connection.go

package srt

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"math"
	"net"
	"strings"
	"sync"
	"time"

	"github.com/datarhei/gosrt/internal/circular"
	"github.com/datarhei/gosrt/internal/congestion"
	"github.com/datarhei/gosrt/internal/crypto"
	"github.com/datarhei/gosrt/internal/packet"
)

// Conn is a SRT network connection.
type Conn interface {
	// Read reads data from the connection.
	// Read can be made to time out and return an error after a fixed
	// time limit; see SetDeadline and SetReadDeadline.
	Read(p []byte) (int, error)

	// Write writes data to the connection.
	// Write can be made to time out and return an error after a fixed
	// time limit; see SetDeadline and SetWriteDeadline.
	Write(p []byte) (int, error)

	// Close closes the connection.
	// Any blocked Read or Write operations will be unblocked and return errors.
	Close() error

	// LocalAddr returns the local network address. The returned net.Addr is not shared by other invocations of LocalAddr.
	LocalAddr() net.Addr

	// RemoteAddr returns the remote network address. The returned net.Addr is not shared by other invocations of RemoteAddr.
	RemoteAddr() net.Addr

	SetDeadline(t time.Time) error
	SetReadDeadline(t time.Time) error
	SetWriteDeadline(t time.Time) error

	// SocketId return the socketid of the connection.
	SocketId() uint32

	// PeerSocketId returns the socketid of the peer of the connection.
	PeerSocketId() uint32

	// StreamId returns the streamid use for the connection.
	StreamId() string

	// Stats returns accumulated and instantaneous statistics of the connection.
	Stats(s *Statistics)

	// Version returns the connection version, either 4 or 5. With version 4, the streamid is not available
	Version() uint32
}

type connStats struct {
	headerSize        uint64
	pktSentACK        uint64
	pktRecvACK        uint64
	pktSentACKACK     uint64
	pktRecvACKACK     uint64
	pktSentNAK        uint64
	pktRecvNAK        uint64
	pktSentKM         uint64
	pktRecvKM         uint64
	pktRecvUndecrypt  uint64
	byteRecvUndecrypt uint64
	pktRecvInvalid    uint64
	pktSentKeepalive  uint64
	pktRecvKeepalive  uint64
	pktSentShutdown   uint64
	pktRecvShutdown   uint64
	mbpsLinkCapacity  float64
}

// Check if we implement the net.Conn interface
var _ net.Conn = &srtConn{}

type srtConn struct {
	version  uint32
	isCaller bool // Only relevant if version == 4

	localAddr  net.Addr
	remoteAddr net.Addr

	start time.Time

	shutdownOnce sync.Once

	socketId     uint32
	peerSocketId uint32

	config Config

	cryptoLock             sync.Mutex
	crypto                 crypto.Crypto
	keyBaseEncryption      packet.PacketEncryption
	kmPreAnnounceCountdown uint64
	kmRefreshCountdown     uint64
	kmConfirmed            bool

	peerIdleTimeout *time.Timer

	rtt    float64 // microseconds
	rttVar float64 // microseconds

	nakInterval float64

	ackLock       sync.RWMutex
	ackNumbers    map[uint32]time.Time
	nextACKNumber circular.Number

	initialPacketSequenceNumber circular.Number

	tsbpdTimeBase       uint64 // microseconds
	tsbpdWrapPeriod     bool
	tsbpdTimeBaseOffset uint64 // microseconds
	tsbpdDelay          uint64 // microseconds
	tsbpdDrift          uint64 // microseconds
	peerTsbpdDelay      uint64 // microseconds
	dropThreshold       uint64 // microseconds

	// Queue for packets that are coming from the network
	networkQueue chan packet.Packet

	// Queue for packets that are written with writePacket() and will be send to the network
	writeQueue  chan packet.Packet
	writeBuffer bytes.Buffer
	writeData   []byte

	// Queue for packets that will be read locally with ReadPacket()
	readQueue  chan packet.Packet
	readBuffer bytes.Buffer

	onSend     func(p packet.Packet)
	onShutdown func(socketId uint32)

	tick time.Duration

	// Congestion control
	recv congestion.Receiver
	snd  congestion.Sender

	// context of all channels and routines
	ctx       context.Context
	cancelCtx context.CancelFunc

	statistics     connStats
	statisticsLock sync.RWMutex

	logger Logger

	debug struct {
		expectedRcvPacketSequenceNumber  circular.Number
		expectedReadPacketSequenceNumber circular.Number
	}

	// HSv4
	stopHSRequests context.CancelFunc
	stopKMRequests context.CancelFunc
}

type srtConnConfig struct {
	version                     uint32
	isCaller                    bool
	localAddr                   net.Addr
	remoteAddr                  net.Addr
	config                      Config
	start                       time.Time
	socketId                    uint32
	peerSocketId                uint32
	tsbpdTimeBase               uint64 // microseconds
	tsbpdDelay                  uint64 // microseconds
	peerTsbpdDelay              uint64 // microseconds
	initialPacketSequenceNumber circular.Number
	crypto                      crypto.Crypto
	keyBaseEncryption           packet.PacketEncryption
	onSend                      func(p packet.Packet)
	onShutdown                  func(socketId uint32)
	logger                      Logger
}

func newSRTConn(config srtConnConfig) *srtConn {
	c := &srtConn{
		version:                     config.version,
		isCaller:                    config.isCaller,
		localAddr:                   config.localAddr,
		remoteAddr:                  config.remoteAddr,
		config:                      config.config,
		start:                       config.start,
		socketId:                    config.socketId,
		peerSocketId:                config.peerSocketId,
		tsbpdTimeBase:               config.tsbpdTimeBase,
		tsbpdDelay:                  config.tsbpdDelay,
		peerTsbpdDelay:              config.peerTsbpdDelay,
		initialPacketSequenceNumber: config.initialPacketSequenceNumber,
		crypto:                      config.crypto,
		keyBaseEncryption:           config.keyBaseEncryption,
		onSend:                      config.onSend,
		onShutdown:                  config.onShutdown,
		logger:                      config.logger,
	}

	if c.onSend == nil {
		c.onSend = func(p packet.Packet) {}
	}

	if c.onShutdown == nil {
		c.onShutdown = func(socketId uint32) {}
	}

	c.nextACKNumber = circular.New(1, packet.MAX_TIMESTAMP)
	c.ackNumbers = make(map[uint32]time.Time)

	c.kmPreAnnounceCountdown = c.config.KMRefreshRate - c.config.KMPreAnnounce
	c.kmRefreshCountdown = c.config.KMRefreshRate

	// 4.10.  Round-Trip Time Estimation
	c.rtt = float64((100 * time.Millisecond).Microseconds())
	c.rttVar = float64((50 * time.Millisecond).Microseconds())

	c.nakInterval = float64((20 * time.Millisecond).Microseconds())

	c.networkQueue = make(chan packet.Packet, 1024)

	c.writeQueue = make(chan packet.Packet, 1024)
	if c.version == 4 {
		// libsrt-1.2.3 receiver doesn't like it when the payload is larger than 7*188 bytes.
		// Here we just take a multiple of a mpegts chunk size.
		c.writeData = make([]byte, int(c.config.PayloadSize/188*188))
	} else {
		// For v5 we use the max. payload size: https://github.com/Haivision/srt/issues/876
		c.writeData = make([]byte, int(c.config.PayloadSize))
	}

	c.readQueue = make(chan packet.Packet, 1024)

	c.peerIdleTimeout = time.AfterFunc(c.config.PeerIdleTimeout, func() {
		c.log("connection:close", func() string {
			return fmt.Sprintf("no more data received from peer for %s. shutting down", c.config.PeerIdleTimeout)
		})
		go c.close()
	})

	c.tick = 10 * time.Millisecond

	// 4.8.1.  Packet Acknowledgement (ACKs, ACKACKs) -> periodicACK = 10 milliseconds
	// 4.8.2.  Packet Retransmission (NAKs) -> periodicNAK at least 20 milliseconds
	c.recv = congestion.NewLiveReceive(congestion.ReceiveConfig{
		InitialSequenceNumber: c.initialPacketSequenceNumber,
		PeriodicACKInterval:   10_000,
		PeriodicNAKInterval:   20_000,
		OnSendACK:             c.sendACK,
		OnSendNAK:             c.sendNAK,
		OnDeliver:             c.deliver,
	})

	// 4.6.  Too-Late Packet Drop -> 125% of SRT latency, at least 1 second
	// https://github.com/Haivision/srt/blob/master/docs/API/API-socket-options.md#SRTO_SNDDROPDELAY
	c.dropThreshold = uint64(float64(c.peerTsbpdDelay)*1.25) + uint64(c.config.SendDropDelay.Microseconds())
	if c.dropThreshold < uint64(time.Second.Microseconds()) {
		c.dropThreshold = uint64(time.Second.Microseconds())
	}
	c.dropThreshold += 20_000

	c.snd = congestion.NewLiveSend(congestion.SendConfig{
		InitialSequenceNumber: c.initialPacketSequenceNumber,
		DropThreshold:         c.dropThreshold,
		MaxBW:                 c.config.MaxBW,
		InputBW:               c.config.InputBW,
		MinInputBW:            c.config.MinInputBW,
		OverheadBW:            c.config.OverheadBW,
		OnDeliver:             c.pop,
	})

	c.ctx, c.cancelCtx = context.WithCancel(context.Background())

	go c.networkQueueReader(c.ctx)
	go c.writeQueueReader(c.ctx)
	go c.ticker(c.ctx)

	c.debug.expectedRcvPacketSequenceNumber = c.initialPacketSequenceNumber
	c.debug.expectedReadPacketSequenceNumber = c.initialPacketSequenceNumber

	c.statistics.headerSize = 8 + 16 // 8 bytes UDP + 16 bytes SRT
	if strings.Count(c.localAddr.String(), ":") < 2 {
		c.statistics.headerSize += 20 // 20 bytes IPv4 header
	} else {
		c.statistics.headerSize += 40 // 40 bytes IPv6 header
	}

	if c.version == 4 && c.isCaller {
		var hsrequestsCtx context.Context
		hsrequestsCtx, c.stopHSRequests = context.WithCancel(context.Background())
		go c.sendHSRequests(hsrequestsCtx)

		if c.crypto != nil {
			var kmrequestsCtx context.Context
			kmrequestsCtx, c.stopKMRequests = context.WithCancel(context.Background())
			go c.sendKMRequests(kmrequestsCtx)
		}
	}

	return c
}

func (c *srtConn) LocalAddr() net.Addr {
	if c.localAddr == nil {
		return nil
	}

	addr, _ := net.ResolveUDPAddr("udp", c.localAddr.String())
	return addr
}

func (c *srtConn) RemoteAddr() net.Addr {
	if c.remoteAddr == nil {
		return nil
	}

	addr, _ := net.ResolveUDPAddr("udp", c.remoteAddr.String())
	return addr
}

func (c *srtConn) SocketId() uint32 {
	return c.socketId
}

func (c *srtConn) PeerSocketId() uint32 {
	return c.peerSocketId
}

func (c *srtConn) StreamId() string {
	return c.config.StreamId
}

func (c *srtConn) Version() uint32 {
	return c.version
}

// ticker invokes the congestion control in regular intervals with
// the current connection time.
func (c *srtConn) ticker(ctx context.Context) {
	ticker := time.NewTicker(c.tick)
	defer ticker.Stop()
	defer func() {
		c.log("connection:close", func() string { return "left ticker loop" })
	}()

	for {
		select {
		case <-ctx.Done():
			return
		case t := <-ticker.C:
			tickTime := uint64(t.Sub(c.start).Microseconds())

			c.recv.Tick(c.tsbpdTimeBase + tickTime)
			c.snd.Tick(tickTime)
		}
	}
}

// readPacket reads a packet from the queue of received packets. It blocks
// if the queue is empty. Only data packets are returned.
func (c *srtConn) readPacket() (packet.Packet, error) {
	var p packet.Packet
	select {
	case <-c.ctx.Done():
		return nil, io.EOF
	case p = <-c.readQueue:
	}

	if p.Header().PacketSequenceNumber.Gt(c.debug.expectedReadPacketSequenceNumber) {
		c.log("connection:error", func() string {
			return fmt.Sprintf("lost packets. got: %d, expected: %d (%d)", p.Header().PacketSequenceNumber.Val(), c.debug.expectedReadPacketSequenceNumber.Val(), c.debug.expectedReadPacketSequenceNumber.Distance(p.Header().PacketSequenceNumber))
		})
	} else if p.Header().PacketSequenceNumber.Lt(c.debug.expectedReadPacketSequenceNumber) {
		c.log("connection:error", func() string {
			return fmt.Sprintf("packet out of order. got: %d, expected: %d (%d)", p.Header().PacketSequenceNumber.Val(), c.debug.expectedReadPacketSequenceNumber.Val(), c.debug.expectedReadPacketSequenceNumber.Distance(p.Header().PacketSequenceNumber))
		})
		return nil, io.EOF
	}

	c.debug.expectedReadPacketSequenceNumber = p.Header().PacketSequenceNumber.Inc()

	return p, nil
}

func (c *srtConn) Read(b []byte) (int, error) {
	if c.readBuffer.Len() != 0 {
		return c.readBuffer.Read(b)
	}

	c.readBuffer.Reset()

	p, err := c.readPacket()
	if err != nil {
		return 0, err
	}

	c.readBuffer.Write(p.Data())

	// The packet is out of congestion control and written to the read buffer
	p.Decommission()

	return c.readBuffer.Read(b)
}

// writePacket writes a packet to the write queue. Packets on the write queue
// will be sent to the peer of the connection. Only data packets will be sent.
func (c *srtConn) writePacket(p packet.Packet) error {
	if p.Header().IsControlPacket {
		// Ignore control packets
		return nil
	}

	_, err := c.Write(p.Data())
	if err != nil {
		return err
	}

	return nil
}

func (c *srtConn) Write(b []byte) (int, error) {
	c.writeBuffer.Write(b)

	for {
		n, err := c.writeBuffer.Read(c.writeData)
		if err != nil {
			return 0, err
		}

		p := packet.NewPacket(nil)

		p.SetData(c.writeData[:n])

		p.Header().IsControlPacket = false
		// Give the packet a deliver timestamp
		p.Header().PktTsbpdTime = c.getTimestamp()

		// Non-blocking write to the write queue
		select {
		case <-c.ctx.Done():
			return 0, io.EOF
		case c.writeQueue <- p:
		default:
			return 0, io.EOF
		}

		if c.writeBuffer.Len() == 0 {
			break
		}
	}

	c.writeBuffer.Reset()

	return len(b), nil
}

// push puts a packet on the network queue. This is where packets go that came in from the network.
func (c *srtConn) push(p packet.Packet) {
	// Non-blocking write to the network queue
	select {
	case <-c.ctx.Done():
	case c.networkQueue <- p:
	default:
		c.log("connection:error", func() string { return "network queue is full" })
	}
}

// getTimestamp returns the elapsed time since the start of the connection in microseconds.
func (c *srtConn) getTimestamp() uint64 {
	return uint64(time.Since(c.start).Microseconds())
}

// getTimestampForPacket returns the elapsed time since the start of the connection in
// microseconds clamped a 32bit value.
func (c *srtConn) getTimestampForPacket() uint32 {
	return uint32(c.getTimestamp() & uint64(packet.MAX_TIMESTAMP))
}

// pop adds the destination address and socketid to the packet and sends it out to the network.
// The packet will be encrypted if required.
func (c *srtConn) pop(p packet.Packet) {
	p.Header().Addr = c.remoteAddr
	p.Header().DestinationSocketId = c.peerSocketId

	if !p.Header().IsControlPacket {
		c.cryptoLock.Lock()
		if c.crypto != nil {
			p.Header().KeyBaseEncryptionFlag = c.keyBaseEncryption
			c.crypto.EncryptOrDecryptPayload(p.Data(), p.Header().KeyBaseEncryptionFlag, p.Header().PacketSequenceNumber.Val())

			c.kmPreAnnounceCountdown--
			c.kmRefreshCountdown--

			if c.kmPreAnnounceCountdown == 0 && !c.kmConfirmed {
				c.sendKMRequest(c.keyBaseEncryption.Opposite())

				// Resend the request until we get a response
				c.kmPreAnnounceCountdown = c.config.KMPreAnnounce/10 + 1
			}

			if c.kmRefreshCountdown == 0 {
				c.kmPreAnnounceCountdown = c.config.KMRefreshRate - c.config.KMPreAnnounce
				c.kmRefreshCountdown = c.config.KMRefreshRate

				// Switch the keys
				c.keyBaseEncryption = c.keyBaseEncryption.Opposite()

				c.kmConfirmed = false
			}

			if c.kmRefreshCountdown == c.config.KMRefreshRate-c.config.KMPreAnnounce {
				// Decommission the previous key, resp. create a new SEK that will
				// be used in the next switch.
				c.crypto.GenerateSEK(c.keyBaseEncryption.Opposite())
			}
		}
		c.cryptoLock.Unlock()

		c.log("data:send:dump", func() string { return p.Dump() })
	}

	// Send the packet on the wire
	c.onSend(p)
}

// networkQueueReader reads the packets from the network queue in order to process them.
func (c *srtConn) networkQueueReader(ctx context.Context) {
	defer func() {
		c.log("connection:close", func() string { return "left network queue reader loop" })
	}()

	for {
		select {
		case <-ctx.Done():
			return
		case p := <-c.networkQueue:
			c.handlePacket(p)
		}
	}
}

// writeQueueReader reads the packets from the write queue and puts them into congestion
// control for sending.
func (c *srtConn) writeQueueReader(ctx context.Context) {
	defer func() {
		c.log("connection:close", func() string { return "left write queue reader loop" })
	}()

	for {
		select {
		case <-ctx.Done():
			return
		case p := <-c.writeQueue:
			// Put the packet into the send congestion control
			c.snd.Push(p)
		}
	}
}

// deliver writes the packets to the read queue in order to be consumed by the Read function.
func (c *srtConn) deliver(p packet.Packet) {
	// Non-blocking write to the read queue
	select {
	case <-c.ctx.Done():
	case c.readQueue <- p:
	default:
		c.log("connection:error", func() string { return "readQueue was blocking, dropping packet" })
	}
}

// handlePacket checks the packet header. If it is a control packet it will forwarded to the
// respective handler. If it is a data packet it will be put into congestion control for
// receiving. The packet will be decrypted if required.
func (c *srtConn) handlePacket(p packet.Packet) {
	if p == nil {
		return
	}

	c.peerIdleTimeout.Reset(c.config.PeerIdleTimeout)

	header := p.Header()

	if header.IsControlPacket {
		if header.ControlType == packet.CTRLTYPE_KEEPALIVE {
			c.handleKeepAlive(p)
		} else if header.ControlType == packet.CTRLTYPE_SHUTDOWN {
			c.handleShutdown(p)
		} else if header.ControlType == packet.CTRLTYPE_NAK {
			c.handleNAK(p)
		} else if header.ControlType == packet.CTRLTYPE_ACK {
			c.handleACK(p)
		} else if header.ControlType == packet.CTRLTYPE_ACKACK {
			c.handleACKACK(p)
		} else if header.ControlType == packet.CTRLTYPE_USER {
			c.log("connection:recv:ctrl:user", func() string {
				return fmt.Sprintf("got CTRLTYPE_USER packet, subType: %s", header.SubType)
			})

			// HSv4 Extension
			if header.SubType == packet.EXTTYPE_HSREQ {
				c.handleHSRequest(p)
			} else if header.SubType == packet.EXTTYPE_HSRSP {
				c.handleHSResponse(p)
			}

			// 3.2.2.  Key Material
			if header.SubType == packet.EXTTYPE_KMREQ {
				c.handleKMRequest(p)
			} else if header.SubType == packet.EXTTYPE_KMRSP {
				c.handleKMResponse(p)
			}
		}

		return
	}

	if header.PacketSequenceNumber.Gt(c.debug.expectedRcvPacketSequenceNumber) {
		c.log("connection:error", func() string {
			return fmt.Sprintf("recv lost packets. got: %d, expected: %d (%d)\n", header.PacketSequenceNumber.Val(), c.debug.expectedRcvPacketSequenceNumber.Val(), c.debug.expectedRcvPacketSequenceNumber.Distance(header.PacketSequenceNumber))
		})
	}

	c.debug.expectedRcvPacketSequenceNumber = header.PacketSequenceNumber.Inc()

	//fmt.Printf("%s\n", p.String())

	// Ignore FEC filter control packets
	// https://github.com/Haivision/srt/blob/master/docs/features/packet-filtering-and-fec.md
	// "An FEC control packet is distinguished from a regular data packet by having
	// its message number equal to 0. This value isn't normally used in SRT (message
	// numbers start from 1, increment to a maximum, and then roll back to 1)."
	if header.MessageNumber == 0 {
		c.log("connection:filter", func() string { return "dropped FEC filter control packet" })
		return
	}

	// 4.5.1.1.  TSBPD Time Base Calculation
	if !c.tsbpdWrapPeriod {
		if header.Timestamp > packet.MAX_TIMESTAMP-(30*1000000) {
			c.tsbpdWrapPeriod = true
			c.log("connection:tsbpd", func() string { return "TSBPD wrapping period started" })
		}
	} else {
		if header.Timestamp >= (30*1000000) && header.Timestamp <= (60*1000000) {
			c.tsbpdWrapPeriod = false
			c.tsbpdTimeBaseOffset += uint64(packet.MAX_TIMESTAMP) + 1
			c.log("connection:tsbpd", func() string { return "TSBPD wrapping period finished" })
		}
	}

	tsbpdTimeBaseOffset := c.tsbpdTimeBaseOffset
	if c.tsbpdWrapPeriod {
		if header.Timestamp < (30 * 1000000) {
			tsbpdTimeBaseOffset += uint64(packet.MAX_TIMESTAMP) + 1
		}
	}

	header.PktTsbpdTime = c.tsbpdTimeBase + tsbpdTimeBaseOffset + uint64(header.Timestamp) + c.tsbpdDelay + c.tsbpdDrift

	c.log("data:recv:dump", func() string { return p.Dump() })

	c.cryptoLock.Lock()
	if c.crypto != nil {
		if header.KeyBaseEncryptionFlag != 0 {
			if err := c.crypto.EncryptOrDecryptPayload(p.Data(), header.KeyBaseEncryptionFlag, header.PacketSequenceNumber.Val()); err != nil {
				c.statisticsLock.Lock()
				c.statistics.pktRecvUndecrypt++
				c.statistics.byteRecvUndecrypt += p.Len()
				c.statisticsLock.Unlock()
			}
		} else {
			c.statisticsLock.Lock()
			c.statistics.pktRecvUndecrypt++
			c.statistics.byteRecvUndecrypt += p.Len()
			c.statisticsLock.Unlock()
		}
	}
	c.cryptoLock.Unlock()

	// Put the packet into receive congestion control
	c.recv.Push(p)
}

// handleKeepAlive resets the idle timeout and sends a keepalive to the peer.
func (c *srtConn) handleKeepAlive(p packet.Packet) {
	c.log("control:recv:keepalive:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktRecvKeepalive++
	c.statistics.pktSentKeepalive++
	c.statisticsLock.Unlock()

	c.peerIdleTimeout.Reset(c.config.PeerIdleTimeout)

	c.log("control:send:keepalive:dump", func() string { return p.Dump() })

	c.pop(p)
}

// handleShutdown closes the connection
func (c *srtConn) handleShutdown(p packet.Packet) {
	c.log("control:recv:shutdown:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktRecvShutdown++
	c.statisticsLock.Unlock()

	go c.close()
}

// handleACK forwards the acknowledge sequence number to the congestion control and
// returns a ACKACK (on a full ACK). The RTT is also updated in case of a full ACK.
func (c *srtConn) handleACK(p packet.Packet) {
	c.log("control:recv:ACK:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktRecvACK++
	c.statisticsLock.Unlock()

	cif := &packet.CIFACK{}

	if err := p.UnmarshalCIF(cif); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:ACK:error", func() string { return fmt.Sprintf("invalid ACK: %s", err) })
		return
	}

	c.log("control:recv:ACK:cif", func() string { return cif.String() })

	c.snd.ACK(cif.LastACKPacketSequenceNumber)

	if !cif.IsLite && !cif.IsSmall {
		// 4.10.  Round-Trip Time Estimation
		c.recalculateRTT(time.Duration(int64(cif.RTT)) * time.Microsecond)

		// Estimated Link Capacity (from packets/s to Mbps)
		c.statisticsLock.Lock()
		c.statistics.mbpsLinkCapacity = float64(cif.EstimatedLinkCapacity) * MAX_PAYLOAD_SIZE * 8 / 1024 / 1024
		c.statisticsLock.Unlock()

		c.sendACKACK(p.Header().TypeSpecific)
	}
}

// handleNAK forwards the lost sequence number to the congestion control.
func (c *srtConn) handleNAK(p packet.Packet) {
	c.log("control:recv:NAK:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktRecvNAK++
	c.statisticsLock.Unlock()

	cif := &packet.CIFNAK{}

	if err := p.UnmarshalCIF(cif); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:NAK:error", func() string { return fmt.Sprintf("invalid NAK: %s", err) })
		return
	}

	c.log("control:recv:NAK:cif", func() string { return cif.String() })

	// Inform congestion control about lost packets
	c.snd.NAK(cif.LostPacketSequenceNumber)
}

// handleACKACK updates the RTT and NAK interval for the congestion control.
func (c *srtConn) handleACKACK(p packet.Packet) {
	c.ackLock.RLock()

	c.statisticsLock.Lock()
	c.statistics.pktRecvACKACK++
	c.statisticsLock.Unlock()

	c.log("control:recv:ACKACK:dump", func() string { return p.Dump() })

	// p.typeSpecific is the ACKNumber
	if ts, ok := c.ackNumbers[p.Header().TypeSpecific]; ok {
		// 4.10.  Round-Trip Time Estimation
		c.recalculateRTT(time.Since(ts))
		delete(c.ackNumbers, p.Header().TypeSpecific)
	} else {
		c.log("control:recv:ACKACK:error", func() string { return fmt.Sprintf("got unknown ACKACK (%d)", p.Header().TypeSpecific) })
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
	}

	for i := range c.ackNumbers {
		if i < p.Header().TypeSpecific {
			delete(c.ackNumbers, i)
		}
	}

	nakInterval := uint64(c.nakInterval)

	c.ackLock.RUnlock()

	c.recv.SetNAKInterval(nakInterval)
}

// recalculateRTT recalculates the RTT based on a full ACK exchange
func (c *srtConn) recalculateRTT(rtt time.Duration) {
	// 4.10.  Round-Trip Time Estimation
	lastRTT := float64(rtt.Microseconds())

	c.rtt = c.rtt*0.875 + lastRTT*0.125
	c.rttVar = c.rttVar*0.75 + math.Abs(c.rtt-lastRTT)*0.25

	// 4.8.2.  Packet Retransmission (NAKs)
	nakInterval := (c.rtt + 4*c.rttVar) / 2
	if nakInterval < 20000 {
		c.nakInterval = 20000 // 20ms
	} else {
		c.nakInterval = nakInterval
	}

	c.log("connection:rtt", func() string {
		return fmt.Sprintf("RTT=%.0fus RTTVar=%.0fus NAKInterval=%.0fms", c.rtt, c.rttVar, c.nakInterval/1000)
	})
}

// handleHSRequest handles the HSv4 handshake extension request and sends the response
func (c *srtConn) handleHSRequest(p packet.Packet) {
	c.log("control:recv:HSReq:dump", func() string { return p.Dump() })

	cif := &packet.CIFHandshakeExtension{}

	if err := p.UnmarshalCIF(cif); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:HSReq:error", func() string { return fmt.Sprintf("invalid HSReq: %s", err) })
		return
	}

	c.log("control:recv:HSReq:cif", func() string { return cif.String() })

	// Check for version
	if cif.SRTVersion < 0x010200 || cif.SRTVersion >= 0x010300 {
		c.log("control:recv:HSReq:error", func() string { return fmt.Sprintf("unsupported version: %#08x", cif.SRTVersion) })
		c.close()
		return
	}

	// Check the required SRT flags
	if !cif.SRTFlags.TSBPDSND {
		c.log("control:recv:HSRes:error", func() string { return "TSBPDSND flag must be set" })
		c.close()

		return
	}

	if !cif.SRTFlags.TLPKTDROP {
		c.log("control:recv:HSRes:error", func() string { return "TLPKTDROP flag must be set" })
		c.close()

		return
	}

	if !cif.SRTFlags.CRYPT {
		c.log("control:recv:HSRes:error", func() string { return "CRYPT flag must be set" })
		c.close()

		return
	}

	if !cif.SRTFlags.REXMITFLG {
		c.log("control:recv:HSRes:error", func() string { return "REXMITFLG flag must be set" })
		c.close()

		return
	}

	// we as receiver don't need this
	cif.SRTFlags.TSBPDSND = false

	// we as receiver are supporting these
	cif.SRTFlags.TSBPDRCV = true
	cif.SRTFlags.PERIODICNAK = true

	// These flag was introduced in HSv5 and should not be set in HSv4
	if cif.SRTFlags.STREAM {
		c.log("control:recv:HSReq:error", func() string { return "STREAM flag is set" })
		c.close()
		return
	}

	if cif.SRTFlags.PACKET_FILTER {
		c.log("control:recv:HSReq:error", func() string { return "PACKET_FILTER flag is set" })
		c.close()
		return
	}

	recvTsbpdDelay := uint16(c.config.ReceiverLatency.Milliseconds())

	if cif.SendTSBPDDelay > recvTsbpdDelay {
		recvTsbpdDelay = cif.SendTSBPDDelay
	}

	c.tsbpdDelay = uint64(recvTsbpdDelay) * 1000

	cif.RecvTSBPDDelay = 0
	cif.SendTSBPDDelay = recvTsbpdDelay

	p.MarshalCIF(cif)

	// Send HS Response
	p.Header().SubType = packet.EXTTYPE_HSRSP

	c.pop(p)
}

// handleHSResponse handles the HSv4 handshake extension response
func (c *srtConn) handleHSResponse(p packet.Packet) {
	c.log("control:recv:HSRes:dump", func() string { return p.Dump() })

	cif := &packet.CIFHandshakeExtension{}

	if err := p.UnmarshalCIF(cif); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:HSRes:error", func() string { return fmt.Sprintf("invalid HSRes: %s", err) })
		return
	}

	c.log("control:recv:HSRes:cif", func() string { return cif.String() })

	if c.version == 4 {
		// Check for version
		if cif.SRTVersion < 0x010200 || cif.SRTVersion >= 0x010300 {
			c.log("control:recv:HSRes:error", func() string { return fmt.Sprintf("unsupported version: %#08x", cif.SRTVersion) })
			c.close()
			return
		}

		// TSBPDSND is not relevant from the receiver
		// PERIODICNAK is the sender's decision, we don't care, but will handle them

		// Check the required SRT flags
		if !cif.SRTFlags.TSBPDRCV {
			c.log("control:recv:HSRes:error", func() string { return "TSBPDRCV flag must be set" })
			c.close()

			return
		}

		if !cif.SRTFlags.TLPKTDROP {
			c.log("control:recv:HSRes:error", func() string { return "TLPKTDROP flag must be set" })
			c.close()

			return
		}

		if !cif.SRTFlags.CRYPT {
			c.log("control:recv:HSRes:error", func() string { return "CRYPT flag must be set" })
			c.close()

			return
		}

		if !cif.SRTFlags.REXMITFLG {
			c.log("control:recv:HSRes:error", func() string { return "REXMITFLG flag must be set" })
			c.close()

			return
		}

		// These flag was introduced in HSv5 and should not be set in HSv4
		if cif.SRTFlags.STREAM {
			c.log("control:recv:HSReq:error", func() string { return "STREAM flag is set" })
			c.close()
			return
		}

		if cif.SRTFlags.PACKET_FILTER {
			c.log("control:recv:HSReq:error", func() string { return "PACKET_FILTER flag is set" })
			c.close()
			return
		}

		sendTsbpdDelay := uint16(c.config.PeerLatency.Milliseconds())

		if cif.SendTSBPDDelay > sendTsbpdDelay {
			sendTsbpdDelay = cif.SendTSBPDDelay
		}

		c.dropThreshold = uint64(float64(sendTsbpdDelay)*1.25) + uint64(c.config.SendDropDelay.Microseconds())
		if c.dropThreshold < uint64(time.Second.Microseconds()) {
			c.dropThreshold = uint64(time.Second.Microseconds())
		}
		c.dropThreshold += 20_000

		c.snd.SetDropThreshold(c.dropThreshold)

		c.stopHSRequests()
	}
}

// handleKMRequest checks if the key material is valid and responds with a KM response.
func (c *srtConn) handleKMRequest(p packet.Packet) {
	c.log("control:recv:KMReq:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktRecvKM++
	c.statisticsLock.Unlock()

	cif := &packet.CIFKeyMaterialExtension{}

	if err := p.UnmarshalCIF(cif); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:KMReq:error", func() string { return fmt.Sprintf("invalid KMReq: %s", err) })
		return
	}

	c.log("control:recv:KMReq:cif", func() string { return cif.String() })

	c.cryptoLock.Lock()

	if c.version == 4 && c.crypto == nil {
		cr, err := crypto.New(int(cif.KLen))
		if err != nil {
			c.log("control:recv:KMReq:error", func() string { return fmt.Sprintf("crypto: %s", err) })
			c.cryptoLock.Unlock()
			c.close()
			return
		}

		c.keyBaseEncryption = cif.KeyBasedEncryption.Opposite()
		c.crypto = cr
	}

	if c.crypto == nil {
		c.log("control:recv:KMReq:error", func() string { return "connection is not encrypted" })
		c.cryptoLock.Unlock()
		return
	}

	if cif.KeyBasedEncryption == c.keyBaseEncryption {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:KMReq:error", func() string {
			return "invalid KM request. wants to reset the key that is already in use"
		})
		c.cryptoLock.Unlock()
		return
	}

	if err := c.crypto.UnmarshalKM(cif, c.config.Passphrase); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:KMReq:error", func() string { return fmt.Sprintf("invalid KMReq: %s", err) })
		c.cryptoLock.Unlock()
		return
	}

	// Switch the keys
	c.keyBaseEncryption = c.keyBaseEncryption.Opposite()

	c.cryptoLock.Unlock()

	// Send KM Response
	p.Header().SubType = packet.EXTTYPE_KMRSP

	c.statisticsLock.Lock()
	c.statistics.pktSentKM++
	c.statisticsLock.Unlock()

	c.pop(p)
}

// handleKMResponse confirms the change of encryption keys.
func (c *srtConn) handleKMResponse(p packet.Packet) {
	c.log("control:recv:KMRes:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktRecvKM++
	c.statisticsLock.Unlock()

	cif := &packet.CIFKeyMaterialExtension{}

	if err := p.UnmarshalCIF(cif); err != nil {
		c.statisticsLock.Lock()
		c.statistics.pktRecvInvalid++
		c.statisticsLock.Unlock()
		c.log("control:recv:KMRes:error", func() string { return fmt.Sprintf("invalid KMRes: %s", err) })
		return
	}

	c.cryptoLock.Lock()
	defer c.cryptoLock.Unlock()

	if c.crypto == nil {
		c.log("control:recv:KMRes:error", func() string { return "connection is not encrypted" })
		return
	}

	if c.version == 4 {
		c.stopKMRequests()

		if cif.Error != 0 {
			if cif.Error == packet.KM_NOSECRET {
				c.log("control:recv:KMRes:error", func() string { return "peer didn't enabled encryption" })
			} else if cif.Error == packet.KM_BADSECRET {
				c.log("control:recv:KMRes:error", func() string { return "peer has a different passphrase" })
			}
			c.close()
			return
		}
	}

	c.log("control:recv:KMRes:cif", func() string { return cif.String() })

	if c.kmPreAnnounceCountdown >= c.config.KMPreAnnounce {
		c.log("control:recv:KMRes:error", func() string { return "not in pre-announce period, ignored" })
		// Ignore the response, we're not in the pre-announce period
		return
	}

	c.kmConfirmed = true
}

// sendShutdown sends a shutdown packet to the peer.
func (c *srtConn) sendShutdown() {
	p := packet.NewPacket(c.remoteAddr)

	p.Header().IsControlPacket = true

	p.Header().ControlType = packet.CTRLTYPE_SHUTDOWN
	p.Header().Timestamp = c.getTimestampForPacket()

	cif := packet.CIFShutdown{}

	p.MarshalCIF(&cif)

	c.log("control:send:shutdown:dump", func() string { return p.Dump() })
	c.log("control:send:shutdown:cif", func() string { return cif.String() })

	c.statisticsLock.Lock()
	c.statistics.pktSentShutdown++
	c.statisticsLock.Unlock()

	c.pop(p)
}

// sendNAK sends a NAK to the peer with the given range of sequence numbers.
func (c *srtConn) sendNAK(from, to circular.Number) {
	p := packet.NewPacket(c.remoteAddr)

	p.Header().IsControlPacket = true

	p.Header().ControlType = packet.CTRLTYPE_NAK
	p.Header().Timestamp = c.getTimestampForPacket()

	cif := packet.CIFNAK{}

	cif.LostPacketSequenceNumber = append(cif.LostPacketSequenceNumber, from)
	cif.LostPacketSequenceNumber = append(cif.LostPacketSequenceNumber, to)

	p.MarshalCIF(&cif)

	c.log("control:send:NAK:dump", func() string { return p.Dump() })
	c.log("control:send:NAK:cif", func() string { return cif.String() })

	c.statisticsLock.Lock()
	c.statistics.pktSentNAK++
	c.statisticsLock.Unlock()

	c.pop(p)
}

// sendACK sends an ACK to the peer with the given sequence number.
func (c *srtConn) sendACK(seq circular.Number, lite bool) {
	p := packet.NewPacket(c.remoteAddr)

	p.Header().IsControlPacket = true

	p.Header().ControlType = packet.CTRLTYPE_ACK
	p.Header().Timestamp = c.getTimestampForPacket()

	cif := packet.CIFACK{
		LastACKPacketSequenceNumber: seq,
	}

	c.ackLock.Lock()
	defer c.ackLock.Unlock()

	if lite {
		cif.IsLite = true

		p.Header().TypeSpecific = 0
	} else {
		pps, bps, capacity := c.recv.PacketRate()

		cif.RTT = uint32(c.rtt)
		cif.RTTVar = uint32(c.rttVar)
		cif.AvailableBufferSize = c.config.FC        // TODO: available buffer size (packets)
		cif.PacketsReceivingRate = uint32(pps)       // packets receiving rate (packets/s)
		cif.EstimatedLinkCapacity = uint32(capacity) // estimated link capacity (packets/s), not relevant for live mode
		cif.ReceivingRate = uint32(bps)              // receiving rate (bytes/s), not relevant for live mode

		p.Header().TypeSpecific = c.nextACKNumber.Val()

		c.ackNumbers[p.Header().TypeSpecific] = time.Now()
		c.nextACKNumber = c.nextACKNumber.Inc()
		if c.nextACKNumber.Val() == 0 {
			c.nextACKNumber = c.nextACKNumber.Inc()
		}
	}

	p.MarshalCIF(&cif)

	c.log("control:send:ACK:dump", func() string { return p.Dump() })
	c.log("control:send:ACK:cif", func() string { return cif.String() })

	c.statisticsLock.Lock()
	c.statistics.pktSentACK++
	c.statisticsLock.Unlock()

	c.pop(p)
}

// sendACKACK sends an ACKACK to the peer with the given ACK sequence.
func (c *srtConn) sendACKACK(ackSequence uint32) {
	p := packet.NewPacket(c.remoteAddr)

	p.Header().IsControlPacket = true

	p.Header().ControlType = packet.CTRLTYPE_ACKACK
	p.Header().Timestamp = c.getTimestampForPacket()

	p.Header().TypeSpecific = ackSequence

	c.log("control:send:ACKACK:dump", func() string { return p.Dump() })

	c.statisticsLock.Lock()
	c.statistics.pktSentACKACK++
	c.statisticsLock.Unlock()

	c.pop(p)
}

func (c *srtConn) sendHSRequests(ctx context.Context) {
	ticker := time.NewTicker(500 * time.Millisecond)
	defer ticker.Stop()

	select {
	case <-ctx.Done():
		return
	case <-ticker.C:
		c.sendHSRequest()
	}
}

func (c *srtConn) sendHSRequest() {
	cif := &packet.CIFHandshakeExtension{
		SRTVersion: 0x00010203,
		SRTFlags: packet.CIFHandshakeExtensionFlags{
			TSBPDSND:      true,  // we send in TSBPD mode
			TSBPDRCV:      false, // not relevant for us as sender
			CRYPT:         true,  // must be always set
			TLPKTDROP:     true,  // must be set in live mode
			PERIODICNAK:   false, // not relevant for us as sender
			REXMITFLG:     true,  // must alwasy be set
			STREAM:        false, // has been introducet in HSv5
			PACKET_FILTER: false, // has been introducet in HSv5
		},
		RecvTSBPDDelay: 0,
		SendTSBPDDelay: uint16(c.config.ReceiverLatency.Milliseconds()),
	}

	p := packet.NewPacket(c.remoteAddr)

	p.Header().IsControlPacket = true

	p.Header().ControlType = packet.CTRLTYPE_USER
	p.Header().SubType = packet.EXTTYPE_HSREQ
	p.Header().Timestamp = c.getTimestampForPacket()

	p.MarshalCIF(cif)

	c.log("control:send:HSReq:dump", func() string { return p.Dump() })
	c.log("control:send:HSReq:cif", func() string { return cif.String() })

	c.pop(p)
}

func (c *srtConn) sendKMRequests(ctx context.Context) {
	ticker := time.NewTicker(500 * time.Millisecond)
	defer ticker.Stop()

	select {
	case <-ctx.Done():
		return
	case <-ticker.C:
		c.sendKMRequest(c.keyBaseEncryption)
	}
}

// sendKMRequest sends a KM request to the peer.
func (c *srtConn) sendKMRequest(key packet.PacketEncryption) {
	if c.crypto == nil {
		c.log("control:send:KMReq:error", func() string { return "connection is not encrypted" })
		return
	}

	cif := &packet.CIFKeyMaterialExtension{}

	c.crypto.MarshalKM(cif, c.config.Passphrase, key)

	p := packet.NewPacket(c.remoteAddr)

	p.Header().IsControlPacket = true

	p.Header().ControlType = packet.CTRLTYPE_USER
	p.Header().SubType = packet.EXTTYPE_KMREQ
	p.Header().Timestamp = c.getTimestampForPacket()

	p.MarshalCIF(cif)

	c.log("control:send:KMReq:dump", func() string { return p.Dump() })
	c.log("control:send:KMReq:cif", func() string { return cif.String() })

	c.statisticsLock.Lock()
	c.statistics.pktSentKM++
	c.statisticsLock.Unlock()

	c.pop(p)
}

// Close closes the connection.
func (c *srtConn) Close() error {
	c.close()

	return nil
}

// close closes the connection.
func (c *srtConn) close() {

	c.shutdownOnce.Do(func() {
		c.log("connection:close", func() string { return "stopping peer idle timeout" })

		c.peerIdleTimeout.Stop()

		c.log("connection:close", func() string { return "sending shutdown message to peer" })

		c.sendShutdown()

		c.log("connection:close", func() string { return "stopping all routines and channels" })

		c.cancelCtx()

		c.log("connection:close", func() string { return "flushing congestion" })

		c.snd.Flush()
		c.recv.Flush()

		c.log("connection:close", func() string { return "shutdown" })

		go func() {
			c.onShutdown(c.socketId)
		}()
	})
}

func (c *srtConn) log(topic string, message func() string) {
	c.logger.Print(topic, c.socketId, 2, message)
}

func (c *srtConn) SetDeadline(t time.Time) error      { return nil }
func (c *srtConn) SetReadDeadline(t time.Time) error  { return nil }
func (c *srtConn) SetWriteDeadline(t time.Time) error { return nil }

func (c *srtConn) Stats(s *Statistics) {
	if s == nil {
		return
	}

	now := uint64(time.Since(c.start).Milliseconds())

	send := c.snd.Stats()
	recv := c.recv.Stats()

	previous := s.Accumulated
	interval := now - s.MsTimeStamp

	c.statisticsLock.RLock()
	defer c.statisticsLock.RUnlock()

	// Accumulated
	s.Accumulated = StatisticsAccumulated{
		PktSent:           send.Pkt,
		PktRecv:           recv.Pkt,
		PktSentUnique:     send.PktUnique,
		PktRecvUnique:     recv.PktUnique,
		PktSendLoss:       send.PktLoss,
		PktRecvLoss:       recv.PktLoss,
		PktRetrans:        send.PktRetrans,
		PktRecvRetrans:    recv.PktRetrans,
		PktSentACK:        c.statistics.pktSentACK,
		PktRecvACK:        c.statistics.pktRecvACK,
		PktSentNAK:        c.statistics.pktSentNAK,
		PktRecvNAK:        c.statistics.pktRecvNAK,
		PktSentKM:         c.statistics.pktSentKM,
		PktRecvKM:         c.statistics.pktRecvKM,
		UsSndDuration:     send.UsSndDuration,
		PktSendDrop:       send.PktDrop,
		PktRecvDrop:       recv.PktDrop,
		PktRecvUndecrypt:  c.statistics.pktRecvUndecrypt,
		ByteSent:          send.Byte + (send.Pkt * c.statistics.headerSize),
		ByteRecv:          recv.Byte + (recv.Pkt * c.statistics.headerSize),
		ByteSentUnique:    send.ByteUnique + (send.PktUnique * c.statistics.headerSize),
		ByteRecvUnique:    recv.ByteUnique + (recv.PktUnique * c.statistics.headerSize),
		ByteRecvLoss:      recv.ByteLoss + (recv.PktLoss * c.statistics.headerSize),
		ByteRetrans:       send.ByteRetrans + (send.PktRetrans * c.statistics.headerSize),
		ByteRecvRetrans:   recv.ByteRetrans + (recv.PktRetrans * c.statistics.headerSize),
		ByteSendDrop:      send.ByteDrop + (send.PktDrop * c.statistics.headerSize),
		ByteRecvDrop:      recv.ByteDrop + (recv.PktDrop * c.statistics.headerSize),
		ByteRecvUndecrypt: c.statistics.byteRecvUndecrypt + (c.statistics.pktRecvUndecrypt * c.statistics.headerSize),
	}

	// Interval
	s.Interval = StatisticsInterval{
		MsInterval:         interval,
		PktSent:            s.Accumulated.PktSent - previous.PktSent,
		PktRecv:            s.Accumulated.PktRecv - previous.PktRecv,
		PktSentUnique:      s.Accumulated.PktSentUnique - previous.PktSentUnique,
		PktRecvUnique:      s.Accumulated.PktRecvUnique - previous.PktRecvUnique,
		PktSendLoss:        s.Accumulated.PktSendLoss - previous.PktSendLoss,
		PktRecvLoss:        s.Accumulated.PktRecvLoss - previous.PktRecvLoss,
		PktRetrans:         s.Accumulated.PktRetrans - previous.PktRetrans,
		PktRecvRetrans:     s.Accumulated.PktRecvRetrans - previous.PktRecvRetrans,
		PktSentACK:         s.Accumulated.PktSentACK - previous.PktSentACK,
		PktRecvACK:         s.Accumulated.PktRecvACK - previous.PktRecvACK,
		PktSentNAK:         s.Accumulated.PktSentNAK - previous.PktSentNAK,
		PktRecvNAK:         s.Accumulated.PktRecvNAK - previous.PktRecvNAK,
		MbpsSendRate:       float64(s.Accumulated.ByteSent-previous.ByteSent) * 8 / 1024 / 1024 / (float64(interval) / 1000),
		MbpsRecvRate:       float64(s.Accumulated.ByteRecv-previous.ByteRecv) * 8 / 1024 / 1024 / (float64(interval) / 1000),
		UsSndDuration:      s.Accumulated.UsSndDuration - previous.UsSndDuration,
		PktReorderDistance: 0,
		PktRecvBelated:     s.Accumulated.PktRecvBelated - previous.PktRecvBelated,
		PktSndDrop:         s.Accumulated.PktSendDrop - previous.PktSendDrop,
		PktRecvDrop:        s.Accumulated.PktRecvDrop - previous.PktRecvDrop,
		PktRecvUndecrypt:   s.Accumulated.PktRecvUndecrypt - previous.PktRecvUndecrypt,
		ByteSent:           s.Accumulated.ByteSent - previous.ByteSent,
		ByteRecv:           s.Accumulated.ByteRecv - previous.ByteRecv,
		ByteSentUnique:     s.Accumulated.ByteSentUnique - previous.ByteSentUnique,
		ByteRecvUnique:     s.Accumulated.ByteRecvUnique - previous.ByteRecvUnique,
		ByteRecvLoss:       s.Accumulated.ByteRecvLoss - previous.ByteRecvLoss,
		ByteRetrans:        s.Accumulated.ByteRetrans - previous.ByteRetrans,
		ByteRecvRetrans:    s.Accumulated.ByteRecvRetrans - previous.ByteRecvRetrans,
		ByteRecvBelated:    s.Accumulated.ByteRecvBelated - previous.ByteRecvBelated,
		ByteSendDrop:       s.Accumulated.ByteSendDrop - previous.ByteSendDrop,
		ByteRecvDrop:       s.Accumulated.ByteRecvDrop - previous.ByteRecvDrop,
		ByteRecvUndecrypt:  s.Accumulated.ByteRecvUndecrypt - previous.ByteRecvUndecrypt,
	}

	// Instantaneous
	s.Instantaneous = StatisticsInstantaneous{
		UsPktSendPeriod:       send.UsPktSndPeriod,
		PktFlowWindow:         uint64(c.config.FC),
		PktFlightSize:         send.PktFlightSize,
		MsRTT:                 c.rtt / 1000,
		MbpsSentRate:          send.MbpsEstimatedSentBandwidth,
		MbpsRecvRate:          recv.MbpsEstimatedRecvBandwidth,
		MbpsLinkCapacity:      recv.MbpsEstimatedLinkCapacity,
		ByteAvailSendBuf:      0, // unlimited
		ByteAvailRecvBuf:      0, // unlimited
		MbpsMaxBW:             float64(c.config.MaxBW) / 1024 / 1024,
		ByteMSS:               uint64(c.config.MSS),
		PktSendBuf:            send.PktBuf,
		ByteSendBuf:           send.ByteBuf,
		MsSendBuf:             send.MsBuf,
		MsSendTsbPdDelay:      c.peerTsbpdDelay / 1000,
		PktRecvBuf:            recv.PktBuf,
		ByteRecvBuf:           recv.ByteBuf,
		MsRecvBuf:             recv.MsBuf,
		MsRecvTsbPdDelay:      c.tsbpdDelay / 1000,
		PktReorderTolerance:   uint64(c.config.LossMaxTTL),
		PktRecvAvgBelatedTime: 0,
		PktSendLossRate:       send.PktLossRate,
		PktRecvLossRate:       recv.PktLossRate,
	}

	// If we're only sending, the receiver congestion control value for the link capacity is zero,
	// use the value that we got from the receiver via the ACK packets.
	if s.Instantaneous.MbpsLinkCapacity == 0 {
		s.Instantaneous.MbpsLinkCapacity = c.statistics.mbpsLinkCapacity
	}

	if c.config.MaxBW < 0 {
		s.Instantaneous.MbpsMaxBW = -1
	}

	s.MsTimeStamp = now
}