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 source tree.
9 #ifdef DNS_COMPR_TESTING
11 # define FAST_FUNC /* nothing */
12 # define xmalloc malloc
21 #define NS_MAXDNAME 1025 /* max domain name length */
22 #define NS_MAXCDNAME 255 /* max compressed domain name length */
23 #define NS_MAXLABEL 63 /* max label length */
24 #define NS_MAXDNSRCH 6 /* max domains in search path */
25 #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
28 /* Expand a RFC1035-compressed list of domain names "cstr", of length "clen";
29 * returns a newly allocated string containing the space-separated domains,
30 * prefixed with the contents of string pre, or NULL if an error occurs.
32 char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
34 char *ret = ret; /* for compiler */
37 /* We make two passes over the cstr string. First, we compute
38 * how long the resulting string would be. Then we allocate a
39 * new buffer of the required length, and fill it in with the
40 * expanded content. The advantage of this approach is not
41 * having to deal with requiring callers to supply their own
42 * buffer, then having to check if it's sufficiently large, etc.
45 /* note: "return NULL" below are leak-safe since
46 * dst isn't allocated yet */
48 unsigned crtpos, retpos, depth, len;
50 crtpos = retpos = depth = len = 0;
51 while (crtpos < clen) {
54 if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
56 if (crtpos + 2 > clen) /* no offset to jump to? abort */
58 if (retpos == 0) /* toplevel? save return spot */
61 crtpos = ((c[0] & 0x3f) << 8) | c[1]; /* jump */
64 if (crtpos + *c + 1 > clen) /* label too long? abort */
67 /* \3com ---> "com." */
68 ((char*)mempcpy(dst + len, c + 1, *c))[0] = '.';
72 /* NUL: end of current domain name */
74 /* toplevel? keep going */
77 /* return to toplevel saved spot */
82 /* \4host\3com\0\4host and we are at \0:
83 * \3com was converted to "com.", change dot to space.
88 if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
89 || len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
95 if (!len) /* expanded string has 0 length? abort */
98 if (!dst) { /* first pass? */
99 /* allocate dst buffer and copy pre */
100 unsigned plen = strlen(pre);
101 ret = xmalloc(plen + len);
102 dst = stpcpy(ret, pre);
112 /* Convert a domain name (src) from human-readable "foo.BLAH.com" format into
113 * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
114 * NULL if an error occurs.
116 static uint8_t *convert_dname(const char *src, int *retlen)
118 uint8_t c, *res, *lenptr, *dst;
121 res = xmalloc(strlen(src) + 2);
127 if (c == '.' || c == '\0') { /* end of label */
128 len = dst - lenptr - 1;
129 /* label too long, too short, or two '.'s in a row? abort */
130 if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
136 if (c == '\0' || *src == '\0') /* "" or ".": end of src */
141 if (c >= 'A' && c <= 'Z') /* uppercase? convert to lower */
146 if (dst - res >= NS_MAXCDNAME) { /* dname too long? abort */
158 /* Returns the offset within cstr at which dname can be found, or -1 */
159 static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
161 const uint8_t *c, *d;
164 /* find all labels in cstr */
169 if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) { /* pointer, skip */
173 if (*c) { /* label, try matching dname */
176 unsigned len1 = *c + 1;
177 if (memcmp(c, d, len1) != 0)
179 if (len1 == 1) /* at terminating NUL - match, return offset */
183 if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) /* pointer, jump */
184 c = cstr + (((c[0] & 0x3f) << 8) | c[1]);
186 off += cstr[off] + 1;
197 uint8_t* FAST_FUNC dname_enc(/*const uint8_t *cstr, int clen,*/ const char *src, int *retlen)
199 #if 0 //UNUSED, was intended for long, repetitive DHCP_DOMAIN_SEARCH options?
201 /* Computes string to be appended to cstr so that src would be added to
202 * the compression (best case, it's a 2-byte pointer to some offset within
203 * cstr; worst case, it's all of src, converted to <4>host<3>com<0> format).
204 * The computed string is returned directly; its length is returned via retlen;
205 * NULL and 0, respectively, are returned if an error occurs.
207 dname = convert_dname(src, retlen);
215 int off = find_offset(cstr, clen, d);
216 if (off >= 0) { /* found a match, add pointer and return */
217 *d++ = NS_CMPRSFLGS | (off >> 8);
225 *retlen = d - dname + 1;
228 return convert_dname(src, retlen);
231 #ifdef DNS_COMPR_TESTING
232 /* gcc -Wall -DDNS_COMPR_TESTING domain_codec.c -o domain_codec && ./domain_codec */
233 int main(int argc, char **argv)
238 uint8_t str[6] = { 0x00, 0x00, 0x02, 0x65, 0x65, 0x00 };
239 printf("NUL:'%s'\n", dname_dec(str, 6, ""));
241 #define DNAME_DEC(encoded,pre) dname_dec((uint8_t*)(encoded), sizeof(encoded), (pre))
242 printf("'%s'\n", DNAME_DEC("\4host\3com\0", "test1:"));
243 printf("test2:'%s'\n", DNAME_DEC("\4host\3com\0\4host\3com\0", ""));
244 printf("test3:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\0", ""));
245 printf("test4:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5", ""));
246 printf("test5:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5\1z\xC0\xA", ""));
248 #define DNAME_ENC(cache,source,lenp) dname_enc((uint8_t*)(cache), sizeof(cache), (source), (lenp))
249 encoded = dname_enc(NULL, 0, "test.net", &len);
250 printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
251 encoded = DNAME_ENC("\3net\0", "test.net", &len);
252 printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
253 encoded = DNAME_ENC("\4test\3net\0", "test.net", &len);
254 printf("test8:'%s' len:%d\n", dname_dec(encoded, len, ""), len);