4c7e5b6c7
Denis Vlasenko
2007-02-27
Subject
I *always* forget svn add :(
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networking/udhcp/domain_codec.c+205 -0
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| + | /* 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 [email protected] |
| + | * |
| + | * 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 */ |