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package datagramsession
import (
"context"
"io"
"time"
"github.com/google/uuid"
)
const (
defaultCloseIdleAfter = time.Second * 210
)
// Each 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
doneChan chan struct{}
}
func newSession(id uuid.UUID, transport transport, dstConn io.ReadWriteCloser) *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),
doneChan: make(chan struct{}),
}
}
func (s *Session) Serve(ctx context.Context, closeAfterIdle time.Duration) error {
serveCtx, cancel := context.WithCancel(ctx)
defer cancel()
go s.waitForCloseCondition(serveCtx, closeAfterIdle)
// 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
readBuffer := make([]byte, s.transport.MTU())
for {
if err := s.dstToTransport(readBuffer); err != nil {
return err
}
}
}
func (s *Session) waitForCloseCondition(ctx context.Context, closeAfterIdle time.Duration) {
if closeAfterIdle == 0 {
// provide deafult is caller doesn't specify one
closeAfterIdle = defaultCloseIdleAfter
}
// Closing dstConn cancels read so Serve function can return
defer s.dstConn.Close()
checkIdleFreq := closeAfterIdle / 8
checkIdleTicker := time.NewTicker(checkIdleFreq)
defer checkIdleTicker.Stop()
activeAt := time.Now()
for {
select {
case <-ctx.Done():
return
case <-s.doneChan:
return
// 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)
if now.After(activeAt.Add(closeAfterIdle)) {
return
}
case activeAt = <-s.activeAtChan: // Update last active time
}
}
}
func (s *Session) dstToTransport(buffer []byte) error {
n, err := s.dstConn.Read(buffer)
s.markActive()
if n > 0 {
if err := s.transport.SendTo(s.id, buffer[:n]); err != nil {
return err
}
}
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() {
close(s.doneChan)
}