diplodocus.org Git - nmh/blob - test/getcanon.c

   1 /*
   2  * getcanon.c - Print the canonical name of a host, default to localhost.
   3  *
   4  * This code is Copyright (c) 2012, by the authors of nmh.  See the
   5  * COPYRIGHT file in the root directory of the nmh distribution for
   6  * complete copyright information.
   7  */
   8
   9 #include <netdb.h>   /* for getaddrinfo */
  10 #include <sys/socket.h>
  11 #include <sys/types.h>
  12 #include <unistd.h>  /* for gethostname */
  13 #include <limits.h>  /* for _POSIX_HOST_NAME_MAX */
  14 #include <string.h>  /* for memset */
  15 #include <stdio.h>
  16 #include <errno.h>
  17
  18
  19 int
  20 main(int argc, char *argv[])
  21 {
  22   char buf[_POSIX_HOST_NAME_MAX + 1];
  23   const char *hostname = buf;
  24   struct addrinfo hints, *res;
  25   int status = 0;
  26
  27   /* Borrowed the important code below from LocalName() in sbr/mts.c. */
  28
  29   if (argc < 2) {
  30     /* First get our local name. */
  31     status = gethostname(buf, sizeof buf);
  32   } else if (argc == 2) {
  33     hostname = argv[1];
  34   } else if (argc > 2) {
  35     fprintf(stderr, "usage: %s [hostname]\n", argv[0]);
  36     return 1;
  37   }
  38
  39   if (status == 0) {
  40     /* Now fully qualify the hostname. */
  41     memset(&hints, 0, sizeof hints);
  42     hints.ai_flags = AI_CANONNAME;
  43     hints.ai_family = AF_UNSPEC;
  44
  45     if ((status = getaddrinfo(hostname, NULL, &hints, &res)) == 0) {
  46       printf("%s\n", res->ai_canonname);
  47       freeaddrinfo(res);
  48     } else {
  49       printf("%s\n", hostname);
  50     }
  51   } else {
  52     fprintf(stderr, "gethostname() failed: %s\n", strerror(errno));
  53   }
  54
  55   return status;
  56 }