Merge pull request #602 from network-intelligence/stun-do-analysis-revision

STUN fingerprints are generated for client requests but not server responses.

Author: andrewchi

src/libmerc/stun.h

@@ -683,6 +683,13 @@ namespace stun {
 
         bool has_magic_cookie() const { return tid_has_magic_cookie; }
 
+        /// returns true if this header corresponds to a success
+        /// response or an error response
+        ///
+        bool is_response() {
+            return (get_message_class() & 0b10) == 0b10;
+        }
+
         // return the number of zero bytes in the transaction_id
         //
         size_t tid_zero_count() const {
@@ -919,6 +926,17 @@ namespace stun {
                 return;
             }
 
+            if (hdr.is_response()) {
+                //
+                // we don't generate fingerprints for responses, so we
+                // set the truncated bit in the fingerprint buffer, to
+                // indicate that it does not contain an actual
+                // fingerprint
+                //
+                buf.set_truncated();
+                return;
+            }
+
             hdr.write_fingerprint(buf);
 
             // the attr_fingerprint_type determines what data from a
@@ -1003,22 +1021,10 @@ namespace stun {
             //
             utf8_safe_string<MAX_USER_AGENT_LEN> utf8_software{software};
 
-            // handle message classes appropriately: reverse the
-            // addresses and ports in the flow key for responses,
-            // leave the flow key untouched for requests, and ignore
-            // all other message classes
-            //
-            key k{flow_key};
-            if ((hdr.get_message_class() & 0b10) == 0b10) {
-                //
-                // success_resp and error_resp: swap addrs and ports
-                //
-                k.reverse();
-            }
             ac.destination.init({nullptr,nullptr},         // domain name
                                 utf8_software.get_datum(), // user agent
                                 {nullptr,nullptr},         // alpn
-                                k                          // flow key, used for dst_addr and dst_port
+                                flow_key                   // flow key, used for dst_addr and dst_port
                                 );
 
             if (c == nullptr) {