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| <h4 class="subsection">16.9.7 Byte Stream Connection Server Example</h4> |
| |
| <p>The server end is much more complicated. Since we want to allow |
| multiple clients to be connected to the server at the same time, it |
| would be incorrect to wait for input from a single client by simply |
| calling <code>read</code> or <code>recv</code>. Instead, the right thing to do is |
| to use <code>select</code> (see <a href="Waiting-for-I_002fO.html#Waiting-for-I_002fO">Waiting for I/O</a>) to wait for input on |
| all of the open sockets. This also allows the server to deal with |
| additional connection requests. |
| |
| <p>This particular server doesn't do anything interesting once it has |
| gotten a message from a client. It does close the socket for that |
| client when it detects an end-of-file condition (resulting from the |
| client shutting down its end of the connection). |
| |
| <p>This program uses <code>make_socket</code> to set up the socket address; see |
| <a href="Inet-Example.html#Inet-Example">Inet Example</a>. |
| |
| <pre class="smallexample"> #include <stdio.h> |
| #include <errno.h> |
| #include <stdlib.h> |
| #include <unistd.h> |
| #include <sys/types.h> |
| #include <sys/socket.h> |
| #include <netinet/in.h> |
| #include <netdb.h> |
| |
| #define PORT 5555 |
| #define MAXMSG 512 |
| |
| int |
| read_from_client (int filedes) |
| { |
| char buffer[MAXMSG]; |
| int nbytes; |
| |
| nbytes = read (filedes, buffer, MAXMSG); |
| if (nbytes < 0) |
| { |
| /* <span class="roman">Read error.</span> */ |
| perror ("read"); |
| exit (EXIT_FAILURE); |
| } |
| else if (nbytes == 0) |
| /* <span class="roman">End-of-file.</span> */ |
| return -1; |
| else |
| { |
| /* <span class="roman">Data read.</span> */ |
| fprintf (stderr, "Server: got message: `%s'\n", buffer); |
| return 0; |
| } |
| } |
| |
| int |
| main (void) |
| { |
| extern int make_socket (uint16_t port); |
| int sock; |
| fd_set active_fd_set, read_fd_set; |
| int i; |
| struct sockaddr_in clientname; |
| size_t size; |
| |
| /* <span class="roman">Create the socket and set it up to accept connections.</span> */ |
| sock = make_socket (PORT); |
| if (listen (sock, 1) < 0) |
| { |
| perror ("listen"); |
| exit (EXIT_FAILURE); |
| } |
| |
| /* <span class="roman">Initialize the set of active sockets.</span> */ |
| FD_ZERO (&active_fd_set); |
| FD_SET (sock, &active_fd_set); |
| |
| while (1) |
| { |
| /* <span class="roman">Block until input arrives on one or more active sockets.</span> */ |
| read_fd_set = active_fd_set; |
| if (select (FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0) |
| { |
| perror ("select"); |
| exit (EXIT_FAILURE); |
| } |
| |
| /* <span class="roman">Service all the sockets with input pending.</span> */ |
| for (i = 0; i < FD_SETSIZE; ++i) |
| if (FD_ISSET (i, &read_fd_set)) |
| { |
| if (i == sock) |
| { |
| /* <span class="roman">Connection request on original socket.</span> */ |
| int new; |
| size = sizeof (clientname); |
| new = accept (sock, |
| (struct sockaddr *) &clientname, |
| &size); |
| if (new < 0) |
| { |
| perror ("accept"); |
| exit (EXIT_FAILURE); |
| } |
| fprintf (stderr, |
| "Server: connect from host %s, port %hd.\n", |
| inet_ntoa (clientname.sin_addr), |
| ntohs (clientname.sin_port)); |
| FD_SET (new, &active_fd_set); |
| } |
| else |
| { |
| /* <span class="roman">Data arriving on an already-connected socket.</span> */ |
| if (read_from_client (i) < 0) |
| { |
| close (i); |
| FD_CLR (i, &active_fd_set); |
| } |
| } |
| } |
| } |
| } |
| </pre> |
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