udp_mux.go

package ice

import (
	"errors"
	"io"
	"net"
	"os"
	"strings"
	"sync"

	"github.com/pion/logging"
	"github.com/pion/stun"
)

// UDPMux allows multiple connections to go over a single UDP port
type UDPMux interface {
	io.Closer
	GetConn(ufrag string, isIPv6 bool) (net.PacketConn, error)
	RemoveConnByUfrag(ufrag string)
}

// UDPMuxDefault is an implementation of the interface
type UDPMuxDefault struct {
	params UDPMuxParams

	closedChan chan struct{}
	closeOnce  sync.Once

	// connsIPv4 and connsIPv6 are maps of all udpMuxedConn indexed by ufrag|network|candidateType
	connsIPv4, connsIPv6 map[string]*udpMuxedConn

	addressMapMu sync.RWMutex
	addressMap   map[string][]*udpMuxedConn

	// buffer pool to recycle buffers for net.UDPAddr encodes/decodes
	pool *sync.Pool

	mu sync.Mutex
}

const maxAddrSize = 512

// UDPMuxParams are parameters for UDPMux.
type UDPMuxParams struct {
	Logger  logging.LeveledLogger
	UDPConn net.PacketConn
}

// NewUDPMuxDefault creates an implementation of UDPMux
func NewUDPMuxDefault(params UDPMuxParams) *UDPMuxDefault {
	if params.Logger == nil {
		params.Logger = logging.NewDefaultLoggerFactory().NewLogger("ice")
	}

	m := &UDPMuxDefault{
		addressMap: map[string][]*udpMuxedConn{},
		params:     params,
		connsIPv4:  make(map[string]*udpMuxedConn),
		connsIPv6:  make(map[string]*udpMuxedConn),
		closedChan: make(chan struct{}, 1),
		pool: &sync.Pool{
			New: func() interface{} {
				// big enough buffer to fit both packet and address
				return newBufferHolder(receiveMTU + maxAddrSize)
			},
		},
	}

	go m.connWorker()

	return m
}

// LocalAddr returns the listening address of this UDPMuxDefault
func (m *UDPMuxDefault) LocalAddr() net.Addr {
	return m.params.UDPConn.LocalAddr()
}

// GetConn returns a PacketConn given the connection's ufrag and network
// creates the connection if an existing one can't be found
func (m *UDPMuxDefault) GetConn(ufrag string, isIPv6 bool) (net.PacketConn, error) {
	m.mu.Lock()
	defer m.mu.Unlock()

	if m.IsClosed() {
		return nil, io.ErrClosedPipe
	}

	if conn, ok := m.getConn(ufrag, isIPv6); ok {
		return conn, nil
	}

	c := m.createMuxedConn(ufrag)
	go func() {
		<-c.CloseChannel()
		m.RemoveConnByUfrag(ufrag)
	}()

	if isIPv6 {
		m.connsIPv6[ufrag] = c
	} else {
		m.connsIPv4[ufrag] = c
	}

	return c, nil
}

// RemoveConnByUfrag stops and removes the muxed packet connection
func (m *UDPMuxDefault) RemoveConnByUfrag(ufrag string) {
	removedConns := make([]*udpMuxedConn, 0, 2)

	// Keep lock section small to avoid deadlock with conn lock
	m.mu.Lock()
	if c, ok := m.connsIPv4[ufrag]; ok {
		delete(m.connsIPv4, ufrag)
		removedConns = append(removedConns, c)
	}
	if c, ok := m.connsIPv6[ufrag]; ok {
		delete(m.connsIPv6, ufrag)
		removedConns = append(removedConns, c)
	}
	m.mu.Unlock()

	if len(removedConns) == 0 {
		// No need to lock if no connection was found
		return
	}

	m.addressMapMu.Lock()
	defer m.addressMapMu.Unlock()

	for _, c := range removedConns {
		addresses := c.getAddresses()
		for _, addr := range addresses {
			if connList, ok := m.addressMap[addr]; ok {
				var newList []*udpMuxedConn
				for _, conn := range connList {
					if conn.params.Key != ufrag {
						newList = append(newList, conn)
					}
				}
				m.addressMap[addr] = newList
			}
		}
	}
}

// IsClosed returns true if the mux had been closed
func (m *UDPMuxDefault) IsClosed() bool {
	select {
	case <-m.closedChan:
		return true
	default:
		return false
	}
}

// Close the mux, no further connections could be created
func (m *UDPMuxDefault) Close() error {
	var err error
	m.closeOnce.Do(func() {
		m.mu.Lock()
		defer m.mu.Unlock()

		for _, c := range m.connsIPv4 {
			_ = c.Close()
		}
		for _, c := range m.connsIPv6 {
			_ = c.Close()
		}

		m.connsIPv4 = make(map[string]*udpMuxedConn)
		m.connsIPv6 = make(map[string]*udpMuxedConn)

		close(m.closedChan)
	})
	return err
}

func (m *UDPMuxDefault) writeTo(buf []byte, raddr net.Addr) (n int, err error) {
	return m.params.UDPConn.WriteTo(buf, raddr)
}

func (m *UDPMuxDefault) registerConnForAddress(conn *udpMuxedConn, addr string) {
	if m.IsClosed() {
		return
	}

	m.addressMapMu.Lock()
	defer m.addressMapMu.Unlock()

	existing, ok := m.addressMap[addr]
	if !ok {
		existing = []*udpMuxedConn{}
	}
	existing = append(existing, conn)
	m.addressMap[addr] = existing

	m.params.Logger.Debugf("Registered %s for %s", addr, conn.params.Key)
}

func (m *UDPMuxDefault) createMuxedConn(key string) *udpMuxedConn {
	c := newUDPMuxedConn(&udpMuxedConnParams{
		Mux:       m,
		Key:       key,
		AddrPool:  m.pool,
		LocalAddr: m.LocalAddr(),
		Logger:    m.params.Logger,
	})
	return c
}

func (m *UDPMuxDefault) connWorker() {
	logger := m.params.Logger

	defer func() {
		_ = m.Close()
	}()

	buf := make([]byte, receiveMTU)
	for {
		n, addr, err := m.params.UDPConn.ReadFrom(buf)
		if m.IsClosed() {
			return
		} else if err != nil {
			if os.IsTimeout(err) {
				continue
			} else if !errors.Is(err, io.EOF) {
				logger.Errorf("could not read udp packet: %v", err)
			}

			return
		}

		udpAddr, ok := addr.(*net.UDPAddr)
		if !ok {
			logger.Errorf("underlying PacketConn did not return a UDPAddr")
			return
		}

		// If we have already seen this address, dispatch to the possible destinations.
		// If you are using the same socket for the Host and SRFLX candidates,
		// there might be more than one muxed connection for the same remote endpoint
		// (UDPMuxDefault registerConnForAddress() has been called twice or more).
		// We will then forward STUN packets to each of these connections.
		m.addressMapMu.Lock()
		var destinationConnList []*udpMuxedConn
		// copy the list
		if connList, ok := m.addressMap[addr.String()]; ok {
			for _, conn := range connList {
				destinationConnList = append(destinationConnList, conn)
			}
		}
		m.addressMapMu.Unlock()

		// We need the following block to discover Peer Reflexive Candidates for which we don't know the Endpoint upfront.
		// However, we can take a username attribute from the STUN message, which contains ufrag.
		// We can use ufrag to identify the destination conn to route the packet.
		if stun.IsMessage(buf[:n]) {
			msg := &stun.Message{
				Raw: append([]byte{}, buf[:n]...),
			}

			if err = msg.Decode(); err != nil {
				m.params.Logger.Warnf("Failed to handle decode ICE from %s: %v", addr.String(), err)
				continue
			}

			attr, stunAttrErr := msg.Get(stun.AttrUsername)
			if stunAttrErr != nil {
				m.params.Logger.Warnf("No Username attribute in STUN message from %s", addr.String())
				continue
			}

			ufrag := strings.Split(string(attr), ":")[0]
			isIPv6 := udpAddr.IP.To4() == nil

			m.mu.Lock()
			if destinationConn, ok := m.getConn(ufrag, isIPv6); ok {
				// check if the ufrag conn is already in the destination list (probably won't ever happen).
				exists := false
				for _, conn := range destinationConnList {
					if conn.params.Key == destinationConn.params.Key {
						exists = true
						break
					}
				}
				if !exists {
					destinationConnList = append(destinationConnList, destinationConn)
				}
			}
			m.mu.Unlock()
		}

		if len(destinationConnList) == 0 {
			m.params.Logger.Tracef("dropping packet from %s, addr: %s", udpAddr.String(), addr.String())
			continue
		}

		// Forward STUN packets to each destination connections even thought the STUN packet might not belong there.
		// It will be discarded by the further ICE candidate logic if so.
		for _, conn := range destinationConnList {
			if err = conn.writePacket(buf[:n], udpAddr); err != nil {
				m.params.Logger.Errorf("could not write packet: %v", err)
			}
		}
	}
}

func (m *UDPMuxDefault) getConn(ufrag string, isIPv6 bool) (val *udpMuxedConn, ok bool) {
	if isIPv6 {
		val, ok = m.connsIPv6[ufrag]
	} else {
		val, ok = m.connsIPv4[ufrag]
	}
	return
}

type bufferHolder struct {
	buffer []byte
}

func newBufferHolder(size int) *bufferHolder {
	return &bufferHolder{
		buffer: make([]byte, size),
	}
}