I *always* forget svn add :(

networking/udhcp/domain_codec.c

@@ -0,0 +1,205 @@
+/* vi: set sw=4 ts=4: */
+
+/* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
+ *
+ * Loosely based on the isc-dhcpd implementation by dhankins@isc.org
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
+ */
+
+#if ENABLE_FEATURE_RFC3397
+
+#include "common.h"
+#include "options.h"
+
+#define NS_MAXDNAME  1025	/* max domain name length */
+#define NS_MAXCDNAME  255	/* max compressed domain name length */
+#define NS_MAXLABEL    63	/* max label length */
+#define NS_MAXDNSRCH    6	/* max domains in search path */
+#define NS_CMPRSFLGS 0xc0	/* name compression pointer flag */
+
+
+/* expand a RFC1035-compressed list of domain names "cstr", of length "clen";
+ * returns a newly allocated string containing the space-separated domains,
+ * prefixed with the contents of string pre, or NULL if an error occurs.
+ */
+char *dname_dec(const uint8_t *cstr, int clen, const char *pre)
+{
+	const uint8_t *c;
+	int crtpos, retpos, depth, plen = 0, len = 0;
+	char *dst = NULL;
+
+	if (!cstr)
+		return NULL;
+
+	if (pre)
+		plen = strlen(pre);
+
+	/* We make two passes over the cstr string. First, we compute
+	 * how long the resulting string would be. Then we allocate a
+	 * new buffer of the required length, and fill it in with the
+	 * expanded content. The advantage of this approach is not
+	 * having to deal with requiring callers to supply their own
+	 * buffer, then having to check if it's sufficiently large, etc.
+	 */
+
+	while (!dst) {
+
+		if (len > 0) {	/* second pass? allocate dst buffer and copy pre */
+			dst = xmalloc(len + plen);
+			memcpy(dst, pre, plen);
+		}
+
+		crtpos = retpos = depth = len = 0;
+
+		while (crtpos < clen) {
+			c = cstr + crtpos;
+
+			if ((*c & NS_CMPRSFLGS) != 0) {	/* pointer */
+				if (crtpos + 2 > clen)		/* no offset to jump to? abort */
+					return NULL;
+				if (retpos == 0)			/* toplevel? save return spot */
+					retpos = crtpos + 2;
+				depth++;
+				crtpos = ((*c & 0x3f) << 8) | (*(c + 1) & 0xff); /* jump */
+			} else if (*c) {			/* label */
+				if (crtpos + *c + 1 > clen)		/* label too long? abort */
+					return NULL;
+				if (dst)
+					memcpy(dst + plen + len, c + 1, *c);
+				len += *c + 1;
+				crtpos += *c + 1;
+				if (dst)
+					*(dst + plen + len - 1) = '.';
+			} else {					/* null: end of current domain name */
+				if (retpos == 0) {			/* toplevel? keep going */
+					crtpos++;
+				} else {					/* return to toplevel saved spot */
+					crtpos = retpos;
+					retpos = depth = 0;
+				}
+				if (dst)
+					*(dst + plen + len - 1) = ' ';
+			}
+
+			if (depth > NS_MAXDNSRCH || /* too many jumps? abort, it's a loop */
+				len > NS_MAXDNAME * NS_MAXDNSRCH) /* result too long? abort */
+				return NULL;
+		}
+
+		if (!len)			/* expanded string has 0 length? abort */
+			return NULL;
+
+		if (dst)
+			*(dst + plen + len - 1) = '\0';
+	}
+
+	return dst;
+}
+
+/* Convert a domain name (src) from human-readable "foo.blah.com" format into
+ * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
+ * NULL if an error occurs.
+ */
+static uint8_t *convert_dname(const char *src)
+{
+	uint8_t c, *res, *lp, *rp;
+	int len;
+
+	res = xmalloc(strlen(src) + 2);
+	rp = lp = res;
+	rp++;
+
+	for (;;) {
+		c = (uint8_t)*src++;
+		if (c == '.' || c == '\0') {	/* end of label */
+			len = rp - lp - 1;
+			/* label too long, too short, or two '.'s in a row? abort */
+			if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
+				free(res);
+				return NULL;
+			}
+			*lp = len;
+			lp = rp++;
+			if (c == '\0' || *src == '\0')	/* end of dname */
+				break;
+		} else {
+			if (c >= 0x41 && c <= 0x5A)		/* uppercase? convert to lower */
+				c += 0x20;
+			*rp++ = c;
+		}
+	}
+
+	*lp = 0;
+	if (rp - res > NS_MAXCDNAME) {	/* dname too long? abort */
+		free(res);
+		return NULL;
+	}
+	return res;
+}
+
+/* returns the offset within cstr at which dname can be found, or -1
+ */
+static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
+{
+	const uint8_t *c, *d;
+	int off, inc;
+
+	/* find all labels in cstr */
+	off = 0;
+	while (off < clen) {
+		c = cstr + off;
+
+		if ((*c & NS_CMPRSFLGS) != 0) {	/* pointer, skip */
+			off += 2;
+		} else if (*c) {	/* label, try matching dname */
+			inc = *c + 1;
+			d = dname;
+			while (*c == *d && memcmp(c + 1, d + 1, *c) == 0) {
+				if (*c == 0)	/* match, return offset */
+					return off;
+				d += *c + 1;
+				c += *c + 1;
+				if ((*c & NS_CMPRSFLGS) != 0)	/* pointer, jump */
+					c = cstr + (((*c & 0x3f) << 8) | (*(c + 1) & 0xff));
+			}
+			off += inc;
+		} else {	/* null, skip */
+			off++;
+		}
+	}
+
+	return -1;
+}
+
+/* computes string to be appended to cstr so that src would be added to
+ * the compression (best case, it's a 2-byte pointer to some offset within
+ * cstr; worst case, it's all of src, converted to rfc3011 format).
+ * The computed string is returned directly; its length is returned via retlen;
+ * NULL and 0, respectively, are returned if an error occurs.
+ */
+uint8_t *dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
+{
+	uint8_t *d, *dname;
+	int off;
+
+	dname = convert_dname(src);
+	if (dname == NULL) {
+		*retlen = 0;
+		return NULL;
+	}
+
+	for (d = dname; *d != 0; d += *d + 1) {
+		off = find_offset(cstr, clen, d);
+		if (off >= 0) {	/* found a match, add pointer and terminate string */
+			*d++ = NS_CMPRSFLGS;
+			*d = off;
+			break;
+		}
+	}
+
+	*retlen = d - dname + 1;
+	return dname;
+}		
+
+#endif /* ENABLE_FEATURE_RFC3397 */