device: simplify peer queue locking

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/receive.go

@@ -174,7 +174,6 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 			elem.Lock()
 
 			// add to decryption queues
-
 			peer.queue.RLock()
 			if peer.isRunning.Get() {
 				peer.queue.inbound <- elem
@@ -433,52 +432,25 @@ func (device *Device) RoutineHandshake() {
 
 func (peer *Peer) RoutineSequentialReceiver() {
 	device := peer.device
-	var elem *QueueInboundElement
-
 	defer func() {
 		device.log.Verbosef("%v - Routine: sequential receiver - stopped", peer)
-		peer.routines.stopping.Done()
-		if elem != nil {
-			device.PutMessageBuffer(elem.buffer)
-			device.PutInboundElement(elem)
-		}
+		peer.stopping.Done()
 	}()
-
 	device.log.Verbosef("%v - Routine: sequential receiver - started", peer)
 
-	for {
-		if elem != nil {
-			device.PutMessageBuffer(elem.buffer)
-			device.PutInboundElement(elem)
-			elem = nil
-		}
-
-		var elemOk bool
-		select {
-		case <-peer.routines.stop:
-			return
-		case elem, elemOk = <-peer.queue.inbound:
-			if !elemOk {
-				return
-			}
-		}
-
-		// wait for decryption
+	for elem := range peer.queue.inbound {
+		var err error
 		elem.Lock()
 		if elem.packet == nil {
 			// decryption failed
-			continue
+			goto skip
 		}
 
-		// check for replay
 		if !elem.keypair.replayFilter.ValidateCounter(elem.counter, RejectAfterMessages) {
-			continue
+			goto skip
 		}
 
-		// update endpoint
 		peer.SetEndpointFromPacket(elem.endpoint)
-
-		// check if using new keypair
 		if peer.ReceivedWithKeypair(elem.keypair) {
 			peer.timersHandshakeComplete()
 			peer.SendStagedPackets()
@@ -489,83 +461,63 @@ func (peer *Peer) RoutineSequentialReceiver() {
 		peer.timersAnyAuthenticatedPacketReceived()
 		atomic.AddUint64(&peer.stats.rxBytes, uint64(len(elem.packet)+MinMessageSize))
 
-		// check for keepalive
-
 		if len(elem.packet) == 0 {
 			device.log.Verbosef("%v - Receiving keepalive packet", peer)
-			continue
+			goto skip
 		}
 		peer.timersDataReceived()
 
-		// verify source and strip padding
-
 		switch elem.packet[0] >> 4 {
 		case ipv4.Version:
-
-			// strip padding
-
 			if len(elem.packet) < ipv4.HeaderLen {
-				continue
+				goto skip
 			}
-
 			field := elem.packet[IPv4offsetTotalLength : IPv4offsetTotalLength+2]
 			length := binary.BigEndian.Uint16(field)
 			if int(length) > len(elem.packet) || int(length) < ipv4.HeaderLen {
-				continue
+				goto skip
 			}
-
 			elem.packet = elem.packet[:length]
-
-			// verify IPv4 source
-
 			src := elem.packet[IPv4offsetSrc : IPv4offsetSrc+net.IPv4len]
 			if device.allowedips.LookupIPv4(src) != peer {
 				device.log.Verbosef("IPv4 packet with disallowed source address from %v", peer)
-				continue
+				goto skip
 			}
 
 		case ipv6.Version:
-
-			// strip padding
-
 			if len(elem.packet) < ipv6.HeaderLen {
-				continue
+				goto skip
 			}
-
 			field := elem.packet[IPv6offsetPayloadLength : IPv6offsetPayloadLength+2]
 			length := binary.BigEndian.Uint16(field)
 			length += ipv6.HeaderLen
 			if int(length) > len(elem.packet) {
-				continue
+				goto skip
 			}
-
 			elem.packet = elem.packet[:length]
-
-			// verify IPv6 source
-
 			src := elem.packet[IPv6offsetSrc : IPv6offsetSrc+net.IPv6len]
 			if device.allowedips.LookupIPv6(src) != peer {
 				device.log.Verbosef("IPv6 packet with disallowed source address from %v", peer)
-				continue
+				goto skip
 			}
 
 		default:
 			device.log.Verbosef("Packet with invalid IP version from %v", peer)
-			continue
+			goto skip
 		}
 
-		// write to tun device
-
-		offset := MessageTransportOffsetContent
-		_, err := device.tun.device.Write(elem.buffer[:offset+len(elem.packet)], offset)
+		_, err = device.tun.device.Write(elem.buffer[:MessageTransportOffsetContent+len(elem.packet)], MessageTransportOffsetContent)
 		if err != nil && !device.isClosed.Get() {
 			device.log.Errorf("Failed to write packet to TUN device: %v", err)
 		}
 		if len(peer.queue.inbound) == 0 {
-			err := device.tun.device.Flush()
+			err = device.tun.device.Flush()
 			if err != nil {
 				peer.device.log.Errorf("Unable to flush packets: %v", err)
 			}
 		}
+	skip:
+		device.PutMessageBuffer(elem.buffer)
+		device.PutInboundElement(elem)
 	}
 }