summaryrefslogtreecommitdiff
path: root/src/include/gnunet_mq_lib.h
blob: f3073d54bc57fdb59f2fbab36120d62ffe3e6527 (plain)
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
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
/*
     This file is part of GNUnet.
     Copyright (C) 2012-2016 GNUnet e.V.

     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     or (at your option) any later version.

     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Affero General Public License for more details.

     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
*/

/**
 * @author Florian Dold
 * @author Christian Grothoff
 *
 * @file
 * General-purpose message queue
 *
 * @defgroup mq  MQ library
 * General-purpose message queue
 *
 * @see [Documentation](https://gnunet.org/message-queue-api)
 *
 * @{
 */
#ifndef GNUNET_MQ_LIB_H
#define GNUNET_MQ_LIB_H

#include "gnunet_scheduler_lib.h"

/**
 * Allocate an envelope, with extra space allocated after the space needed
 * by the message struct.
 * The allocated message will already have the type and size field set.
 *
 * @param mvar variable to store the allocated message in;
 *             must have a header field;
 *             can be NULL
 * @param esize extra space to allocate after the message
 * @param type type of the message
 * @return the MQ message
 */
#define GNUNET_MQ_msg_extra(mvar, esize, type)                \
  GNUNET_MQ_msg_ (((struct GNUNET_MessageHeader **) &(mvar)), \
                  (esize) + sizeof *(mvar),                   \
                  (type))

/**
 * Allocate a GNUNET_MQ_Envelope.
 * The contained message will already have the type and size field set.
 *
 * @param mvar variable to store the allocated message in;
 *             must have a header field;
 *             can be NULL
 * @param type type of the message
 * @return the allocated envelope
 */
#define GNUNET_MQ_msg(mvar, type) GNUNET_MQ_msg_extra (mvar, 0, type)


/**
 * Allocate a GNUNET_MQ_Envelope, where the message only consists of a header.
 * The allocated message will already have the type and size field set.
 *
 * @param type type of the message
 */
#define GNUNET_MQ_msg_header(type) \
  GNUNET_MQ_msg_ (NULL, sizeof (struct GNUNET_MessageHeader), type)


/**
 * Allocate a GNUNET_MQ_Envelope, where the message only consists of a header and extra space.
 * The allocated message will already have the type and size field set.
 *
 * @param mh pointer that will changed to point at to the allocated message header
 * @param esize extra space to allocate after the message header
 * @param type type of the message
 */
#define GNUNET_MQ_msg_header_extra(mh, esize, type) \
  GNUNET_MQ_msg_ (&mh, (esize) + sizeof (struct GNUNET_MessageHeader), type)


/**
 * Allocate a GNUNET_MQ_Envelope, and append a payload message after the given
 * message struct.
 *
 * @param mvar pointer to a message struct, will be changed to point at the newly allocated message,
 *        whose size is 'sizeof(*mvar) + ntohs (mh->size)'
 * @param type message type of the allocated message, has no effect on the nested message
 * @param mh message to nest
 * @return a newly allocated 'struct GNUNET_MQ_Envelope *'
 */
#define GNUNET_MQ_msg_nested_mh(mvar, type, mh)                               \
  ({                                                                          \
    struct GNUNET_MQ_Envelope *_ev;                                           \
    _ev = GNUNET_MQ_msg_nested_mh_ ((struct GNUNET_MessageHeader **) &(mvar), \
                                    sizeof (*(mvar)),                         \
                                    (type),                                   \
                                    (mh));                                    \
    (void) (mvar)->header; /* type check */                                   \
    _ev;                                                                      \
  })


/**
 * Return a pointer to the message at the end of the given message.
 *
 * @param var pointer to a message struct, the type of the expression determines the base size,
 *        the space after the base size is the nested message
 * @return a 'struct GNUNET_MessageHeader *' that points at the nested message of the given message,
 *         or NULL if the given message in @a var does not have any space after the message struct
 */
#define GNUNET_MQ_extract_nested_mh(var)                               \
  GNUNET_MQ_extract_nested_mh_ ((struct GNUNET_MessageHeader *) (var), \
                                sizeof (*(var)))


/**
 * Implementation of the #GNUNET_MQ_extract_nexted_mh macro.
 *
 * @param mh message header to extract nested message header from
 * @param base_size size of the message before the nested message's header appears
 * @return pointer to the nested message, does not copy the message
 *         OR NULL in case of a malformed message.
 */
const struct GNUNET_MessageHeader *
GNUNET_MQ_extract_nested_mh_ (const struct GNUNET_MessageHeader *mh,
                              uint16_t base_size);


/**
 * Opaque handle to an envelope.
 */
struct GNUNET_MQ_Envelope;


/**
 * Obtain message contained in envelope.
 *
 * @param env the envelope
 * @return message contained in the envelope
 */
const struct GNUNET_MessageHeader *
GNUNET_MQ_env_get_msg (const struct GNUNET_MQ_Envelope *env);


/**
 * Return next envelope in queue.
 *
 * @param env a queued envelope
 * @return next one, or NULL
 */
const struct GNUNET_MQ_Envelope *
GNUNET_MQ_env_next (const struct GNUNET_MQ_Envelope *env);


/**
 * Implementation of the #GNUNET_MQ_msg_nested_mh macro.
 *
 * @param mhp pointer to the message header pointer that will be changed to allocate at
 *        the newly allocated space for the message.
 * @param base_size size of the data before the nested message
 * @param type type of the message in the envelope
 * @param nested_mh the message to append to the message after base_size
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_msg_nested_mh_ (struct GNUNET_MessageHeader **mhp,
                          uint16_t base_size,
                          uint16_t type,
                          const struct GNUNET_MessageHeader *nested_mh);


/**
 * Opaque handle to a message queue.
 */
struct GNUNET_MQ_Handle;


/**
 * Error codes for the queue.
 */
enum GNUNET_MQ_Error
{
  /**
   * Failed to read message from the network.
   * FIXME: Likely not properly distinguished
   * from TIMEOUT case in the code!
   */
  GNUNET_MQ_ERROR_READ = 1,

  /**
   * FIXME: document!
   */
  GNUNET_MQ_ERROR_WRITE = 2,

  /**
   * FIXME: document!
   */
  GNUNET_MQ_ERROR_TIMEOUT = 4,

  /**
   * We received a message that was malformed and thus
   * could not be passed to its handler.
   */
  GNUNET_MQ_ERROR_MALFORMED = 8,

  /**
   * We received a message for which we have no matching
   * handler.
   */
  GNUNET_MQ_ERROR_NO_MATCH = 16
};


/**
 * Per envelope preferences and priorities.
 */
enum GNUNET_MQ_PriorityPreferences
{

  /**
   * Lowest priority, i.e. background traffic (i.e. NSE, FS).
   * This is the default!
   */
  GNUNET_MQ_PRIO_BACKGROUND = 0,

  /**
   * Best-effort traffic (i.e. CADET relay, DHT)
   */
  GNUNET_MQ_PRIO_BEST_EFFORT = 1,

  /**
   * Urgent traffic (local peer, i.e. Conversation).
   */
  GNUNET_MQ_PRIO_URGENT = 2,

  /**
   * Highest priority, control traffic (i.e. CORE/CADET KX).
   */
  GNUNET_MQ_PRIO_CRITICAL_CONTROL = 3,

  /**
   * Bit mask to apply to extract the priority bits.
   */
  GNUNET_MQ_PRIORITY_MASK = 3,

  /**
   * Flag to indicate that unreliable delivery is acceptable.  This
   * means TRANSPORT will not attempt to receive an
   * acknowledgment. CORE will just pass this flag through.  CADET
   * will use unreliable delivery if this flag is set.
   *
   * Note that even without this flag, messages may be lost by
   * TRANSPORT and CORE.
   *
   * Thus, how "strong" the semantics of reliable delivery are depends
   * on the layer!
   */
  GNUNET_MQ_PREF_UNRELIABLE = 16,

  /**
   * Flag to indicate that low latency is important.  This flag must
   * generally not be used in combination with
   * #GNUNET_MQ_PREF_CORKING_ALLOWED as it would be a contradiction.
   * When this flags is set, the envelope may skip forward in the
   * queue (depending on priority) and also TRANSPORT should attempt
   * to pick a communicator with particularly low latency.
   */
  GNUNET_MQ_PREF_LOW_LATENCY = 32,

  /**
   * Flag to indicate that CORKing is acceptable. This allows the
   * receiver to delay transmission in hope of combining this message
   * with other messages into a larger transmission with less
   * per-message overhead.
   */
  GNUNET_MQ_PREF_CORK_ALLOWED = 64,

  /**
   * Flag to indicate that high bandwidth is desired. This flag
   * indicates that the method chosen for transmission should focus on
   * overall goodput.  It rarely makes sense to combine this flag with
   * #GNUNET_MQ_PREF_LOW_LATENCY.
   */
  GNUNET_MQ_PREF_GOODPUT = 128,

  /**
   * Flag to indicate that out-of-order delivery is OK.
   */
  GNUNET_MQ_PREF_OUT_OF_ORDER = 256,

};


/**
 * Called when a message has been received.
 *
 * @param cls closure
 * @param msg the received message
 */
typedef void (*GNUNET_MQ_MessageCallback) (
  void *cls,
  const struct GNUNET_MessageHeader *msg);


/**
 * Called when a message needs to be validated.
 *
 * @param cls closure
 * @param msg the received message
 * @return #GNUNET_OK if the message is well-formed,
 *         #GNUNET_SYSERR if not
 */
typedef int (*GNUNET_MQ_MessageValidationCallback) (
  void *cls,
  const struct GNUNET_MessageHeader *msg);


/**
 * Signature of functions implementing the
 * sending functionality of a message queue.
 *
 * @param mq the message queue
 * @param msg the message to send
 * @param impl_state state of the implementation
 */
typedef void (*GNUNET_MQ_SendImpl) (struct GNUNET_MQ_Handle *mq,
                                    const struct GNUNET_MessageHeader *msg,
                                    void *impl_state);


/**
 * Signature of functions implementing the
 * destruction of a message queue.
 * Implementations must not free @a mq, but should
 * take care of @a impl_state.
 *
 * @param mq the message queue to destroy
 * @param impl_state state of the implementation
 */
typedef void (*GNUNET_MQ_DestroyImpl) (struct GNUNET_MQ_Handle *mq,
                                       void *impl_state);


/**
 * Implementation function that cancels the currently sent message.
 *
 * @param mq message queue
 * @param impl_state state specific to the implementation
 */
typedef void (*GNUNET_MQ_CancelImpl) (struct GNUNET_MQ_Handle *mq,
                                      void *impl_state);


/**
 * Generic error handler, called with the appropriate
 * error code and the same closure specified at the creation of
 * the message queue.
 * Not every message queue implementation supports an error handler.
 *
 * @param cls closure
 * @param error error code
 */
typedef void (*GNUNET_MQ_ErrorHandler) (void *cls, enum GNUNET_MQ_Error error);


/**
 * Insert @a env into the envelope DLL starting at @a env_head
 * Note that @a env must not be in any MQ while this function
 * is used with DLLs defined outside of the MQ module.  This
 * is just in case some application needs to also manage a
 * FIFO of envelopes independent of MQ itself and wants to
 * re-use the pointers internal to @a env.  Use with caution.
 *
 * @param[in|out] env_head of envelope DLL
 * @param[in|out] env_tail tail of envelope DLL
 * @param[in|out] env element to insert at the tail
 */
void
GNUNET_MQ_dll_insert_head (struct GNUNET_MQ_Envelope **env_head,
                           struct GNUNET_MQ_Envelope **env_tail,
                           struct GNUNET_MQ_Envelope *env);


/**
 * Insert @a env into the envelope DLL starting at @a env_head
 * Note that @a env must not be in any MQ while this function
 * is used with DLLs defined outside of the MQ module.  This
 * is just in case some application needs to also manage a
 * FIFO of envelopes independent of MQ itself and wants to
 * re-use the pointers internal to @a env.  Use with caution.
 *
 * @param[in|out] env_head of envelope DLL
 * @param[in|out] env_tail tail of envelope DLL
 * @param[in|out] env element to insert at the tail
 */
void
GNUNET_MQ_dll_insert_tail (struct GNUNET_MQ_Envelope **env_head,
                           struct GNUNET_MQ_Envelope **env_tail,
                           struct GNUNET_MQ_Envelope *env);


/**
 * Remove @a env from the envelope DLL starting at @a env_head.
 * Note that @a env must not be in any MQ while this function
 * is used with DLLs defined outside of the MQ module. This
 * is just in case some application needs to also manage a
 * FIFO of envelopes independent of MQ itself and wants to
 * re-use the pointers internal to @a env.  Use with caution.
 *
 * @param[in|out] env_head of envelope DLL
 * @param[in|out] env_tail tail of envelope DLL
 * @param[in|out] env element to remove from the DLL
 */
void
GNUNET_MQ_dll_remove (struct GNUNET_MQ_Envelope **env_head,
                      struct GNUNET_MQ_Envelope **env_tail,
                      struct GNUNET_MQ_Envelope *env);


/**
 * Copy an array of handlers.
 *
 * Useful if the array has been delared in local memory and needs to be
 * persisted for future use.
 *
 * @param handlers Array of handlers to be copied.
 * @return A newly allocated array of handlers.
 *         Needs to be freed with #GNUNET_free.
 */
struct GNUNET_MQ_MessageHandler *
GNUNET_MQ_copy_handlers (const struct GNUNET_MQ_MessageHandler *handlers);


/**
 * Copy an array of handlers, appending AGPL handler.
 *
 * Useful if the array has been delared in local memory and needs to be
 * persisted for future use.
 *
 * @param handlers Array of handlers to be copied. Can be NULL (nothing done).
 * @param agpl_handler function to call for AGPL handling
 * @param agpl_cls closure for @a agpl_handler
 * @return A newly allocated array of handlers.
 *         Needs to be freed with #GNUNET_free.
 */
struct GNUNET_MQ_MessageHandler *
GNUNET_MQ_copy_handlers2 (const struct GNUNET_MQ_MessageHandler *handlers,
                          GNUNET_MQ_MessageCallback agpl_handler,
                          void *agpl_cls);


/**
 * Count the handlers in a handler array.
 *
 * @param handlers Array of handlers to be counted.
 * @return The number of handlers in the array.
 */
unsigned int
GNUNET_MQ_count_handlers (const struct GNUNET_MQ_MessageHandler *handlers);


/**
 * Message handler for a specific message type.
 */
struct GNUNET_MQ_MessageHandler
{
  /**
   * Callback to validate a message of the specified @e type.
   * The closure given to @e mv will be this struct (not @e ctx).
   * Using NULL means only size-validation using
   * @e expected_size.  In this case, @e expected_size must
   * be non-zero.
   */
  GNUNET_MQ_MessageValidationCallback mv;

  /**
   * Callback, called every time a new message of
   * the specified @e type has been receied.
   * The closure given to @e mv will be this struct (not @e ctx).
   */
  GNUNET_MQ_MessageCallback cb;

  /**
   * Closure for @e mv and @e cb.
   */
  void *cls;

  /**
   * Type of the message this handler covers, in host byte order.
   */
  uint16_t type;

  /**
   * Expected size of messages of this type.  Minimum size of the
   * message if @e mv is non-NULL.  Messages of the given type will be
   * discarded (and the connection closed with an error reported to
   * the application) if they do not have the right size.
   */
  uint16_t expected_size;
};


/**
 * End-marker for the handlers array
 */
#define GNUNET_MQ_handler_end() \
  {                             \
    NULL, NULL, NULL, 0, 0      \
  }


/**
 * Defines a static function @a name which takes as a single argument
 * a message handler for fixed-sized messages of type @a code and with
 * a message type argument of @a str.  Given such an argument, the
 * function @name will return a `struct GNUNET_MQ_MessageHandler`
 * for the given message type.
 *
 * The macro is to be used as follows:
 * <code>
 * struct GNUNET_MessageTest { ... }; // must be fixed size
 * static void
 * handle_test_message (void *cls,
 *                      const struct GNUNET_MessageTest *msg)
 * { ... }
 *
 * struct GNUNET_MQ_MessageHandler handlers[] = {
 *   GNUNET_MQ_hd_fixed_size(test_message,
 *                           GNUNET_MESSAGE_TYPE_TEST,
 *                           struct GNUNET_MessageTest,
 *                           "context"),
 *   GNUNET_MQ_handler_end()
 * };
 *
 * @param name unique basename for the functions
 * @param code message type constant
 * @param str type of the message (a struct)
 * @param ctx context for the callbacks
 */
#define GNUNET_MQ_hd_fixed_size(name, code, str, ctx)                   \
  ({                                                                    \
    void (*_cb) (void *cls, const str *msg) = &handle_##name;           \
    ((struct GNUNET_MQ_MessageHandler){NULL,                            \
                                       (GNUNET_MQ_MessageCallback) _cb, \
                                       (ctx),                           \
                                       (code),                          \
                                       sizeof (str)});                  \
  })


/**
 * Defines a static function @a name which takes two arguments and a
 * context-pointer for validating and handling variable-sized messages
 * of type @a code and with a message type argument of @a str.  Given
 * such arguments, the function @name will return a `struct
 * GNUNET_MQ_MessageHandler` for the given message type.
 *
 * The macro is to be used as follows:
 * <code>
 * struct GNUNET_MessageTest { ... }; // can be variable size
 * static int
 * check_test (void *cls,
 *             const struct GNUNET_MessageTest *msg)
 * {
 *   const char *ctx = cls;
 *   GNUNET_assert (0 == strcmp ("context", ctx));
 *   // ...
 * }
 * static void
 * handle_test (void *cls,
 *              const struct GNUNET_MessageTest *msg)
 * {
 *   const char *ctx = cls;
 *   GNUNET_assert (0 == strcmp ("context", ctx));
 *   // ...
 * }
 *
 * struct GNUNET_MQ_MessageHandler handlers[] = {
 *   GNUNET_MQ_hd_var_size(test_message,
 *                         GNUNET_MESSAGE_TYPE_TEST,
 *                         struct GNUNET_MessageTest,
 *                         "context"),
 *   GNUNET_MQ_handler_end()
 * };
 *
 * @param name unique basename for the functions
 * @param code message type constant
 * @param str type of the message (a struct)
 * @param ctx context for the callbacks
 */
#define GNUNET_MQ_hd_var_size(name, code, str, ctx)                          \
  __extension__({                                                            \
    int (*_mv) (void *cls, const str *msg) = &check_##name;                  \
    void (*_cb) (void *cls, const str *msg) = &handle_##name;                \
    ((struct GNUNET_MQ_MessageHandler){(GNUNET_MQ_MessageValidationCallback) \
                                         _mv,                                \
                                       (GNUNET_MQ_MessageCallback) _cb,      \
                                       (ctx),                                \
                                       (code),                               \
                                       sizeof (str)});                       \
  })


/**
 * Insert code for a "check_" function that verifies that
 * a given variable-length message received over the network
 * is followed by a 0-terminated string.  If the message @a m
 * is not followed by a 0-terminated string, an error is logged
 * and the function is returned with #GNUNET_NO.
 *
 * @param an IPC message with proper type to determine
 *  the size, starting with a `struct GNUNET_MessageHeader`
 */
#define GNUNET_MQ_check_zero_termination(m)                       \
  {                                                               \
    const char *str = (const char *) &m[1];                       \
    const struct GNUNET_MessageHeader *hdr =                      \
      (const struct GNUNET_MessageHeader *) m;                    \
    uint16_t slen = ntohs (hdr->size) - sizeof (*m);              \
    if ((0 == slen) || (memchr (str, 0, slen) != &str[slen - 1])) \
    {                                                             \
      GNUNET_break (0);                                           \
      return GNUNET_NO;                                           \
    }                                                             \
  }


/**
 * Insert code for a "check_" function that verifies that
 * a given variable-length message received over the network
 * is followed by another variable-length message that fits
 * exactly with the given size.  If the message @a m
 * is not followed by another `struct GNUNET_MessageHeader`
 * with a size that adds up to the total size, an error is logged
 * and the function is returned with #GNUNET_NO.
 *
 * @param an IPC message with proper type to determine
 *  the size, starting with a `struct GNUNET_MessageHeader`
 */
#define GNUNET_MQ_check_boxed_message(m)                 \
  {                                                      \
    const struct GNUNET_MessageHeader *inbox =           \
      (const struct GNUNET_MessageHeader *) &m[1];       \
    const struct GNUNET_MessageHeader *hdr =             \
      (const struct GNUNET_MessageHeader *) m;           \
    uint16_t slen = ntohs (hdr->size) - sizeof (*m);     \
    if ((slen < sizeof (struct GNUNET_MessageHeader)) || \
        (slen != ntohs (inbox->size)))                   \
    {                                                    \
      GNUNET_break (0);                                  \
      return GNUNET_NO;                                  \
    }                                                    \
  }


/**
 * Call the message message handler that was registered
 * for the type of the given message in the given @a handlers list.
 *
 * This function is indended to be used for the implementation
 * of message queues.
 *
 * @param handlers a set of handlers
 * @param mh message to dispatch
 * @return #GNUNET_OK on success, #GNUNET_NO if no handler matched,
 *         #GNUNET_SYSERR if message was rejected by check function
 */
int
GNUNET_MQ_handle_message (const struct GNUNET_MQ_MessageHandler *handlers,
                          const struct GNUNET_MessageHeader *mh);


/**
 * Create a new envelope.
 *
 * @param mhp message header to store the allocated message header in, can be NULL
 * @param size size of the message to allocate
 * @param type type of the message, will be set in the allocated message
 * @return the allocated MQ message
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_msg_ (struct GNUNET_MessageHeader **mhp,
                uint16_t size,
                uint16_t type);


/**
 * Create a new envelope by copying an existing message.
 *
 * @param hdr header of the message to copy
 * @return envelope containing @a hdr
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_msg_copy (const struct GNUNET_MessageHeader *hdr);


/**
 * Discard the message queue message, free all
 * allocated resources. Must be called in the event
 * that a message is created but should not actually be sent.
 *
 * @param mqm the message to discard
 */
void
GNUNET_MQ_discard (struct GNUNET_MQ_Envelope *mqm);


/**
 * Function to obtain the current envelope
 * from within #GNUNET_MQ_SendImpl implementations.
 *
 * @param mq message queue to interrogate
 * @return the current envelope
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_get_current_envelope (struct GNUNET_MQ_Handle *mq);


/**
 * Function to copy an envelope.  The envelope must not yet
 * be in any queue or have any options or callbacks set.
 *
 * @param env envelope to copy
 * @return copy of @a env
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_env_copy (struct GNUNET_MQ_Envelope *env);


/**
 * Function to obtain the last envelope in the queue.
 *
 * @param mq message queue to interrogate
 * @return the last envelope in the queue
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_get_last_envelope (struct GNUNET_MQ_Handle *mq);


/**
 * Set application-specific options for this envelope.
 * Overrides the options set for the queue with
 * #GNUNET_MQ_set_options() for this message only.
 *
 * @param env message to set options for
 * @param pp priority and preferences to set for @a env
 */
void
GNUNET_MQ_env_set_options (struct GNUNET_MQ_Envelope *env,
                           enum GNUNET_MQ_PriorityPreferences pp);


/**
 * Get performance preferences set for this envelope.
 *
 * @param env message to set options for
 * @return priority and preferences to use
 */
enum GNUNET_MQ_PriorityPreferences
GNUNET_MQ_env_get_options (struct GNUNET_MQ_Envelope *env);


/**
 * Combine performance preferences set for different
 * envelopes that are being combined into one larger envelope.
 *
 * @param p1 one set of preferences
 * @param p2 second set of preferences
 * @return combined priority and preferences to use
 */
enum GNUNET_MQ_PriorityPreferences
GNUNET_MQ_env_combine_options (enum GNUNET_MQ_PriorityPreferences p1,
                               enum GNUNET_MQ_PriorityPreferences p2);


/**
 * Remove the first envelope that has not yet been sent from the message
 * queue and return it.
 *
 * @param mq queue to remove envelope from
 * @return NULL if queue is empty (or has no envelope that is not under transmission)
 */
struct GNUNET_MQ_Envelope *
GNUNET_MQ_unsent_head (struct GNUNET_MQ_Handle *mq);


/**
 * Set application-specific options for this queue.
 *
 * @param mq message queue to set options for
 * @param pp priority and preferences to use by default
 */
void
GNUNET_MQ_set_options (struct GNUNET_MQ_Handle *mq,
                       enum GNUNET_MQ_PriorityPreferences pp);


/**
 * Obtain the current length of the message queue.
 *
 * @param mq queue to inspect
 * @return number of queued, non-transmitted messages
 */
unsigned int
GNUNET_MQ_get_length (struct GNUNET_MQ_Handle *mq);


/**
 * Send a message with the given message queue.
 * May only be called once per message.
 *
 * @param mq message queue
 * @param ev the envelope with the message to send.
 */
void
GNUNET_MQ_send (struct GNUNET_MQ_Handle *mq, struct GNUNET_MQ_Envelope *ev);


/**
 * Send a copy of a message with the given message queue.
 * Can be called repeatedly on the same envelope.
 *
 * @param mq message queue
 * @param ev the envelope with the message to send.
 */
void
GNUNET_MQ_send_copy (struct GNUNET_MQ_Handle *mq,
                     const struct GNUNET_MQ_Envelope *ev);


/**
 * Cancel sending the message. Message must have been sent with
 * #GNUNET_MQ_send before.  May not be called after the notify sent
 * callback has been called
 *
 * @param ev queued envelope to cancel
 */
void
GNUNET_MQ_send_cancel (struct GNUNET_MQ_Envelope *ev);


/**
 * Associate the assoc_data in @a mq with a unique request id.
 *
 * @param mq message queue, id will be unique for the queue
 * @param assoc_data to associate
 */
uint32_t
GNUNET_MQ_assoc_add (struct GNUNET_MQ_Handle *mq, void *assoc_data);


/**
 * Get the data associated with a @a request_id in a queue
 *
 * @param mq the message queue with the association
 * @param request_id the request id we are interested in
 * @return the associated data
 */
void *
GNUNET_MQ_assoc_get (struct GNUNET_MQ_Handle *mq, uint32_t request_id);


/**
 * Remove the association for a @a request_id
 *
 * @param mq the message queue with the association
 * @param request_id the request id we want to remove
 * @return the associated data
 */
void *
GNUNET_MQ_assoc_remove (struct GNUNET_MQ_Handle *mq, uint32_t request_id);


/**
 * Create a message queue for the specified handlers.
 *
 * @param send function the implements sending messages
 * @param destroy function that implements destroying the queue
 * @param cancel function that implements canceling a message
 * @param impl_state for the queue, passed to @a send, @a destroy and @a cancel
 * @param handlers array of message handlers
 * @param error_handler handler for read and write errors
 * @param cls closure for message handlers and error handler
 * @return a new message queue
 */
struct GNUNET_MQ_Handle *
GNUNET_MQ_queue_for_callbacks (GNUNET_MQ_SendImpl send,
                               GNUNET_MQ_DestroyImpl destroy,
                               GNUNET_MQ_CancelImpl cancel,
                               void *impl_state,
                               const struct GNUNET_MQ_MessageHandler *handlers,
                               GNUNET_MQ_ErrorHandler error_handler,
                               void *cls);


/**
 * Change the closure argument in all of the `handlers` of the
 * @a mq.
 *
 * @param mq to modify
 * @param handlers_cls new closure to use
 */
void
GNUNET_MQ_set_handlers_closure (struct GNUNET_MQ_Handle *mq,
                                void *handlers_cls);


/**
 * Call a callback once the envelope has been sent, that is,
 * sending it can not be canceled anymore.
 * There can be only one notify sent callback per envelope.
 *
 * @param ev message to call the notify callback for
 * @param cb the notify callback
 * @param cb_cls closure for the callback
 */
void
GNUNET_MQ_notify_sent (struct GNUNET_MQ_Envelope *ev,
                       GNUNET_SCHEDULER_TaskCallback cb,
                       void *cb_cls);


/**
 * Destroy the message queue.
 *
 * @param mq message queue to destroy
 */
void
GNUNET_MQ_destroy (struct GNUNET_MQ_Handle *mq);


/**
 * Handle we return for callbacks registered to be
 * notified when #GNUNET_MQ_destroy() is called on a queue.
 */
struct GNUNET_MQ_DestroyNotificationHandle;


/**
 * Register function to be called whenever @a mq is being
 * destroyed.
 *
 * @param mq message queue to watch
 * @param cb function to call on @a mq destruction
 * @param cb_cls closure for @a cb
 * @return handle for #GNUNET_MQ_destroy_notify_cancel().
 */
struct GNUNET_MQ_DestroyNotificationHandle *
GNUNET_MQ_destroy_notify (struct GNUNET_MQ_Handle *mq,
                          GNUNET_SCHEDULER_TaskCallback cb,
                          void *cb_cls);

/**
 * Cancel registration from #GNUNET_MQ_destroy_notify().
 *
 * @param dnh handle for registration to cancel
 */
void
GNUNET_MQ_destroy_notify_cancel (
  struct GNUNET_MQ_DestroyNotificationHandle *dnh);


/**
 * Call the message message handler that was registered
 * for the type of the given message in the given message queue.
 *
 * This function is indended to be used for the implementation
 * of message queues.
 *
 * @param mq message queue with the handlers
 * @param mh message to dispatch
 */
void
GNUNET_MQ_inject_message (struct GNUNET_MQ_Handle *mq,
                          const struct GNUNET_MessageHeader *mh);


/**
 * Call the error handler of a message queue with the given
 * error code.  If there is no error handler, log a warning.
 *
 * This function is intended to be used for the implementation
 * of message queues.
 *
 * @param mq message queue
 * @param error the error type
 */
void
GNUNET_MQ_inject_error (struct GNUNET_MQ_Handle *mq,
                        enum GNUNET_MQ_Error error);


/**
 * Call the send implementation for the next queued message, if any.
 * Calls the send notification for the current message unless
 * #GNUNET_MQ_impl_send_in_flight was called for this envelope.
 *
 * Only useful for implementing message queues, results in undefined
 * behavior if not used carefully.
 *
 * @param mq message queue to send the next message with
 */
void
GNUNET_MQ_impl_send_continue (struct GNUNET_MQ_Handle *mq);


/**
 * Call the send notification for the current message, but do not
 * try to send the next message until #gnunet_mq_impl_send_continue
 * is called.
 *
 * Only useful for implementing message queues, results in undefined
 * behavior if not used carefully.
 *
 * @param mq message queue to send the next message with
 */
void
GNUNET_MQ_impl_send_in_flight (struct GNUNET_MQ_Handle *mq);


/**
 * Get the implementation state associated with the
 * message queue.
 *
 * While the GNUNET_MQ_Impl* callbacks receive the
 * implementation state, continuations that are scheduled
 * by the implementation function often only have one closure
 * argument, with this function it is possible to get at the
 * implementation state when only passing the `struct GNUNET_MQ_Handle`
 * as closure.
 *
 * @param mq message queue with the current message
 * @return message to send, never NULL
 */
void *
GNUNET_MQ_impl_state (struct GNUNET_MQ_Handle *mq);


/**
 * Get the message that should currently be sent.
 * Fails if there is no current message.
 * Only useful for implementing message queues,
 * results in undefined behavior if not used carefully.
 *
 * @param mq message queue with the current message
 * @return message to send, never NULL
 */
const struct GNUNET_MessageHeader *
GNUNET_MQ_impl_current (struct GNUNET_MQ_Handle *mq);


/**
 * Enum defining all known preference categories.
 *
 * @deprecated will be replaced by `enum GNUNET_MQ_PriorityPreference`
 */
enum GNUNET_MQ_PreferenceKind
{

  /**
   * No preference was expressed.
   */
  GNUNET_MQ_PREFERENCE_NONE = 0,

  /**
   * The preferred transmission for this envelope focuses on
   * maximizing bandwidth.
   */
  GNUNET_MQ_PREFERENCE_BANDWIDTH = 1,

  /**
   * The preferred transmission for this envelope foces on
   * minimizing latency.
   */
  GNUNET_MQ_PREFERENCE_LATENCY = 2,

  /**
   * The preferred transmission for this envelope foces on
   * reliability.
   */
  GNUNET_MQ_PREFERENCE_RELIABILITY = 3

/**
   * Number of preference values allowed.
   */
#define GNUNET_MQ_PREFERENCE_COUNT 4

};


/**
 * Convert an `enum GNUNET_MQ_PreferenceType` to a string
 *
 * @param type the preference type
 * @return a string or NULL if invalid
 *
 * @deprecated will be replaced by `enum GNUNET_MQ_PriorityPreference`
 */
const char *
GNUNET_MQ_preference_to_string (enum GNUNET_MQ_PreferenceKind type);


#endif

/** @} */ /* end of group mq */