From f401a73d271b76a353313de227fb19ff53a8bedd Mon Sep 17 00:00:00 2001
From: Sukun <sukunrt@gmail.com>
Date: Sat, 20 May 2023 13:23:18 +0530
Subject: [PATCH] transport: send stateless reset packets from a single Go
 routine (#3842)

* don't spawn new go routine for every stateless packet

* pass *receivedPacket around
---
 transport.go | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/transport.go b/transport.go
index 55bc7c48..c62ee388 100644
--- a/transport.go
+++ b/transport.go
@@ -66,7 +66,8 @@ type Transport struct {
 
 	conn rawConn
 
-	closeQueue chan closePacket
+	closeQueue          chan closePacket
+	statelessResetQueue chan *receivedPacket
 
 	listening   chan struct{} // is closed when listen returns
 	closed      bool
@@ -182,6 +183,7 @@ func (t *Transport) init(isServer bool) error {
 		t.listening = make(chan struct{})
 
 		t.closeQueue = make(chan closePacket, 4)
+		t.statelessResetQueue = make(chan *receivedPacket, 4)
 
 		if t.ConnectionIDGenerator != nil {
 			t.connIDGenerator = t.ConnectionIDGenerator
@@ -196,7 +198,7 @@ func (t *Transport) init(isServer bool) error {
 		}
 
 		go t.listen(conn)
-		go t.runCloseQueue()
+		go t.runSendQueue()
 	})
 	return t.initErr
 }
@@ -210,13 +212,15 @@ func (t *Transport) enqueueClosePacket(p closePacket) {
 	}
 }
 
-func (t *Transport) runCloseQueue() {
+func (t *Transport) runSendQueue() {
 	for {
 		select {
 		case <-t.listening:
 			return
 		case p := <-t.closeQueue:
 			t.conn.WritePacket(p.payload, p.addr, p.info.OOB())
+		case p := <-t.statelessResetQueue:
+			t.sendStatelessReset(p)
 		}
 	}
 }
@@ -340,7 +344,7 @@ func (t *Transport) handlePacket(p *receivedPacket) {
 		return
 	}
 	if !wire.IsLongHeaderPacket(p.data[0]) {
-		go t.maybeSendStatelessReset(p, connID)
+		t.maybeSendStatelessReset(p)
 		return
 	}
 
@@ -353,14 +357,33 @@ func (t *Transport) handlePacket(p *receivedPacket) {
 	t.server.handlePacket(p)
 }
 
-func (t *Transport) maybeSendStatelessReset(p *receivedPacket, connID protocol.ConnectionID) {
-	defer p.buffer.Release()
+func (t *Transport) maybeSendStatelessReset(p *receivedPacket) {
 	if t.StatelessResetKey == nil {
+		p.buffer.Release()
 		return
 	}
+
 	// Don't send a stateless reset in response to very small packets.
 	// This includes packets that could be stateless resets.
 	if len(p.data) <= protocol.MinStatelessResetSize {
+		p.buffer.Release()
+		return
+	}
+
+	select {
+	case t.statelessResetQueue <- p:
+	default:
+		// it's fine to not send a stateless reset when we're busy
+		p.buffer.Release()
+	}
+}
+
+func (t *Transport) sendStatelessReset(p *receivedPacket) {
+	defer p.buffer.Release()
+
+	connID, err := wire.ParseConnectionID(p.data, t.connIDLen)
+	if err != nil {
+		t.logger.Errorf("error parsing connection ID on packet from %s: %s", p.remoteAddr, err)
 		return
 	}
 	token := t.handlerMap.GetStatelessResetToken(connID)
@@ -370,7 +393,7 @@ func (t *Transport) maybeSendStatelessReset(p *receivedPacket, connID protocol.C
 	data[0] = (data[0] & 0x7f) | 0x40
 	data = append(data, token[:]...)
 	if _, err := t.conn.WritePacket(data, p.remoteAddr, p.info.OOB()); err != nil {
-		t.logger.Debugf("Error sending Stateless Reset: %s", err)
+		t.logger.Debugf("Error sending Stateless Reset to %s: %s", p.remoteAddr, err)
 	}
 }