write our own simple case insensitive comparison

diff --git a/src/lib/util/value.c b/src/lib/util/value.c
index b8231d34036fb7dd230f48d6e839a2ccd07e4958..0ea23be2e1730f0810614213477ed4bb6dd3d610 100644 (file)
--- a/src/lib/util/value.c
+++ b/src/lib/util/value.c
@@ -1296,6 +1296,45 @@ ssize_t fr_value_box_to_network(size_t *need, uint8_t *dst, size_t dst_len, fr_v
        return min;
 }
 
+/** Compare two labels in a case-insensitive fashion.
+ *
+ *  This function requires that the input is valid, i.e. all
+ *  characters are within [-0-9A-Za-z].  If any other input is given,
+ *  it will break.
+ */
+static bool labelcmp(uint8_t const *a, uint8_t const *b, size_t len)
+{
+       for (/* nothing */; len > 0; len--) {
+               if (*a == *b) {
+                       a++;
+                       b++;
+                       continue;
+               }
+
+               /*
+                *      If one or the other isn't a letter, we can't
+                *      do case insensitive comparisons of them, so
+                *      they can't match.
+                */
+               if ((*a < 'A') || (*b < 'A')) {
+                       return false;
+               }
+
+               /*
+                *      If they're equal but different case, then the
+                *      only bit that's different is 0x20.
+                */
+               if (((*a)^(*b)) != 0x20) {
+                       return false;
+               }
+
+               a++;
+               b++;
+       }
+
+       return true;
+}
+
 /** Compress "label" by looking at it recursively.
  *
  *  For "ftp.example.com", it searches the input buffer for a matching
@@ -1508,15 +1547,8 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
                        /*
                         *      Only now do case-insensitive
                         *      comparisons.
-                        *
-                        *      @todo - use something a bit smarter
-                        *      and less generic than strncasecmp().
-                        *      We know that the data is ASCII, and
-                        *      that the only case insensitivity is
-                        *      between [a-z] and [A-Z].  So we might
-                        *      use a table lookup here.
                         */
-                       if (strncasecmp((char const *) q + 1, (char const *) label +1, *label) != 0) {
+                       if (!labelcmp(q + 1, label + 1, *label)) {
                                q = ptr;
                                continue;
                        }
@@ -1671,7 +1703,7 @@ static bool dns_label_compress(uint8_t const *start, uint8_t const *end, uint8_t
                 *      Only now do case-insensitive
                 *      comparisons.
                 */
-               if (strncasecmp((char const *) q + 1, (char const *) label +1, *label) != 0) {
+               if (!labelcmp(q + 1, label + 1, *label)) {
                        q = ptr;
                        continue;
                }