fixed a bug in message compression pointer handling

dns.unpack-labels.js

@@ -29,18 +29,19 @@ exports.DNS_UNPACK_LABELS = function (ui8, ptr, q) {
       break;
     }
 
-    if (0xc0 === len) {
-      var cpptr = ui8[total + 1];
+    // Handle message compression pointers. See 4.1.4 of RFC1035 for details.
+    if (len >= 0xc0) {
+      var cpptr = ((ui8[total] & 0x3f) << 8) |  ui8[total + 1];
 
-      // we're not coming back!
-      ptr = cpptr;
+      // We're not coming back, so if this is the first time we're following one of
+      // these pointers we up the byteLength to mark the pointer as part of the label
       if (!q.cpcount) {
         q.byteLength += 2; // cp and len
       }
       q.cpcount += 1;
 
       // recursion
-      return exports.DNS_UNPACK_LABELS(ui8, ptr, q);
+      return exports.DNS_UNPACK_LABELS(ui8, cpptr, q);
     }
 
     //str.length = 0; // fast empty array
@@ -51,27 +52,28 @@ exports.DNS_UNPACK_LABELS = function (ui8, ptr, q) {
       );
     }
 
+    // Advance the pointer to after the length indicator, then read the string in.
+    total += 1;
     for (i = 0; i < len; i += 1) {
-      total += 1;
       // TODO check url-allowable characters
       label.push(String.fromCharCode(ui8[total]));
+      total += 1;
     }
 
     if (label.length) {
       q.labels.push(label.join(''));
     }
 
-    total += 1;
-
+    // It is important this be done every time, so that if we run into a message compression
+    // pointer later we still have a record of what was consumed before that.
+    if (0 === q.cpcount) {
+      q.byteLength = total - ptr;
+    }
   } while (0 !== len && undefined !== len);
 
   //str.pop(); // remove trailing '.'
 
   q.name = q.labels.join('.');
-  if (0 === q.cpcount) {
-    q.byteLength = total - ptr;
-  }
-
   return q;
 };
 

test/fixtures/canone30522.local.js

@@ -0,0 +1,59 @@
+module.exports = {
+    "header": {
+        "id": 0,
+        "qr": 1,
+        "opcode": 0,
+        "aa": 0,
+        "tc": 0,
+        "rd": 0,
+        "ra": 0,
+        "res1": 0,
+        "res2": 0,
+        "res3": 0,
+        "rcode": 0
+    },
+    "question": [],
+    "answer": [
+        {
+            "name": "_pdl-datastream._tcp.local",
+            "type": 12,
+            "class": 1,
+            "ttl": 255,
+            "data": "Canon MF620C Series._pdl-datastream._tcp.local"
+        }
+    ],
+    "additional": [
+        {
+            "name": "Canone30522.local",
+            "type": 1,
+            "class": 32769,
+            "ttl": 255,
+        },
+        {
+            "name": "Canon MF620C Series._pdl-datastream._tcp.local",
+            "type": 33,
+            "class": 32769,
+            "ttl": 255,
+        },
+        {
+            "name": "Canon MF620C Series._pdl-datastream._tcp.local",
+            "type": 16,
+            "class": 32769,
+            "ttl": 255,
+        },
+        {
+            "name": "Canone30522.local",
+            "type": 47,
+            "class": 32769,
+            "ttl": 255,
+        },
+        {
+            "name": "Canon MF620C Series._pdl-datastream._tcp.local",
+            "type": 47,
+            "class": 32769,
+            "ttl": 255,
+        }
+    ],
+    "authority": [],
+    "edns_options": []
+};