quic: compute pnum len from max ack received, not sent

QUIC packet numbers are truncated to include only the least
significant bits of the packet number. The number of bits
which must be retained is computed based on the largest
packet number known to have been received by the peer.
See RFC 9000, section 17.1.

We were incorrectly using the largest packet number
we have received *from* the peer. Oops.

(Test infrastructure change: Include the header byte
in the testPacket structure, so we can see how many
bytes the packet number was encoded with. Ignore this
byte when comparing packets.)

Change-Id: Iec17c69f007f8b39d14d24b0ca216c6a0018ae22
Reviewed-on: https://go-review.googlesource.com/c/net/+/545575
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

internal/quic/conn_send.go

@@ -60,7 +60,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 		pad := false
 		var sentInitial *sentPacket
 		if c.keysInitial.canWrite() {
-			pnumMaxAcked := c.acks[initialSpace].largestSeen()
+			pnumMaxAcked := c.loss.spaces[initialSpace].maxAcked
 			pnum := c.loss.nextNumber(initialSpace)
 			p := longPacket{
 				ptype:     packetTypeInitial,
@@ -93,7 +93,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 
 		// Handshake packet.
 		if c.keysHandshake.canWrite() {
-			pnumMaxAcked := c.acks[handshakeSpace].largestSeen()
+			pnumMaxAcked := c.loss.spaces[handshakeSpace].maxAcked
 			pnum := c.loss.nextNumber(handshakeSpace)
 			p := longPacket{
 				ptype:     packetTypeHandshake,
@@ -124,7 +124,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 
 		// 1-RTT packet.
 		if c.keysAppData.canWrite() {
-			pnumMaxAcked := c.acks[appDataSpace].largestSeen()
+			pnumMaxAcked := c.loss.spaces[appDataSpace].maxAcked
 			pnum := c.loss.nextNumber(appDataSpace)
 			c.w.start1RTTPacket(pnum, pnumMaxAcked, dstConnID)
 			c.appendFrames(now, appDataSpace, pnum, limit)

internal/quic/conn_send_test.go

@@ -38,3 +38,46 @@ func TestAckElicitingAck(t *testing.T) {
 	}
 	t.Errorf("after sending %v PINGs, got no ack-eliciting response", count)
 }
+
+func TestSendPacketNumberSize(t *testing.T) {
+	tc := newTestConn(t, clientSide, permissiveTransportParameters)
+	tc.handshake()
+
+	recvPing := func() *testPacket {
+		t.Helper()
+		tc.conn.ping(appDataSpace)
+		p := tc.readPacket()
+		if p == nil {
+			t.Fatalf("want packet containing PING, got none")
+		}
+		return p
+	}
+
+	// Desynchronize the packet numbers the conn is sending and the ones it is receiving,
+	// by having the conn send a number of unacked packets.
+	for i := 0; i < 16; i++ {
+		recvPing()
+	}
+
+	// Establish the maximum packet number the conn has received an ACK for.
+	maxAcked := recvPing().num
+	tc.writeAckForAll()
+
+	// Make the conn send a sequence of packets.
+	// Check that the packet number is encoded with two bytes once the difference between the
+	// current packet and the max acked one is sufficiently large.
+	for want := maxAcked + 1; want < maxAcked+0x100; want++ {
+		p := recvPing()
+		if p.num != want {
+			t.Fatalf("received packet number %v, want %v", p.num, want)
+		}
+		gotPnumLen := int(p.header&0x03) + 1
+		wantPnumLen := 1
+		if p.num-maxAcked >= 0x80 {
+			wantPnumLen = 2
+		}
+		if gotPnumLen != wantPnumLen {
+			t.Fatalf("packet number 0x%x encoded with %v bytes, want %v (max acked = %v)", p.num, gotPnumLen, wantPnumLen, maxAcked)
+		}
+	}
+}

internal/quic/conn_test.go

@@ -82,6 +82,7 @@ func (d testDatagram) String() string {
 
 type testPacket struct {
 	ptype             packetType
+	header            byte
 	version           uint32
 	num               packetNumber
 	keyPhaseBit       bool
@@ -599,12 +600,18 @@ func (tc *testConn) readFrame() (debugFrame, packetType) {
 func (tc *testConn) wantDatagram(expectation string, want *testDatagram) {
 	tc.t.Helper()
 	got := tc.readDatagram()
-	if !reflect.DeepEqual(got, want) {
+	if !datagramEqual(got, want) {
 		tc.t.Fatalf("%v:\ngot datagram:  %v\nwant datagram: %v", expectation, got, want)
 	}
 }
 
 func datagramEqual(a, b *testDatagram) bool {
+	if a == nil && b == nil {
+		return true
+	}
+	if a == nil || b == nil {
+		return false
+	}
 	if a.paddedSize != b.paddedSize ||
 		a.addr != b.addr ||
 		len(a.packets) != len(b.packets) {
@@ -622,16 +629,18 @@ func datagramEqual(a, b *testDatagram) bool {
 func (tc *testConn) wantPacket(expectation string, want *testPacket) {
 	tc.t.Helper()
 	got := tc.readPacket()
-	if !reflect.DeepEqual(got, want) {
+	if !packetEqual(got, want) {
 		tc.t.Fatalf("%v:\ngot packet:  %v\nwant packet: %v", expectation, got, want)
 	}
 }
 
 func packetEqual(a, b *testPacket) bool {
 	ac := *a
 	ac.frames = nil
+	ac.header = 0
 	bc := *b
 	bc.frames = nil
+	bc.header = 0
 	if !reflect.DeepEqual(ac, bc) {
 		return false
 	}
@@ -839,6 +848,7 @@ func parseTestDatagram(t *testing.T, te *testEndpoint, tc *testConn, buf []byte)
 			}
 			d.packets = append(d.packets, &testPacket{
 				ptype:     p.ptype,
+				header:    buf[0],
 				version:   p.version,
 				num:       p.num,
 				dstConnID: p.dstConnID,
@@ -880,6 +890,7 @@ func parseTestDatagram(t *testing.T, te *testEndpoint, tc *testConn, buf []byte)
 			}
 			d.packets = append(d.packets, &testPacket{
 				ptype:       packetType1RTT,
+				header:      hdr[0],
 				num:         pnum,
 				dstConnID:   hdr[1:][:len(tc.peerConnID)],
 				keyPhaseBit: hdr[0]&keyPhaseBit != 0,

internal/quic/endpoint_test.go

@@ -13,7 +13,6 @@ import (
 	"io"
 	"net"
 	"net/netip"
-	"reflect"
 	"testing"
 	"time"
 )
@@ -242,7 +241,7 @@ func (te *testEndpoint) readDatagram() *testDatagram {
 func (te *testEndpoint) wantDatagram(expectation string, want *testDatagram) {
 	te.t.Helper()
 	got := te.readDatagram()
-	if !reflect.DeepEqual(got, want) {
+	if !datagramEqual(got, want) {
 		te.t.Fatalf("%v:\ngot datagram:  %v\nwant datagram: %v", expectation, got, want)
 	}
 }

internal/quic/tls_test.go

@@ -10,7 +10,6 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"errors"
-	"reflect"
 	"testing"
 	"time"
 )
@@ -56,7 +55,7 @@ func (tc *testConn) handshake() {
 			fillCryptoFrames(want, tc.cryptoDataOut)
 			i++
 		}
-		if !reflect.DeepEqual(got, want) {
+		if !datagramEqual(got, want) {
 			t.Fatalf("dgram %v:\ngot %v\n\nwant %v", i, got, want)
 		}
 		if i >= len(dgrams) {