cloudflared-mirror/datagramsession/session.go

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package datagramsession
import (
"context"
"fmt"
"io"
"time"
"github.com/google/uuid"
"github.com/rs/zerolog"
)
const (
defaultCloseIdleAfter = time.Second * 210
)
func SessionIdleErr(timeout time.Duration) error {
return fmt.Errorf("session idle for %v", timeout)
}
// Session is a bidirectional pipe of datagrams between transport and dstConn
// Currently the only implementation of transport is quic DatagramMuxer
// Destination can be a connection with origin or with eyeball
// When the destination is origin:
// - Datagrams from edge are read by Manager from the transport. Manager finds the corresponding Session and calls the
// write method of the Session to send to origin
// - Datagrams from origin are read from conn and SentTo transport. Transport will return them to eyeball
// When the destination is eyeball:
// - Datagrams from eyeball are read from conn and SentTo transport. Transport will send them to cloudflared
// - Datagrams from cloudflared are read by Manager from the transport. Manager finds the corresponding Session and calls the
// write method of the Session to send to eyeball
type Session struct {
ID uuid.UUID
transport transport
dstConn io.ReadWriteCloser
// activeAtChan is used to communicate the last read/write time
activeAtChan chan time.Time
closeChan chan error
log *zerolog.Logger
}
func newSession(id uuid.UUID, transport transport, dstConn io.ReadWriteCloser, log *zerolog.Logger) *Session {
return &Session{
ID: id,
transport: transport,
dstConn: dstConn,
// activeAtChan has low capacity. It can be full when there are many concurrent read/write. markActive() will
// drop instead of blocking because last active time only needs to be an approximation
activeAtChan: make(chan time.Time, 2),
// capacity is 2 because close() and dstToTransport routine in Serve() can write to this channel
closeChan: make(chan error, 2),
log: log,
}
}
func (s *Session) Serve(ctx context.Context, closeAfterIdle time.Duration) (closedByRemote bool, err error) {
go func() {
// QUIC implementation copies data to another buffer before returning https://github.com/lucas-clemente/quic-go/blob/v0.24.0/session.go#L1967-L1975
// This makes it safe to share readBuffer between iterations
const maxPacketSize = 1500
readBuffer := make([]byte, maxPacketSize)
for {
if err := s.dstToTransport(readBuffer); err != nil {
s.closeChan <- err
return
}
}
}()
err = s.waitForCloseCondition(ctx, closeAfterIdle)
if closeSession, ok := err.(*errClosedSession); ok {
closedByRemote = closeSession.byRemote
}
return closedByRemote, err
}
func (s *Session) waitForCloseCondition(ctx context.Context, closeAfterIdle time.Duration) error {
// Closing dstConn cancels read so dstToTransport routine in Serve() can return
defer s.dstConn.Close()
if closeAfterIdle == 0 {
// provide deafult is caller doesn't specify one
closeAfterIdle = defaultCloseIdleAfter
}
checkIdleFreq := closeAfterIdle / 8
checkIdleTicker := time.NewTicker(checkIdleFreq)
defer checkIdleTicker.Stop()
activeAt := time.Now()
for {
select {
case <-ctx.Done():
return ctx.Err()
case reason := <-s.closeChan:
return reason
2021-12-13 13:35:40 +00:00
// TODO: TUN-5423 evaluate if using atomic is more efficient
case now := <-checkIdleTicker.C:
// The session is considered inactive if current time is after (last active time + allowed idle time)
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if now.After(activeAt.Add(closeAfterIdle)) {
return SessionIdleErr(closeAfterIdle)
}
case activeAt = <-s.activeAtChan: // Update last active time
}
}
}
func (s *Session) dstToTransport(buffer []byte) error {
n, err := s.dstConn.Read(buffer)
s.markActive()
// https://pkg.go.dev/io#Reader suggests caller should always process n > 0 bytes
if n > 0 {
if n <= int(s.transport.MTU()) {
err = s.transport.SendTo(s.ID, buffer[:n])
} else {
// drop packet for now, eventually reply with ICMP for PMTUD
s.log.Debug().
Str("session", s.ID.String()).
Int("len", n).
Int("mtu", s.transport.MTU()).
Msg("dropped packet exceeding MTU")
}
}
// Some UDP application might send 0-size payload.
if err == nil && n == 0 {
err = s.transport.SendTo(s.ID, []byte{})
}
return err
}
func (s *Session) transportToDst(payload []byte) (int, error) {
s.markActive()
return s.dstConn.Write(payload)
}
// Sends the last active time to the idle checker loop without blocking. activeAtChan will only be full when there
// are many concurrent read/write. It is fine to lose some precision
func (s *Session) markActive() {
select {
case s.activeAtChan <- time.Now():
default:
}
}
func (s *Session) close(err *errClosedSession) {
s.closeChan <- err
}