github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/test/packetimpact/tests/tcp_rack_test.go

// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package tcp_rack_test

import (
	"flag"
	"testing"
	"time"

	"golang.org/x/sys/unix"
	"github.com/SagerNet/gvisor/pkg/abi/linux"
	"github.com/SagerNet/gvisor/pkg/tcpip/header"
	"github.com/SagerNet/gvisor/pkg/tcpip/seqnum"
	"github.com/SagerNet/gvisor/test/packetimpact/testbench"
)

func init() {
	testbench.Initialize(flag.CommandLine)
}

const (
	// payloadSize is the size used to send packets.
	payloadSize = header.TCPDefaultMSS

	// simulatedRTT is the time delay between packets sent and acked to
	// increase the RTT.
	simulatedRTT = 30 * time.Millisecond

	// numPktsForRTT is the number of packets sent and acked to establish
	// RTT.
	numPktsForRTT = 10
)

func createSACKConnection(t *testing.T) (testbench.DUT, testbench.TCPIPv4, int32, int32) {
	dut := testbench.NewDUT(t)
	listenFd, remotePort := dut.CreateListener(t, unix.SOCK_STREAM, unix.IPPROTO_TCP, 1)
	conn := dut.Net.NewTCPIPv4(t, testbench.TCP{DstPort: &remotePort}, testbench.TCP{SrcPort: &remotePort})

	// Enable SACK.
	opts := make([]byte, 40)
	optsOff := 0
	optsOff += header.EncodeNOP(opts[optsOff:])
	optsOff += header.EncodeNOP(opts[optsOff:])
	optsOff += header.EncodeSACKPermittedOption(opts[optsOff:])

	conn.ConnectWithOptions(t, opts[:optsOff])
	acceptFd, _ := dut.Accept(t, listenFd)
	return dut, conn, acceptFd, listenFd
}

func closeSACKConnection(t *testing.T, dut testbench.DUT, conn testbench.TCPIPv4, acceptFd, listenFd int32) {
	dut.Close(t, acceptFd)
	dut.Close(t, listenFd)
	conn.Close(t)
}

func getRTTAndRTO(t *testing.T, dut testbench.DUT, acceptFd int32) (rtt, rto time.Duration) {
	info := dut.GetSockOptTCPInfo(t, acceptFd)
	return time.Duration(info.RTT) * time.Microsecond, time.Duration(info.RTO) * time.Microsecond
}

func sendAndReceive(t *testing.T, dut testbench.DUT, conn testbench.TCPIPv4, numPkts int, acceptFd int32, sendACK bool) time.Time {
	seqNum1 := *conn.RemoteSeqNum(t)
	payload := make([]byte, payloadSize)
	var lastSent time.Time
	for i, sn := 0, seqNum1; i < numPkts; i++ {
		lastSent = time.Now()
		dut.Send(t, acceptFd, payload, 0)
		gotOne, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(sn))}, time.Second)
		if err != nil {
			t.Fatalf("Expect #%d: %s", i+1, err)
			continue
		}
		if gotOne == nil {
			t.Fatalf("#%d: expected a packet within a second but got none", i+1)
		}
		sn.UpdateForward(seqnum.Size(payloadSize))

		if sendACK {
			time.Sleep(simulatedRTT)
			conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(sn))})
		}
	}
	return lastSent
}

// TestRACKTLPAllPacketsLost tests TLP when an entire flight of data is lost.
func TestRACKTLPAllPacketsLost(t *testing.T) {
	dut, conn, acceptFd, listenFd := createSACKConnection(t)
	seqNum1 := *conn.RemoteSeqNum(t)

	// Send ACK for data packets to establish RTT.
	sendAndReceive(t, dut, conn, numPktsForRTT, acceptFd, true /* sendACK */)
	seqNum1.UpdateForward(seqnum.Size(numPktsForRTT * payloadSize))

	// We are not sending ACK for these packets.
	const numPkts = 5
	lastSent := sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	// Probe Timeout (PTO) should be two times RTT. Check that the last
	// packet is retransmitted after probe timeout.
	rtt, _ := getRTTAndRTO(t, dut, acceptFd)
	pto := rtt * 2
	// We expect the 5th packet (the last unacknowledged packet) to be
	// retransmitted.
	tlpProbe := testbench.Uint32(uint32(seqNum1) + uint32((numPkts-1)*payloadSize))
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: tlpProbe}, time.Second); err != nil {
		t.Fatalf("expected payload was not received: %s %v %v", err, rtt, pto)
	}
	diff := time.Now().Sub(lastSent)
	if diff < pto {
		t.Fatalf("expected payload was received before the probe timeout, got: %v, want: %v", diff, pto)
	}
	closeSACKConnection(t, dut, conn, acceptFd, listenFd)
}

// TestRACKTLPLost tests TLP when there are tail losses.
// See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-7.4
func TestRACKTLPLost(t *testing.T) {
	dut, conn, acceptFd, listenFd := createSACKConnection(t)
	seqNum1 := *conn.RemoteSeqNum(t)

	// Send ACK for data packets to establish RTT.
	sendAndReceive(t, dut, conn, numPktsForRTT, acceptFd, true /* sendACK */)
	seqNum1.UpdateForward(seqnum.Size(numPktsForRTT * payloadSize))

	// We are not sending ACK for these packets.
	const numPkts = 10
	lastSent := sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	// Cumulative ACK for #[1-5] packets.
	ackNum := seqNum1.Add(seqnum.Size(6 * payloadSize))
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(ackNum))})

	// Probe Timeout (PTO) should be two times RTT. Check that the last
	// packet is retransmitted after probe timeout.
	rtt, _ := getRTTAndRTO(t, dut, acceptFd)
	pto := rtt * 2
	// We expect the 10th packet (the last unacknowledged packet) to be
	// retransmitted.
	tlpProbe := testbench.Uint32(uint32(seqNum1) + uint32((numPkts-1)*payloadSize))
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: tlpProbe}, time.Second); err != nil {
		t.Fatalf("expected payload was not received: %s", err)
	}
	diff := time.Now().Sub(lastSent)
	if diff < pto {
		t.Fatalf("expected payload was received before the probe timeout, got: %v, want: %v", diff, pto)
	}
	closeSACKConnection(t, dut, conn, acceptFd, listenFd)
}

// TestRACKWithSACK tests that RACK marks the packets as lost after receiving
// the ACK for retransmitted packets.
// See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-8.1
func TestRACKWithSACK(t *testing.T) {
	dut, conn, acceptFd, listenFd := createSACKConnection(t)
	seqNum1 := *conn.RemoteSeqNum(t)

	// Send ACK for data packets to establish RTT.
	sendAndReceive(t, dut, conn, numPktsForRTT, acceptFd, true /* sendACK */)
	seqNum1.UpdateForward(seqnum.Size(numPktsForRTT * payloadSize))

	// We are not sending ACK for these packets.
	const numPkts = 3
	sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	time.Sleep(simulatedRTT)
	// SACK for #2 packet.
	sackBlock := make([]byte, 40)
	start := seqNum1.Add(seqnum.Size(payloadSize))
	end := start.Add(seqnum.Size(payloadSize))
	sbOff := 0
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		start, end,
	}}, sackBlock[sbOff:])
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1)), Options: sackBlock[:sbOff]})

	rtt, _ := getRTTAndRTO(t, dut, acceptFd)
	timeout := 2 * rtt
	// RACK marks #1 packet as lost after RTT+reorderWindow(RTT/4) and
	// retransmits it.
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(seqNum1))}, timeout); err != nil {
		t.Fatalf("expected payload was not received: %s", err)
	}

	time.Sleep(simulatedRTT)
	// ACK for #1 packet.
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(end))})

	// RACK considers transmission times of the packets to mark them lost.
	// As the 3rd packet was sent before the retransmitted 1st packet, RACK
	// marks it as lost and retransmits it..
	expectedSeqNum := testbench.Uint32(uint32(seqNum1) + uint32((numPkts-1)*payloadSize))
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: expectedSeqNum}, timeout); err != nil {
		t.Fatalf("expected payload was not received: %s", err)
	}
	closeSACKConnection(t, dut, conn, acceptFd, listenFd)
}

// TestRACKWithoutReorder tests that without reordering RACK will retransmit the
// lost packets after reorder timer expires.
func TestRACKWithoutReorder(t *testing.T) {
	dut, conn, acceptFd, listenFd := createSACKConnection(t)
	seqNum1 := *conn.RemoteSeqNum(t)

	// Send ACK for data packets to establish RTT.
	sendAndReceive(t, dut, conn, numPktsForRTT, acceptFd, true /* sendACK */)
	seqNum1.UpdateForward(seqnum.Size(numPktsForRTT * payloadSize))

	// We are not sending ACK for these packets.
	const numPkts = 4
	sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	// SACK for [3,4] packets.
	sackBlock := make([]byte, 40)
	start := seqNum1.Add(seqnum.Size(2 * payloadSize))
	end := start.Add(seqnum.Size(2 * payloadSize))
	sbOff := 0
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		start, end,
	}}, sackBlock[sbOff:])
	time.Sleep(simulatedRTT)
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1)), Options: sackBlock[:sbOff]})

	// RACK marks #1 and #2 packets as lost and retransmits both after
	// RTT + reorderWindow. The reorderWindow initially will be a small
	// fraction of RTT.
	rtt, _ := getRTTAndRTO(t, dut, acceptFd)
	timeout := 2 * rtt
	for i, sn := 0, seqNum1; i < 2; i++ {
		if _, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(sn))}, timeout); err != nil {
			t.Fatalf("expected payload was not received: %s", err)
		}
		sn.UpdateForward(seqnum.Size(payloadSize))
	}
	closeSACKConnection(t, dut, conn, acceptFd, listenFd)
}

// TestRACKWithReorder tests that RACK will retransmit segments when there is
// reordering in the connection and reorder timer expires.
func TestRACKWithReorder(t *testing.T) {
	dut, conn, acceptFd, listenFd := createSACKConnection(t)
	seqNum1 := *conn.RemoteSeqNum(t)

	// Send ACK for data packets to establish RTT.
	sendAndReceive(t, dut, conn, numPktsForRTT, acceptFd, true /* sendACK */)
	seqNum1.UpdateForward(seqnum.Size(numPktsForRTT * payloadSize))

	// We are not sending ACK for these packets.
	const numPkts = 4
	sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	time.Sleep(simulatedRTT)
	// SACK in reverse order for the connection to detect reorder.
	var start seqnum.Value
	var end seqnum.Value
	for i := 0; i < numPkts-1; i++ {
		sackBlock := make([]byte, 40)
		sbOff := 0
		start = seqNum1.Add(seqnum.Size((numPkts - i - 1) * payloadSize))
		end = start.Add(seqnum.Size((i + 1) * payloadSize))
		sackBlock = make([]byte, 40)
		sbOff = 0
		sbOff += header.EncodeNOP(sackBlock[sbOff:])
		sbOff += header.EncodeNOP(sackBlock[sbOff:])
		sbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
			start, end,
		}}, sackBlock[sbOff:])
		conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1)), Options: sackBlock[:sbOff]})
	}

	// Send a DSACK block indicating both original and retransmitted
	// packets are received, RACK will increase the reordering window on
	// every DSACK.
	dsackBlock := make([]byte, 40)
	dbOff := 0
	start = seqNum1
	end = start.Add(seqnum.Size(2 * payloadSize))
	dbOff += header.EncodeNOP(dsackBlock[dbOff:])
	dbOff += header.EncodeNOP(dsackBlock[dbOff:])
	dbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		start, end,
	}}, dsackBlock[dbOff:])
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1 + numPkts*payloadSize)), Options: dsackBlock[:dbOff]})

	seqNum1.UpdateForward(seqnum.Size(numPkts * payloadSize))
	sendTime := time.Now()
	sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	time.Sleep(simulatedRTT)
	// Send SACK for [2-5] packets.
	sackBlock := make([]byte, 40)
	sbOff := 0
	start = seqNum1.Add(seqnum.Size(payloadSize))
	end = start.Add(seqnum.Size(3 * payloadSize))
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		start, end,
	}}, sackBlock[sbOff:])
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1)), Options: sackBlock[:sbOff]})

	// Expect the retransmission of #1 packet after RTT+ReorderWindow.
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(seqNum1))}, time.Second); err != nil {
		t.Fatalf("expected payload was not received: %s", err)
	}
	rtt, _ := getRTTAndRTO(t, dut, acceptFd)
	diff := time.Now().Sub(sendTime)
	if diff < rtt {
		t.Fatalf("expected payload was received too sonn, within RTT")
	}

	closeSACKConnection(t, dut, conn, acceptFd, listenFd)
}

// TestRACKWithLostRetransmission tests that RACK will not enter RTO when a
// retransmitted segment is lost and enters fast recovery.
func TestRACKWithLostRetransmission(t *testing.T) {
	dut, conn, acceptFd, listenFd := createSACKConnection(t)
	seqNum1 := *conn.RemoteSeqNum(t)

	// Send ACK for data packets to establish RTT.
	sendAndReceive(t, dut, conn, numPktsForRTT, acceptFd, true /* sendACK */)
	seqNum1.UpdateForward(seqnum.Size(numPktsForRTT * payloadSize))

	// We are not sending ACK for these packets.
	const numPkts = 5
	sendAndReceive(t, dut, conn, numPkts, acceptFd, false /* sendACK */)

	// SACK for [2-5] packets.
	sackBlock := make([]byte, 40)
	start := seqNum1.Add(seqnum.Size(payloadSize))
	end := start.Add(seqnum.Size(4 * payloadSize))
	sbOff := 0
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		start, end,
	}}, sackBlock[sbOff:])
	time.Sleep(simulatedRTT)
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1)), Options: sackBlock[:sbOff]})

	// RACK marks #1 packet as lost and retransmits it after
	// RTT + reorderWindow. The reorderWindow is bounded between a small
	// fraction of RTT and 1 RTT.
	rtt, _ := getRTTAndRTO(t, dut, acceptFd)
	timeout := 2 * rtt
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(seqNum1))}, timeout); err != nil {
		t.Fatalf("expected payload was not received: %s", err)
	}

	// Send #6 packet.
	payload := make([]byte, payloadSize)
	dut.Send(t, acceptFd, payload, 0)
	gotOne, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(seqNum1 + 5*payloadSize))}, time.Second)
	if err != nil {
		t.Fatalf("Expect #6: %s", err)
	}
	if gotOne == nil {
		t.Fatalf("#6: expected a packet within a second but got none")
	}

	// SACK for [2-6] packets.
	sackBlock1 := make([]byte, 40)
	start = seqNum1.Add(seqnum.Size(payloadSize))
	end = start.Add(seqnum.Size(5 * payloadSize))
	sbOff1 := 0
	sbOff1 += header.EncodeNOP(sackBlock1[sbOff1:])
	sbOff1 += header.EncodeNOP(sackBlock1[sbOff1:])
	sbOff1 += header.EncodeSACKBlocks([]header.SACKBlock{{
		start, end,
	}}, sackBlock1[sbOff1:])
	time.Sleep(simulatedRTT)
	conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck), AckNum: testbench.Uint32(uint32(seqNum1)), Options: sackBlock1[:sbOff1]})

	// Expect re-retransmission of #1 packet without entering an RTO.
	if _, err := conn.Expect(t, testbench.TCP{SeqNum: testbench.Uint32(uint32(seqNum1))}, timeout); err != nil {
		t.Fatalf("expected payload was not received: %s", err)
	}

	// Check the congestion control state.
	info := dut.GetSockOptTCPInfo(t, acceptFd)
	if info.CaState != linux.TCP_CA_Recovery {
		t.Fatalf("expected connection to be in fast recovery, want: %v got: %v", linux.TCP_CA_Recovery, info.CaState)
	}

	closeSACKConnection(t, dut, conn, acceptFd, listenFd)
}