domain_codec: optimize dname_dec and convert_dname

dname_dec: now iterates over the packet only once.
convert_dname: remove redundant checks and code shrink.

While testing I've noticed that some of the tests didn't compile
properly, so I fixed them.

function                                             old     new   delta
dname_dec                                            286     267     -19
dname_enc                                            166     143     -23
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-42)             Total: -42 bytes

Signed-off-by: Martin Lewis <martin.lewis.x84@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 79 insertions, 78 deletions

diff --git a/networking/udhcp/domain_codec.c b/networking/udhcp/domain_codec.c
index 752c0a863..eab4da68b 100644
--- a/networking/udhcp/domain_codec.c
+++ b/networking/udhcp/domain_codec.c
@@ -10,10 +10,14 @@
 # define _GNU_SOURCE
 # define FAST_FUNC /* nothing */
 # define xmalloc malloc
+# define xzalloc(s) calloc(s, 1)
+# define xstrdup strdup
+# define xrealloc realloc
 # include <stdlib.h>
 # include <stdint.h>
 # include <string.h>
 # include <stdio.h>
+# include <ctype.h>
 #else
 # include "common.h"
 #endif
@@ -26,86 +30,77 @@
 
 
 /* Expand a RFC1035-compressed list of domain names "cstr", of length "clen";
- * returns a newly allocated string containing the space-separated domains,
+ * return a newly allocated string containing the space-separated domains,
  * prefixed with the contents of string pre, or NULL if an error occurs.
  */
 char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
 {
-        char *ret = ret; /* for compiler */
-        char *dst = NULL;
+        char *ret, *end;
+        unsigned len, crtpos, retpos, depth;
 
-        /* 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 (1) {
-                /* note: "return NULL" below are leak-safe since
-                 * dst isn't allocated yet */
+        crtpos = retpos = depth = 0;
+        len = strlen(pre);
+        end = ret = xstrdup(pre);
+
+        /* Scan the string once, allocating new memory as needed */
+        while (crtpos < clen) {
                 const uint8_t *c;
-                unsigned crtpos, retpos, depth, len;
+                c = cstr + crtpos;
 
-                crtpos = retpos = depth = len = 0;
-                while (crtpos < clen) {
-                        c = cstr + crtpos;
+                if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
+                        /* pointer */
+                        if (crtpos + 2 > clen) /* no offset to jump to? abort */
+                                goto error;
+                        if (retpos == 0) /* toplevel? save return spot */
+                                retpos = crtpos + 2;
+                        depth++;
+                        crtpos = ((c[0] << 8) | c[1]) & 0x3fff; /* jump */
+                } else if (*c) {
+                        unsigned label_len;
+                        /* label */
+                        if (crtpos + *c + 1 > clen) /* label too long? abort */
+                                goto error;
+                        ret = xrealloc(ret, len + *c + 1);
+                        /* \3com ---> "com." */
+                        end = (char *)mempcpy(ret + len, c + 1, *c);
+                        *end = '.';
 
-                        if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
-                                /* 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[0] & 0x3f) << 8) | c[1]; /* jump */
-                        } else if (*c) {
-                                /* label */
-                                if (crtpos + *c + 1 > clen) /* label too long? abort */
-                                        return NULL;
-                                if (dst)
-                                        /* \3com ---> "com." */
-                                        ((char*)mempcpy(dst + len, c + 1, *c))[0] = '.';
-                                len += *c + 1;
-                                crtpos += *c + 1;
+                        label_len = *c + 1;
+                        len += label_len;
+                        crtpos += label_len;
+                } else {
+                        /* NUL: end of current domain name */
+                        if (retpos == 0) {
+                                /* toplevel? keep going */
+                                crtpos++;
                         } else {
-                                /* NUL: 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 && len != 0)
-                                        /* \4host\3com\0\4host and we are at \0:
-                                         * \3com was converted to "com.", change dot to space.
-                                         */
-                                        dst[len - 1] = ' ';
+                                /* return to toplevel saved spot */
+                                crtpos = retpos;
+                                retpos = depth = 0;
                         }
 
-                        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 != 0) {
+                                /* \4host\3com\0\4host and we are at \0:
+                                 * \3com was converted to "com.", change dot to space.
+                                 */
+                                ret[len - 1] = ' ';
                         }
                 }
 
-                if (!len) /* expanded string has 0 length? abort */
-                        return NULL;
-
-                if (!dst) { /* first pass? */
-                        /* allocate dst buffer and copy pre */
-                        unsigned plen = strlen(pre);
-                        ret = xmalloc(plen + len);
-                        dst = stpcpy(ret, pre);
-                } else {
-                        dst[len - 1] = '\0';
-                        break;
+                if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
+                 || len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
+                ) {
+                        goto error;
                 }
         }
 
+        if (ret == end) { /* expanded string is empty? abort */
+ error:
+                free(ret);
+                return NULL;
+        }
+
+        *end = '\0';
         return ret;
 }
 
@@ -115,42 +110,40 @@ char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
  */
 static uint8_t *convert_dname(const char *src, int *retlen)
 {
-        uint8_t c, *res, *lenptr, *dst;
-        int len;
+        uint8_t *res, *lenptr, *dst;
 
-        res = xmalloc(strlen(src) + 2);
+        res = xzalloc(strlen(src) + 2);
         dst = lenptr = res;
         dst++;
 
         for (;;) {
+                uint8_t c;
+                int len;
+
                 c = (uint8_t)*src++;
                 if (c == '.' || c == '\0') {  /* end of label */
                         len = dst - lenptr - 1;
-                        /* label too long, too short, or two '.'s in a row? abort */
-                        if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
-                                free(res);
-                                *retlen = 0;
-                                return NULL;
-                        }
+                        /* label too long, too short, or two '.'s in a row (len will be 0) */
+                        if (len > NS_MAXLABEL || len == 0)
+                                goto error;
+
                         *lenptr = len;
                         if (c == '\0' || *src == '\0')  /* "" or ".": end of src */
                                 break;
                         lenptr = dst++;
                         continue;
                 }
-                if (c >= 'A' && c <= 'Z')  /* uppercase? convert to lower */
-                        c += ('a' - 'A');
-                *dst++ = c;
+                *dst++ = tolower(c);
         }
 
-        if (dst - res >= NS_MAXCDNAME) {  /* dname too long? abort */
+        *retlen = dst + 1 - res;
+        if (*retlen > NS_MAXCDNAME) {  /* dname too long? abort */
+ error:
                 free(res);
                 *retlen = 0;
                 return NULL;
         }
 
-        *dst++ = 0;
-        *retlen = dst - res;
         return res;
 }
 
@@ -245,6 +238,7 @@ int main(int argc, char **argv)
         printf("test4:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5", ""));
         printf("test5:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5\1z\xC0\xA", ""));
 
+#if 0
 #define DNAME_ENC(cache,source,lenp) dname_enc((uint8_t*)(cache), sizeof(cache), (source), (lenp))
         encoded = dname_enc(NULL, 0, "test.net", &len);
         printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
@@ -252,6 +246,13 @@ int main(int argc, char **argv)
         printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
         encoded = DNAME_ENC("\4test\3net\0", "test.net", &len);
         printf("test8:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
+#endif
+
+        encoded = dname_enc("test.net", &len);
+        printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
+        encoded = dname_enc("test.host.com", &len);
+        printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
+
         return 0;
 }
 #endif