1 /* vi: set sw=4 ts=4: */
3 /* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
5 * Loosely based on the isc-dhcpd implementation by dhankins@isc.org
7 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
10 #if ENABLE_FEATURE_UDHCP_RFC3397
14 #define NS_MAXDNAME 1025 /* max domain name length */
15 #define NS_MAXCDNAME 255 /* max compressed domain name length */
16 #define NS_MAXLABEL 63 /* max label length */
17 #define NS_MAXDNSRCH 6 /* max domains in search path */
18 #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
21 /* expand a RFC1035-compressed list of domain names "cstr", of length "clen";
22 * returns a newly allocated string containing the space-separated domains,
23 * prefixed with the contents of string pre, or NULL if an error occurs.
25 char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
27 char *ret = ret; /* for compiler */
30 /* We make two passes over the cstr string. First, we compute
31 * how long the resulting string would be. Then we allocate a
32 * new buffer of the required length, and fill it in with the
33 * expanded content. The advantage of this approach is not
34 * having to deal with requiring callers to supply their own
35 * buffer, then having to check if it's sufficiently large, etc.
38 /* note: "return NULL" below are leak-safe since
39 * dst isn't yet allocated */
41 unsigned crtpos, retpos, depth, len;
43 crtpos = retpos = depth = len = 0;
44 while (crtpos < clen) {
47 if (*c & NS_CMPRSFLGS) {
49 if (crtpos + 2 > clen) /* no offset to jump to? abort */
51 if (retpos == 0) /* toplevel? save return spot */
54 crtpos = ((c[0] & 0x3f) << 8) | (c[1] & 0xff); /* jump */
57 if (crtpos + *c + 1 > clen) /* label too long? abort */
60 memcpy(dst + len, c + 1, *c);
66 /* null: end of current domain name */
68 /* toplevel? keep going */
71 /* return to toplevel saved spot */
79 if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
80 || len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
86 if (!len) /* expanded string has 0 length? abort */
89 if (!dst) { /* first pass? */
90 /* allocate dst buffer and copy pre */
91 unsigned plen = strlen(pre);
92 ret = dst = xmalloc(plen + len);
93 memcpy(dst, pre, plen);
104 /* Convert a domain name (src) from human-readable "foo.blah.com" format into
105 * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
106 * NULL if an error occurs.
108 static uint8_t *convert_dname(const char *src)
110 uint8_t c, *res, *lp, *rp;
113 res = xmalloc(strlen(src) + 2);
119 if (c == '.' || c == '\0') { /* end of label */
121 /* label too long, too short, or two '.'s in a row? abort */
122 if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
128 if (c == '\0' || *src == '\0') /* end of dname */
131 if (c >= 0x41 && c <= 0x5A) /* uppercase? convert to lower */
138 if (rp - res > NS_MAXCDNAME) { /* dname too long? abort */
145 /* returns the offset within cstr at which dname can be found, or -1
147 static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
149 const uint8_t *c, *d;
152 /* find all labels in cstr */
157 if ((*c & NS_CMPRSFLGS) != 0) { /* pointer, skip */
159 } else if (*c) { /* label, try matching dname */
162 while (*c == *d && memcmp(c + 1, d + 1, *c) == 0) {
163 if (*c == 0) /* match, return offset */
167 if ((*c & NS_CMPRSFLGS) != 0) /* pointer, jump */
168 c = cstr + (((*c & 0x3f) << 8) | (*(c + 1) & 0xff));
171 } else { /* null, skip */
179 /* computes string to be appended to cstr so that src would be added to
180 * the compression (best case, it's a 2-byte pointer to some offset within
181 * cstr; worst case, it's all of src, converted to rfc3011 format).
182 * The computed string is returned directly; its length is returned via retlen;
183 * NULL and 0, respectively, are returned if an error occurs.
185 uint8_t* FAST_FUNC dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
190 dname = convert_dname(src);
196 for (d = dname; *d != 0; d += *d + 1) {
197 off = find_offset(cstr, clen, d);
198 if (off >= 0) { /* found a match, add pointer and terminate string */
205 *retlen = d - dname + 1;
209 #endif /* ENABLE_FEATURE_UDHCP_RFC3397 */