device: remove QueueInboundElement.dropped

Now that we block when enqueueing to the decryption queue,
there is only one case in which we "drop" a inbound element,
when decryption fails.

We can use a simple, obvious, sync-free sentinel for that, elem.packet == nil.
Also, we can return the message buffer to the pool slightly later,
which further simplifies the code.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

diff --git a/device/receive.go b/device/receive.go
index 972b34204cfa48c314777e3179912b09d7bb45c8..701e30899148699bc68a5c3293b2b9060548bf86 100644 (file)
--- a/device/receive.go
+++ b/device/receive.go
@@ -30,7 +30,6 @@ type QueueHandshakeElement struct {
 }
 
 type QueueInboundElement struct {
-       dropped int32
        sync.Mutex
        buffer   *[MaxMessageSize]byte
        packet   []byte
@@ -50,14 +49,6 @@ func (elem *QueueInboundElement) clearPointers() {
        elem.endpoint = nil
 }
 
-func (elem *QueueInboundElement) Drop() {
-       atomic.StoreInt32(&elem.dropped, AtomicTrue)
-}
-
-func (elem *QueueInboundElement) IsDropped() bool {
-       return atomic.LoadInt32(&elem.dropped) == AtomicTrue
-}
-
 func (device *Device) addToHandshakeQueue(queue chan QueueHandshakeElement, elem QueueHandshakeElement) bool {
        select {
        case queue <- elem:
@@ -180,7 +171,6 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
                        elem.packet = packet
                        elem.buffer = buffer
                        elem.keypair = keypair
-                       elem.dropped = AtomicFalse
                        elem.endpoint = endpoint
                        elem.counter = 0
                        elem.Mutex = sync.Mutex{}
@@ -243,19 +233,11 @@ func (device *Device) RoutineDecryption() {
        logDebug.Println("Routine: decryption worker - started")
 
        for elem := range device.queue.decryption.c {
-               // check if dropped
-
-               if elem.IsDropped() {
-                       continue
-               }
-
                // split message into fields
-
                counter := elem.packet[MessageTransportOffsetCounter:MessageTransportOffsetContent]
                content := elem.packet[MessageTransportOffsetContent:]
 
                // decrypt and release to consumer
-
                var err error
                elem.counter = binary.LittleEndian.Uint64(counter)
                // copy counter to nonce
@@ -267,8 +249,7 @@ func (device *Device) RoutineDecryption() {
                        nil,
                )
                if err != nil {
-                       elem.Drop()
-                       device.PutMessageBuffer(elem.buffer)
+                       elem.packet = nil
                }
                elem.Unlock()
        }
@@ -484,9 +465,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
                logDebug.Println(peer, "- Routine: sequential receiver - stopped")
                peer.routines.stopping.Done()
                if elem != nil {
-                       if !elem.IsDropped() {
-                               device.PutMessageBuffer(elem.buffer)
-                       }
+                       device.PutMessageBuffer(elem.buffer)
                        device.PutInboundElement(elem)
                }
        }()
@@ -495,9 +474,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
        for {
                if elem != nil {
-                       if !elem.IsDropped() {
-                               device.PutMessageBuffer(elem.buffer)
-                       }
+                       device.PutMessageBuffer(elem.buffer)
                        device.PutInboundElement(elem)
                        elem = nil
                }
@@ -513,15 +490,13 @@ func (peer *Peer) RoutineSequentialReceiver() {
                }
 
                // wait for decryption
-
                elem.Lock()
-
-               if elem.IsDropped() {
+               if elem.packet == nil {
+                       // decryption failed
                        continue
                }
 
                // check for replay
-
                if !elem.keypair.replayFilter.ValidateCounter(elem.counter, RejectAfterMessages) {
                        continue
                }