lx: re-graft AmneziaWG 2.0 obfuscation onto sagernet/wireguard-go v0.0.5

Rebase of the AWG obf graft (was e5feca7 on v0.0.3) onto v0.0.5
(2c27bbf4f9, 'Add L3 forwarding support'). 15 of 16 graft files
applied clean via 3-way; only send.go conflicted, on a single line
(upstream queuedOutboundPackets backpressure decrement vs a graft
blank line — took upstream).

Key invariant preserved: MessageEncapsulatingTransportSize=0 (graft
zeroes the sagernet encapsulating headroom; AWG obfuscation composes
the prefix itself via SendBuffers, not Bind.Send prepend). Upstream's
InputPacket/InputPackets and the new size-based outbound buffer pool
(GetOutboundBuffer/PutOutboundBuffer) are taken verbatim; the graft's
RoutineEncryption (header at buffer start) and transport-padding shift
in RoutineSequentialSender re-woven around them.

Builds clean on linux/android/windows/darwin (device/conn/tun).

device/receive.go

@@ -76,7 +76,10 @@ func (peer *Peer) keepKeyFreshReceiving() {
  * Every time the bind is updated a new routine is started for
  * IPv4 and IPv6 (separately)
  */
-func (device *Device) RoutineReceiveIncoming(maxBatchSize int, recv conn.ReceiveFunc) {
+func (device *Device) RoutineReceiveIncoming(
+	maxBatchSize int,
+	recv conn.ReceiveFunc,
+) {
 	recvName := recv.PrettyName()
 	defer func() {
 		device.log.Verbosef("Routine: receive incoming %s - stopped", recvName)
@@ -139,9 +142,14 @@ func (device *Device) RoutineReceiveIncoming(maxBatchSize int, recv conn.Receive
 			}
 
 			// check size of packet
-
 			packet := bufsArrs[i][:size]
-			msgType := binary.LittleEndian.Uint32(packet[:4])
+
+			// get message padding and type based on information from S1-S4 and H1-H4
+			msgType, padding := device.DeterminePacketTypeAndPadding(packet, MessageUnknownType)
+			if padding > 0 {
+				copy(packet, packet[padding:])
+				packet = packet[:len(packet)-padding]
+			}
 
 			switch msgType {
 
@@ -283,7 +291,6 @@ func (device *Device) RoutineHandshake(id int) {
 	device.log.Verbosef("Routine: handshake worker %d - started", id)
 
 	for elem := range device.queue.handshake.c {
-
 		// handle cookie fields and ratelimiting
 
 		switch elem.msgType {
@@ -310,9 +317,14 @@ func (device *Device) RoutineHandshake(id int) {
 			// consume reply
 
 			if peer := entry.peer; peer.isRunning.Load() {
-				device.log.Verbosef("Receiving cookie response from %s", elem.endpoint.DstToString())
+				device.log.Verbosef(
+					"Receiving cookie response from %s",
+					elem.endpoint.DstToString(),
+				)
 				if !peer.cookieGenerator.ConsumeReply(&reply) {
-					device.log.Verbosef("Could not decrypt invalid cookie response")
+					device.log.Verbosef(
+						"Could not decrypt invalid cookie response",
+					)
 				}
 			}
 
@@ -354,9 +366,7 @@ func (device *Device) RoutineHandshake(id int) {
 
 		switch elem.msgType {
 		case MessageInitiationType:
-
 			// unmarshal
-
 			var msg MessageInitiation
 			err := msg.unmarshal(elem.packet)
 			if err != nil {
@@ -364,7 +374,8 @@ func (device *Device) RoutineHandshake(id int) {
 				goto skip
 			}
 
-			// consume initiation
+			// have to reassign msgType for ranged msgType to work
+			msg.Type = elem.msgType
 
 			peer := device.ConsumeMessageInitiation(&msg, elem.endpoint)
 			if peer == nil {
@@ -396,6 +407,9 @@ func (device *Device) RoutineHandshake(id int) {
 				goto skip
 			}
 
+			// have to reassign msgType for ranged msgType to work
+			msg.Type = elem.msgType
+
 			// consume response
 
 			peer := device.ConsumeMessageResponse(&msg)
@@ -573,3 +587,57 @@ func (peer *Peer) processInboundContainer(elemsContainer *QueueInboundElementsCo
 		device.PutInboundElement(elem)
 	}
 }
+
+func (device *Device) DeterminePacketTypeAndPadding(packet []byte, expectedType uint32) (uint32, int) {
+	size := len(packet)
+
+	if expectedType == MessageUnknownType || expectedType == MessageInitiationType {
+		padding := device.paddings.init
+		header := device.headers.init
+
+		if size == padding+MessageInitiationSize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageInitiationType, padding
+			}
+		}
+	}
+
+	if expectedType == MessageUnknownType || expectedType == MessageResponseType {
+		padding := device.paddings.response
+		header := device.headers.response
+
+		if size == padding+MessageResponseSize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageResponseType, padding
+			}
+		}
+	}
+
+	if expectedType == MessageUnknownType || expectedType == MessageCookieReplyType {
+		padding := device.paddings.cookie
+		header := device.headers.cookie
+
+		if size == padding+MessageCookieReplySize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageCookieReplyType, padding
+			}
+		}
+	}
+
+	if expectedType == MessageUnknownType || expectedType == MessageTransportType {
+		padding := device.paddings.transport
+		header := device.headers.transport
+
+		if size >= padding+MessageTransportHeaderSize {
+			data := packet[padding:]
+			if header.Validate(binary.LittleEndian.Uint32(data)) {
+				return MessageTransportType, padding
+			}
+		}
+	}
+
+	return MessageUnknownType, 0
+}