sockets/is_echo_cl.c

+/* is_echo_cl.c
+
+   A simple client to communicate with the standard "echo" server.
+
+   In many Linux distributions, the "echo" server is not started by default.
+   Normally it is implemented internally by inetd(8), and to enable we must
+   do the following *as root*:
+
+   1.   Edit the file /etc/inetd.conf, and uncomment the two lines
+        for the the "echo" service by removing the '#' character at the
+        beginning of the line. The lines typically look like this:
+
+                # echo    stream  tcp     nowait  root    internal
+                # echo    dgram   udp     wait    root    internal
+
+        and we must change them to this:
+
+                echo    stream  tcp     nowait  root    internal
+                echo    dgram   udp     wait    root    internal
+
+   2.   Inform inetd(8) of the change using the following command:
+
+                bash# killall -HUP inetd
+
+   If your system uses xinetd(8) instead of inetd(8), then read the
+   xinetd.conf(5) manual page. (You may also find that your system has a GUI
+   admin tool that allows you to easily enable/disable the "echo" service.)
+
+   See also is_echo_sv.c.
+*/
 #include "inet_sockets.h"
 #include "tlpi_hdr.h"
 
 #define BUF_SIZE 100
 
 int
 main(int argc, char *argv[])
 {
     int sfd;
     ssize_t numRead;
     char buf[BUF_SIZE];
 
     if (argc != 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s host\n", argv[0]);
 
     sfd = inetConnect(argv[1], "echo", SOCK_STREAM);
     if (sfd == -1)
         errExit("inetConnect");
 
     switch (fork()) {
     case -1:
         errExit("fork");
 
     case 0:             /* Child: read server's response, echo on stdout */
         for (;;) {
             numRead = read(sfd, buf, BUF_SIZE);
             if (numRead <= 0)                   /* Exit on EOF or error */
                 break;
             printf("%.*s", (int) numRead, buf);
         }
         exit(EXIT_SUCCESS);
 
     default:            /* Parent: write contents of stdin to socket */
         for (;;) {
             numRead = read(STDIN_FILENO, buf, BUF_SIZE);
             if (numRead <= 0)                   /* Exit loop on EOF or error */
                 break;
             if (write(sfd, buf, numRead) != numRead)
                 fatal("write() failed");
         }
 
         /* Close writing channel, so server sees EOF */
 
         if (shutdown(sfd, SHUT_WR) == -1)
             errExit("shutdown");
         exit(EXIT_SUCCESS);
     }
 }