gresolv: Implement RFC3484 rule 9 (prefer longest matching prefix)

diff --git a/gweb/gresolv.c b/gweb/gresolv.c
index ed1ccab..0c7613d 100644 (file)
--- a/gweb/gresolv.c
+++ b/gweb/gresolv.c
@@ -920,6 +920,41 @@ static int rfc3484_compare(const void *__one, const void *__two)
                return one->dst_scope - two->dst_scope;
 
        /* Rule 9: Use longest matching prefix */
+       if (one->dst.sa.sa_family == AF_INET) {
+               /* Rule 9 is meaningless and counterproductive for Legacy IP
+                  unless perhaps we can tell that it's actually on the local
+                  subnet. But we don't (yet) have local interface config
+                  information, so do nothing here for Legacy IP for now. */
+       } else {
+               int i;
+
+               for (i = 0; i < 4; i++) {
+                       guint32 cmp_one, cmp_two;
+
+                       cmp_one = one->src.sin6.sin6_addr.s6_addr32[i] ^
+                               one->dst.sin6.sin6_addr.s6_addr32[i];
+                       cmp_two = two->src.sin6.sin6_addr.s6_addr32[i] ^
+                               two->dst.sin6.sin6_addr.s6_addr32[i];
+
+                       if (!cmp_two && !cmp_one)
+                               continue;
+
+                       if (cmp_one && !cmp_two)
+                               return 1;
+                       if (cmp_two && !cmp_one)
+                               return -1;
+
+                       /* g_bit_storage() is effectively fls() */
+                       cmp_one = g_bit_storage(ntohl(cmp_one));
+                       cmp_two = g_bit_storage(ntohl(cmp_two));
+
+                       if (cmp_one == cmp_two)
+                               break;
+
+                       return cmp_one - cmp_two;
+               }
+       }
+
 
        /* Rule 10: Otherwise, leave the order unchanged */
        if (one < two)