manual/examples/inetsrv.c

   1 /* Byte Stream Connection Server Example
   2    Copyright (C) 1991-2024 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU General Public License
   6    as published by the Free Software Foundation; either version 2
   7    of the License, or (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <https://www.gnu.org/licenses/>.
  16 */
  17
  18 #include <stdio.h>
  19 #include <errno.h>
  20 #include <stdlib.h>
  21 #include <unistd.h>
  22 #include <sys/types.h>
  23 #include <sys/socket.h>
  24 #include <netinet/in.h>
  25 #include <netdb.h>
  26
  27 #define PORT    5555
  28 #define MAXMSG  512
  29
  30 int
  31 read_from_client (int filedes)
  32 {
  33   char buffer[MAXMSG];
  34   int nbytes;
  35
  36   nbytes = read (filedes, buffer, MAXMSG);
  37   if (nbytes < 0)
  38     {
  39       /* Read error. */
  40       perror ("read");
  41       exit (EXIT_FAILURE);
  42     }
  43   else if (nbytes == 0)
  44     /* End-of-file. */
  45     return -1;
  46   else
  47     {
  48       /* Data read. */
  49       fprintf (stderr, "Server: got message: `%s'\n", buffer);
  50       return 0;
  51     }
  52 }
  53
  54 int
  55 main (void)
  56 {
  57   extern int make_socket (uint16_t port);
  58   int sock;
  59   fd_set active_fd_set, read_fd_set;
  60   int i;
  61   struct sockaddr_in clientname;
  62   size_t size;
  63
  64   /* Create the socket and set it up to accept connections. */
  65   sock = make_socket (PORT);
  66   if (listen (sock, 1) < 0)
  67     {
  68       perror ("listen");
  69       exit (EXIT_FAILURE);
  70     }
  71
  72   /* Initialize the set of active sockets. */
  73   FD_ZERO (&active_fd_set);
  74   FD_SET (sock, &active_fd_set);
  75
  76   while (1)
  77     {
  78       /* Block until input arrives on one or more active sockets. */
  79       read_fd_set = active_fd_set;
  80       if (select (FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0)
  81         {
  82           perror ("select");
  83           exit (EXIT_FAILURE);
  84         }
  85
  86       /* Service all the sockets with input pending. */
  87       for (i = 0; i < FD_SETSIZE; ++i)
  88         if (FD_ISSET (i, &read_fd_set))
  89           {
  90             if (i == sock)
  91               {
  92                 /* Connection request on original socket. */
  93                 int new;
  94                 size = sizeof (clientname);
  95                 new = accept (sock,
  96                               (struct sockaddr *) &clientname,
  97                               &size);
  98                 if (new < 0)
  99                   {
 100                     perror ("accept");
 101                     exit (EXIT_FAILURE);
 102                   }
 103                 fprintf (stderr,
 104                          "Server: connect from host %s, port %hd.\n",
 105                          inet_ntoa (clientname.sin_addr),
 106                          ntohs (clientname.sin_port));
 107                 FD_SET (new, &active_fd_set);
 108               }
 109             else
 110               {
 111                 /* Data arriving on an already-connected socket. */
 112                 if (read_from_client (i) < 0)
 113                   {
 114                     close (i);
 115                     FD_CLR (i, &active_fd_set);
 116                   }
 117               }
 118           }
 119     }
 120 }