cloudflared-mirror/quic/datagram.go

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package quic
import (
"context"
"fmt"
"github.com/google/uuid"
"github.com/lucas-clemente/quic-go"
"github.com/pkg/errors"
"github.com/rs/zerolog"
"github.com/cloudflare/cloudflared/packet"
)
const (
sessionIDLen = len(uuid.UUID{})
)
type BaseDatagramMuxer interface {
// SendToSession suffix the session ID to the payload so the other end of the QUIC connection can demultiplex the
// payload from multiple datagram sessions.
SendToSession(session *packet.Session) error
// ServeReceive starts a loop to receive datagrams from the QUIC connection
ServeReceive(ctx context.Context) error
}
type DatagramMuxer struct {
session quic.Connection
logger *zerolog.Logger
demuxChan chan<- *packet.Session
}
func NewDatagramMuxer(quicSession quic.Connection, log *zerolog.Logger, demuxChan chan<- *packet.Session) *DatagramMuxer {
logger := log.With().Uint8("datagramVersion", 1).Logger()
return &DatagramMuxer{
session: quicSession,
logger: &logger,
demuxChan: demuxChan,
}
}
// Maximum application payload to send to / receive from QUIC datagram frame
func (dm *DatagramMuxer) mtu() int {
return maxDatagramPayloadSize
}
func (dm *DatagramMuxer) SendToSession(session *packet.Session) error {
if len(session.Payload) > dm.mtu() {
// TODO: TUN-5302 return ICMP packet too big message
// drop packet for now, eventually reply with ICMP for PMTUD
return fmt.Errorf("origin UDP payload has %d bytes, which exceeds transport MTU %d", len(session.Payload), dm.mtu())
}
payloadWithMetadata, err := suffixSessionID(session.ID, session.Payload)
if err != nil {
return errors.Wrap(err, "Failed to suffix session ID to datagram, it will be dropped")
}
if err := dm.session.SendMessage(payloadWithMetadata); err != nil {
return errors.Wrap(err, "Failed to send datagram back to edge")
}
return nil
}
func (dm *DatagramMuxer) ServeReceive(ctx context.Context) error {
for {
// Extracts datagram session ID, then sends the session ID and payload to receiver
// which determines how to proxy to the origin. It assumes the datagram session has already been
// registered with receiver through other side channel
msg, err := dm.session.ReceiveMessage()
if err != nil {
return err
}
if err := dm.demux(ctx, msg); err != nil {
dm.logger.Error().Err(err).Msg("Failed to demux datagram")
if err == context.Canceled {
return err
}
}
}
}
func (dm *DatagramMuxer) demux(ctx context.Context, msg []byte) error {
sessionID, payload, err := extractSessionID(msg)
if err != nil {
return err
}
sessionDatagram := packet.Session{
ID: sessionID,
Payload: payload,
}
select {
case dm.demuxChan <- &sessionDatagram:
return nil
case <-ctx.Done():
return ctx.Err()
}
}
// Each QUIC datagram should be suffixed with session ID.
// extractSessionID extracts the session ID and a slice with only the payload
func extractSessionID(b []byte) (uuid.UUID, []byte, error) {
msgLen := len(b)
if msgLen < sessionIDLen {
return uuid.Nil, nil, fmt.Errorf("session ID has %d bytes, but data only has %d", sessionIDLen, len(b))
}
// Parse last 16 bytess as UUID and remove it from slice
sessionID, err := uuid.FromBytes(b[len(b)-sessionIDLen:])
if err != nil {
return uuid.Nil, nil, err
}
b = b[:len(b)-sessionIDLen]
return sessionID, b, nil
}
// SuffixSessionID appends the session ID at the end of the payload. Suffix is more performant than prefix because
// the payload slice might already have enough capacity to append the session ID at the end
func suffixSessionID(sessionID uuid.UUID, b []byte) ([]byte, error) {
if len(b)+len(sessionID) > MaxDatagramFrameSize {
return nil, fmt.Errorf("datagram size exceed %d", MaxDatagramFrameSize)
}
b = append(b, sessionID[:]...)
return b, nil
}