the server's IP address and port number. We take the server's IP address from the command-line argument and the server's well-known port (SERV_PORT) is from our unp.h header.

Connect to server

1415 connect establishes the connection with the server. The function str_cli (Figure 5.5) handles the rest of the client processing.