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.