summaryrefslogtreecommitdiff
path: root/src/microhttpd/internal.h
blob: aef6f17a9a5b5bb84f90c465d6a95ef23098f718 (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
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
/*
  This file is part of libmicrohttpd
  Copyright (C) 2007-2015 Daniel Pittman and Christian Grothoff

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/

/**
 * @file microhttpd/internal.h
 * @brief  internal shared structures
 * @author Daniel Pittman
 * @author Christian Grothoff
 */

#ifndef INTERNAL_H
#define INTERNAL_H

#include "platform.h"
#include "microhttpd.h"
#include "platform_interface.h"
#if HTTPS_SUPPORT
#include <gnutls/gnutls.h>
#if GNUTLS_VERSION_MAJOR >= 3
#include <gnutls/abstract.h>
#endif
#endif
#if EPOLL_SUPPORT
#include <sys/epoll.h>
#endif
#if HAVE_NETINET_TCP_H
/* for TCP_FASTOPEN */
#include <netinet/tcp.h>
#endif
#include "mhd_threads.h"


/**
 * Should we perform additional sanity checks at runtime (on our internal
 * invariants)?  This may lead to aborts, but can be useful for debugging.
 */
#define EXTRA_CHECKS MHD_NO

#define MHD_MAX(a,b) (((a)<(b)) ? (b) : (a))
#define MHD_MIN(a,b) (((a)<(b)) ? (a) : (b))


/**
 * Minimum size by which MHD tries to increment read/write buffers.
 * We usually begin with half the available pool space for the
 * IO-buffer, but if absolutely needed we additively grow by the
 * number of bytes given here (up to -- theoretically -- the full pool
 * space).
 */
#define MHD_BUF_INC_SIZE 1024


/**
 * Handler for fatal errors.
 */
extern MHD_PanicCallback mhd_panic;

/**
 * Closure argument for "mhd_panic".
 */
extern void *mhd_panic_cls;

/* If we have Clang or gcc >= 4.5, use __buildin_unreachable() */
#if defined(__clang__) || (__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
#define BUILTIN_NOT_REACHED __builtin_unreachable()
#elif defined(_MSC_FULL_VER)
#define BUILTIN_NOT_REACHED __assume(0)
#else
#define BUILTIN_NOT_REACHED
#endif


#ifdef HAVE_MESSAGES
/**
 * Trigger 'panic' action based on fatal errors.
 *
 * @param msg error message (const char *)
 */
#define MHD_PANIC(msg) do { mhd_panic (mhd_panic_cls, __FILE__, __LINE__, msg); BUILTIN_NOT_REACHED; } while (0)
#else
/**
 * Trigger 'panic' action based on fatal errors.
 *
 * @param msg error message (const char *)
 */
#define MHD_PANIC(msg) do { mhd_panic (mhd_panic_cls, __FILE__, __LINE__, NULL); BUILTIN_NOT_REACHED; } while (0)
#endif


/**
 * State of the socket with respect to epoll (bitmask).
 */
enum MHD_EpollState
  {

    /**
     * The socket is not involved with a defined state in epoll() right
     * now.
     */
    MHD_EPOLL_STATE_UNREADY = 0,

    /**
     * epoll() told us that data was ready for reading, and we did
     * not consume all of it yet.
     */
    MHD_EPOLL_STATE_READ_READY = 1,

    /**
     * epoll() told us that space was available for writing, and we did
     * not consume all of it yet.
     */
    MHD_EPOLL_STATE_WRITE_READY = 2,

    /**
     * Is this connection currently in the 'eready' EDLL?
     */
    MHD_EPOLL_STATE_IN_EREADY_EDLL = 4,

    /**
     * Is this connection currently in the epoll() set?
     */
    MHD_EPOLL_STATE_IN_EPOLL_SET = 8,

    /**
     * Is this connection currently suspended?
     */
    MHD_EPOLL_STATE_SUSPENDED = 16
  };


/**
 * What is this connection waiting for?
 */
enum MHD_ConnectionEventLoopInfo
  {
    /**
     * We are waiting to be able to read.
     */
    MHD_EVENT_LOOP_INFO_READ = 0,

    /**
     * We are waiting to be able to write.
     */
    MHD_EVENT_LOOP_INFO_WRITE = 1,

    /**
     * We are waiting for the application to provide data.
     */
    MHD_EVENT_LOOP_INFO_BLOCK = 2,

    /**
     * We are finished and are awaiting cleanup.
     */
    MHD_EVENT_LOOP_INFO_CLEANUP = 3
  };


/**
 * Maximum length of a nonce in digest authentication.  32(MD5 Hex) +
 * 8(Timestamp Hex) + 1(NULL); hence 41 should suffice, but Opera
 * (already) takes more (see Mantis #1633), so we've increased the
 * value to support something longer...
 */
#define MAX_NONCE_LENGTH 129


/**
 * A structure representing the internal holder of the
 * nonce-nc map.
 */
struct MHD_NonceNc
{

  /**
   * Nonce counter, a value that increases for each subsequent
   * request for the same nonce.
   */
  uint64_t nc;

  /**
   * Nonce value:
   */
  char nonce[MAX_NONCE_LENGTH];

};

#ifdef HAVE_MESSAGES
/**
 * fprintf()-like helper function for logging debug
 * messages.
 */
void
MHD_DLOG (const struct MHD_Daemon *daemon,
	  const char *format, ...);
#endif


/**
 * Header or cookie in HTTP request or response.
 */
struct MHD_HTTP_Header
{
  /**
   * Headers are kept in a linked list.
   */
  struct MHD_HTTP_Header *next;

  /**
   * The name of the header (key), without
   * the colon.
   */
  char *header;

  /**
   * The value of the header.
   */
  char *value;

  /**
   * Type of the header (where in the HTTP
   * protocol is this header from).
   */
  enum MHD_ValueKind kind;

};


/**
 * Representation of a response.
 */
struct MHD_Response
{

  /**
   * Headers to send for the response.  Initially
   * the linked list is created in inverse order;
   * the order should be inverted before sending!
   */
  struct MHD_HTTP_Header *first_header;

  /**
   * Buffer pointing to data that we are supposed
   * to send as a response.
   */
  char *data;

  /**
   * Closure to give to the content reader @e crc
   * and content reader free callback @e crfc.
   */
  void *crc_cls;

  /**
   * How do we get more data?  NULL if we are
   * given all of the data up front.
   */
  MHD_ContentReaderCallback crc;

  /**
   * NULL if data must not be freed, otherwise
   * either user-specified callback or "&free".
   */
  MHD_ContentReaderFreeCallback crfc;

  /**
   * Mutex to synchronize access to @e data, @e size and
   * @e reference_count.
   */
  MHD_mutex_ mutex;

  /**
   * Set to #MHD_SIZE_UNKNOWN if size is not known.
   */
  uint64_t total_size;

  /**
   * At what offset in the stream is the
   * beginning of @e data located?
   */
  uint64_t data_start;

  /**
   * Offset to start reading from when using @e fd.
   */
  uint64_t fd_off;

  /**
   * Number of bytes ready in @e data (buffer may be larger
   * than what is filled with payload).
   */
  size_t data_size;

  /**
   * Size of the data buffer @e data.
   */
  size_t data_buffer_size;

  /**
   * Reference count for this response.  Free once the counter hits
   * zero.
   */
  unsigned int reference_count;

  /**
   * File-descriptor if this response is FD-backed.
   */
  int fd;

  /**
   * Flags set for the MHD response.
   */
  enum MHD_ResponseFlags flags;

};


/**
 * States in a state machine for a connection.
 *
 * The main transitions are any-state to #MHD_CONNECTION_CLOSED, any
 * state to state+1, #MHD_CONNECTION_FOOTERS_SENT to
 * #MHD_CONNECTION_INIT.  #MHD_CONNECTION_CLOSED is the terminal state
 * and #MHD_CONNECTION_INIT the initial state.
 *
 * Note that transitions for *reading* happen only after the input has
 * been processed; transitions for *writing* happen after the
 * respective data has been put into the write buffer (the write does
 * not have to be completed yet).  A transition to
 * #MHD_CONNECTION_CLOSED or #MHD_CONNECTION_INIT requires the write
 * to be complete.
 */
enum MHD_CONNECTION_STATE
{
  /**
   * Connection just started (no headers received).
   * Waiting for the line with the request type, URL and version.
   */
  MHD_CONNECTION_INIT = 0,

  /**
   * 1: We got the URL (and request type and version).  Wait for a header line.
   */
  MHD_CONNECTION_URL_RECEIVED = MHD_CONNECTION_INIT + 1,

  /**
   * 2: We got part of a multi-line request header.  Wait for the rest.
   */
  MHD_CONNECTION_HEADER_PART_RECEIVED = MHD_CONNECTION_URL_RECEIVED + 1,

  /**
   * 3: We got the request headers.  Process them.
   */
  MHD_CONNECTION_HEADERS_RECEIVED = MHD_CONNECTION_HEADER_PART_RECEIVED + 1,

  /**
   * 4: We have processed the request headers.  Send 100 continue.
   */
  MHD_CONNECTION_HEADERS_PROCESSED = MHD_CONNECTION_HEADERS_RECEIVED + 1,

  /**
   * 5: We have processed the headers and need to send 100 CONTINUE.
   */
  MHD_CONNECTION_CONTINUE_SENDING = MHD_CONNECTION_HEADERS_PROCESSED + 1,

  /**
   * 6: We have sent 100 CONTINUE (or do not need to).  Read the message body.
   */
  MHD_CONNECTION_CONTINUE_SENT = MHD_CONNECTION_CONTINUE_SENDING + 1,

  /**
   * 7: We got the request body.  Wait for a line of the footer.
   */
  MHD_CONNECTION_BODY_RECEIVED = MHD_CONNECTION_CONTINUE_SENT + 1,

  /**
   * 8: We got part of a line of the footer.  Wait for the
   * rest.
   */
  MHD_CONNECTION_FOOTER_PART_RECEIVED = MHD_CONNECTION_BODY_RECEIVED + 1,

  /**
   * 9: We received the entire footer.  Wait for a response to be queued
   * and prepare the response headers.
   */
  MHD_CONNECTION_FOOTERS_RECEIVED = MHD_CONNECTION_FOOTER_PART_RECEIVED + 1,

  /**
   * 10: We have prepared the response headers in the writ buffer.
   * Send the response headers.
   */
  MHD_CONNECTION_HEADERS_SENDING = MHD_CONNECTION_FOOTERS_RECEIVED + 1,

  /**
   * 11: We have sent the response headers.  Get ready to send the body.
   */
  MHD_CONNECTION_HEADERS_SENT = MHD_CONNECTION_HEADERS_SENDING + 1,

  /**
   * 12: We are ready to send a part of a non-chunked body.  Send it.
   */
  MHD_CONNECTION_NORMAL_BODY_READY = MHD_CONNECTION_HEADERS_SENT + 1,

  /**
   * 13: We are waiting for the client to provide more
   * data of a non-chunked body.
   */
  MHD_CONNECTION_NORMAL_BODY_UNREADY = MHD_CONNECTION_NORMAL_BODY_READY + 1,

  /**
   * 14: We are ready to send a chunk.
   */
  MHD_CONNECTION_CHUNKED_BODY_READY = MHD_CONNECTION_NORMAL_BODY_UNREADY + 1,

  /**
   * 15: We are waiting for the client to provide a chunk of the body.
   */
  MHD_CONNECTION_CHUNKED_BODY_UNREADY = MHD_CONNECTION_CHUNKED_BODY_READY + 1,

  /**
   * 16: We have sent the response body. Prepare the footers.
   */
  MHD_CONNECTION_BODY_SENT = MHD_CONNECTION_CHUNKED_BODY_UNREADY + 1,

  /**
   * 17: We have prepared the response footer.  Send it.
   */
  MHD_CONNECTION_FOOTERS_SENDING = MHD_CONNECTION_BODY_SENT + 1,

  /**
   * 18: We have sent the response footer.  Shutdown or restart.
   */
  MHD_CONNECTION_FOOTERS_SENT = MHD_CONNECTION_FOOTERS_SENDING + 1,

  /**
   * 19: This connection is to be closed.
   */
  MHD_CONNECTION_CLOSED = MHD_CONNECTION_FOOTERS_SENT + 1,

  /**
   * 20: This connection is finished (only to be freed)
   */
  MHD_CONNECTION_IN_CLEANUP = MHD_CONNECTION_CLOSED + 1,

  /*
   *  SSL/TLS connection states
   */

  /**
   * The initial connection state for all secure connectoins
   * Handshake messages will be processed in this state & while
   * in the #MHD_TLS_HELLO_REQUEST state
   */
  MHD_TLS_CONNECTION_INIT = MHD_CONNECTION_IN_CLEANUP + 1

};

/**
 * Should all state transitions be printed to stderr?
 */
#define DEBUG_STATES MHD_NO


#ifdef HAVE_MESSAGES
#if DEBUG_STATES
const char *
MHD_state_to_string (enum MHD_CONNECTION_STATE state);
#endif
#endif

/**
 * Function to receive plaintext data.
 *
 * @param conn the connection struct
 * @param write_to where to write received data
 * @param max_bytes maximum number of bytes to receive
 * @return number of bytes written to @a write_to
 */
typedef ssize_t
(*ReceiveCallback) (struct MHD_Connection *conn,
                    void *write_to,
                    size_t max_bytes);


/**
 * Function to transmit plaintext data.
 *
 * @param conn the connection struct
 * @param read_from where to read data to transmit
 * @param max_bytes maximum number of bytes to transmit
 * @return number of bytes transmitted
 */
typedef ssize_t
(*TransmitCallback) (struct MHD_Connection *conn,
                     const void *write_to,
                     size_t max_bytes);


/**
 * State kept for each HTTP request.
 */
struct MHD_Connection
{

#if EPOLL_SUPPORT
  /**
   * Next pointer for the EDLL listing connections that are epoll-ready.
   */
  struct MHD_Connection *nextE;

  /**
   * Previous pointer for the EDLL listing connections that are epoll-ready.
   */
  struct MHD_Connection *prevE;
#endif

  /**
   * Next pointer for the DLL describing our IO state.
   */
  struct MHD_Connection *next;

  /**
   * Previous pointer for the DLL describing our IO state.
   */
  struct MHD_Connection *prev;

  /**
   * Next pointer for the XDLL organizing connections by timeout.
   * This DLL can be either the
   * 'manual_timeout_head/manual_timeout_tail' or the
   * 'normal_timeout_head/normal_timeout_tail', depending on whether a
   * custom timeout is set for the connection.
   */
  struct MHD_Connection *nextX;

  /**
   * Previous pointer for the XDLL organizing connections by timeout.
   */
  struct MHD_Connection *prevX;

  /**
   * Reference to the MHD_Daemon struct.
   */
  struct MHD_Daemon *daemon;

  /**
   * Linked list of parsed headers.
   */
  struct MHD_HTTP_Header *headers_received;

  /**
   * Tail of linked list of parsed headers.
   */
  struct MHD_HTTP_Header *headers_received_tail;

  /**
   * Response to transmit (initially NULL).
   */
  struct MHD_Response *response;

  /**
   * The memory pool is created whenever we first read
   * from the TCP stream and destroyed at the end of
   * each request (and re-created for the next request).
   * In the meantime, this pointer is NULL.  The
   * pool is used for all connection-related data
   * except for the response (which maybe shared between
   * connections) and the IP address (which persists
   * across individual requests).
   */
  struct MemoryPool *pool;

  /**
   * We allow the main application to associate some pointer with the
   * HTTP request, which is passed to each #MHD_AccessHandlerCallback
   * and some other API calls.  Here is where we store it.  (MHD does
   * not know or care what it is).
   */
  void *client_context;

  /**
   * We allow the main application to associate some pointer with the
   * TCP connection (which may span multiple HTTP requests).  Here is
   * where we store it.  (MHD does not know or care what it is).
   * The location is given to the #MHD_NotifyConnectionCallback and
   * also accessible via #MHD_CONNECTION_INFO_SOCKET_CONTEXT.
   */
  void *socket_context;

  /**
   * Request method.  Should be GET/POST/etc.  Allocated
   * in pool.
   */
  char *method;

  /**
   * Requested URL (everything after "GET" only).  Allocated
   * in pool.
   */
  char *url;

  /**
   * HTTP version string (i.e. http/1.1).  Allocated
   * in pool.
   */
  char *version;

  /**
   * Buffer for reading requests.   Allocated
   * in pool.  Actually one byte larger than
   * @e read_buffer_size (if non-NULL) to allow for
   * 0-termination.
   */
  char *read_buffer;

  /**
   * Buffer for writing response (headers only).  Allocated
   * in pool.
   */
  char *write_buffer;

  /**
   * Last incomplete header line during parsing of headers.
   * Allocated in pool.  Only valid if state is
   * either #MHD_CONNECTION_HEADER_PART_RECEIVED or
   * #MHD_CONNECTION_FOOTER_PART_RECEIVED.
   */
  char *last;

  /**
   * Position after the colon on the last incomplete header
   * line during parsing of headers.
   * Allocated in pool.  Only valid if state is
   * either #MHD_CONNECTION_HEADER_PART_RECEIVED or
   * #MHD_CONNECTION_FOOTER_PART_RECEIVED.
   */
  char *colon;

  /**
   * Foreign address (of length @e addr_len).  MALLOCED (not
   * in pool!).
   */
  struct sockaddr *addr;

  /**
   * Thread handle for this connection (if we are using
   * one thread per connection).
   */
  MHD_thread_handle_ pid;

  /**
   * Size of @e read_buffer (in bytes).  This value indicates
   * how many bytes we're willing to read into the buffer;
   * the real buffer is one byte longer to allow for
   * adding zero-termination (when needed).
   */
  size_t read_buffer_size;

  /**
   * Position where we currently append data in
   * @e read_buffer (last valid position).
   */
  size_t read_buffer_offset;

  /**
   * Size of @e write_buffer (in bytes).
   */
  size_t write_buffer_size;

  /**
   * Offset where we are with sending from @e write_buffer.
   */
  size_t write_buffer_send_offset;

  /**
   * Last valid location in write_buffer (where do we
   * append and up to where is it safe to send?)
   */
  size_t write_buffer_append_offset;

  /**
   * How many more bytes of the body do we expect
   * to read? #MHD_SIZE_UNKNOWN for unknown.
   */
  uint64_t remaining_upload_size;

  /**
   * Current write position in the actual response
   * (excluding headers, content only; should be 0
   * while sending headers).
   */
  uint64_t response_write_position;

  /**
   * Position in the 100 CONTINUE message that
   * we need to send when receiving http 1.1 requests.
   */
  size_t continue_message_write_offset;

  /**
   * Length of the foreign address.
   */
  socklen_t addr_len;

  /**
   * Last time this connection had any activity
   * (reading or writing).
   */
  time_t last_activity;

  /**
   * After how many seconds of inactivity should
   * this connection time out?  Zero for no timeout.
   */
  unsigned int connection_timeout;

  /**
   * Did we ever call the "default_handler" on this connection?  (this
   * flag will determine if we call the #MHD_OPTION_NOTIFY_COMPLETED
   * handler when the connection closes down).
   */
  int client_aware;

  /**
   * Socket for this connection.  Set to #MHD_INVALID_SOCKET if
   * this connection has died (daemon should clean
   * up in that case).
   */
  MHD_socket socket_fd;

  /**
   * Has this socket been closed for reading (i.e.  other side closed
   * the connection)?  If so, we must completely close the connection
   * once we are done sending our response (and stop trying to read
   * from this socket).
   */
  int read_closed;

  /**
   * Set to #MHD_YES if the thread has been joined.
   */
  int thread_joined;

  /**
   * Are we currently inside the "idle" handler (to avoid recursively
   * invoking it).
   */
  int in_idle;

#if EPOLL_SUPPORT
  /**
   * What is the state of this socket in relation to epoll?
   */
  enum MHD_EpollState epoll_state;
#endif

  /**
   * State in the FSM for this connection.
   */
  enum MHD_CONNECTION_STATE state;

  /**
   * What is this connection waiting for?
   */
  enum MHD_ConnectionEventLoopInfo event_loop_info;

  /**
   * HTTP response code.  Only valid if response object
   * is already set.
   */
  unsigned int responseCode;

  /**
   * Set to #MHD_YES if the response's content reader
   * callback failed to provide data the last time
   * we tried to read from it.  In that case, the
   * write socket should be marked as unready until
   * the CRC call succeeds.
   */
  int response_unready;

  /**
   * Are we receiving with chunked encoding?  This will be set to
   * #MHD_YES after we parse the headers and are processing the body
   * with chunks.  After we are done with the body and we are
   * processing the footers; once the footers are also done, this will
   * be set to #MHD_NO again (before the final call to the handler).
   */
  int have_chunked_upload;

  /**
   * If we are receiving with chunked encoding, where are we right
   * now?  Set to 0 if we are waiting to receive the chunk size;
   * otherwise, this is the size of the current chunk.  A value of
   * zero is also used when we're at the end of the chunks.
   */
  size_t current_chunk_size;

  /**
   * If we are receiving with chunked encoding, where are we currently
   * with respect to the current chunk (at what offset / position)?
   */
  size_t current_chunk_offset;

  /**
   * Handler used for processing read connection operations
   */
  int (*read_handler) (struct MHD_Connection *connection);

  /**
   * Handler used for processing write connection operations
   */
  int (*write_handler) (struct MHD_Connection *connection);

  /**
   * Handler used for processing idle connection operations
   */
  int (*idle_handler) (struct MHD_Connection *connection);

  /**
   * Function used for reading HTTP request stream.
   */
  ReceiveCallback recv_cls;

  /**
   * Function used for writing HTTP response stream.
   */
  TransmitCallback send_cls;

#if HTTPS_SUPPORT
  /**
   * State required for HTTPS/SSL/TLS support.
   */
  gnutls_session_t tls_session;

  /**
   * Memory location to return for protocol session info.
   */
  int protocol;

  /**
   * Memory location to return for protocol session info.
   */
  int cipher;

  /**
   * Could it be that we are ready to read due to TLS buffers
   * even though the socket is not?
   */
  int tls_read_ready;
#endif

  /**
   * Is the connection suspended?
   */
  int suspended;

  /**
   * Is the connection wanting to resume?
   */
  int resuming;
};

/**
 * Signature of function called to log URI accesses.
 *
 * @param cls closure
 * @param uri uri being accessed
 * @param con connection handle
 * @return new closure
 */
typedef void *
(*LogCallback)(void *cls,
               const char *uri,
               struct MHD_Connection *con);

/**
 * Signature of function called to unescape URIs.  See also
 * #MHD_http_unescape().
 *
 * @param cls closure
 * @param conn connection handle
 * @param uri 0-terminated string to unescape (should be updated)
 * @return length of the resulting string
 */
typedef size_t
(*UnescapeCallback)(void *cls,
                    struct MHD_Connection *conn,
                    char *uri);


/**
 * State kept for each MHD daemon.  All connections are kept in two
 * doubly-linked lists.  The first one reflects the state of the
 * connection in terms of what operations we are waiting for (read,
 * write, locally blocked, cleanup) whereas the second is about its
 * timeout state (default or custom).
 */
struct MHD_Daemon
{

  /**
   * Callback function for all requests.
   */
  MHD_AccessHandlerCallback default_handler;

  /**
   * Closure argument to default_handler.
   */
  void *default_handler_cls;

  /**
   * Head of doubly-linked list of our current, active connections.
   */
  struct MHD_Connection *connections_head;

  /**
   * Tail of doubly-linked list of our current, active connections.
   */
  struct MHD_Connection *connections_tail;

  /**
   * Head of doubly-linked list of our current but suspended connections.
   */
  struct MHD_Connection *suspended_connections_head;

  /**
   * Tail of doubly-linked list of our current but suspended connections.
   */
  struct MHD_Connection *suspended_connections_tail;

  /**
   * Head of doubly-linked list of connections to clean up.
   */
  struct MHD_Connection *cleanup_head;

  /**
   * Tail of doubly-linked list of connections to clean up.
   */
  struct MHD_Connection *cleanup_tail;

#if EPOLL_SUPPORT
  /**
   * Head of EDLL of connections ready for processing (in epoll mode).
   */
  struct MHD_Connection *eready_head;

  /**
   * Tail of EDLL of connections ready for processing (in epoll mode)
   */
  struct MHD_Connection *eready_tail;
#endif

  /**
   * Head of the XDLL of ALL connections with a default ('normal')
   * timeout, sorted by timeout (earliest at the tail, most recently
   * used connection at the head).  MHD can just look at the tail of
   * this list to determine the timeout for all of its elements;
   * whenever there is an event of a connection, the connection is
   * moved back to the tail of the list.
   *
   * All connections by default start in this list; if a custom
   * timeout that does not match @e connection_timeout is set, they
   * are moved to the @e manual_timeout_head-XDLL.
   * Not used in MHD_USE_THREAD_PER_CONNECTION mode as each thread
   * needs only one connection-specific timeout.
   */
  struct MHD_Connection *normal_timeout_head;

  /**
   * Tail of the XDLL of ALL connections with a default timeout,
   * sorted by timeout (earliest timeout at the tail).
   * Not used in MHD_USE_THREAD_PER_CONNECTION mode.
   */
  struct MHD_Connection *normal_timeout_tail;

  /**
   * Head of the XDLL of ALL connections with a non-default/custom
   * timeout, unsorted.  MHD will do a O(n) scan over this list to
   * determine the current timeout.
   * Not used in MHD_USE_THREAD_PER_CONNECTION mode.
   */
  struct MHD_Connection *manual_timeout_head;

  /**
   * Tail of the XDLL of ALL connections with a non-default/custom
   * timeout, unsorted.
   * Not used in MHD_USE_THREAD_PER_CONNECTION mode.
   */
  struct MHD_Connection *manual_timeout_tail;

  /**
   * Function to call to check if we should accept or reject an
   * incoming request.  May be NULL.
   */
  MHD_AcceptPolicyCallback apc;

  /**
   * Closure argument to apc.
   */
  void *apc_cls;

  /**
   * Function to call when we are done processing
   * a particular request.  May be NULL.
   */
  MHD_RequestCompletedCallback notify_completed;

  /**
   * Closure argument to @e notify_completed.
   */
  void *notify_completed_cls;

  /**
   * Function to call when we are starting/stopping
   * a connection.  May be NULL.
   */
  MHD_NotifyConnectionCallback notify_connection;

  /**
   * Closure argument to @e notify_connection.
   */
  void *notify_connection_cls;

  /**
   * Function to call with the full URI at the
   * beginning of request processing.  May be NULL.
   * <p>
   * Returns the initial pointer to internal state
   * kept by the client for the request.
   */
  LogCallback uri_log_callback;

  /**
   * Closure argument to @e uri_log_callback.
   */
  void *uri_log_callback_cls;

  /**
   * Function to call when we unescape escape sequences.
   */
  UnescapeCallback unescape_callback;

  /**
   * Closure for @e unescape_callback.
   */
  void *unescape_callback_cls;

#ifdef HAVE_MESSAGES
  /**
   * Function for logging error messages (if we
   * support error reporting).
   */
  void (*custom_error_log) (void *cls, const char *fmt, va_list va);

  /**
   * Closure argument to @e custom_error_log.
   */
  void *custom_error_log_cls;
#endif

  /**
   * Pointer to master daemon (NULL if this is the master)
   */
  struct MHD_Daemon *master;

  /**
   * Worker daemons (one per thread)
   */
  struct MHD_Daemon *worker_pool;

  /**
   * Table storing number of connections per IP
   */
  void *per_ip_connection_count;

  /**
   * Size of the per-connection memory pools.
   */
  size_t pool_size;

  /**
   * Increment for growth of the per-connection memory pools.
   */
  size_t pool_increment;

  /**
   * Size of threads created by MHD.
   */
  size_t thread_stack_size;

  /**
   * Number of worker daemons
   */
  unsigned int worker_pool_size;

  /**
   * The select thread handle (if we have internal select)
   */
  MHD_thread_handle_ pid;

  /**
   * Mutex for per-IP connection counts.
   */
  MHD_mutex_ per_ip_connection_mutex;

  /**
   * Mutex for (modifying) access to the "cleanup" connection DLL.
   */
  MHD_mutex_ cleanup_connection_mutex;

  /**
   * Listen socket.
   */
  MHD_socket socket_fd;

  /**
   * Whether to allow/disallow/ignore reuse of listening address.
   * The semantics is the following:
   * 0: ignore (user did not ask for neither allow/disallow, use SO_REUSEADDR)
   * >0: allow (use SO_REUSEPORT on most platforms, SO_REUSEADDR on Windows)
   * <0: disallow (mostly no action, SO_EXCLUSIVEADDRUSE on Windows)
   */
  int listening_address_reuse;

#if EPOLL_SUPPORT
  /**
   * File descriptor associated with our epoll loop.
   */
  int epoll_fd;

  /**
   * MHD_YES if the listen socket is in the 'epoll' set,
   * MHD_NO if not.
   */
  int listen_socket_in_epoll;
#endif

  /**
   * Pipe we use to signal shutdown, unless
   * 'HAVE_LISTEN_SHUTDOWN' is defined AND we have a listen
   * socket (which we can then 'shutdown' to stop listening).
   * MHD can be build with usage of socketpair instead of
   * pipe (forced on W32).
   */
  MHD_pipe wpipe[2];

  /**
   * Are we shutting down?
   */
  int shutdown;

  /**
   * Did we hit some system or process-wide resource limit while
   * trying to accept() the last time? If so, we don't accept new
   * connections until we close an existing one.  This effectively
   * temporarily lowers the "connection_limit" to the current
   * number of connections.
   */
  int at_limit;

  /*
   * Do we need to process resuming connections?
   */
  int resuming;

  /**
   * Number of active parallel connections.
   */
  unsigned int connections;

  /**
   * Limit on the number of parallel connections.
   */
  unsigned int connection_limit;

  /**
   * After how many seconds of inactivity should
   * connections time out?  Zero for no timeout.
   */
  unsigned int connection_timeout;

  /**
   * Maximum number of connections per IP, or 0 for
   * unlimited.
   */
  unsigned int per_ip_connection_limit;

  /**
   * Daemon's flags (bitfield).
   */
  enum MHD_FLAG options;

  /**
   * Listen port.
   */
  uint16_t port;

#if HTTPS_SUPPORT
  /**
   * Desired cipher algorithms.
   */
  gnutls_priority_t priority_cache;

  /**
   * What kind of credentials are we offering
   * for SSL/TLS?
   */
  gnutls_credentials_type_t cred_type;

  /**
   * Server x509 credentials
   */
  gnutls_certificate_credentials_t x509_cred;

  /**
   * Diffie-Hellman parameters
   */
  gnutls_dh_params_t dh_params;

#if GNUTLS_VERSION_MAJOR >= 3
  /**
   * Function that can be used to obtain the certificate.  Needed
   * for SNI support.  See #MHD_OPTION_HTTPS_CERT_CALLBACK.
   */
  gnutls_certificate_retrieve_function2 *cert_callback;
#endif

  /**
   * Pointer to our SSL/TLS key (in ASCII) in memory.
   */
  const char *https_mem_key;

  /**
   * Pointer to our SSL/TLS certificate (in ASCII) in memory.
   */
  const char *https_mem_cert;

  /**
   * Pointer to 0-terminated HTTPS passphrase in memory.
   */
  const char *https_key_password;

  /**
   * Pointer to our SSL/TLS certificate authority (in ASCII) in memory.
   */
  const char *https_mem_trust;

  /**
   * Our Diffie-Hellman parameters in memory.
   */
  gnutls_dh_params_t https_mem_dhparams;

  /**
   * #MHD_YES if we have initialized @e https_mem_dhparams.
   */
  int have_dhparams;

  /**
   * For how many connections do we have 'tls_read_ready' set to MHD_YES?
   * Used to avoid O(n) traversal over all connections when determining
   * event-loop timeout (as it needs to be zero if there is any connection
   * which might have ready data within TLS).
   */
  unsigned int num_tls_read_ready;

#endif

#ifdef DAUTH_SUPPORT

  /**
   * Character array of random values.
   */
  const char *digest_auth_random;

  /**
   * An array that contains the map nonce-nc.
   */
  struct MHD_NonceNc *nnc;

  /**
   * A rw-lock for synchronizing access to `nnc'.
   */
  MHD_mutex_ nnc_lock;

  /**
   * Size of `digest_auth_random.
   */
  size_t digest_auth_rand_size;

  /**
   * Size of the nonce-nc array.
   */
  unsigned int nonce_nc_size;

#endif

#ifdef TCP_FASTOPEN
  /**
   * The queue size for incoming SYN + DATA packets.
   */
  unsigned int fastopen_queue_size;
#endif

  /**
   * The size of queue for listen socket.
   */
  unsigned int listen_backlog_size;
};


#if EXTRA_CHECKS
#define EXTRA_CHECK(a) do { if (!(a)) abort(); } while (0)
#else
#define EXTRA_CHECK(a)
#endif


/**
 * Insert an element at the head of a DLL. Assumes that head, tail and
 * element are structs with prev and next fields.
 *
 * @param head pointer to the head of the DLL
 * @param tail pointer to the tail of the DLL
 * @param element element to insert
 */
#define DLL_insert(head,tail,element) do { \
  EXTRA_CHECK (NULL == (element)->next); \
  EXTRA_CHECK (NULL == (element)->prev); \
  (element)->next = (head); \
  (element)->prev = NULL; \
  if ((tail) == NULL) \
    (tail) = element; \
  else \
    (head)->prev = element; \
  (head) = (element); } while (0)


/**
 * Remove an element from a DLL. Assumes
 * that head, tail and element are structs
 * with prev and next fields.
 *
 * @param head pointer to the head of the DLL
 * @param tail pointer to the tail of the DLL
 * @param element element to remove
 */
#define DLL_remove(head,tail,element) do { \
  EXTRA_CHECK ( (NULL != (element)->next) || ((element) == (tail)));  \
  EXTRA_CHECK ( (NULL != (element)->prev) || ((element) == (head)));  \
  if ((element)->prev == NULL) \
    (head) = (element)->next;  \
  else \
    (element)->prev->next = (element)->next; \
  if ((element)->next == NULL) \
    (tail) = (element)->prev;  \
  else \
    (element)->next->prev = (element)->prev; \
  (element)->next = NULL; \
  (element)->prev = NULL; } while (0)



/**
 * Insert an element at the head of a XDLL. Assumes that head, tail and
 * element are structs with prevX and nextX fields.
 *
 * @param head pointer to the head of the XDLL
 * @param tail pointer to the tail of the XDLL
 * @param element element to insert
 */
#define XDLL_insert(head,tail,element) do { \
  EXTRA_CHECK (NULL == (element)->nextX); \
  EXTRA_CHECK (NULL == (element)->prevX); \
  (element)->nextX = (head); \
  (element)->prevX = NULL; \
  if (NULL == (tail)) \
    (tail) = element; \
  else \
    (head)->prevX = element; \
  (head) = (element); } while (0)


/**
 * Remove an element from a XDLL. Assumes
 * that head, tail and element are structs
 * with prevX and nextX fields.
 *
 * @param head pointer to the head of the XDLL
 * @param tail pointer to the tail of the XDLL
 * @param element element to remove
 */
#define XDLL_remove(head,tail,element) do { \
  EXTRA_CHECK ( (NULL != (element)->nextX) || ((element) == (tail)));  \
  EXTRA_CHECK ( (NULL != (element)->prevX) || ((element) == (head)));  \
  if (NULL == (element)->prevX) \
    (head) = (element)->nextX;  \
  else \
    (element)->prevX->nextX = (element)->nextX; \
  if (NULL == (element)->nextX) \
    (tail) = (element)->prevX;  \
  else \
    (element)->nextX->prevX = (element)->prevX; \
  (element)->nextX = NULL; \
  (element)->prevX = NULL; } while (0)


/**
 * Insert an element at the head of a EDLL. Assumes that head, tail and
 * element are structs with prevE and nextE fields.
 *
 * @param head pointer to the head of the EDLL
 * @param tail pointer to the tail of the EDLL
 * @param element element to insert
 */
#define EDLL_insert(head,tail,element) do { \
  (element)->nextE = (head); \
  (element)->prevE = NULL; \
  if ((tail) == NULL) \
    (tail) = element; \
  else \
    (head)->prevE = element; \
  (head) = (element); } while (0)


/**
 * Remove an element from a EDLL. Assumes
 * that head, tail and element are structs
 * with prevE and nextE fields.
 *
 * @param head pointer to the head of the EDLL
 * @param tail pointer to the tail of the EDLL
 * @param element element to remove
 */
#define EDLL_remove(head,tail,element) do { \
  if ((element)->prevE == NULL) \
    (head) = (element)->nextE;  \
  else \
    (element)->prevE->nextE = (element)->nextE; \
  if ((element)->nextE == NULL) \
    (tail) = (element)->prevE;  \
  else \
    (element)->nextE->prevE = (element)->prevE; \
  (element)->nextE = NULL; \
  (element)->prevE = NULL; } while (0)


/**
 * Convert all occurrences of '+' to ' '.
 *
 * @param arg string that is modified (in place), must be 0-terminated
 */
void
MHD_unescape_plus (char *arg);


/**
 * Callback invoked when iterating over @a key / @a value
 * argument pairs during parsing.
 *
 * @param connection context of the iteration
 * @param key 0-terminated key string, never NULL
 * @param value 0-terminated value string, may be NULL
 * @param kind origin of the key-value pair
 * @return #MHD_YES on success (continue to iterate)
 *         #MHD_NO to signal failure (and abort iteration)
 */
typedef int
(*MHD_ArgumentIterator_)(struct MHD_Connection *connection,
			 const char *key,
			 const char *value,
			 enum MHD_ValueKind kind);


/**
 * Parse and unescape the arguments given by the client
 * as part of the HTTP request URI.
 *
 * @param kind header kind to pass to @a cb
 * @param connection connection to add headers to
 * @param[in|out] args argument URI string (after "?" in URI),
 *        clobbered in the process!
 * @param cb function to call on each key-value pair found
 * @param[out] num_headers set to the number of headers found
 * @return #MHD_NO on failure (@a cb returned #MHD_NO),
 *         #MHD_YES for success (parsing succeeded, @a cb always
 *                               returned #MHD_YES)
 */
int
MHD_parse_arguments_ (struct MHD_Connection *connection,
		      enum MHD_ValueKind kind,
		      char *args,
		      MHD_ArgumentIterator_ cb,
		      unsigned int *num_headers);


#endif