Unix Network Programming, Volume 1: The Sockets Networking API (3rd Edition)

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

9 “13 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

14 “15 connect establishes the connection with the server. The function str_cli (Figure 5.5) handles the rest of the client processing.