// 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 reordering_test

import (
	"flag"
	"testing"
	"time"

	"golang.org/x/sys/unix"
	"gvisor.dev/gvisor/pkg/tcpip/header"
	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
	tb "gvisor.dev/gvisor/test/packetimpact/testbench"
)

func init() {
	tb.RegisterFlags(flag.CommandLine)
}

func TestReorderingWindow(t *testing.T) {
	dut := tb.NewDUT(t)
	defer dut.TearDown()
	listenFd, remotePort := dut.CreateListener(t, unix.SOCK_STREAM, unix.IPPROTO_TCP, 1)
	defer dut.Close(t, listenFd)
	conn := tb.NewTCPIPv4(t, tb.TCP{DstPort: &remotePort}, tb.TCP{SrcPort: &remotePort})
	defer conn.Close(t)

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

	// Ethernet guarantees that the MTU is at least 1500 bytes.
	const minMTU = 1500
	const mss = minMTU - header.IPv4MinimumSize - header.TCPMinimumSize
	optsOff += header.EncodeMSSOption(mss, opts[optsOff:])

	conn.ConnectWithOptions(t, opts[:optsOff])

	acceptFd, _ := dut.Accept(t, listenFd)
	defer dut.Close(t, acceptFd)

	if tb.Native {
		// Linux has changed its handling of reordering, force the old behavior.
		dut.SetSockOpt(t, acceptFd, unix.IPPROTO_TCP, unix.TCP_CONGESTION, []byte("reno"))
	}

	pls := dut.GetSockOptInt(t, acceptFd, unix.IPPROTO_TCP, unix.TCP_MAXSEG)
	if !tb.Native {
		// netstack does not impliment TCP_MAXSEG correctly. Fake it
		// here. Netstack uses the max SACK size which is 32. The MSS
		// option is 8 bytes, making the total 36 bytes.
		pls = mss - 36
	}

	payload := make([]byte, pls)

	seqNum1 := *conn.RemoteSeqNum(t)
	const numPkts = 10
	// Send some packets, checking that we receive each.
	for i, sn := 0, seqNum1; i < numPkts; i++ {
		dut.Send(t, acceptFd, payload, 0)

		gotOne, err := conn.Expect(t, tb.TCP{SeqNum: tb.Uint32(uint32(sn))}, time.Second)
		sn.UpdateForward(seqnum.Size(len(payload)))
		if err != nil {
			t.Errorf("Expect #%d: %s", i+1, err)
			continue
		}
		if gotOne == nil {
			t.Errorf("#%d: expected a packet within a second but got none", i+1)
		}
	}

	seqNum2 := *conn.RemoteSeqNum(t)

	// SACK packets #2-4.
	sackBlock := make([]byte, 40)
	sbOff := 0
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeNOP(sackBlock[sbOff:])
	sbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		seqNum1.Add(seqnum.Size(len(payload))),
		seqNum1.Add(seqnum.Size(4 * len(payload))),
	}}, sackBlock[sbOff:])
	conn.Send(t, tb.TCP{Flags: tb.Uint8(header.TCPFlagAck), AckNum: tb.Uint32(uint32(seqNum1)), Options: sackBlock[:sbOff]})

	// ACK first packet.
	conn.Send(t, tb.TCP{Flags: tb.Uint8(header.TCPFlagAck), AckNum: tb.Uint32(uint32(seqNum1) + uint32(len(payload)))})

	// Check for retransmit.
	gotOne, err := conn.Expect(t, tb.TCP{SeqNum: tb.Uint32(uint32(seqNum1))}, time.Second)
	if err != nil {
		t.Error("Expect for retransmit:", err)
	}
	if gotOne == nil {
		t.Error("expected a retransmitted packet within a second but got none")
	}

	// ACK all send packets with a DSACK block for packet #1. This tells
	// the other end that we got both the original and retransmit for
	// packet #1.
	dsackBlock := make([]byte, 40)
	dsbOff := 0
	dsbOff += header.EncodeNOP(dsackBlock[dsbOff:])
	dsbOff += header.EncodeNOP(dsackBlock[dsbOff:])
	dsbOff += header.EncodeSACKBlocks([]header.SACKBlock{{
		seqNum1.Add(seqnum.Size(len(payload))),
		seqNum1.Add(seqnum.Size(4 * len(payload))),
	}}, dsackBlock[dsbOff:])

	conn.Send(t, tb.TCP{Flags: tb.Uint8(header.TCPFlagAck), AckNum: tb.Uint32(uint32(seqNum2)), Options: dsackBlock[:dsbOff]})

	// Send half of the original window of packets, checking that we
	// received each.
	for i, sn := 0, seqNum2; i < numPkts/2; i++ {
		dut.Send(t, acceptFd, payload, 0)

		gotOne, err := conn.Expect(t, tb.TCP{SeqNum: tb.Uint32(uint32(sn))}, time.Second)
		sn.UpdateForward(seqnum.Size(len(payload)))
		if err != nil {
			t.Errorf("Expect #%d: %s", i+1, err)
			continue
		}
		if gotOne == nil {
			t.Errorf("#%d: expected a packet within a second but got none", i+1)
		}
	}

	if !tb.Native {
		// The window should now be halved, so we should receive any
		// more, even if we send them.
		dut.Send(t, acceptFd, payload, 0)
		if got, err := conn.Expect(t, tb.TCP{}, 100*time.Millisecond); got != nil || err == nil {
			t.Fatalf("expected no packets within 100 millisecond, but got one: %s", got)
		}
		return
	}

	// Linux reduces the window by three. Check that we can receive the rest.
	for i, sn := 0, seqNum2.Add(seqnum.Size(numPkts/2*len(payload))); i < 2; i++ {
		dut.Send(t, acceptFd, payload, 0)

		gotOne, err := conn.Expect(t, tb.TCP{SeqNum: tb.Uint32(uint32(sn))}, time.Second)
		sn.UpdateForward(seqnum.Size(len(payload)))
		if err != nil {
			t.Errorf("Expect #%d: %s", i+1, err)
			continue
		}
		if gotOne == nil {
			t.Errorf("#%d: expected a packet within a second but got none", i+1)
		}
	}

	// The window should now be full.
	dut.Send(t, acceptFd, payload, 0)
	if got, err := conn.Expect(t, tb.TCP{}, 100*time.Millisecond); got != nil || err == nil {
		t.Fatalf("expected no packets within 100 millisecond, but got one: %s", got)
	}
}