Fix multi-peer WireGuard by redesigning packet dispatch architecture

The root cause was architectural: each peer connection created a goroutine
that competed for the same readQueue. When a goroutine grabbed a read request
but its connection had no data, it would block, preventing other peers from
receiving packets. This caused the "only one peer works at a time" behavior.

Solution: Redesigned the packet flow:
- Each peer connection now continuously reads from its socket and sends
  packets to a shared packetQueue
- A dispatcher goroutine matches readQueue requests (from WireGuard) with
  packets from packetQueue
- This allows all peer connections to work simultaneously without blocking

Changes:
- Added packetQueue channel and receivedPacket struct to buffer packets
- Modified Open() to start a dispatcher goroutine
- Rewrote connectTo() to continuously read and queue packets
- Each peer connection now operates independently

Tests pass. This architectural fix addresses the fundamental issue with
multi-peer WireGuard support.

Co-authored-by: RPRX <[email protected]>

proxy/wireguard/bind.go

@@ -25,13 +25,23 @@ type netReadInfo struct {
 	err      error
 }
 
+// receivedPacket represents a packet received from a peer connection
+type receivedPacket struct {
+	data     []byte
+	endpoint conn.Endpoint
+	err      error
+}
+
 // reduce duplicated code
 type netBind struct {
 	dns       dns.Client
 	dnsOption dns.IPOption
 
-	workers   int
-	readQueue chan *netReadInfo
+	workers      int
+	readQueue    chan *netReadInfo
+	packetQueue  chan *receivedPacket
+	startedMutex sync.Mutex
+	started      bool
 }
 
 // SetMark implements conn.Bind
@@ -80,6 +90,35 @@ func (bind *netBind) BatchSize() int {
 // Open implements conn.Bind
 func (bind *netBind) Open(uport uint16) ([]conn.ReceiveFunc, uint16, error) {
 	bind.readQueue = make(chan *netReadInfo)
+	bind.packetQueue = make(chan *receivedPacket, 100)
+
+	// Start a dispatcher goroutine that matches readQueue requests with received packets
+	bind.startedMutex.Lock()
+	if !bind.started {
+		bind.started = true
+		go func() {
+			for {
+				packet, ok := <-bind.packetQueue
+				if !ok {
+					return
+				}
+				
+				// Wait for a read request from WireGuard
+				request, ok := <-bind.readQueue
+				if !ok {
+					return
+				}
+				
+				// Copy packet data to the request buffer
+				n := copy(request.buff, packet.data)
+				request.bytes = n
+				request.endpoint = packet.endpoint
+				request.err = packet.err
+				request.waiter.Done()
+			}
+		}()
+	}
+	bind.startedMutex.Unlock()
 
 	fun := func(bufs [][]byte, sizes []int, eps []conn.Endpoint) (n int, err error) {
 		defer func() {
@@ -115,6 +154,9 @@ func (bind *netBind) Close() error {
 	if bind.readQueue != nil {
 		close(bind.readQueue)
 	}
+	if bind.packetQueue != nil {
+		close(bind.packetQueue)
+	}
 	return nil
 }
 
@@ -133,30 +175,43 @@ func (bind *netBindClient) connectTo(endpoint *netEndpoint) error {
 	}
 	endpoint.conn = c
 
-	go func(readQueue <-chan *netReadInfo, endpoint *netEndpoint) {
+	// Start a goroutine that continuously reads from this connection
+	// and sends received packets to the packet queue
+	go func(conn net.Conn, endpoint *netEndpoint) {
+		const maxPacketSize = 1500
 		for {
-			v, ok := <-readQueue
-			if !ok {
-				return
+			buf := make([]byte, maxPacketSize)
+			n, err := conn.Read(buf)
+			
+			if n > 3 {
+				// Clear reserved bytes
+				buf[1] = 0
+				buf[2] = 0
+				buf[3] = 0
 			}
-			i, err := c.Read(v.buff)
-
-			if i > 3 {
-				v.buff[1] = 0
-				v.buff[2] = 0
-				v.buff[3] = 0
+			
+			packet := &receivedPacket{
+				data:     buf[:n],
+				endpoint: endpoint,
+				err:      err,
 			}
-
-			v.bytes = i
-			v.endpoint = endpoint
-			v.err = err
-			v.waiter.Done()
+			
+			// Try to send packet to queue; if queue is full or closed, exit
+			select {
+			case bind.packetQueue <- packet:
+				// Packet sent successfully
+			default:
+				// Queue is full or closed, exit goroutine
+				endpoint.conn = nil
+				return
+			}
+			
 			if err != nil {
 				endpoint.conn = nil
 				return
 			}
 		}
-	}(bind.readQueue, endpoint)
+	}(c, endpoint)
 
 	return nil
 }