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

5.5 TCP Echo Client: str_cli Function

This function, shown in Figure 5.5, handles the client processing loop: It reads a line of text from standard input, writes it to the server, reads back the server's echo of the line, and outputs the echoed line to standard output.

Figure 5.5 str_cli function: client processing loop.

lib/str_cli.c

1 #include "unp.h" 2 void 3 str_cli(FILE *fp, int sockfd) 4 { 5 char sendline[MAXLINE], recvline[MAXLINE]; 6 while (Fgets(sendline, MAXLINE, fp) != NULL) { 7 Writen(sockfd, sendline, strlen (sendline)); 8 if (Readline(sockfd, recvline, MAXLINE) == 0) 9 err_quit("str_cli: server terminated prematurely"); 10 Fputs(recvline, stdout); 11 } 12 }

Read a line, write to server

6 “7 fgets reads a line of text and writen sends the line to the server.

Read echoed line from server, write to standard output

8 “10 readline reads the line echoed back from the server and fputs writes it to standard output.

Return to main

11 “12 The loop terminates when fgets returns a null pointer, which occurs when it encounters either an end-of-file (EOF) or an error. Our Fgets wrapper function checks for an error and aborts if one occurs, so Fgets returns a null pointer only when an end-of-file is encountered .