sockets/ud_ucase_cl.c

This is sockets/ud_ucase_cl.c (Listing 57-7, page 1173), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, 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_cl.c
+
+   A UNIX domain client that communicates with the server in ud_ucase_sv.c.
+   This client sends each command-line argument as a datagram to the server,
+   and then displays the contents of the server's response datagram.
+*/
 #include "ud_ucase.h"
 
 int
 main(int argc, char *argv[])
 {
     struct sockaddr_un svaddr, claddr;
     int sfd, j;
     size_t msgLen;
     ssize_t numBytes;
     char resp[BUF_SIZE];
 
     if (argc < 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s msg...\n", argv[0]);
 
     /* Create client socket; bind to unique pathname (based on PID) */
 
     sfd = socket(AF_UNIX, SOCK_DGRAM, 0);
     if (sfd == -1)
         errExit("socket");
 
     memset(&claddr, 0, sizeof(struct sockaddr_un));
     claddr.sun_family = AF_UNIX;
     snprintf(claddr.sun_path, sizeof(claddr.sun_path),
             "/tmp/ud_ucase_cl.%ld", (long) getpid());
 
     if (bind(sfd, (struct sockaddr *) &claddr, sizeof(struct sockaddr_un)) == -1)
         errExit("bind");
 
     /* Construct address of server */
 
     memset(&svaddr, 0, sizeof(struct sockaddr_un));
     svaddr.sun_family = AF_UNIX;
     strncpy(svaddr.sun_path, SV_SOCK_PATH, sizeof(svaddr.sun_path) - 1);
 
     /* Send messages to server; echo responses on stdout */
 
     for (j = 1; j < argc; j++) {
         msgLen = strlen(argv[j]);       /* May be longer than BUF_SIZE */
         if (sendto(sfd, argv[j], msgLen, 0, (struct sockaddr *) &svaddr,
                 sizeof(struct sockaddr_un)) != msgLen)
             fatal("sendto");
 
         numBytes = recvfrom(sfd, resp, BUF_SIZE, 0, NULL, NULL);
+        /* Or equivalently: numBytes = recv(sfd, resp, BUF_SIZE, 0);
+                        or: numBytes = read(sfd, resp, BUF_SIZE); */
         if (numBytes == -1)
             errExit("recvfrom");
         printf("Response %d: %.*s\n", j, (int) numBytes, resp);
     }
 
     remove(claddr.sun_path);            /* Remove client socket pathname */
     exit(EXIT_SUCCESS);
 }

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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