speed up the search a bit by changing the search start

so that we start searching from where compression succeeded,
and not from the start of the input buffer.

diff --git a/src/lib/util/value.c b/src/lib/util/value.c
index ac88b853d4f03924f175b1e6cc1f9eccadc39a34..47bf88de89f3f95836086ce3c9e1ff5f245cc7f2 100644 (file)
--- a/src/lib/util/value.c
+++ b/src/lib/util/value.c
@@ -1299,10 +1299,11 @@ ssize_t fr_value_box_to_network(size_t *need, uint8_t *dst, size_t dst_len, fr_v
 /** Compress "label" by looking at it recursively.
  *
  */
-static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t *label, uint8_t **new_end)
+static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t const **new_search,
+                              uint8_t *label, uint8_t **new_end)
 {
        uint8_t *next;
-       uint8_t const *q, *ptr, *suffix;
+       uint8_t const *q, *ptr, *suffix, *search;
        uint16_t offset;
 
        /*
@@ -1317,6 +1318,7 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
         *      "end".  It also MUST be a valid, uncompressed label.
         */
        next = label + *label + 1;
+       search = start;
 
        /*
         *      We're at the last uncompressed label, scan the input
@@ -1326,12 +1328,28 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
         *      that matches, AND "next" label which is 0x00.  Only
         *      then does it do the string compare of the label
         *      values.
+        *
+        *      We speed this up slightly by tracking the previous
+        *      uncompressed pointer.  If we do compress the current
+        *      label, then we should also tell the caller where the
+        *      previous uncompressed label was found.  That way the
+        *      caller can start looking there for the next piece to
+        *      compress.  There's no need to search from the
+        *      beginning of the input buffer, as we're sure that
+        *      there is no earlier instance of the suffix we found.
+        *
+        *      i.e. as we compress the current name, we start
+        *      searching not at the input buffer, but at the name
+        *      that ends with the label we just compressed.  We're
+        *      guaranteed that no name *before* that one will match
+        *      the suffix we're looking for.
         */
        if (*next == 0x00) {
-               q = start;
+               q = search;
                while (q < end) {
                        if (*q == 0x00) {
                                q++;
+                               search = q;
                                continue;
                        }
 
@@ -1387,6 +1405,7 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
                        label[0] = (offset >> 8) | 0xc0;
                        label[1] = offset & 0xff;
                        *new_end = label + 2;
+                       if (new_search) *new_search = search;
                        return true;
                }
 
@@ -1398,7 +1417,7 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
         *      ourselves recursively in order to compress it.
         */
        if (*next < 63) {
-               if (!dns_label_compress(start, end, next, new_end)) return false;
+               if (!dns_label_compress(start, end, &search, next, new_end)) return false;
 
                /*
                 *      Else it WAS compressed.
@@ -1425,11 +1444,19 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
         *      which ends with the same compressed pointer, OR we
         *      find an uncompressed label which ends AT our
         *      compressed pointer.
+        *
+        *      Note that we start searching from the beginning of the
+        *      label which resulted in us finding the compressed
+        *      pointer!
+        *
+        *      We're guaranteed that any label BEFORE that one
+        *      doesn't end with a matching compressed pointer.
         */
-       q = start;
+       q = search;
        while (q < end) {
                if (*q == 0x00) {
                        q++;
+                       search = q;
                        continue;
                }
 
@@ -1508,6 +1535,7 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
                label[0] = (offset >> 8) | 0xc0;
                label[1] = offset & 0xff;
                *new_end = label + 2;
+               if (new_search) *new_search = search;
                return true;
        }
 
@@ -1686,7 +1714,7 @@ ssize_t fr_value_box_to_dns_label(size_t *need, uint8_t *buf, size_t buf_len, ui
        /*
         *      Compress it, AND tell us where the new end buffer is located.
         */
-       (void) dns_label_compress(buf, where, where, &data);
+       (void) dns_label_compress(buf, where, NULL, where, &data);
 
 done:
        if (need) *need = 0;