do not shut down connections on PacketDecodingError

router/crypto.go

@@ -271,8 +271,7 @@ type NaClDecryptorInstance struct {
 }
 
 type PacketDecodingError struct {
-	Fatal bool
-	Desc  string
+	Desc string
 }
 
 func NewNonDecryptor(conn *LocalConnection) *NonDecryptor {
@@ -335,7 +334,7 @@ func (nd *NaClDecryptor) ReceiveNonce(msg []byte) {
 func (nd *NaClDecryptor) IterateFrames(packet []byte, consumer FrameConsumer) error {
 	buf, err := nd.decrypt(packet)
 	if err != nil {
-		return PacketDecodingError{Fatal: true, Desc: fmt.Sprint("decryption failed; ", err)}
+		return PacketDecodingError{Desc: fmt.Sprint("decryption failed; ", err)}
 	}
 	return nd.NonDecryptor.IterateFrames(buf, consumer)
 }

router/router.go

@@ -250,16 +250,18 @@ func (router *Router) udpReader(conn *net.UDPConn, po PacketSink) {
 		if !ok {
 			continue
 		}
-		err = relayConn.Decryptor.IterateFrames(packet, router.handleUDPPacketFunc(dec, sender, po))
-		if pde, ok := err.(PacketDecodingError); ok {
-			if pde.Fatal {
-				relayConn.Shutdown(pde)
-			} else {
-				relayConn.Log(pde.Error())
-			}
-			continue
-		}
-		if err != nil {
+		if err := relayConn.Decryptor.IterateFrames(packet, router.handleUDPPacketFunc(dec, sender, po)); err != nil {
+			// Errors during UDP packet decoding / processing are
+			// non-fatal. One common cause is that we receive and
+			// attempt to decrypt a "stray" packet. This can actually
+			// happen quite easily if there is some connection churn
+			// between two peers. After all, UDP isn't a
+			// connection-oriented protocol, yet we pretend it is.
+			//
+			// If anything really is seriously, unrecoverably amiss
+			// with a connection, that will typically result in missed
+			// heartbeats and the connection getting shut down because
+			// of that.
 			relayConn.Log(err)
 		}
 	}