stack

type ControlType int

type DirectionStats struct {
	Packets *tcpip.StatCounter
	Bytes   *tcpip.StatCounter
}

type GSO struct {
	// Type is one of GSONone, GSOTCPv4, etc.
	Type GSOType
	// NeedsCsum is set if the checksum offload is enabled.
	NeedsCsum bool
	// CsumOffset is offset after that to place checksum.
	CsumOffset uint16

	// Mss is maximum segment size.
	MSS uint16
	// L3Len is L3 (IP) header length.
	L3HdrLen uint16

	// MaxSize is maximum GSO packet size.
	MaxSize uint32
}

type GSOEndpoint interface {
	// GSOMaxSize returns the maximum GSO packet size.
	GSOMaxSize() uint32
}

type GSOType int

type ICMPRateLimiter struct {
	*rate.Limiter
}

type InjectableLinkEndpoint interface {
	LinkEndpoint

	// InjectInbound injects an inbound packet.
	InjectInbound(protocol tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer)

	// InjectOutbound writes a fully formed outbound packet directly to the
	// link.
	//
	// dest is used by endpoints with multiple raw destinations.
	InjectOutbound(dest tcpip.Address, packet []byte) *tcpip.Error
}

type LinkAddressCache interface {
	// CheckLocalAddress determines if the given local address exists, and if it
	// does not exist.
	CheckLocalAddress(nicID tcpip.NICID, protocol tcpip.NetworkProtocolNumber, addr tcpip.Address) tcpip.NICID

	// AddLinkAddress adds a link address to the cache.
	AddLinkAddress(nicID tcpip.NICID, addr tcpip.Address, linkAddr tcpip.LinkAddress)

	// GetLinkAddress looks up the cache to translate address to link address (e.g. IP -> MAC).
	// If the LinkEndpoint requests address resolution and there is a LinkAddressResolver
	// registered with the network protocol, the cache attempts to resolve the address
	// and returns ErrWouldBlock. Waker is notified when address resolution is
	// complete (success or not).
	//
	// If address resolution is required, ErrNoLinkAddress and a notification channel is
	// returned for the top level caller to block. Channel is closed once address resolution
	// is complete (success or not).
	GetLinkAddress(nicID tcpip.NICID, addr, localAddr tcpip.Address, protocol tcpip.NetworkProtocolNumber, w *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error)

	// RemoveWaker removes a waker that has been added in GetLinkAddress().
	RemoveWaker(nicID tcpip.NICID, addr tcpip.Address, waker *sleep.Waker)
}

type LinkAddressResolver interface {
	// LinkAddressRequest sends a request for the LinkAddress of addr.
	// The request is sent on linkEP with localAddr as the source.
	//
	// A valid response will cause the discovery protocol's network
	// endpoint to call AddLinkAddress.
	LinkAddressRequest(addr, localAddr tcpip.Address, linkEP LinkEndpoint) *tcpip.Error

	// ResolveStaticAddress attempts to resolve address without sending
	// requests. It either resolves the name immediately or returns the
	// empty LinkAddress.
	//
	// It can be used to resolve broadcast addresses for example.
	ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool)

	// LinkAddressProtocol returns the network protocol of the
	// addresses this this resolver can resolve.
	LinkAddressProtocol() tcpip.NetworkProtocolNumber
}

type LinkEndpoint interface {
	// MTU is the maximum transmission unit for this endpoint. This is
	// usually dictated by the backing physical network; when such a
	// physical network doesn't exist, the limit is generally 64k, which
	// includes the maximum size of an IP packet.
	MTU() uint32

	// Capabilities returns the set of capabilities supported by the
	// endpoint.
	Capabilities() LinkEndpointCapabilities

	// MaxHeaderLength returns the maximum size the data link (and
	// lower level layers combined) headers can have. Higher levels use this
	// information to reserve space in the front of the packets they're
	// building.
	MaxHeaderLength() uint16

	// LinkAddress returns the link address (typically a MAC) of the
	// link endpoint.
	LinkAddress() tcpip.LinkAddress

	// WritePacket writes a packet with the given protocol through the
	// given route. It sets pkt.LinkHeader if a link layer header exists.
	// pkt.NetworkHeader and pkt.TransportHeader must have already been
	// set.
	//
	// To participate in transparent bridging, a LinkEndpoint implementation
	// should call eth.Encode with header.EthernetFields.SrcAddr set to
	// r.LocalLinkAddress if it is provided.
	WritePacket(r *Route, gso *GSO, protocol tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer) *tcpip.Error

	// WritePackets writes packets with the given protocol through the
	// given route.
	//
	// Right now, WritePackets is used only when the software segmentation
	// offload is enabled. If it will be used for something else, it may
	// require to change syscall filters.
	WritePackets(r *Route, gso *GSO, hdrs []PacketDescriptor, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error)

	// WriteRawPacket writes a packet directly to the link. The packet
	// should already have an ethernet header.
	WriteRawPacket(vv buffer.VectorisedView) *tcpip.Error

	// Attach attaches the data link layer endpoint to the network-layer
	// dispatcher of the stack.
	Attach(dispatcher NetworkDispatcher)

	// IsAttached returns whether a NetworkDispatcher is attached to the
	// endpoint.
	IsAttached() bool

	// Wait waits for any worker goroutines owned by the endpoint to stop.
	//
	// For now, requesting that an endpoint's worker goroutine(s) stop is
	// implementation specific.
	//
	// Wait will not block if the endpoint hasn't started any goroutines
	// yet, even if it might later.
	Wait()
}

type LinkEndpointCapabilities uint

type NDPConfigurations struct {
	// The number of Neighbor Solicitation messages to send when doing
	// Duplicate Address Detection for a tentative address.
	//
	// Note, a value of zero effectively disables DAD.
	DupAddrDetectTransmits uint8

	// The amount of time to wait between sending Neighbor solicitation
	// messages.
	//
	// Must be greater than 0.5s.
	RetransmitTimer time.Duration

	// HandleRAs determines whether or not Router Advertisements will be
	// processed.
	HandleRAs bool

	// DiscoverDefaultRouters determines whether or not default routers will
	// be discovered from Router Advertisements. This configuration is
	// ignored if HandleRAs is false.
	DiscoverDefaultRouters bool

	// DiscoverOnLinkPrefixes determines whether or not on-link prefixes
	// will be discovered from Router Advertisements' Prefix Information
	// option. This configuration is ignored if HandleRAs is false.
	DiscoverOnLinkPrefixes bool
}

type NDPDispatcher interface {
	// OnDuplicateAddressDetectionStatus will be called when the DAD process
	// for an address (addr) on a NIC (with ID nicID) completes. resolved
	// will be set to true if DAD completed successfully (no duplicate addr
	// detected); false otherwise (addr was detected to be a duplicate on
	// the link the NIC is a part of, or it was stopped for some other
	// reason, such as the address being removed). If an error occured
	// during DAD, err will be set and resolved must be ignored.
	//
	// This function is permitted to block indefinitely without interfering
	// with the stack's operation.
	OnDuplicateAddressDetectionStatus(nicID tcpip.NICID, addr tcpip.Address, resolved bool, err *tcpip.Error)

	// OnDefaultRouterDiscovered will be called when a new default router is
	// discovered. Implementations must return true along with a new valid
	// route table if the newly discovered router should be remembered. If
	// an implementation returns false, the second return value will be
	// ignored.
	//
	// This function is not permitted to block indefinitely. This function
	// is also not permitted to call into the stack.
	OnDefaultRouterDiscovered(nicID tcpip.NICID, addr tcpip.Address) (bool, []tcpip.Route)

	// OnDefaultRouterInvalidated will be called when a discovered default
	// router is invalidated. Implementers must return a new valid route
	// table.
	//
	// This function is not permitted to block indefinitely. This function
	// is also not permitted to call into the stack.
	OnDefaultRouterInvalidated(nicID tcpip.NICID, addr tcpip.Address) []tcpip.Route

	// OnOnLinkPrefixDiscovered will be called when a new on-link prefix is
	// discovered. Implementations must return true along with a new valid
	// route table if the newly discovered on-link prefix should be
	// remembered. If an implementation returns false, the second return
	// value will be ignored.
	//
	// This function is not permitted to block indefinitely. This function
	// is also not permitted to call into the stack.
	OnOnLinkPrefixDiscovered(nicID tcpip.NICID, prefix tcpip.Subnet) (bool, []tcpip.Route)

	// OnOnLinkPrefixInvalidated will be called when a discovered on-link
	// prefix is invalidated. Implementers must return a new valid route
	// table.
	//
	// This function is not permitted to block indefinitely. This function
	// is also not permitted to call into the stack.
	OnOnLinkPrefixInvalidated(nicID tcpip.NICID, prefix tcpip.Subnet) []tcpip.Route
}

type NIC struct {
	// contains filtered or unexported fields
}

type NICInfo struct {
	Name              string
	LinkAddress       tcpip.LinkAddress
	ProtocolAddresses []tcpip.ProtocolAddress

	// Flags indicate the state of the NIC.
	Flags NICStateFlags

	// MTU is the maximum transmission unit.
	MTU uint32

	Stats NICStats
}

type NICStateFlags struct {
	// Up indicates whether the interface is running.
	Up bool

	// Running indicates whether resources are allocated.
	Running bool

	// Promiscuous indicates whether the interface is in promiscuous mode.
	Promiscuous bool

	// Loopback indicates whether the interface is a loopback.
	Loopback bool
}

type NICStats struct {
	Tx DirectionStats
	Rx DirectionStats
}

type NetworkDispatcher interface {
	// DeliverNetworkPacket finds the appropriate network protocol endpoint
	// and hands the packet over for further processing.
	//
	// pkt.LinkHeader may or may not be set before calling
	// DeliverNetworkPacket. Some packets do not have link headers (e.g.
	// packets sent via loopback), and won't have the field set.
	//
	// DeliverNetworkPacket takes ownership of pkt.
	DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer)
}

type NetworkEndpoint interface {
	// DefaultTTL is the default time-to-live value (or hop limit, in ipv6)
	// for this endpoint.
	DefaultTTL() uint8

	// MTU is the maximum transmission unit for this endpoint. This is
	// generally calculated as the MTU of the underlying data link endpoint
	// minus the network endpoint max header length.
	MTU() uint32

	// Capabilities returns the set of capabilities supported by the
	// underlying link-layer endpoint.
	Capabilities() LinkEndpointCapabilities

	// MaxHeaderLength returns the maximum size the network (and lower
	// level layers combined) headers can have. Higher levels use this
	// information to reserve space in the front of the packets they're
	// building.
	MaxHeaderLength() uint16

	// WritePacket writes a packet to the given destination address and
	// protocol. It sets pkt.NetworkHeader. pkt.TransportHeader must have
	// already been set.
	WritePacket(r *Route, gso *GSO, params NetworkHeaderParams, loop PacketLooping, pkt tcpip.PacketBuffer) *tcpip.Error

	// WritePackets writes packets to the given destination address and
	// protocol.
	WritePackets(r *Route, gso *GSO, hdrs []PacketDescriptor, payload buffer.VectorisedView, params NetworkHeaderParams, loop PacketLooping) (int, *tcpip.Error)

	// WriteHeaderIncludedPacket writes a packet that includes a network
	// header to the given destination address.
	WriteHeaderIncludedPacket(r *Route, loop PacketLooping, pkt tcpip.PacketBuffer) *tcpip.Error

	// ID returns the network protocol endpoint ID.
	ID() *NetworkEndpointID

	// PrefixLen returns the network endpoint's subnet prefix length in bits.
	PrefixLen() int

	// NICID returns the id of the NIC this endpoint belongs to.
	NICID() tcpip.NICID

	// HandlePacket is called by the link layer when new packets arrive to
	// this network endpoint. It sets pkt.NetworkHeader.
	//
	// HandlePacket takes ownership of pkt.
	HandlePacket(r *Route, pkt tcpip.PacketBuffer)

	// Close is called when the endpoint is reomved from a stack.
	Close()
}

type NetworkEndpointID struct {
	LocalAddress tcpip.Address
}

type NetworkHeaderParams struct {
	// Protocol refers to the transport protocol number.
	Protocol tcpip.TransportProtocolNumber

	// TTL refers to Time To Live field of the IP-header.
	TTL uint8

	// TOS refers to TypeOfService or TrafficClass field of the IP-header.
	TOS uint8
}

type NetworkProtocol interface {
	// Number returns the network protocol number.
	Number() tcpip.NetworkProtocolNumber

	// MinimumPacketSize returns the minimum valid packet size of this
	// network protocol. The stack automatically drops any packets smaller
	// than this targeted at this protocol.
	MinimumPacketSize() int

	// DefaultPrefixLen returns the protocol's default prefix length.
	DefaultPrefixLen() int

	// ParsePorts returns the source and destination addresses stored in a
	// packet of this protocol.
	ParseAddresses(v buffer.View) (src, dst tcpip.Address)

	// NewEndpoint creates a new endpoint of this protocol.
	NewEndpoint(nicID tcpip.NICID, addrWithPrefix tcpip.AddressWithPrefix, linkAddrCache LinkAddressCache, dispatcher TransportDispatcher, sender LinkEndpoint) (NetworkEndpoint, *tcpip.Error)

	// SetOption allows enabling/disabling protocol specific features.
	// SetOption returns an error if the option is not supported or the
	// provided option value is invalid.
	SetOption(option interface{}) *tcpip.Error

	// Option allows retrieving protocol specific option values.
	// Option returns an error if the option is not supported or the
	// provided option value is invalid.
	Option(option interface{}) *tcpip.Error
}

type Options struct {
	// NetworkProtocols lists the network protocols to enable.
	NetworkProtocols []NetworkProtocol

	// TransportProtocols lists the transport protocols to enable.
	TransportProtocols []TransportProtocol

	// Clock is an optional clock source used for timestampping packets.
	//
	// If no Clock is specified, the clock source will be time.Now.
	Clock tcpip.Clock

	// Stats are optional statistic counters.
	Stats tcpip.Stats

	// HandleLocal indicates whether packets destined to their source
	// should be handled by the stack internally (true) or outside the
	// stack (false).
	HandleLocal bool

	// UniqueID is an optional generator of unique identifiers.
	UniqueID UniqueID

	// NDPConfigs is the default NDP configurations used by interfaces.
	//
	// By default, NDPConfigs will have a zero value for its
	// DupAddrDetectTransmits field, implying that DAD will not be performed
	// before assigning an address to a NIC.
	NDPConfigs NDPConfigurations

	// AutoGenIPv6LinkLocal determins whether or not the stack will attempt
	// to auto-generate an IPv6 link-local address for newly enabled NICs.
	// Note, setting this to true does not mean that a link-local address
	// will be assigned right away, or at all. If Duplicate Address
	// Detection is enabled, an address will only be assigned if it
	// successfully resolves. If it fails, no further attempt will be made
	// to auto-generate an IPv6 link-local address.
	//
	// The generated link-local address will follow RFC 4291 Appendix A
	// guidelines.
	AutoGenIPv6LinkLocal bool

	// NDPDisp is the NDP event dispatcher that an integrator can provide to
	// receive NDP related events.
	NDPDisp NDPDispatcher

	// RawFactory produces raw endpoints. Raw endpoints are enabled only if
	// this is non-nil.
	RawFactory RawFactory
}

type PacketDescriptor struct {
	Hdr  buffer.Prependable
	Off  int
	Size int
}

type PacketEndpoint interface {
	// HandlePacket is called by the stack when new packets arrive that
	// match the endpoint.
	//
	// Implementers should treat packet as immutable and should copy it
	// before before modification.
	//
	// linkHeader may have a length of 0, in which case the PacketEndpoint
	// should construct its own ethernet header for applications.
	//
	// HandlePacket takes ownership of pkt.
	HandlePacket(nicID tcpip.NICID, addr tcpip.LinkAddress, netProto tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer)
}

type PacketLooping byte

type PrimaryEndpointBehavior int

type RawFactory interface {
	// NewUnassociatedEndpoint produces endpoints for writing packets not
	// associated with a particular transport protocol. Such endpoints can
	// be used to write arbitrary packets that include the network header.
	NewUnassociatedEndpoint(stack *Stack, netProto tcpip.NetworkProtocolNumber, transProto tcpip.TransportProtocolNumber, waiterQueue *waiter.Queue) (tcpip.Endpoint, *tcpip.Error)

	// NewPacketEndpoint produces endpoints for reading and writing packets
	// that include network and (when cooked is false) link layer headers.
	NewPacketEndpoint(stack *Stack, cooked bool, netProto tcpip.NetworkProtocolNumber, waiterQueue *waiter.Queue) (tcpip.Endpoint, *tcpip.Error)
}

type RawTransportEndpoint interface {
	// HandlePacket is called by the stack when new packets arrive to
	// this transport endpoint. The packet contains all data from the link
	// layer up.
	//
	// HandlePacket takes ownership of pkt.
	HandlePacket(r *Route, pkt tcpip.PacketBuffer)
}

type RcvBufAutoTuneParams struct {
	// MeasureTime is the time at which the current measurement
	// was started.
	MeasureTime time.Time

	// CopiedBytes is the number of bytes copied to user space since
	// this measure began.
	CopiedBytes int

	// PrevCopiedBytes is the number of bytes copied to user space in
	// the previous RTT period.
	PrevCopiedBytes int

	// RcvBufSize is the auto tuned receive buffer size.
	RcvBufSize int

	// RTT is the smoothed RTT as measured by observing the time between
	// when a byte is first acknowledged and the receipt of data that is at
	// least one window beyond the sequence number that was acknowledged.
	RTT time.Duration

	// RTTVar is the "round-trip time variation" as defined in section 2
	// of RFC6298.
	RTTVar time.Duration

	// RTTMeasureSeqNumber is the highest acceptable sequence number at the
	// time this RTT measurement period began.
	RTTMeasureSeqNumber seqnum.Value

	// RTTMeasureTime is the absolute time at which the current RTT
	// measurement period began.
	RTTMeasureTime time.Time

	// Disabled is true if an explicit receive buffer is set for the
	// endpoint.
	Disabled bool
}

type ResumableEndpoint interface {
	// Resume resumes an endpoint after restore. This can be used to restart
	// background workers such as protocol goroutines. This must be called after
	// all indirect dependencies of the endpoint has been restored, which
	// generally implies at the end of the restore process.
	Resume(*Stack)
}

type Route struct {
	// RemoteAddress is the final destination of the route.
	RemoteAddress tcpip.Address

	// RemoteLinkAddress is the link-layer (MAC) address of the
	// final destination of the route.
	RemoteLinkAddress tcpip.LinkAddress

	// LocalAddress is the local address where the route starts.
	LocalAddress tcpip.Address

	// LocalLinkAddress is the link-layer (MAC) address of the
	// where the route starts.
	LocalLinkAddress tcpip.LinkAddress

	// NextHop is the next node in the path to the destination.
	NextHop tcpip.Address

	// NetProto is the network-layer protocol.
	NetProto tcpip.NetworkProtocolNumber

	// Loop controls where WritePacket should send packets.
	Loop PacketLooping
	// contains filtered or unexported fields
}

type Stack struct {
	*ports.PortManager
	// contains filtered or unexported fields
}

type TCPCubicState struct {
	WLastMax                float64
	WMax                    float64
	T                       time.Time
	TimeSinceLastCongestion time.Duration
	C                       float64
	K                       float64
	Beta                    float64
	WC                      float64
	WEst                    float64
}

type TCPEndpointID struct {
	// LocalPort is the local port associated with the endpoint.
	LocalPort uint16

	// LocalAddress is the local [network layer] address associated with
	// the endpoint.
	LocalAddress tcpip.Address

	// RemotePort is the remote port associated with the endpoint.
	RemotePort uint16

	// RemoteAddress it the remote [network layer] address associated with
	// the endpoint.
	RemoteAddress tcpip.Address
}

type TCPEndpointState struct {
	// ID is a copy of the TransportEndpointID for the endpoint.
	ID TCPEndpointID

	// SegTime denotes the absolute time when this segment was received.
	SegTime time.Time

	// RcvBufSize is the size of the receive socket buffer for the endpoint.
	RcvBufSize int

	// RcvBufUsed is the amount of bytes actually held in the receive socket
	// buffer for the endpoint.
	RcvBufUsed int

	// RcvBufAutoTuneParams is used to hold state variables to compute
	// the auto tuned receive buffer size.
	RcvAutoParams RcvBufAutoTuneParams

	// RcvClosed if true, indicates the endpoint has been closed for reading.
	RcvClosed bool

	// SendTSOk is used to indicate when the TS Option has been negotiated.
	// When sendTSOk is true every non-RST segment should carry a TS as per
	// RFC7323#section-1.1.
	SendTSOk bool

	// RecentTS is the timestamp that should be sent in the TSEcr field of
	// the timestamp for future segments sent by the endpoint. This field is
	// updated if required when a new segment is received by this endpoint.
	RecentTS uint32

	// TSOffset is a randomized offset added to the value of the TSVal field
	// in the timestamp option.
	TSOffset uint32

	// SACKPermitted is set to true if the peer sends the TCPSACKPermitted
	// option in the SYN/SYN-ACK.
	SACKPermitted bool

	// SACK holds TCP SACK related information for this endpoint.
	SACK TCPSACKInfo

	// SndBufSize is the size of the socket send buffer.
	SndBufSize int

	// SndBufUsed is the number of bytes held in the socket send buffer.
	SndBufUsed int

	// SndClosed indicates that the endpoint has been closed for sends.
	SndClosed bool

	// SndBufInQueue is the number of bytes in the send queue.
	SndBufInQueue seqnum.Size

	// PacketTooBigCount is used to notify the main protocol routine how
	// many times a "packet too big" control packet is received.
	PacketTooBigCount int

	// SndMTU is the smallest MTU seen in the control packets received.
	SndMTU int

	// Receiver holds variables related to the TCP receiver for the endpoint.
	Receiver TCPReceiverState

	// Sender holds state related to the TCP Sender for the endpoint.
	Sender TCPSenderState
}

type TCPFastRecoveryState struct {
	// Active if true indicates the endpoint is in fast recovery.
	Active bool

	// First is the first unacknowledged sequence number being recovered.
	First seqnum.Value

	// Last is the 'recover' sequence number that indicates the point at
	// which we should exit recovery barring any timeouts etc.
	Last seqnum.Value

	// MaxCwnd is the maximum value we are permitted to grow the congestion
	// window during recovery. This is set at the time we enter recovery.
	MaxCwnd int

	// HighRxt is the highest sequence number which has been retransmitted
	// during the current loss recovery phase.
	// See: RFC 6675 Section 2 for details.
	HighRxt seqnum.Value

	// RescueRxt is the highest sequence number which has been
	// optimistically retransmitted to prevent stalling of the ACK clock
	// when there is loss at the end of the window and no new data is
	// available for transmission.
	// See: RFC 6675 Section 2 for details.
	RescueRxt seqnum.Value
}

type TCPProbeFunc func(s TCPEndpointState)

type TCPReceiverState struct {
	// RcvNxt is the TCP variable RCV.NXT.
	RcvNxt seqnum.Value

	// RcvAcc is the TCP variable RCV.ACC.
	RcvAcc seqnum.Value

	// RcvWndScale is the window scaling to use for inbound segments.
	RcvWndScale uint8

	// PendingBufUsed is the number of bytes pending in the receive
	// queue.
	PendingBufUsed seqnum.Size

	// PendingBufSize is the size of the socket receive buffer.
	PendingBufSize seqnum.Size
}

type TCPSACKInfo struct {
	// Blocks is the list of SACK Blocks that identify the out of order segments
	// held by a given TCP endpoint.
	Blocks []header.SACKBlock

	// ReceivedBlocks are the SACK blocks received by this endpoint
	// from the peer endpoint.
	ReceivedBlocks []header.SACKBlock

	// MaxSACKED is the highest sequence number that has been SACKED
	// by the peer.
	MaxSACKED seqnum.Value
}

type TCPSenderState struct {
	// LastSendTime is the time at which we sent the last segment.
	LastSendTime time.Time

	// DupAckCount is the number of Duplicate ACK's received.
	DupAckCount int

	// SndCwnd is the size of the sending congestion window in packets.
	SndCwnd int

	// Ssthresh is the slow start threshold in packets.
	Ssthresh int

	// SndCAAckCount is the number of packets consumed in congestion
	// avoidance mode.
	SndCAAckCount int

	// Outstanding is the number of packets in flight.
	Outstanding int

	// SndWnd is the send window size in bytes.
	SndWnd seqnum.Size

	// SndUna is the next unacknowledged sequence number.
	SndUna seqnum.Value

	// SndNxt is the sequence number of the next segment to be sent.
	SndNxt seqnum.Value

	// RTTMeasureSeqNum is the sequence number being used for the latest RTT
	// measurement.
	RTTMeasureSeqNum seqnum.Value

	// RTTMeasureTime is the time when the RTTMeasureSeqNum was sent.
	RTTMeasureTime time.Time

	// Closed indicates that the caller has closed the endpoint for sending.
	Closed bool

	// SRTT is the smoothed round-trip time as defined in section 2 of
	// RFC 6298.
	SRTT time.Duration

	// RTO is the retransmit timeout as defined in section of 2 of RFC 6298.
	RTO time.Duration

	// RTTVar is the round-trip time variation as defined in section 2 of
	// RFC 6298.
	RTTVar time.Duration

	// SRTTInited if true indicates take a valid RTT measurement has been
	// completed.
	SRTTInited bool

	// MaxPayloadSize is the maximum size of the payload of a given segment.
	// It is initialized on demand.
	MaxPayloadSize int

	// SndWndScale is the number of bits to shift left when reading the send
	// window size from a segment.
	SndWndScale uint8

	// MaxSentAck is the highest acknowledgement number sent till now.
	MaxSentAck seqnum.Value

	// FastRecovery holds the fast recovery state for the endpoint.
	FastRecovery TCPFastRecoveryState

	// Cubic holds the state related to CUBIC congestion control.
	Cubic TCPCubicState
}

type TransportDispatcher interface {
	// DeliverTransportPacket delivers packets to the appropriate
	// transport protocol endpoint.
	//
	// pkt.NetworkHeader must be set before calling DeliverTransportPacket.
	//
	// DeliverTransportPacket takes ownership of pkt.
	DeliverTransportPacket(r *Route, protocol tcpip.TransportProtocolNumber, pkt tcpip.PacketBuffer)

	// DeliverTransportControlPacket delivers control packets to the
	// appropriate transport protocol endpoint.
	//
	// pkt.NetworkHeader must be set before calling
	// DeliverTransportControlPacket.
	//
	// DeliverTransportControlPacket takes ownership of pkt.
	DeliverTransportControlPacket(local, remote tcpip.Address, net tcpip.NetworkProtocolNumber, trans tcpip.TransportProtocolNumber, typ ControlType, extra uint32, pkt tcpip.PacketBuffer)
}

type TransportEndpoint interface {
	// UniqueID returns an unique ID for this transport endpoint.
	UniqueID() uint64

	// HandlePacket is called by the stack when new packets arrive to
	// this transport endpoint. It sets pkt.TransportHeader.
	//
	// HandlePacket takes ownership of pkt.
	HandlePacket(r *Route, id TransportEndpointID, pkt tcpip.PacketBuffer)

	// HandleControlPacket is called by the stack when new control (e.g.
	// ICMP) packets arrive to this transport endpoint.
	// HandleControlPacket takes ownership of pkt.
	HandleControlPacket(id TransportEndpointID, typ ControlType, extra uint32, pkt tcpip.PacketBuffer)

	// Close puts the endpoint in a closed state and frees all resources
	// associated with it. This cleanup may happen asynchronously. Wait can
	// be used to block on this asynchronous cleanup.
	Close()

	// Wait waits for any worker goroutines owned by the endpoint to stop.
	//
	// An endpoint can be requested to stop its worker goroutines by calling
	// its Close method.
	//
	// Wait will not block if the endpoint hasn't started any goroutines
	// yet, even if it might later.
	Wait()
}

type TransportEndpointID struct {
	// LocalPort is the local port associated with the endpoint.
	LocalPort uint16

	// LocalAddress is the local [network layer] address associated with
	// the endpoint.
	LocalAddress tcpip.Address

	// RemotePort is the remote port associated with the endpoint.
	RemotePort uint16

	// RemoteAddress it the remote [network layer] address associated with
	// the endpoint.
	RemoteAddress tcpip.Address
}

type TransportEndpointInfo struct {
	NetProto   tcpip.NetworkProtocolNumber
	TransProto tcpip.TransportProtocolNumber

	ID TransportEndpointID
	// BindNICID and bindAddr are set via calls to Bind(). They are used to
	// reject attempts to send data or connect via a different NIC or
	// address
	BindNICID tcpip.NICID
	BindAddr  tcpip.Address
	// RegisterNICID is the default NICID registered as a side-effect of
	// connect or datagram write.
	RegisterNICID tcpip.NICID
}

type TransportProtocol interface {
	// Number returns the transport protocol number.
	Number() tcpip.TransportProtocolNumber

	// NewEndpoint creates a new endpoint of the transport protocol.
	NewEndpoint(stack *Stack, netProto tcpip.NetworkProtocolNumber, waitQueue *waiter.Queue) (tcpip.Endpoint, *tcpip.Error)

	// NewRawEndpoint creates a new raw endpoint of the transport protocol.
	NewRawEndpoint(stack *Stack, netProto tcpip.NetworkProtocolNumber, waitQueue *waiter.Queue) (tcpip.Endpoint, *tcpip.Error)

	// MinimumPacketSize returns the minimum valid packet size of this
	// transport protocol. The stack automatically drops any packets smaller
	// than this targeted at this protocol.
	MinimumPacketSize() int

	// ParsePorts returns the source and destination ports stored in a
	// packet of this protocol.
	ParsePorts(v buffer.View) (src, dst uint16, err *tcpip.Error)

	// HandleUnknownDestinationPacket handles packets targeted at this
	// protocol but that don't match any existing endpoint. For example,
	// it is targeted at a port that have no listeners.
	//
	// The return value indicates whether the packet was well-formed (for
	// stats purposes only).
	//
	// HandleUnknownDestinationPacket takes ownership of pkt.
	HandleUnknownDestinationPacket(r *Route, id TransportEndpointID, pkt tcpip.PacketBuffer) bool

	// SetOption allows enabling/disabling protocol specific features.
	// SetOption returns an error if the option is not supported or the
	// provided option value is invalid.
	SetOption(option interface{}) *tcpip.Error

	// Option allows retrieving protocol specific option values.
	// Option returns an error if the option is not supported or the
	// provided option value is invalid.
	Option(option interface{}) *tcpip.Error
}

type UniqueID interface {
	UniqueID() uint64
}