1 /* Byte Stream Connection Server Example
2 Copyright (C) 1991-2021 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
read_from_client(int filedes)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
main(void)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 }
121