examples:dns_matching: fixed loop break condition

The for loop was copying garbase characters after domain name.
Fixed this by adding correct terminating condition. Also removed
unnecessary code
Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>

examples/networking/dns_matching/dns_matching.c

@@ -70,10 +70,6 @@ int dns_matching(struct __sk_buff *skb)
       struct udp_t *udp = cursor_advance(cursor, sizeof(*udp));
       if(udp->dport == 53){
 
-        // Our Cursor + the length of our udp packet - size of the udp header
-        // - the two 16bit values for QTYPE and QCLASS.
-        u8 *sentinel = cursor + udp->length - sizeof(*udp) - 4;
-
         struct dns_hdr_t *dns_hdr = cursor_advance(cursor, sizeof(*dns_hdr));
 
         // Do nothing if packet is not a request.
@@ -86,15 +82,17 @@ int dns_matching(struct __sk_buff *skb)
         struct dns_char_t *c;
         #pragma unroll
         for(i = 0; i<255;i++){
-          if (cursor == sentinel) goto end; c = cursor_advance(cursor, 1); key.p[i] = c->c;
+          c = cursor_advance(cursor, 1);
+          if (c->c == 0)
+            break;
+          key.p[i] = c->c;
         }
-        end:
-        {}
 
         struct Leaf * lookup_leaf = cache.lookup(&key);
 
         // If DNS name is contained in our map, drop packet.
         if(lookup_leaf) {
+          bpf_trace_printk("Matched1\n");
           return 0;
         }
       }