Ensure verification tag is zero for INIT packets

This test verifies that the verification tag is correctly set to 0 for all INIT packets,
including retransmissions.

association.go

@@ -452,7 +452,7 @@ func (a *Association) sendInit() error {
 	}
 
 	outbound := &packet{}
-	outbound.verificationTag = a.peerVerificationTag
+	outbound.verificationTag = 0
 	a.sourcePort = defaultSCTPSrcDstPort
 	a.destinationPort = defaultSCTPSrcDstPort
 	outbound.sourcePort = a.sourcePort

association_test.go

@@ -1181,6 +1181,145 @@ func TestAssocUnreliable(t *testing.T) {
 	})
 }
 
+// This test ensures that verification tag is set to 0 for all INIT packets.
+// A test for this PR https://github.com/pion/sctp/pull/341
+// We drop the first INIT ACK, and we expect the verification tag to be 0 on
+// retransmission.
+func TestInitVerificationTagIsZero(t *testing.T) {
+	lim := test.TimeOut(time.Second * 10)
+	defer lim.Stop()
+
+	const si uint16 = 1
+	const msg = "ABC"
+	br := test.NewBridge()
+	ackCount := 0
+	recvBufSize := uint32(0)
+
+	var a0, a1 *Association
+	var err0, err1 error
+	loggerFactory := logging.NewDefaultLoggerFactory()
+
+	handshake0Ch := make(chan bool)
+	handshake1Ch := make(chan bool)
+	fatalChannel := make(chan error)
+
+	fitlerFunc := func(pkt []byte) bool {
+		t.Helper()
+
+		packetData := packet{}
+
+		assert.NoError(t, packetData.unmarshal(true, pkt))
+
+		// Init chunk and Init Ack chunk are never bundled.
+		if len(packetData.chunks) != 1 {
+			return true
+		}
+
+		switch packetData.chunks[0].(type) {
+		case *chunkInit:
+			if packetData.verificationTag != 0 {
+				// Even without this we will get WARNING:
+				// failed validating packet init chunk expects a verification tag of 0 on the packet when out-of-the-blue
+				// And the connection will fail silently.
+				go func() {
+					fatalChannel <- errors.New("verification tag should be 0 for Init chunk") //nolint:err113
+				}()
+
+				return false
+			}
+		// Drop the first two Init Ack chunk.
+		case *chunkInitAck:
+			ackCount++
+			return ackCount > 2
+		}
+
+		return true
+	}
+
+	br.Filter(0, fitlerFunc)
+
+	br.Filter(1, fitlerFunc)
+
+	go func() {
+		a0, err0 = Client(Config{
+			Name:                 "a0",
+			NetConn:              br.GetConn0(),
+			MaxReceiveBufferSize: recvBufSize,
+			LoggerFactory:        loggerFactory,
+		})
+
+		handshake0Ch <- true
+	}()
+	go func() {
+		a1, err1 = Client(Config{
+			Name:                 "a1",
+			NetConn:              br.GetConn1(),
+			MaxReceiveBufferSize: recvBufSize,
+			LoggerFactory:        loggerFactory,
+		})
+		handshake1Ch <- true
+	}()
+
+	a0handshakeDone := false
+	a1handshakeDone := false
+
+loop1:
+	for i := 0; i < 1e3; i++ {
+		time.Sleep(10 * time.Millisecond)
+		br.Tick()
+
+		select {
+		case a0handshakeDone = <-handshake0Ch:
+			if a1handshakeDone {
+				break loop1
+			}
+		case a1handshakeDone = <-handshake1Ch:
+			if a0handshakeDone {
+				break loop1
+			}
+		case err := <-fatalChannel:
+			t.Fatal(err)
+		default:
+		}
+	}
+
+	assert.Equal(t, a0handshakeDone, true, "handshake failed e0")
+	assert.Equal(t, a1handshakeDone, true, "handshake failed e1")
+
+	assert.NoError(t, err0, "failed to create association a0")
+	assert.NoError(t, err1, "failed to create association a1")
+
+	a0.ackMode = ackModeNoDelay
+	a1.ackMode = ackModeNoDelay
+
+	s0, s1, err := establishSessionPair(br, a0, a1, si)
+	assert.Nil(t, err, "failed to establish session pair")
+
+	assert.Equal(t, 0, a0.bufferedAmount(), "incorrect bufferedAmount")
+
+	n, err := s0.WriteSCTP([]byte(msg), PayloadTypeWebRTCBinary)
+	if err != nil {
+		assert.FailNow(t, "failed due to earlier error")
+	}
+	assert.Equal(t, len(msg), n, "unexpected length of received data")
+	assert.Equal(t, len(msg), a0.bufferedAmount(), "incorrect bufferedAmount")
+
+	flushBuffers(br, a0, a1)
+
+	buf := make([]byte, 32)
+	n, ppi, err := s1.ReadSCTP(buf)
+	if !assert.Nil(t, err, "ReadSCTP failed") {
+		assert.FailNow(t, "failed due to earlier error")
+	}
+	assert.Equal(t, n, len(msg), "unexpected length of received data")
+	assert.Equal(t, ppi, PayloadTypeWebRTCBinary, "unexpected ppi")
+
+	assert.False(t, s0.reassemblyQueue.isReadable(), "should no longer be readable")
+	assert.Equal(t, 0, a0.bufferedAmount(), "incorrect bufferedAmount")
+
+	closeAssociationPair(br, a0, a1)
+}
+
 func TestCreateForwardTSN(t *testing.T) {
 	loggerFactory := logging.NewDefaultLoggerFactory()