lib/ip/dhcp_gettag.c

   1 /*      dhcp_gettag()                                   Author: Kees J. Bot
   2  *                                                              1 Dec 2000
   3  */
   4 #define nil ((void*)0)
   5 #include <stddef.h>
   6 #include <string.h>
   7 #include <sys/types.h>
   8 #include <net/hton.h>
   9 #include <net/gen/in.h>
  10 #include <net/gen/dhcp.h>
  11
  12 #define arraysize(a)    (sizeof(a) / sizeof((a)[0]))
  13
  14 int dhcp_gettag(dhcp_t *dp, int searchtag, u8_t **pdata, size_t *plen)
  15 {
  16     /* Find a tag in the options field, or possibly in the file or sname
  17      * fields.  Return true iff found, and return the data and/or length if
  18      * their pointers are non-null.
  19      */
  20     u8_t *p;
  21     u8_t *optfield[3];
  22     size_t optlen[3];
  23     int i, tag, len;
  24
  25     /* The DHCP magic number must be correct, or no tags. */
  26     if (dp->magic != DHCP_MAGIC) return 0;
  27
  28     optfield[0]= dp->options;
  29     optlen[0]= arraysize(dp->options);
  30     optfield[1]= dp->file;
  31     optlen[1]= 0;               /* Unknown if used for options yet. */
  32     optfield[2]= dp->sname;
  33     optlen[2]= 0;
  34
  35     for (i= 0; i < 3; i++) {
  36         p= optfield[i];
  37         while (p < optfield[i] + optlen[i]) {
  38             tag= *p++;
  39             if (tag == 255) break;
  40             len= tag == 0 ? 0 : *p++;
  41             if (tag == searchtag) {
  42                 if (pdata != nil) *pdata= p;
  43                 if (plen != nil) *plen= len;
  44                 return 1;
  45             }
  46             if (tag == DHCP_TAG_OVERLOAD) {
  47                 /* There are also options in the file or sname field. */
  48                 if (*p & 1) optlen[1]= arraysize(dp->file);
  49                 if (*p & 2) optlen[1]= arraysize(dp->sname);
  50             }
  51             p += len;
  52         }
  53     }
  54     return 0;
  55 }