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package turn
import (
"encoding/binary"
"errors"
"net"
"time"
"github.com/pion/stun"
"github.com/pion/turn/v2/internal/proto"
)
var (
errInvalidTURNFrame = errors.New("data is not a valid TURN frame, no STUN or ChannelData found")
errIncompleteTURNFrame = errors.New("data contains incomplete STUN or TURN frame")
)
// STUNConn wraps a net.Conn and implements
// net.PacketConn by being STUN aware and
// packetizing the stream
type STUNConn struct {
nextConn net.Conn
buff []byte
}
const (
stunHeaderSize = 20
channelDataLengthSize = 2
channelDataNumberSize = channelDataLengthSize
channelDataHeaderSize = channelDataLengthSize + channelDataNumberSize
channelDataPadding = 4
)
// Given a buffer give the last offset of the TURN frame
// If the buffer isn't a valid STUN or ChannelData packet
// or the length doesn't match return false
func consumeSingleTURNFrame(p []byte) (int, error) {
// Too short to determine if ChannelData or STUN
if len(p) < 9 {
return 0, errIncompleteTURNFrame
}
var datagramSize uint16
if stun.IsMessage(p) {
datagramSize = binary.BigEndian.Uint16(p[2:4]) + stunHeaderSize
} else if num := binary.BigEndian.Uint16(p[0:4]); proto.ChannelNumber(num).Valid() {
datagramSize = binary.BigEndian.Uint16(p[channelDataNumberSize:channelDataHeaderSize])
if paddingOverflow := (datagramSize + channelDataPadding) % channelDataPadding; paddingOverflow != 0 {
datagramSize = (datagramSize + channelDataPadding) - paddingOverflow
}
datagramSize += channelDataHeaderSize
} else {
return 0, errInvalidTURNFrame
}
if len(p) < int(datagramSize) {
return 0, errIncompleteTURNFrame
}
return int(datagramSize), nil
}
// ReadFrom implements ReadFrom from net.PacketConn
func (s *STUNConn) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
// First pass any buffered data from previous reads
n, err = consumeSingleTURNFrame(s.buff)
if errors.Is(err, errInvalidTURNFrame) {
return 0, nil, err
} else if err == nil {
copy(p, s.buff[:n])
s.buff = s.buff[n:]
return n, s.nextConn.RemoteAddr(), nil
}
// Then read from the nextConn, appending to our buff
n, err = s.nextConn.Read(p)
if err != nil {
return 0, nil, err
}
s.buff = append(s.buff, append([]byte{}, p[:n]...)...)
return s.ReadFrom(p)
}
// WriteTo implements WriteTo from net.PacketConn
func (s *STUNConn) WriteTo(p []byte, addr net.Addr) (n int, err error) {
return s.nextConn.Write(p)
}
// Close implements Close from net.PacketConn
func (s *STUNConn) Close() error {
return s.nextConn.Close()
}
// LocalAddr implements LocalAddr from net.PacketConn
func (s *STUNConn) LocalAddr() net.Addr {
return s.nextConn.LocalAddr()
}
// SetDeadline implements SetDeadline from net.PacketConn
func (s *STUNConn) SetDeadline(t time.Time) error {
return s.nextConn.SetDeadline(t)
}
// SetReadDeadline implements SetReadDeadline from net.PacketConn
func (s *STUNConn) SetReadDeadline(t time.Time) error {
return s.nextConn.SetReadDeadline(t)
}
// SetWriteDeadline implements SetWriteDeadline from net.PacketConn
func (s *STUNConn) SetWriteDeadline(t time.Time) error {
return s.nextConn.SetWriteDeadline(t)
}
// NewSTUNConn creates a STUNConn
func NewSTUNConn(nextConn net.Conn) *STUNConn {
return &STUNConn{nextConn: nextConn}
}
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