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linux 名字与地址转换

分类： linux

2015-06-04 23:27:42

在网络中，主机都是用ip地址标示的；但是，出于很多理由，我们应该使用名字，而非纯数字：名字比较好记，数值地址可以变动但名字可以不变（如域名），随着往ipv6上转移，地址变得很长，数值书写容易出错等等。本文示例linux几个处理名字与地址转换的函数的使用：

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  1. #include <netdb.h>
  2. #include <sys/socket.h>
  3. #include <arpa/inet.h>
  4. #include <stdio.h>
  5. #include <stdlib.h>
  6. #include <netinet/in.h>
  7. #include <getopt.h>

  9. struct option g_opts[] = {
  10.     {"host", required_argument, null, 'h'},
  11.     {"server", required_argument, null, 's'},
  12.     {"protocol", required_argument, null, 'p'},
  13.     {"help", no_argument, null, 'h'}
  14. };

  16. /* struct hostent
  17.    {
  18.     char *h_name;
  19.     char **h_aliases;
  20.     int h_addrtype;
  21.     int h_length;
  22.     char **h_addr_list;
  23.     #define h_addr h_addr_list[0]
  24.    };
  25.  */

  27. /*
  28. struct servent {
  29.     char *s_name;    //official service name
  30.     char **s_aliases;    //alias list
  31.     int s_port;         //port number, network-byte order
  32.     char *s_proto;        // protocol to use
  33. */
  34. void showusage()
  35. {
  36.     printf("usage:\n\tidns -h [ipstr/hostname]\n\t -s [servname/servport] -g [protocol]\n");
  37. }

  39. static void printservent(struct servent *sptr)
  40. {
  41.     char **pptr;

  43.     printf("server name: %s\n", sptr->s_name);

  45.     pptr = sptr->s_aliases;
  46.     while (pptr && *pptr != null)
  47.     {
  48.         printf("\taliases: %s\n", *pptr);
  49.         pptr;
  50.     }

  52.     printf("\tport: %d\n", ntohs(sptr->s_port));
  53.     printf("\tproto: %s\n", sptr->s_proto);
  54. }

  56. static void printhostent(struct hostent *hptr)
  57. {
  58.     char str[33] = { 0, };
  59.     char **pptr;

  61.     if (null == hptr)
  62.         return;

  64.     printf("official hostname:%s\n", hptr->h_name);

  66.     for (pptr = hptr->h_aliases; *pptr != null; pptr)
  67.         printf("alias:%s\n", *pptr);

  69.     switch (hptr->h_addrtype)
  70.     {
  71.     case af_inet:
  72.     case af_inet6:
  73.         pptr = hptr->h_addr_list;
  74.         for (; pptr && *pptr != null; pptr)
  75.             printf("address: %s\n", inet_ntop(hptr->h_addrtype, *pptr, str, 32));
  76.         break;
  77.     default:
  78.         printf("unknow address type\n");
  79.         break;
  80.     }

  82. }

  84. static void printherror(int perror)
  85. {
  86.     switch (perror)
  87.     {
  88.     case host_not_found:
  89.         printf("host not found!\n");
  90.         break;
  91. // case no_address:
  92. // case no_data:printf("112\n");break;
  93.     case no_recovery:
  94.         printf("no recovery!\n");
  95.         break;
  96.     case try_again:
  97.         printf("try again\n");
  98.         break;
  99.     default:
  100.         printf("unknow error type:%d\n", perror);
  101.         return;
  102.     }
  103. }

  105. void igethostbyname_common(char *name)
  106. {
  107.     struct addrinfo *answer, hint, *curr;
  108.     char ipstr[16];
  109.     int ret;

  111.     memset(&hint, 0, sizeof(hint));
  112.     hint.ai_flags = ai_canonname;

  114.     ret = getaddrinfo(name, null, &hint, &answer);
  115.     if (ret != 0)
  116.     {
  117.         fprintf(stderr, "getaddrinfo fail: %s\n", gai_strerror(ret));
  118.         exit(1);
  119.     }

  121.     for (curr = answer; curr != null; curr = curr->ai_next)
  122.     {
  123.         printf("host name: %s\n", curr->ai_canonname == null ? "" : curr->ai_canonname);

  125.         inet_ntop(af_inet, &(((struct sockaddr_in *)(curr->ai_addr))->sin_addr), ipstr, 16);
  126.         printf("addr: %s\n", ipstr);
  127.     }

  129.     freeaddrinfo(answer);
  130. }

  132. void igethostbyname_ipv4(char *name)
  133. {
  134.     struct hostent *hptr;
  135.     if ((hptr = gethostbyname(name)) == null)
  136.     {
  137.         printf("gethostbyname fail for host:%s\n", name);
  138.         return;
  139.     }
  140.     printhostent(hptr);
  141. }

  143. void igethostbyaddr_ipv4(char *addr)
  144. {
  145.     struct hostent *hptr;
  146.     in_addr_t nip;
  147.     int trytimes = 3;

  149.     nip = inet_addr(addr);

  151.   l_try_again:
  152.     if ((hptr = gethostbyaddr(&nip, 4, af_inet)) == null)
  153.     {
  154.         if (h_errno == try_again && trytimes > 0)
  155.         {
  156.             trytimes--;
  157.             goto l_try_again;
  158.         }

  160.         printf("fail to get host by addr<%s>: ", addr);
  161.         printherror(h_errno);
  162.         return;
  163.     }
  164.     printhostent(hptr);
  165. }

  167. void igetservbyname(char *name, char *proto)
  168. {
  169.     struct servent *sptr;

  171.     if ((sptr = getservbyname(name, proto)) == null)
  172.     {
  173.         printf("can not find server with name:%s and protocol:%s\n", name, proto);
  174.         return;
  175.     }

  177.     printservent(sptr);

  179. }

  181. void igetservbyport(int port, char *proto)
  182. {
  183.     struct servent *sptr;

  185.     if ((sptr = getservbyport(htons(port), proto)) == null)
  186.     {
  187.         printf("can not find server with port:%d and protocol:%s\n", port, proto);
  188.         return;
  189.     }
  190.     printservent(sptr);
  191. }

  193. char g_buf[64] = { 0, };
  194. char g_proto[16] = { 0, };

  196. int main(int argc, char **argv)
  197. {
  198.     int opt;
  199.     int cmdtype = 0;

  201.     int temp = 0;

  203.     if (argc < 2)
  204.     {
  205.         showusage();
  206.         return 0;
  207.     }

  209.     while ((opt = getopt_long(argc, argv, "s:h:p:", g_opts, null)) != -1)
  210.     {
  211.         switch (opt)
  212.         {
  213.         case 's':
  214.             strcpy(g_buf, optarg);
  215.             cmdtype = 1;
  216.             break;
  217.         case 'h':
  218.             strcpy(g_buf, optarg);
  219.             cmdtype = 2;
  220.             break;
  221.         case 'p':
  222.             strcpy(g_proto, optarg);
  223.             break;
  224.         case 'h':
  225.             showusage();
  226.             break;
  227.         default:
  228.             showusage();
  229.             return;
  230.         }
  231.     }

  233.     if (cmdtype == 2 && (inet_addr(g_buf)) == inaddr_none)
  234.     {
  235.         igethostbyname_ipv4(g_buf);
  236.     }
  237.     else if (cmdtype == 2)
  238.     {
  239.         igethostbyaddr_ipv4(g_buf);
  240.     }
  241.     else if (cmdtype == 1)
  242.     {
  243.         temp = atoi(g_buf);
  244.         if (temp > 0)
  245.             igetservbyport(temp, g_proto);
  246.         else
  247.             igetservbyname(g_buf, g_proto);
  248.     }
  249.     else
  250.         showusage();

  252.     return 0;
  253. }



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