// Copyright 2016 The Netstack Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package stack

import (
	"sync"
	"time"

	"github.com/google/netstack/tcpip"
	"github.com/google/netstack/tcpip/buffer"
	"github.com/google/netstack/waiter"
)

// NetworkEndpointID is the identifier of a network layer protocol endpoint.
// Currently the local address is sufficient because all supported protocols
// (i.e., IPv4 and IPv6) have different sizes for their addresses.
type NetworkEndpointID struct {
	LocalAddress tcpip.Address
}

// TransportEndpointID is the identifier of a transport layer protocol endpoint.
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
}

// TransportEndpoint is the interface that needs to be implemented by transport
// protocol (e.g., tcp, udp) endpoints that can handle packets.
type TransportEndpoint interface {
	// HandlePacket is called by the stack when new packets arrive to
	// this transport endpoint.
	HandlePacket(r *Route, id TransportEndpointID, vv *buffer.VectorisedView)
}

// TransportProtocol is the interface that needs to be implemented by transport
// protocols (e.g., tcp, udp) that want to be part of the networking stack.
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)

	// 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(r *Route, id TransportEndpointID, vv *buffer.VectorisedView) 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
}

// TransportDispatcher contains the methods used by the network stack to deliver
// packets to the appropriate transport endpoint after it has been handled by
// the network layer.
type TransportDispatcher interface {
	// DeliverTransportPacket delivers the packets to the appropriate
	// transport protocol endpoint.
	DeliverTransportPacket(r *Route, protocol tcpip.TransportProtocolNumber, vv *buffer.VectorisedView)
}

// NetworkEndpoint is the interface that needs to be implemented by endpoints
// of network layer protocols (e.g., ipv4, ipv6).
type NetworkEndpoint interface {
	// Default TTL 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

	// 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.
	WritePacket(r *Route, hdr *buffer.Prependable, payload buffer.View, protocol tcpip.TransportProtocolNumber, ttl uint8) *tcpip.Error

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

	// 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.
	HandlePacket(r *Route, vv *buffer.VectorisedView)

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

// NetworkProtocol is the interface that needs to be implemented by network
// protocols (e.g., ipv4, ipv6) that want to be part of the networking stack.
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

	// 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, addr tcpip.Address, 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
}

// NetworkDispatcher contains the methods used by the network stack to deliver
// packets to the appropriate network endpoint after it has been handled by
// the data link layer.
type NetworkDispatcher interface {
	// DeliverNetworkPacket finds the appropriate network protocol
	// endpoint and hands the packet over for further processing.
	DeliverNetworkPacket(linkEP LinkEndpoint, remoteLinkAddr tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, vv *buffer.VectorisedView)
}

// LinkEndpoint is the interface implemented by data link layer protocols (e.g.,
// ethernet, loopback, raw) and used by network layer protocols to send packets
// out through the implementer's data link endpoint.
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

	// 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.
	WritePacket(r *Route, hdr *buffer.Prependable, payload buffer.View, protocol tcpip.NetworkProtocolNumber) *tcpip.Error

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

// A LinkAddressResolver is an extension to a NetworkProtocol that
// can resolve link addresses.
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

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

// A LinkAddressCache caches link addresses.
type LinkAddressCache interface {
	// CheckLocalAddress determines if the given local address exists, and if it
	// does, returns the id of the NIC it's bound to. Returns 0 if the address
	// does not exist.
	CheckLocalAddress(nicid tcpip.NICID, addr tcpip.Address) tcpip.NICID

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

	GetLinkAddress(nicid tcpip.NICID, addr tcpip.Address, timeout time.Duration) tcpip.LinkAddress
}

// TransportProtocolFactory functions are used by the stack to instantiate
// transport protocols.
type TransportProtocolFactory func() TransportProtocol

// NetworkProtocolFactory provides methods to be used by the stack to
// instantiate network protocols.
type NetworkProtocolFactory func() NetworkProtocol

var (
	transportProtocols = make(map[string]TransportProtocolFactory)
	networkProtocols   = make(map[string]NetworkProtocolFactory)

	linkEPMu           sync.RWMutex
	nextLinkEndpointID tcpip.LinkEndpointID = 1
	linkEndpoints                           = make(map[tcpip.LinkEndpointID]LinkEndpoint)
)

// RegisterTransportProtocolFactory registers a new transport protocol factory
// with the stack so that it becomes available to users of the stack. This
// function is intended to be called by init() functions of the protocols.
func RegisterTransportProtocolFactory(name string, p TransportProtocolFactory) {
	transportProtocols[name] = p
}

// RegisterNetworkProtocolFactory registers a new network protocol factory with
// the stack so that it becomes available to users of the stack. This function
// is intended to be called by init() functions of the protocols.
func RegisterNetworkProtocolFactory(name string, p NetworkProtocolFactory) {
	networkProtocols[name] = p
}

// RegisterLinkEndpoint register a link-layer protocol endpoint and returns an
// ID that can be used to refer to it.
func RegisterLinkEndpoint(linkEP LinkEndpoint) tcpip.LinkEndpointID {
	linkEPMu.Lock()
	defer linkEPMu.Unlock()

	v := nextLinkEndpointID
	nextLinkEndpointID++

	linkEndpoints[v] = linkEP

	return v
}

// FindLinkEndpoint finds the link endpoint associated with the given ID.
func FindLinkEndpoint(id tcpip.LinkEndpointID) LinkEndpoint {
	linkEPMu.RLock()
	defer linkEPMu.RUnlock()

	return linkEndpoints[id]
}