[PATCH] domain_codec: optimize dname_dec and convert_dname
Martin Lewis
martin.lewis.x84 at gmail.com
Thu Jul 9 19:47:05 UTC 2020
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
text data bss dec hex filename
981645 16915 1872 1000432 f43f0 busybox_old
981603 16915 1872 1000390 f43c6 busybox_unstripped
Signed-off-by: Martin Lewis <martin.lewis.x84 at gmail.com>
---
networking/udhcp/domain_codec.c | 157 ++++++++++++++++++++--------------------
1 file changed, 79 insertions(+), 78 deletions(-)
diff --git a/networking/udhcp/domain_codec.c b/networking/udhcp/domain_codec.c
index 752c0a863..092cd6661 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
@@ -31,81 +35,72 @@
*/
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[0] = '.';
- 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;
+ } else {
+ *dst++ = tolower(c);
}
- if (c >= 'A' && c <= 'Z') /* uppercase? convert to lower */
- c += ('a' - 'A');
- *dst++ = 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
--
2.11.0
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