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session.go
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session.go
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package sockjs
import (
"encoding/gob"
"errors"
"io"
"net/http"
"sync"
"time"
)
type sessionState uint32
const (
// brand new session, need to send "h" to receiver
sessionOpening sessionState = iota
// active session
sessionActive
// session being closed, sending "closeFrame" to receivers
sessionClosing
// closed session, no activity at all, should be removed from handler completely and not reused
sessionClosed
)
var (
// ErrSessionNotOpen error is used to denote session not in open state.
// Recv() and Send() operations are not suppored if session is closed.
ErrSessionNotOpen = errors.New("sockjs: session not in open state")
errSessionReceiverAttached = errors.New("sockjs: another receiver already attached")
)
type session struct {
sync.Mutex
id string
req *http.Request
state sessionState
// protocol dependent receiver (xhr, eventsource, ...)
recv receiver
// messages to be sent to client
sendBuffer []string
// messages received from client to be consumed by application
// receivedBuffer chan string
msgReader *io.PipeReader
msgWriter *io.PipeWriter
msgEncoder *gob.Encoder
msgDecoder *gob.Decoder
// closeFrame to send after session is closed
closeFrame string
// internal timer used to handle session expiration if no receiver is attached, or heartbeats if recevier is attached
sessionTimeoutInterval time.Duration
heartbeatInterval time.Duration
timer *time.Timer
// once the session timeouts this channel also closes
closeCh chan struct{}
}
type receiver interface {
// sendBulk send multiple data messages in frame frame in format: a["msg 1", "msg 2", ....]
sendBulk(...string)
// sendFrame sends given frame over the wire (with possible chunking depending on receiver)
sendFrame(string)
// close closes the receiver in a "done" way (idempotent)
close()
canSend() bool
// done notification channel gets closed whenever receiver ends
doneNotify() <-chan struct{}
// interrupted channel gets closed whenever receiver is interrupted (i.e. http connection drops,...)
interruptedNotify() <-chan struct{}
}
// Session is a central component that handles receiving and sending frames. It maintains internal state
func newSession(req *http.Request, sessionID string, sessionTimeoutInterval, heartbeatInterval time.Duration) *session {
r, w := io.Pipe()
s := &session{
id: sessionID,
req: req,
msgReader: r,
msgWriter: w,
msgEncoder: gob.NewEncoder(w),
msgDecoder: gob.NewDecoder(r),
sessionTimeoutInterval: sessionTimeoutInterval,
heartbeatInterval: heartbeatInterval,
closeCh: make(chan struct{})}
s.Lock() // "go test -race" complains if ommited, not sure why as no race can happen here
s.timer = time.AfterFunc(sessionTimeoutInterval, s.close)
s.Unlock()
return s
}
func (s *session) sendMessage(msg string) error {
s.Lock()
defer s.Unlock()
if s.state > sessionActive {
return ErrSessionNotOpen
}
s.sendBuffer = append(s.sendBuffer, msg)
if s.recv != nil && s.recv.canSend() {
s.recv.sendBulk(s.sendBuffer...)
s.sendBuffer = nil
}
return nil
}
func (s *session) attachReceiver(recv receiver) error {
s.Lock()
defer s.Unlock()
if s.recv != nil {
return errSessionReceiverAttached
}
s.recv = recv
go func(r receiver) {
select {
case <-r.doneNotify():
s.detachReceiver()
case <-r.interruptedNotify():
s.detachReceiver()
s.close()
}
}(recv)
if s.state == sessionClosing {
s.recv.sendFrame(s.closeFrame)
s.recv.close()
return nil
}
if s.state == sessionOpening {
s.recv.sendFrame("o")
s.state = sessionActive
}
s.recv.sendBulk(s.sendBuffer...)
s.sendBuffer = nil
s.timer.Stop()
s.timer = time.AfterFunc(s.heartbeatInterval, s.heartbeat)
return nil
}
func (s *session) detachReceiver() {
s.Lock()
defer s.Unlock()
s.timer.Stop()
s.timer = time.AfterFunc(s.sessionTimeoutInterval, s.close)
s.recv = nil
}
func (s *session) heartbeat() {
s.Lock()
defer s.Unlock()
if s.recv != nil { // timer could have fired between Lock and timer.Stop in detachReceiver
s.recv.sendFrame("h")
s.timer = time.AfterFunc(s.heartbeatInterval, s.heartbeat)
}
}
func (s *session) accept(messages ...string) error {
for _, msg := range messages {
if err := s.msgEncoder.Encode(msg); err != nil {
return err
}
}
return nil
}
// idempotent operation
func (s *session) closing() {
s.Lock()
defer s.Unlock()
if s.state < sessionClosing {
s.msgReader.Close()
s.msgWriter.Close()
s.state = sessionClosing
if s.recv != nil {
s.recv.sendFrame(s.closeFrame)
s.recv.close()
}
}
}
// idempotent operation
func (s *session) close() {
s.closing()
s.Lock()
defer s.Unlock()
if s.state < sessionClosed {
s.state = sessionClosed
s.timer.Stop()
close(s.closeCh)
}
}
func (s *session) closedNotify() <-chan struct{} { return s.closeCh }
// Conn interface implementation
func (s *session) Close(status uint32, reason string) error {
s.Lock()
if s.state < sessionClosing {
s.closeFrame = closeFrame(status, reason)
s.Unlock()
s.closing()
return nil
}
s.Unlock()
return ErrSessionNotOpen
}
func (s *session) Recv() (string, error) {
var msg string
err := s.msgDecoder.Decode(&msg)
if err == io.ErrClosedPipe {
err = ErrSessionNotOpen
}
return msg, err
}
func (s *session) Send(msg string) error {
return s.sendMessage(msg)
}
func (s *session) ID() string { return s.id }
func (s *session) Request() *http.Request {
return s.req
}