sockets/ud_ucase_sv.c

This is sockets/ud_ucase_sv.c (Listing 57-6, page 1172), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* ud_ucase_sv.c
+
+   A server that uses a UNIX domain datagram socket to receive datagrams,
+   convert their contents to uppercase, and then return them to the senders.
+
+   See also ud_ucase_cl.c.
+*/
 #include "ud_ucase.h"
 
 int
 main(int argc, char *argv[])
 {
     struct sockaddr_un svaddr, claddr;
     int sfd, j;
     ssize_t numBytes;
     socklen_t len;
     char buf[BUF_SIZE];
 
     sfd = socket(AF_UNIX, SOCK_DGRAM, 0);       /* Create server socket */
     if (sfd == -1)
         errExit("socket");
 
     /* Construct well-known address and bind server socket to it */
 
+    /* For an explanation of the following check, see the erratum note for
+       page 1168 at http://www.man7.org/tlpi/errata/. */
+
+    if (strlen(SV_SOCK_PATH) > sizeof(svaddr.sun_path) - 1)
+        fatal("Server socket path too long: %s", SV_SOCK_PATH);
+
     if (remove(SV_SOCK_PATH) == -1 && errno != ENOENT)
         errExit("remove-%s", SV_SOCK_PATH);
 
     memset(&svaddr, 0, sizeof(struct sockaddr_un));
     svaddr.sun_family = AF_UNIX;
     strncpy(svaddr.sun_path, SV_SOCK_PATH, sizeof(svaddr.sun_path) - 1);
 
     if (bind(sfd, (struct sockaddr *) &svaddr, sizeof(struct sockaddr_un)) == -1)
         errExit("bind");
 
     /* Receive messages, convert to uppercase, and return to client */
 
     for (;;) {
         len = sizeof(struct sockaddr_un);
         numBytes = recvfrom(sfd, buf, BUF_SIZE, 0,
                             (struct sockaddr *) &claddr, &len);
         if (numBytes == -1)
             errExit("recvfrom");
 
         printf("Server received %ld bytes from %s\n", (long) numBytes,
                 claddr.sun_path);
 
         for (j = 0; j < numBytes; j++)
             buf[j] = toupper((unsigned char) buf[j]);
 
         if (sendto(sfd, buf, numBytes, 0, (struct sockaddr *) &claddr, len) !=
                 numBytes)
             fatal("sendto");
     }
 }

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

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