~samwhited/xmpp

xmpp/session.go -rw-r--r-- 28.7 KiB
37f589e6Sam Whited dial: simplify dialing and update docs 4 days ago
                                                                                
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
// Copyright 2016 The Mellium Contributors.
// Use of this source code is governed by the BSD 2-clause
// license that can be found in the LICENSE file.

//go:generate go run -tags=tools golang.org/x/tools/cmd/stringer -type=SessionState

package xmpp

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"net"
	"sync"
	"time"

	"mellium.im/xmlstream"
	"mellium.im/xmpp/dial"
	"mellium.im/xmpp/internal/attr"
	"mellium.im/xmpp/internal/marshal"
	"mellium.im/xmpp/internal/ns"
	intstream "mellium.im/xmpp/internal/stream"
	"mellium.im/xmpp/jid"
	"mellium.im/xmpp/stanza"
	"mellium.im/xmpp/stream"
)

// Errors returned by the XMPP package.
var (
	ErrInputStreamClosed  = errors.New("xmpp: attempted to read token from closed stream")
	ErrOutputStreamClosed = errors.New("xmpp: attempted to write token to closed stream")
)

var errNotStart = errors.New("xmpp: SendElement did not begin with a StartElement")

const (
	closeStreamTag   = `</stream:stream>`
	closeStreamWSTag = `<close xmlns="urn:ietf:params:xml:ns:xmpp-framing"/>`
)

// aLongTimeAgo is a convenient way to cancel dials.
var aLongTimeAgo = time.Unix(1, 0)

// SessionState is a bitmask that represents the current state of an XMPP
// session. For a description of each bit, see the various SessionState typed
// constants.
type SessionState uint8

const (
	// Secure indicates that the underlying connection has been secured. For
	// instance, after STARTTLS has been performed or if a pre-secured connection
	// is being used such as websockets over HTTPS.
	Secure SessionState = 1 << iota

	// Authn indicates that the session has been authenticated (probably with
	// SASL).
	Authn

	// Ready indicates that the session is fully negotiated and that XMPP stanzas
	// may be sent and received.
	Ready

	// Received indicates that the session was initiated by a foreign entity.
	Received

	// OutputStreamClosed indicates that the output stream has been closed with a
	// stream end tag.  When set all write operations will return an error even if
	// the underlying TCP connection is still open.
	OutputStreamClosed

	// InputStreamClosed indicates that the input stream has been closed with a
	// stream end tag. When set all read operations will return an error.
	InputStreamClosed

	// S2S indicates that this is a server-to-server connection.
	S2S
)

// A Session represents an XMPP session comprising an input and an output XML
// stream.
type Session struct {
	conn      net.Conn
	connState func() tls.ConnectionState

	state      SessionState
	stateMutex sync.RWMutex

	// The stream feature namespaces advertised for the current streams.
	features map[string]interface{}

	// The negotiated features (by namespace) for the current session.
	negotiated map[string]struct{}

	sentIQMutex sync.Mutex
	sentIQs     map[string]chan xmlstream.TokenReadCloser

	in struct {
		stream.Info
		d      xml.TokenReader
		ctx    context.Context
		cancel context.CancelFunc
		sync.Locker
	}
	out struct {
		stream.Info
		e interface {
			xmlstream.TokenWriter
			xmlstream.Flusher
		}
		sync.Locker
	}
}

var _ tlsConn = (*Session)(nil)

// ConnectionState returns the underlying connection's TLS state or the zero
// value if TLS has not been negotiated.
func (s *Session) ConnectionState() tls.ConnectionState {
	if s.connState == nil {
		return tls.ConnectionState{}
	}
	return s.connState()
}

// NewSession creates an XMPP session from the initiating entity's perspective
// using negotiate to manage the initial handshake.
// Calling NewSession with a nil Negotiator panics.
//
// For more information see the Negotiator type.
func NewSession(ctx context.Context, location, origin jid.JID, rw io.ReadWriter, state SessionState, negotiate Negotiator) (*Session, error) {
	return negotiateSession(ctx, location, origin, rw, state, negotiate)
}

// ReceiveSession creates an XMPP session from the receiving server's
// perspective using negotiate to manage the initial handshake.
// Calling ReceiveSession with a nil Negotiator panics.
//
// For more information see the Negotiator type.
func ReceiveSession(ctx context.Context, rw io.ReadWriter, state SessionState, negotiate Negotiator) (*Session, error) {
	return negotiateSession(ctx, jid.JID{}, jid.JID{}, rw, Received|state, negotiate)
}

func setDeadline(ctx context.Context, conn net.Conn) context.CancelFunc {
	cancelCtx, cancel := context.WithCancel(context.Background())
	go func() {
		select {
		case <-ctx.Done():
			/* #nosec */
			conn.SetDeadline(aLongTimeAgo)
			/* #nosec */
			conn.SetDeadline(time.Time{})
		case <-cancelCtx.Done():
		}
	}()
	return cancel
}

func setWriteDeadline(ctx context.Context, conn net.Conn) context.CancelFunc {
	cancelCtx, cancel := context.WithCancel(context.Background())
	go func() {
		select {
		case <-ctx.Done():
			/* #nosec */
			conn.SetWriteDeadline(aLongTimeAgo)
			/* #nosec */
			conn.SetWriteDeadline(time.Time{})
		case <-cancelCtx.Done():
		}
	}()
	return cancel
}

func negotiateSession(ctx context.Context, location, origin jid.JID, rw io.ReadWriter, state SessionState, negotiate Negotiator) (*Session, error) {
	if negotiate == nil {
		panic("xmpp: attempted to negotiate session with nil negotiator")
	}

	// If the ReadWriter is a net.Conn, respect context deadlines.
	if conn, ok := rw.(net.Conn); ok {
		defer setDeadline(ctx, conn)()
	}

	s := &Session{
		conn:       newConn(rw, nil),
		features:   make(map[string]interface{}),
		negotiated: make(map[string]struct{}),
		sentIQs:    make(map[string]chan xmlstream.TokenReadCloser),
		state:      state,
	}

	if s.state&Received == Received {
		s.in.Info.To = location
		s.in.Info.From = origin
		s.out.Info.To = origin
		s.out.Info.From = location
	} else {
		s.in.Info.To = origin
		s.in.Info.From = location
		s.out.Info.To = location
		s.out.Info.From = origin
	}

	if tc, ok := s.conn.(tlsConn); ok {
		s.connState = tc.ConnectionState
	}
	s.out.Locker = &sync.Mutex{}
	s.in.Locker = &sync.Mutex{}
	s.in.d = xml.NewDecoder(s.conn)
	s.out.e = xml.NewEncoder(s.conn)
	s.in.ctx, s.in.cancel = context.WithCancel(context.Background())

	// If rw was already a *tls.Conn, go ahead and mark the connection as secure
	// so that we don't try to negotiate StartTLS.
	if _, ok := s.conn.(*tls.Conn); ok {
		s.state |= Secure
	}

	// Call negotiate until the ready bit is set.
	var data interface{}
	for s.state&Ready == 0 {
		var mask SessionState
		var err error
		// Clear the info if the stream was restarted (but preserve to/from so that
		// we can verify that it has not changed).
		if rw != nil {
			s.in.Info = stream.Info{
				To:   s.in.Info.To,
				From: s.in.Info.From,
			}
			s.out.Info = stream.Info{
				To:   s.out.Info.To,
				From: s.out.Info.From,
			}
		}
		mask, rw, data, err = negotiate(ctx, &s.in.Info, &s.out.Info, s, data)
		if err != nil {
			return s, err
		}
		if rw != nil {
			for k := range s.features {
				delete(s.features, k)
			}
			for k := range s.negotiated {
				delete(s.negotiated, k)
			}
			s.conn = newConn(rw, s.conn)
			if tc, ok := s.conn.(tlsConn); ok {
				s.connState = tc.ConnectionState
			}
			s.in.d = xml.NewDecoder(s.conn)
			s.out.e = xml.NewEncoder(s.conn)
		}
		s.state |= mask
	}

	s.in.d = intstream.Reader(s.in.d)
	streamNS := ns.Client
	if s.state&S2S == S2S {
		streamNS = ns.Server
	}
	se := &stanzaEncoder{TokenWriteFlusher: s.out.e, ns: streamNS}
	if s.state&S2S == S2S {
		se.from = s.LocalAddr()
	}
	s.out.e = se

	return s, nil
}

// DialSession uses a default client or server dialer to create a TCP connection
// and attempts to negotiate an XMPP session over it.
func DialSession(ctx context.Context, location, origin jid.JID, state SessionState, negotiate Negotiator) (*Session, error) {
	var conn net.Conn
	var err error
	if state&S2S == S2S {
		conn, err = dial.Server(ctx, "tcp", location)
	} else {
		conn, err = dial.Client(ctx, "tcp", origin)
	}
	if err != nil {
		return nil, err
	}
	return NewSession(ctx, location, origin, conn, state, negotiate)
}

// DialClientSession uses a default dialer to create a TCP connection and
// attempts to negotiate an XMPP client-to-server session over it.
//
// If the provided context is canceled after stream negotiation is complete it
// has no effect on the session.
func DialClientSession(ctx context.Context, origin jid.JID, features ...StreamFeature) (*Session, error) {
	conn, err := dial.Client(ctx, "tcp", origin)
	if err != nil {
		return nil, err
	}
	return NewSession(ctx, origin.Domain(), origin, conn, 0, NewNegotiator(func(*Session, *StreamConfig) StreamConfig {
		return StreamConfig{
			Features: features,
		}
	}))
}

// DialServerSession uses a default dialer to create a TCP connection and
// attempts to negotiate an XMPP server-to-server session over it.
//
// If the provided context is canceled after stream negotiation is complete it
// has no effect on the session.
func DialServerSession(ctx context.Context, location, origin jid.JID, features ...StreamFeature) (*Session, error) {
	conn, err := dial.Server(ctx, "tcp", location)
	if err != nil {
		return nil, err
	}
	return NewSession(ctx, location, origin, conn, S2S, NewNegotiator(func(*Session, *StreamConfig) StreamConfig {
		return StreamConfig{
			Features: features,
		}
	}))
}

// NewClientSession attempts to use an existing connection (or any
// io.ReadWriter) to negotiate an XMPP client-to-server session from the
// initiating client's perspective.
// If the provided context is canceled before stream negotiation is complete an
// error is returned.
// After stream negotiation if the context is canceled it has no effect.
func NewClientSession(ctx context.Context, origin jid.JID, rw io.ReadWriter, features ...StreamFeature) (*Session, error) {
	return NewSession(ctx, origin.Domain(), origin, rw, 0, NewNegotiator(func(*Session, *StreamConfig) StreamConfig {
		return StreamConfig{
			Features: features,
		}
	}))
}

// ReceiveClientSession attempts to use an existing connection (or any
// io.ReadWriter) to negotiate an XMPP client-to-server session from the
// server's perspective.
// If the provided context is canceled before stream negotiation is complete an
// error is returned.
// After stream negotiation if the context is canceled it has no effect.
func ReceiveClientSession(ctx context.Context, origin jid.JID, rw io.ReadWriter, features ...StreamFeature) (*Session, error) {
	return ReceiveSession(ctx, rw, 0, NewNegotiator(func(*Session, *StreamConfig) StreamConfig {
		return StreamConfig{
			Features: features,
		}
	}))
}

// NewServerSession attempts to use an existing connection (or any
// io.ReadWriter) to negotiate an XMPP server-to-server session from the
// initiating server's perspective.
// If the provided context is canceled before stream negotiation is complete an
// error is returned.
// After stream negotiation if the context is canceled it has no effect.
func NewServerSession(ctx context.Context, location, origin jid.JID, rw io.ReadWriter, features ...StreamFeature) (*Session, error) {
	return NewSession(ctx, location, origin, rw, S2S, NewNegotiator(func(*Session, *StreamConfig) StreamConfig {
		return StreamConfig{
			Features: features,
		}
	}))
}

// ReceiveServerSession attempts to use an existing connection (or any
// io.ReadWriter) to negotiate an XMPP server-to-server session from the
// receiving server's perspective.
// If the provided context is canceled before stream negotiation is complete an
// error is returned.
// After stream negotiation if the context is canceled it has no effect.
func ReceiveServerSession(ctx context.Context, location, origin jid.JID, rw io.ReadWriter, features ...StreamFeature) (*Session, error) {
	return ReceiveSession(ctx, rw, S2S, NewNegotiator(func(*Session, *StreamConfig) StreamConfig {
		return StreamConfig{
			Features: features,
		}
	}))
}

// Serve decodes incoming XML tokens from the connection and delegates handling
// them to h.
// If an error is returned from the handler and it is of type stanza.Error or
// stream.Error, the error is marshaled and sent over the XML stream.
// If any other error type is returned, it is marshaled as an
// undefined-condition StreamError.
// If a stream error is received while serving it is not passed to the handler.
// Instead, Serve unmarshals the error, closes the session, and returns it (h
// handles stanza level errors, the session handles stream level errors).
// If serve handles an incoming IQ stanza and the handler does not write a
// response (an IQ with the same ID and type "result" or "error"), Serve writes
// an error IQ with a service-unavailable payload.
//
// If the user closes the output stream by calling Close, Serve continues until
// the input stream is closed by the remote entity as above, or the deadline set
// by SetCloseDeadline is reached in which case a timeout error is returned.
// Serve takes a lock on the input and output stream before calling the handler,
// so the handler should not close over the session or use any of its send
// methods or a deadlock will occur.
// After Serve finishes running the handler, it flushes the output stream.
func (s *Session) Serve(h Handler) (err error) {
	if h == nil {
		h = nopHandler{}
	}

	defer func() {
		s.closeInputStream()
		e := s.Close()
		if err == nil {
			err = e
		}
	}()

	for {
		select {
		case <-s.in.ctx.Done():
			return s.in.ctx.Err()
		default:
		}
		err := handleInputStream(s, h)
		switch err {
		case nil:
			// No error and no sentinal error telling us to shut down; try again!
		case io.EOF:
			return nil
		default:
			return s.sendError(err)
		}
	}
}

// sendError transmits an error on the session. If the error is not a standard
// stream error an UndefinedCondition stream error is sent.
// If an error is returned (the original error or a different one), it has not
// been handled fully and must be handled by the caller.
func (s *Session) sendError(err error) (e error) {
	s.out.Lock()
	defer s.out.Unlock()
	s.stateMutex.Lock()
	defer s.stateMutex.Unlock()

	if s.state&OutputStreamClosed == OutputStreamClosed {
		return err
	}

	se := stream.Error{}
	if errors.As(err, &se) {
		if _, e = se.WriteXML(s.out.e); e != nil {
			return e
		}
		if e = s.closeSession(); e != nil {
			return e
		}
		return err
	}

	// TODO: What should we do here? RFC 6120 §4.9.3.21. undefined-condition
	// says:
	//
	//     The error condition is not one of those defined by the other
	//     conditions in this list; this error condition SHOULD NOT be used
	//     except in conjunction with an application-specific condition.
	if _, e = stream.UndefinedCondition.WriteXML(s.out.e); e != nil {
		return e
	}
	if e = s.closeSession(); e != nil {
		return e
	}
	return err
}

type nopHandler struct{}

func (nopHandler) HandleXMPP(xmlstream.TokenReadEncoder, *xml.StartElement) error {
	return nil
}

type iqResponder struct {
	r xml.TokenReader
	c chan xmlstream.TokenReadCloser
}

func (r iqResponder) Token() (xml.Token, error) {
	return r.r.Token()
}

func (r iqResponder) Close() error {
	close(r.c)
	return nil
}

func handleInputStream(s *Session, handler Handler) (err error) {
	discard := xmlstream.Discard()
	rc := s.TokenReader()
	defer rc.Close()
	r := intstream.Reader(rc)

	tok, err := r.Token()
	if err != nil {
		return err
	}

	var start xml.StartElement
	switch t := tok.(type) {
	case xml.StartElement:
		start = t
	case xml.CharData:
		if len(bytes.TrimLeft(t, " \t\r\n")) != 0 {
			// Whitespace is allowed, but anything else at the top of the stream is
			// disallowed.
			return errors.New("xmpp: unexpected stream-level chardata")
		}
		return nil
	default:
		// If this isn't a start element or a whitespace keepalive, the stream is in
		// a bad state.
		return fmt.Errorf("xmpp: stream in a bad state, expected start element or whitespace but got %T", tok)
	}

	// If this is a stanza, normalize the "from" attribute.
	if stanza.Is(start.Name) {
		for i, attr := range start.Attr {
			if attr.Name.Local == "from" /*&& attr.Name.Space == start.Name.Space*/ {
				local := s.LocalAddr().Bare().String()
				// Try a direct comparison first to avoid expensive JID parsing.
				// TODO: really we should be parsing the JID here in case the server
				// is using a different version of PRECIS, stringprep, etc. and the
				// canonical representation isn't the same.
				if attr.Value == local {
					start.Attr[i].Value = ""
				}
				break
			}
		}
	}

	iqOk := isIQ(start.Name)
	_, _, id, typ := getIDTyp(start.Attr)

	if typ == string(stanza.ResultIQ) || typ == "error" {
		s.sentIQMutex.Lock()
		c := s.sentIQs[id]
		s.sentIQMutex.Unlock()
		if c != nil {
			inner := xmlstream.Inner(r)
			c <- iqResponder{
				r: xmlstream.Wrap(inner, start),
				c: c,
			}
			<-c
			// Consume the rest of the stream before continuing the loop.
			_, err = xmlstream.Copy(discard, inner)
			if err != nil {
				return err
			}
			return nil
		}
	}

	w := s.TokenWriter()
	defer w.Close()
	rw := &responseChecker{
		TokenReader: xmlstream.MultiReader(xmlstream.Inner(r), xmlstream.Token(start.End())),
		TokenWriter: w,
		id:          id,
	}
	if err := handler.HandleXMPP(rw, &start); err != nil {
		return err
	}

	iqNeedsResp := typ == string(stanza.GetIQ) || typ == string(stanza.SetIQ)
	// If the user did not write a response to an IQ, send a default one.
	if iqOk && iqNeedsResp && !rw.wroteResp {
		_, toAttr := attr.Get(start.Attr, "to")
		var to jid.JID
		if toAttr != "" {
			to, err = jid.Parse(toAttr)
			if err != nil {
				return err
			}
		}
		_, err := xmlstream.Copy(w, stanza.IQ{
			ID:   id,
			Type: stanza.ErrorIQ,
			To:   to,
		}.Wrap(stanza.Error{
			Type:      stanza.Cancel,
			Condition: stanza.ServiceUnavailable,
		}.TokenReader()))
		if err != nil {
			return err
		}
	}

	if err := w.Flush(); err != nil {
		return err
	}

	// Advance to the end of the current element before attempting to read the
	// next.
	_, err = xmlstream.Copy(discard, rw)
	return err
}

func getIDTyp(attrs []xml.Attr) (int, int, string, string) {
	var id, typ string
	idIdx := -1
	typIdx := -1
	for idx, attr := range attrs {
		switch attr.Name.Local {
		case "id":
			id = attr.Value
			idIdx = idx
		case "type":
			typ = attr.Value
			typIdx = idx
		}
		if idIdx > -1 && typIdx > -1 {
			break
		}
	}
	return idIdx, typIdx, id, typ
}

type responseChecker struct {
	xml.TokenReader
	xmlstream.TokenWriter
	id        string
	wroteResp bool
	level     int
}

func (rw *responseChecker) EncodeToken(t xml.Token) error {
	switch tok := t.(type) {
	case xml.StartElement:
		_, _, id, typ := getIDTyp(tok.Attr)
		if rw.level < 1 && isIQEmptySpace(tok.Name) && id == rw.id && (typ != string(stanza.GetIQ) && typ != string(stanza.SetIQ)) {
			rw.wroteResp = true
		}
		rw.level++
	case xml.EndElement:
		rw.level--
	}

	return rw.TokenWriter.EncodeToken(t)
}

func (rw *responseChecker) Encode(v interface{}) error {
	return marshal.EncodeXML(rw, v)
}

func (rw *responseChecker) EncodeElement(v interface{}, start xml.StartElement) error {
	return marshal.EncodeXMLElement(rw, v, start)
}

// Feature checks if a feature with the given namespace was advertised
// by the server for the current stream. If it was data will be the canonical
// representation of the feature as returned by the feature's Parse function.
func (s *Session) Feature(namespace string) (data interface{}, ok bool) {
	data, ok = s.features[namespace]
	return data, ok
}

// Conn returns the Session's backing connection.
//
// This should almost never be read from or written to, but is useful during
// stream negotiation for wrapping the existing connection in a new layer (eg.
// compression or TLS).
func (s *Session) Conn() net.Conn {
	return s.conn
}

type lockWriteCloser struct {
	w   *Session
	err error
	m   sync.Locker
}

func (lwc *lockWriteCloser) EncodeToken(t xml.Token) error {
	if lwc.err != nil {
		return lwc.err
	}

	lwc.w.stateMutex.RLock()
	if lwc.w.state&OutputStreamClosed == OutputStreamClosed {
		lwc.w.stateMutex.RUnlock()
		return ErrOutputStreamClosed
	}
	lwc.w.stateMutex.RUnlock()

	return lwc.w.out.e.EncodeToken(t)
}

func (lwc *lockWriteCloser) Flush() error {
	if lwc.err != nil {
		return nil
	}
	lwc.w.stateMutex.RLock()
	if lwc.w.state&OutputStreamClosed == OutputStreamClosed {
		lwc.w.stateMutex.RUnlock()
		return ErrOutputStreamClosed
	}
	lwc.w.stateMutex.RUnlock()
	return lwc.w.out.e.Flush()
}

func (lwc *lockWriteCloser) Close() error {
	if lwc.err != nil {
		return nil
	}
	defer lwc.m.Unlock()
	if err := lwc.Flush(); err != nil {
		lwc.err = err
		return err
	}
	lwc.err = io.EOF
	return nil
}

type lockReadCloser struct {
	s   *Session
	err error
	m   sync.Locker
}

func (lrc *lockReadCloser) Token() (xml.Token, error) {
	if lrc.err != nil {
		return nil, lrc.err
	}

	lrc.s.stateMutex.RLock()
	if lrc.s.state&InputStreamClosed == InputStreamClosed {
		lrc.s.stateMutex.RUnlock()
		return nil, ErrInputStreamClosed
	}
	lrc.s.stateMutex.RUnlock()

	return lrc.s.in.d.Token()
}

func (lrc *lockReadCloser) Close() error {
	if lrc.err != nil {
		return nil
	}
	lrc.err = io.EOF
	lrc.m.Unlock()
	return nil
}

// TokenWriter returns a new xmlstream.TokenWriteCloser that can be used to
// write raw XML tokens to the session.
// All other writes and future calls to TokenWriter will block until the Close
// method is called.
// After the TokenWriteCloser has been closed, any future writes will return
// io.EOF.
func (s *Session) TokenWriter() xmlstream.TokenWriteFlushCloser {
	s.out.Lock()

	return &lockWriteCloser{
		m: s.out.Locker,
		w: s,
	}
}

// TokenReader returns a new xmlstream.TokenReadCloser that can be used to read
// raw XML tokens from the session.
// All other reads and future calls to TokenReader will block until the Close
// method is called.
// After the TokenReadCloser has been closed, any future reads will return
// io.EOF.
func (s *Session) TokenReader() xmlstream.TokenReadCloser {
	s.in.Lock()

	return &lockReadCloser{
		m: s.in.Locker,
		s: s,
	}
}

// Close ends the output stream (by sending a closing </stream:stream> token).
// It does not close the underlying connection.
// Calling Close() multiple times will only result in one closing
// </stream:stream> being sent.
func (s *Session) Close() error {
	s.out.Lock()
	defer s.out.Unlock()
	s.stateMutex.Lock()
	defer s.stateMutex.Unlock()

	return s.closeSession()
}

func (s *Session) closeSession() error {
	if s.state&OutputStreamClosed == OutputStreamClosed {
		return nil
	}

	s.state |= OutputStreamClosed
	// We wrote the opening stream instead of encoding it, so do the same with the
	// closing to ensure that the encoder doesn't think the tokens are mismatched.
	var err error
	switch xmlns := s.out.Info.Name.Space; xmlns {
	case ns.WS:
		_, err = s.Conn().Write([]byte(closeStreamWSTag))
	default:
		// case stream.NS:
		_, err = s.Conn().Write([]byte(closeStreamTag))
	}
	return err
}

// State returns the current state of the session. For more information, see the
// SessionState type.
func (s *Session) State() SessionState {
	s.stateMutex.RLock()
	defer s.stateMutex.RUnlock()
	return s.state
}

// InSID returns the stream ID for the input stream.
func (s *Session) InSID() string {
	return s.in.ID
}

// OutSID returns the stream ID for the output stream.
func (s *Session) OutSID() string {
	return s.out.ID
}

// LocalAddr returns the Origin address for initiated connections, or the
// Location for received connections.
func (s *Session) LocalAddr() jid.JID {
	return s.in.Info.To
}

// RemoteAddr returns the Location address for initiated connections, or the
// Origin address for received connections.
func (s *Session) RemoteAddr() jid.JID {
	return s.in.Info.From
}

// SetCloseDeadline sets a deadline for the input stream to be closed by the
// other side.
// If the input stream is not closed by the deadline, the input stream is marked
// as closed and any blocking calls to Serve will return an error.
// This is normally called just before a call to Close.
func (s *Session) SetCloseDeadline(t time.Time) error {
	oldCancel := s.in.cancel
	s.in.ctx, s.in.cancel = context.WithDeadline(context.Background(), t)
	if oldCancel != nil {
		oldCancel()
	}
	return s.Conn().SetReadDeadline(t)
}

// Encode writes the XML encoding of v to the stream.
//
// For more information see "encoding/xml".Encode.
func (s *Session) Encode(ctx context.Context, v interface{}) error {
	s.out.Lock()
	defer s.out.Unlock()

	defer setWriteDeadline(ctx, s.conn)()
	return marshal.EncodeXML(s.out.e, v)
}

// EncodeElement writes the XML encoding of v to the stream, using start as the
// outermost tag in the encoding.
//
// For more information see "encoding/xml".EncodeElement.
func (s *Session) EncodeElement(ctx context.Context, v interface{}, start xml.StartElement) error {
	s.out.Lock()
	defer s.out.Unlock()

	defer setWriteDeadline(ctx, s.conn)()
	return marshal.EncodeXMLElement(s.out.e, v, start)
}

// Send transmits the first element read from the provided token reader.
//
// Send is safe for concurrent use by multiple goroutines.
func (s *Session) Send(ctx context.Context, r xml.TokenReader) error {
	return send(ctx, s, r, nil)
}

// SendElement is like Send except that it uses start as the outermost tag in
// the encoding and uses the entire token stream as the payload.
//
// SendElement is safe for concurrent use by multiple goroutines.
func (s *Session) SendElement(ctx context.Context, r xml.TokenReader, start xml.StartElement) error {
	return send(ctx, s, r, &start)
}

func send(ctx context.Context, s *Session, r xml.TokenReader, start *xml.StartElement) error {
	s.out.Lock()
	defer s.out.Unlock()

	defer setWriteDeadline(ctx, s.conn)()

	if start == nil {
		tok, err := r.Token()
		if err != nil {
			return err
		}

		el, ok := tok.(xml.StartElement)
		if !ok {
			return errNotStart
		}
		start = &el
		r = xmlstream.Inner(r)
	}

	err := s.out.e.EncodeToken(*start)
	if err != nil {
		return err
	}
	_, err = xmlstream.Copy(s.out.e, r)
	if err != nil {
		return err
	}
	err = s.out.e.EncodeToken(start.End())
	if err != nil {
		return err
	}
	return s.out.e.Flush()
}

func isIQ(name xml.Name) bool {
	return name.Local == "iq" && (name.Space == ns.Client || name.Space == ns.Server)
}

func isIQEmptySpace(name xml.Name) bool {
	return name.Local == "iq" && (name.Space == "" || name.Space == ns.Client || name.Space == ns.Server)
}

func isStanzaEmptySpace(name xml.Name) bool {
	return (name.Local == "iq" || name.Local == "message" || name.Local == "presence") &&
		(name.Space == ns.Client || name.Space == ns.Server || name.Space == "")
}

func (s *Session) sendResp(ctx context.Context, id string, payload xml.TokenReader, start xml.StartElement) (xmlstream.TokenReadCloser, error) {
	c := make(chan xmlstream.TokenReadCloser)

	s.sentIQMutex.Lock()
	s.sentIQs[id] = c
	s.sentIQMutex.Unlock()
	defer func() {
		s.sentIQMutex.Lock()
		delete(s.sentIQs, id)
		s.sentIQMutex.Unlock()
	}()

	err := s.SendElement(ctx, payload, start)
	if err != nil {
		return nil, err
	}

	select {
	case rr := <-c:
		return rr, nil
	case <-ctx.Done():
		close(c)
		return nil, ctx.Err()
	}
}

// closeInputStream immediately marks the input stream as closed and cancels any
// deadlines associated with it.
func (s *Session) closeInputStream() {
	s.in.Lock()
	defer s.in.Unlock()
	s.stateMutex.Lock()
	defer s.stateMutex.Unlock()
	s.state |= InputStreamClosed
	s.in.cancel()
}

type stanzaEncoder struct {
	xmlstream.TokenWriteFlusher
	depth int
	from  jid.JID
	ns    string
}

func (se *stanzaEncoder) EncodeToken(t xml.Token) error {
	switch tok := t.(type) {
	case xml.StartElement:
		se.depth++
		// Add required attributes if missing:
		if se.depth == 1 && isStanzaEmptySpace(tok.Name) {
			if tok.Name.Space == "" {
				tok.Name.Space = se.ns
			}
			var foundID, foundFrom bool
			attrs := tok.Attr[:0]
			for _, attr := range tok.Attr {
				switch attr.Name.Local {
				case "id":
					// RFC6120 § 8.1.3
					// For <message/> and <presence/> stanzas, it is RECOMMENDED for the
					// originating entity to include an 'id' attribute; for <iq/> stanzas,
					// it is REQUIRED.
					if attr.Value == "" {
						continue
					}
					foundID = true
				case "from":
					// RFC6120 § 4.7.1
					// the 'to' and 'from' attributes are OPTIONAL on stanzas sent over
					// XML streams qualified by the 'jabber:client' namespace, whereas
					// they are REQUIRED on stanzas sent over XML streams qualified by the
					// 'jabber: server' namespace
					if attr.Value == "" {
						continue
					}
					foundFrom = true
				}
				attrs = append(attrs, attr)
			}
			tok.Attr = attrs
			if f := se.from.String(); f != "" && !foundFrom {
				tok.Attr = append(tok.Attr, xml.Attr{
					Name:  xml.Name{Local: "from"},
					Value: se.from.String(),
				})
			}
			if !foundID {
				tok.Attr = append(tok.Attr, xml.Attr{
					Name:  xml.Name{Local: "id"},
					Value: attr.RandomID(),
				})
			}
		}

		// For all start elements, regardless of depth, prevent duplicate xmlns
		// attributes. See https://mellium.im/issue/75
		attrs := tok.Attr[:0]
		for _, attr := range tok.Attr {
			if attr.Name.Local == "xmlns" && tok.Name.Space != "" {
				continue
			}
			attrs = append(attrs, attr)
		}
		tok.Attr = attrs
		t = tok
	case xml.EndElement:
		if se.depth == 1 && tok.Name.Space == "" && isStanzaEmptySpace(tok.Name) {
			tok.Name.Space = se.ns
			t = tok
		}
		se.depth--
	}

	return se.TokenWriteFlusher.EncodeToken(t)
}