aboutsummaryrefslogtreecommitdiff
path: root/src/or/circuitlist.c
blob: 85f529194b3c5ebddd7a909324326edfeaaddc30 (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
/* Copyright 2001 Matej Pfajfar.
 * Copyright (c) 2001-2004, Roger Dingledine.
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2011, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file circuitlist.c
 * \brief Manage the global circuit list.
 **/

#include "or.h"
#include "circuitbuild.h"
#include "circuitlist.h"
#include "circuituse.h"
#include "connection.h"
#include "config.h"
#include "connection_edge.h"
#include "connection_or.h"
#include "control.h"
#include "networkstatus.h"
#include "nodelist.h"
#include "onion.h"
#include "relay.h"
#include "rendclient.h"
#include "rendcommon.h"
#include "rephist.h"
#include "routerlist.h"
#include "ht.h"

/********* START VARIABLES **********/

/** A global list of all circuits at this hop. */
circuit_t *global_circuitlist=NULL;

/** A list of all the circuits in CIRCUIT_STATE_OR_WAIT. */
static smartlist_t *circuits_pending_or_conns=NULL;

static void circuit_free(circuit_t *circ);
static void circuit_free_cpath(crypt_path_t *cpath);
static void circuit_free_cpath_node(crypt_path_t *victim);
static void cpath_ref_decref(crypt_path_reference_t *cpath_ref);

/********* END VARIABLES ************/

/** A map from OR connection and circuit ID to circuit.  (Lookup performance is
 * very important here, since we need to do it every time a cell arrives.) */
typedef struct orconn_circid_circuit_map_t {
  HT_ENTRY(orconn_circid_circuit_map_t) node;
  or_connection_t *or_conn;
  circid_t circ_id;
  circuit_t *circuit;
} orconn_circid_circuit_map_t;

/** Helper for hash tables: compare the OR connection and circuit ID for a and
 * b, and return less than, equal to, or greater than zero appropriately.
 */
static INLINE int
_orconn_circid_entries_eq(orconn_circid_circuit_map_t *a,
                          orconn_circid_circuit_map_t *b)
{
  return a->or_conn == b->or_conn && a->circ_id == b->circ_id;
}

/** Helper: return a hash based on circuit ID and the pointer value of
 * or_conn in <b>a</b>. */
static INLINE unsigned int
_orconn_circid_entry_hash(orconn_circid_circuit_map_t *a)
{
  return (((unsigned)a->circ_id)<<8) ^ (unsigned)(uintptr_t)(a->or_conn);
}

/** Map from [orconn,circid] to circuit. */
static HT_HEAD(orconn_circid_map, orconn_circid_circuit_map_t)
     orconn_circid_circuit_map = HT_INITIALIZER();
HT_PROTOTYPE(orconn_circid_map, orconn_circid_circuit_map_t, node,
             _orconn_circid_entry_hash, _orconn_circid_entries_eq)
HT_GENERATE(orconn_circid_map, orconn_circid_circuit_map_t, node,
            _orconn_circid_entry_hash, _orconn_circid_entries_eq, 0.6,
            malloc, realloc, free)

/** The most recently returned entry from circuit_get_by_circid_orconn;
 * used to improve performance when many cells arrive in a row from the
 * same circuit.
 */
orconn_circid_circuit_map_t *_last_circid_orconn_ent = NULL;

/** Implementation helper for circuit_set_{p,n}_circid_orconn: A circuit ID
 * and/or or_connection for circ has just changed from <b>old_conn, old_id</b>
 * to <b>conn, id</b>.  Adjust the conn,circid map as appropriate, removing
 * the old entry (if any) and adding a new one. */
static void
circuit_set_circid_orconn_helper(circuit_t *circ, int direction,
                                 circid_t id,
                                 or_connection_t *conn)
{
  orconn_circid_circuit_map_t search;
  orconn_circid_circuit_map_t *found;
  or_connection_t *old_conn, **conn_ptr;
  circid_t old_id, *circid_ptr;
  int was_active, make_active;

  if (direction == CELL_DIRECTION_OUT) {
    conn_ptr = &circ->n_conn;
    circid_ptr = &circ->n_circ_id;
    was_active = circ->next_active_on_n_conn != NULL;
    make_active = circ->n_conn_cells.n > 0;
  } else {
    or_circuit_t *c = TO_OR_CIRCUIT(circ);
    conn_ptr = &c->p_conn;
    circid_ptr = &c->p_circ_id;
    was_active = c->next_active_on_p_conn != NULL;
    make_active = c->p_conn_cells.n > 0;
  }
  old_conn = *conn_ptr;
  old_id = *circid_ptr;

  if (id == old_id && conn == old_conn)
    return;

  if (_last_circid_orconn_ent &&
      ((old_id == _last_circid_orconn_ent->circ_id &&
        old_conn == _last_circid_orconn_ent->or_conn) ||
       (id == _last_circid_orconn_ent->circ_id &&
        conn == _last_circid_orconn_ent->or_conn))) {
    _last_circid_orconn_ent = NULL;
  }

  if (old_conn) { /* we may need to remove it from the conn-circid map */
    tor_assert(old_conn->_base.magic == OR_CONNECTION_MAGIC);
    search.circ_id = old_id;
    search.or_conn = old_conn;
    found = HT_REMOVE(orconn_circid_map, &orconn_circid_circuit_map, &search);
    if (found) {
      tor_free(found);
      --old_conn->n_circuits;
    }
    if (was_active && old_conn != conn)
      make_circuit_inactive_on_conn(circ,old_conn);
  }

  /* Change the values only after we have possibly made the circuit inactive
   * on the previous conn. */
  *conn_ptr = conn;
  *circid_ptr = id;

  if (conn == NULL)
    return;

  /* now add the new one to the conn-circid map */
  search.circ_id = id;
  search.or_conn = conn;
  found = HT_FIND(orconn_circid_map, &orconn_circid_circuit_map, &search);
  if (found) {
    found->circuit = circ;
  } else {
    found = tor_malloc_zero(sizeof(orconn_circid_circuit_map_t));
    found->circ_id = id;
    found->or_conn = conn;
    found->circuit = circ;
    HT_INSERT(orconn_circid_map, &orconn_circid_circuit_map, found);
  }
  if (make_active && old_conn != conn)
    make_circuit_active_on_conn(circ,conn);

  ++conn->n_circuits;
}

/** Set the p_conn field of a circuit <b>circ</b>, along
 * with the corresponding circuit ID, and add the circuit as appropriate
 * to the (orconn,id)-\>circuit map. */
void
circuit_set_p_circid_orconn(or_circuit_t *circ, circid_t id,
                            or_connection_t *conn)
{
  circuit_set_circid_orconn_helper(TO_CIRCUIT(circ), CELL_DIRECTION_IN,
                                   id, conn);

  if (conn)
    tor_assert(bool_eq(circ->p_conn_cells.n, circ->next_active_on_p_conn));
}

/** Set the n_conn field of a circuit <b>circ</b>, along
 * with the corresponding circuit ID, and add the circuit as appropriate
 * to the (orconn,id)-\>circuit map. */
void
circuit_set_n_circid_orconn(circuit_t *circ, circid_t id,
                            or_connection_t *conn)
{
  circuit_set_circid_orconn_helper(circ, CELL_DIRECTION_OUT, id, conn);

  if (conn)
    tor_assert(bool_eq(circ->n_conn_cells.n, circ->next_active_on_n_conn));
}

/** Change the state of <b>circ</b> to <b>state</b>, adding it to or removing
 * it from lists as appropriate. */
void
circuit_set_state(circuit_t *circ, uint8_t state)
{
  tor_assert(circ);
  if (state == circ->state)
    return;
  if (!circuits_pending_or_conns)
    circuits_pending_or_conns = smartlist_new();
  if (circ->state == CIRCUIT_STATE_OR_WAIT) {
    /* remove from waiting-circuit list. */
    smartlist_remove(circuits_pending_or_conns, circ);
  }
  if (state == CIRCUIT_STATE_OR_WAIT) {
    /* add to waiting-circuit list. */
    smartlist_add(circuits_pending_or_conns, circ);
  }
  if (state == CIRCUIT_STATE_OPEN)
    tor_assert(!circ->n_conn_onionskin);
  circ->state = state;
}

/** Add <b>circ</b> to the global list of circuits. This is called only from
 * within circuit_new.
 */
static void
circuit_add(circuit_t *circ)
{
  if (!global_circuitlist) { /* first one */
    global_circuitlist = circ;
    circ->next = NULL;
  } else {
    circ->next = global_circuitlist;
    global_circuitlist = circ;
  }
}

/** Append to <b>out</b> all circuits in state OR_WAIT waiting for
 * the given connection. */
void
circuit_get_all_pending_on_or_conn(smartlist_t *out, or_connection_t *or_conn)
{
  tor_assert(out);
  tor_assert(or_conn);

  if (!circuits_pending_or_conns)
    return;

  SMARTLIST_FOREACH_BEGIN(circuits_pending_or_conns, circuit_t *, circ) {
    if (circ->marked_for_close)
      continue;
    if (!circ->n_hop)
      continue;
    tor_assert(circ->state == CIRCUIT_STATE_OR_WAIT);
    if (tor_digest_is_zero(circ->n_hop->identity_digest)) {
      /* Look at addr/port. This is an unkeyed connection. */
      if (!tor_addr_eq(&circ->n_hop->addr, &or_conn->_base.addr) ||
          circ->n_hop->port != or_conn->_base.port)
        continue;
    } else {
      /* We expected a key. See if it's the right one. */
      if (tor_memneq(or_conn->identity_digest,
                 circ->n_hop->identity_digest, DIGEST_LEN))
        continue;
    }
    smartlist_add(out, circ);
  } SMARTLIST_FOREACH_END(circ);
}

/** Return the number of circuits in state OR_WAIT, waiting for the given
 * connection. */
int
circuit_count_pending_on_or_conn(or_connection_t *or_conn)
{
  int cnt;
  smartlist_t *sl = smartlist_new();
  circuit_get_all_pending_on_or_conn(sl, or_conn);
  cnt = smartlist_len(sl);
  smartlist_free(sl);
  log_debug(LD_CIRC,"or_conn to %s at %s, %d pending circs",
            or_conn->nickname ? or_conn->nickname : "NULL",
            or_conn->_base.address,
            cnt);
  return cnt;
}

/** Detach from the global circuit list, and deallocate, all
 * circuits that have been marked for close.
 */
void
circuit_close_all_marked(void)
{
  circuit_t *tmp,*m;

  while (global_circuitlist && global_circuitlist->marked_for_close) {
    tmp = global_circuitlist->next;
    circuit_free(global_circuitlist);
    global_circuitlist = tmp;
  }

  tmp = global_circuitlist;
  while (tmp && tmp->next) {
    if (tmp->next->marked_for_close) {
      m = tmp->next->next;
      circuit_free(tmp->next);
      tmp->next = m;
      /* Need to check new tmp->next; don't advance tmp. */
    } else {
      /* Advance tmp. */
      tmp = tmp->next;
    }
  }
}

/** Return the head of the global linked list of circuits. */
circuit_t *
_circuit_get_global_list(void)
{
  return global_circuitlist;
}

/** Function to make circ-\>state human-readable */
const char *
circuit_state_to_string(int state)
{
  static char buf[64];
  switch (state) {
    case CIRCUIT_STATE_BUILDING: return "doing handshakes";
    case CIRCUIT_STATE_ONIONSKIN_PENDING: return "processing the onion";
    case CIRCUIT_STATE_OR_WAIT: return "connecting to server";
    case CIRCUIT_STATE_OPEN: return "open";
    default:
      log_warn(LD_BUG, "Unknown circuit state %d", state);
      tor_snprintf(buf, sizeof(buf), "unknown state [%d]", state);
      return buf;
  }
}

/** Map a circuit purpose to a string suitable to be displayed to a
 * controller. */
const char *
circuit_purpose_to_controller_string(uint8_t purpose)
{
  static char buf[32];
  switch (purpose) {
    case CIRCUIT_PURPOSE_OR:
    case CIRCUIT_PURPOSE_INTRO_POINT:
    case CIRCUIT_PURPOSE_REND_POINT_WAITING:
    case CIRCUIT_PURPOSE_REND_ESTABLISHED:
      return "SERVER"; /* A controller should never see these, actually. */

    case CIRCUIT_PURPOSE_C_GENERAL:
      return "GENERAL";
    case CIRCUIT_PURPOSE_C_INTRODUCING:
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACKED:
      return "HS_CLIENT_INTRO";

    case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
    case CIRCUIT_PURPOSE_C_REND_READY:
    case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      return "HS_CLIENT_REND";

    case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
    case CIRCUIT_PURPOSE_S_INTRO:
      return "HS_SERVICE_INTRO";

    case CIRCUIT_PURPOSE_S_CONNECT_REND:
    case CIRCUIT_PURPOSE_S_REND_JOINED:
      return "HS_SERVICE_REND";

    case CIRCUIT_PURPOSE_TESTING:
      return "TESTING";
    case CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT:
      return "MEASURE_TIMEOUT";
    case CIRCUIT_PURPOSE_CONTROLLER:
      return "CONTROLLER";

    default:
      tor_snprintf(buf, sizeof(buf), "UNKNOWN_%d", (int)purpose);
      return buf;
  }
}

/** Return a string specifying the state of the hidden-service circuit
 * purpose <b>purpose</b>, or NULL if <b>purpose</b> is not a
 * hidden-service-related circuit purpose. */
const char *
circuit_purpose_to_controller_hs_state_string(uint8_t purpose)
{
  switch (purpose)
    {
    default:
      log_fn(LOG_WARN, LD_BUG,
             "Unrecognized circuit purpose: %d",
             (int)purpose);
      tor_fragile_assert();
      /* fall through */

    case CIRCUIT_PURPOSE_OR:
    case CIRCUIT_PURPOSE_C_GENERAL:
    case CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT:
    case CIRCUIT_PURPOSE_TESTING:
    case CIRCUIT_PURPOSE_CONTROLLER:
      return NULL;

    case CIRCUIT_PURPOSE_INTRO_POINT:
      return "OR_HSSI_ESTABLISHED";
    case CIRCUIT_PURPOSE_REND_POINT_WAITING:
      return "OR_HSCR_ESTABLISHED";
    case CIRCUIT_PURPOSE_REND_ESTABLISHED:
      return "OR_HS_R_JOINED";

    case CIRCUIT_PURPOSE_C_INTRODUCING:
      return "HSCI_CONNECTING";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
      return "HSCI_INTRO_SENT";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACKED:
      return "HSCI_DONE";

    case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
      return "HSCR_CONNECTING";
    case CIRCUIT_PURPOSE_C_REND_READY:
      return "HSCR_ESTABLISHED_IDLE";
    case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
      return "HSCR_ESTABLISHED_WAITING";
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      return "HSCR_JOINED";

    case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
      return "HSSI_CONNECTING";
    case CIRCUIT_PURPOSE_S_INTRO:
      return "HSSI_ESTABLISHED";

    case CIRCUIT_PURPOSE_S_CONNECT_REND:
      return "HSSR_CONNECTING";
    case CIRCUIT_PURPOSE_S_REND_JOINED:
      return "HSSR_JOINED";
    }
}

/** Return a human-readable string for the circuit purpose <b>purpose</b>. */
const char *
circuit_purpose_to_string(uint8_t purpose)
{
  static char buf[32];

  switch (purpose)
    {
    case CIRCUIT_PURPOSE_OR:
      return "Circuit at relay";
    case CIRCUIT_PURPOSE_INTRO_POINT:
      return "Acting as intro point";
    case CIRCUIT_PURPOSE_REND_POINT_WAITING:
      return "Acting as rendevous (pending)";
    case CIRCUIT_PURPOSE_REND_ESTABLISHED:
      return "Acting as rendevous (established)";
    case CIRCUIT_PURPOSE_C_GENERAL:
      return "General-purpose client";
    case CIRCUIT_PURPOSE_C_INTRODUCING:
      return "Hidden service client: Connecting to intro point";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT:
      return "Hidden service client: Waiting for ack from intro point";
    case CIRCUIT_PURPOSE_C_INTRODUCE_ACKED:
      return "Hidden service client: Received ack from intro point";
    case CIRCUIT_PURPOSE_C_ESTABLISH_REND:
      return "Hidden service client: Establishing rendezvous point";
    case CIRCUIT_PURPOSE_C_REND_READY:
      return "Hidden service client: Pending rendezvous point";
    case CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED:
      return "Hidden service client: Pending rendezvous point (ack received)";
    case CIRCUIT_PURPOSE_C_REND_JOINED:
      return "Hidden service client: Active rendezvous point";
    case CIRCUIT_PURPOSE_C_MEASURE_TIMEOUT:
      return "Measuring circuit timeout";

    case CIRCUIT_PURPOSE_S_ESTABLISH_INTRO:
      return "Hidden service: Establishing introduction point";
    case CIRCUIT_PURPOSE_S_INTRO:
      return "Hidden service: Introduction point";
    case CIRCUIT_PURPOSE_S_CONNECT_REND:
      return "Hidden service: Connecting to rendezvous point";
    case CIRCUIT_PURPOSE_S_REND_JOINED:
      return "Hidden service: Active rendezvous point";

    case CIRCUIT_PURPOSE_TESTING:
      return "Testing circuit";

    case CIRCUIT_PURPOSE_CONTROLLER:
      return "Circuit made by controller";

    default:
      tor_snprintf(buf, sizeof(buf), "UNKNOWN_%d", (int)purpose);
      return buf;
  }
}

/** Pick a reasonable package_window to start out for our circuits.
 * Originally this was hard-coded at 1000, but now the consensus votes
 * on the answer. See proposal 168. */
int32_t
circuit_initial_package_window(void)
{
  int32_t num = networkstatus_get_param(NULL, "circwindow", CIRCWINDOW_START,
                                        CIRCWINDOW_START_MIN,
                                        CIRCWINDOW_START_MAX);
  /* If the consensus tells us a negative number, we'd assert. */
  if (num < 0)
    num = CIRCWINDOW_START;
  return num;
}

/** Initialize the common elements in a circuit_t, and add it to the global
 * list. */
static void
init_circuit_base(circuit_t *circ)
{
  tor_gettimeofday(&circ->timestamp_created);

  circ->package_window = circuit_initial_package_window();
  circ->deliver_window = CIRCWINDOW_START;

  /* Initialize the cell_ewma_t structure */
  circ->n_cell_ewma.last_adjusted_tick = cell_ewma_get_tick();
  circ->n_cell_ewma.cell_count = 0.0;
  circ->n_cell_ewma.heap_index = -1;
  circ->n_cell_ewma.is_for_p_conn = 0;

  circuit_add(circ);
}

/** Allocate space for a new circuit, initializing with <b>p_circ_id</b>
 * and <b>p_conn</b>. Add it to the global circuit list.
 */
origin_circuit_t *
origin_circuit_new(void)
{
  origin_circuit_t *circ;
  /* never zero, since a global ID of 0 is treated specially by the
   * controller */
  static uint32_t n_circuits_allocated = 1;

  circ = tor_malloc_zero(sizeof(origin_circuit_t));
  circ->_base.magic = ORIGIN_CIRCUIT_MAGIC;

  circ->next_stream_id = crypto_rand_int(1<<16);
  circ->global_identifier = n_circuits_allocated++;
  circ->remaining_relay_early_cells = MAX_RELAY_EARLY_CELLS_PER_CIRCUIT;
  circ->remaining_relay_early_cells -= crypto_rand_int(2);

  init_circuit_base(TO_CIRCUIT(circ));

  circ_times.last_circ_at = approx_time();

  return circ;
}

/** Allocate a new or_circuit_t, connected to <b>p_conn</b> as
 * <b>p_circ_id</b>.  If <b>p_conn</b> is NULL, the circuit is unattached. */
or_circuit_t *
or_circuit_new(circid_t p_circ_id, or_connection_t *p_conn)
{
  /* CircIDs */
  or_circuit_t *circ;

  circ = tor_malloc_zero(sizeof(or_circuit_t));
  circ->_base.magic = OR_CIRCUIT_MAGIC;

  if (p_conn)
    circuit_set_p_circid_orconn(circ, p_circ_id, p_conn);

  circ->remaining_relay_early_cells = MAX_RELAY_EARLY_CELLS_PER_CIRCUIT;

  init_circuit_base(TO_CIRCUIT(circ));

  /* Initialize the cell_ewma_t structure */

  /* Initialize the cell counts to 0 */
  circ->p_cell_ewma.cell_count = 0.0;
  circ->p_cell_ewma.last_adjusted_tick = cell_ewma_get_tick();
  circ->p_cell_ewma.is_for_p_conn = 1;

  /* It's not in any heap yet. */
  circ->p_cell_ewma.heap_index = -1;

  return circ;
}

/** Deallocate space associated with circ.
 */
static void
circuit_free(circuit_t *circ)
{
  void *mem;
  size_t memlen;
  if (!circ)
    return;

  if (CIRCUIT_IS_ORIGIN(circ)) {
    origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
    mem = ocirc;
    memlen = sizeof(origin_circuit_t);
    tor_assert(circ->magic == ORIGIN_CIRCUIT_MAGIC);
    if (ocirc->build_state) {
        extend_info_free(ocirc->build_state->chosen_exit);
        circuit_free_cpath_node(ocirc->build_state->pending_final_cpath);
        cpath_ref_decref(ocirc->build_state->service_pending_final_cpath_ref);
    }
    tor_free(ocirc->build_state);

    circuit_free_cpath(ocirc->cpath);

    crypto_pk_free(ocirc->intro_key);
    rend_data_free(ocirc->rend_data);

    tor_free(ocirc->dest_address);
    if (ocirc->socks_username) {
      memset(ocirc->socks_username, 0x12, ocirc->socks_username_len);
      tor_free(ocirc->socks_username);
    }
    if (ocirc->socks_password) {
      memset(ocirc->socks_password, 0x06, ocirc->socks_password_len);
      tor_free(ocirc->socks_password);
    }
  } else {
    or_circuit_t *ocirc = TO_OR_CIRCUIT(circ);
    /* Remember cell statistics for this circuit before deallocating. */
    if (get_options()->CellStatistics)
      rep_hist_buffer_stats_add_circ(circ, time(NULL));
    mem = ocirc;
    memlen = sizeof(or_circuit_t);
    tor_assert(circ->magic == OR_CIRCUIT_MAGIC);

    crypto_cipher_free(ocirc->p_crypto);
    crypto_digest_free(ocirc->p_digest);
    crypto_cipher_free(ocirc->n_crypto);
    crypto_digest_free(ocirc->n_digest);

    if (ocirc->rend_splice) {
      or_circuit_t *other = ocirc->rend_splice;
      tor_assert(other->_base.magic == OR_CIRCUIT_MAGIC);
      other->rend_splice = NULL;
    }

    /* remove from map. */
    circuit_set_p_circid_orconn(ocirc, 0, NULL);

    /* Clear cell queue _after_ removing it from the map.  Otherwise our
     * "active" checks will be violated. */
    cell_queue_clear(&ocirc->p_conn_cells);
  }

  extend_info_free(circ->n_hop);
  tor_free(circ->n_conn_onionskin);

  /* Remove from map. */
  circuit_set_n_circid_orconn(circ, 0, NULL);

  /* Clear cell queue _after_ removing it from the map.  Otherwise our
   * "active" checks will be violated. */
  cell_queue_clear(&circ->n_conn_cells);

  memset(mem, 0xAA, memlen); /* poison memory */
  tor_free(mem);
}

/** Deallocate space associated with the linked list <b>cpath</b>. */
static void
circuit_free_cpath(crypt_path_t *cpath)
{
  crypt_path_t *victim, *head=cpath;

  if (!cpath)
    return;

  /* it's a doubly linked list, so we have to notice when we've
   * gone through it once. */
  while (cpath->next && cpath->next != head) {
    victim = cpath;
    cpath = victim->next;
    circuit_free_cpath_node(victim);
  }

  circuit_free_cpath_node(cpath);
}

/** Release all storage held by circuits. */
void
circuit_free_all(void)
{
  circuit_t *next;
  while (global_circuitlist) {
    next = global_circuitlist->next;
    if (! CIRCUIT_IS_ORIGIN(global_circuitlist)) {
      or_circuit_t *or_circ = TO_OR_CIRCUIT(global_circuitlist);
      while (or_circ->resolving_streams) {
        edge_connection_t *next_conn;
        next_conn = or_circ->resolving_streams->next_stream;
        connection_free(TO_CONN(or_circ->resolving_streams));
        or_circ->resolving_streams = next_conn;
      }
    }
    circuit_free(global_circuitlist);
    global_circuitlist = next;
  }

  smartlist_free(circuits_pending_or_conns);
  circuits_pending_or_conns = NULL;

  HT_CLEAR(orconn_circid_map, &orconn_circid_circuit_map);
}

/** Deallocate space associated with the cpath node <b>victim</b>. */
static void
circuit_free_cpath_node(crypt_path_t *victim)
{
  if (!victim)
    return;

  crypto_cipher_free(victim->f_crypto);
  crypto_cipher_free(victim->b_crypto);
  crypto_digest_free(victim->f_digest);
  crypto_digest_free(victim->b_digest);
  crypto_dh_free(victim->dh_handshake_state);
  extend_info_free(victim->extend_info);

  memset(victim, 0xBB, sizeof(crypt_path_t)); /* poison memory */
  tor_free(victim);
}

/** Release a crypt_path_reference_t*, which may be NULL. */
static void
cpath_ref_decref(crypt_path_reference_t *cpath_ref)
{
  if (cpath_ref != NULL) {
    if (--(cpath_ref->refcount) == 0) {
      circuit_free_cpath_node(cpath_ref->cpath);
      tor_free(cpath_ref);
    }
  }
}

/** A helper function for circuit_dump_by_conn() below. Log a bunch
 * of information about circuit <b>circ</b>.
 */
static void
circuit_dump_details(int severity, circuit_t *circ, int conn_array_index,
                     const char *type, int this_circid, int other_circid)
{
  log(severity, LD_CIRC, "Conn %d has %s circuit: circID %d (other side %d), "
      "state %d (%s), born %ld:",
      conn_array_index, type, this_circid, other_circid, circ->state,
      circuit_state_to_string(circ->state),
      (long)circ->timestamp_created.tv_sec);
  if (CIRCUIT_IS_ORIGIN(circ)) { /* circ starts at this node */
    circuit_log_path(severity, LD_CIRC, TO_ORIGIN_CIRCUIT(circ));
  }
}

/** Log, at severity <b>severity</b>, information about each circuit
 * that is connected to <b>conn</b>.
 */
void
circuit_dump_by_conn(connection_t *conn, int severity)
{
  circuit_t *circ;
  edge_connection_t *tmpconn;

  for (circ=global_circuitlist;circ;circ = circ->next) {
    circid_t n_circ_id = circ->n_circ_id, p_circ_id = 0;
    if (circ->marked_for_close)
      continue;

    if (! CIRCUIT_IS_ORIGIN(circ))
      p_circ_id = TO_OR_CIRCUIT(circ)->p_circ_id;

    if (! CIRCUIT_IS_ORIGIN(circ) && TO_OR_CIRCUIT(circ)->p_conn &&
        TO_CONN(TO_OR_CIRCUIT(circ)->p_conn) == conn)
      circuit_dump_details(severity, circ, conn->conn_array_index, "App-ward",
                           p_circ_id, n_circ_id);
    if (CIRCUIT_IS_ORIGIN(circ)) {
      for (tmpconn=TO_ORIGIN_CIRCUIT(circ)->p_streams; tmpconn;
           tmpconn=tmpconn->next_stream) {
        if (TO_CONN(tmpconn) == conn) {
          circuit_dump_details(severity, circ, conn->conn_array_index,
                               "App-ward", p_circ_id, n_circ_id);
        }
      }
    }
    if (circ->n_conn && TO_CONN(circ->n_conn) == conn)
      circuit_dump_details(severity, circ, conn->conn_array_index, "Exit-ward",
                           n_circ_id, p_circ_id);
    if (! CIRCUIT_IS_ORIGIN(circ)) {
      for (tmpconn=TO_OR_CIRCUIT(circ)->n_streams; tmpconn;
           tmpconn=tmpconn->next_stream) {
        if (TO_CONN(tmpconn) == conn) {
          circuit_dump_details(severity, circ, conn->conn_array_index,
                               "Exit-ward", n_circ_id, p_circ_id);
        }
      }
    }
    if (!circ->n_conn && circ->n_hop &&
        tor_addr_eq(&circ->n_hop->addr, &conn->addr) &&
        circ->n_hop->port == conn->port &&
        conn->type == CONN_TYPE_OR &&
        tor_memeq(TO_OR_CONN(conn)->identity_digest,
                circ->n_hop->identity_digest, DIGEST_LEN)) {
      circuit_dump_details(severity, circ, conn->conn_array_index,
                           (circ->state == CIRCUIT_STATE_OPEN &&
                            !CIRCUIT_IS_ORIGIN(circ)) ?
                             "Endpoint" : "Pending",
                           n_circ_id, p_circ_id);
    }
  }
}

/** Return the circuit whose global ID is <b>id</b>, or NULL if no
 * such circuit exists. */
origin_circuit_t *
circuit_get_by_global_id(uint32_t id)
{
  circuit_t *circ;
  for (circ=global_circuitlist;circ;circ = circ->next) {
    if (CIRCUIT_IS_ORIGIN(circ) &&
        TO_ORIGIN_CIRCUIT(circ)->global_identifier == id) {
      if (circ->marked_for_close)
        return NULL;
      else
        return TO_ORIGIN_CIRCUIT(circ);
    }
  }
  return NULL;
}

/** Return a circ such that:
 *  - circ-\>n_circ_id or circ-\>p_circ_id is equal to <b>circ_id</b>, and
 *  - circ is attached to <b>conn</b>, either as p_conn or n_conn.
 * Return NULL if no such circuit exists.
 */
static INLINE circuit_t *
circuit_get_by_circid_orconn_impl(circid_t circ_id, or_connection_t *conn)
{
  orconn_circid_circuit_map_t search;
  orconn_circid_circuit_map_t *found;

  if (_last_circid_orconn_ent &&
      circ_id == _last_circid_orconn_ent->circ_id &&
      conn == _last_circid_orconn_ent->or_conn) {
    found = _last_circid_orconn_ent;
  } else {
    search.circ_id = circ_id;
    search.or_conn = conn;
    found = HT_FIND(orconn_circid_map, &orconn_circid_circuit_map, &search);
    _last_circid_orconn_ent = found;
  }
  if (found && found->circuit)
    return found->circuit;

  return NULL;
  /* The rest of this checks for bugs. Disabled by default. */
  /* We comment it out because coverity complains otherwise.
  {
    circuit_t *circ;
    for (circ=global_circuitlist;circ;circ = circ->next) {
      if (! CIRCUIT_IS_ORIGIN(circ)) {
        or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
        if (or_circ->p_conn == conn && or_circ->p_circ_id == circ_id) {
          log_warn(LD_BUG,
                   "circuit matches p_conn, but not in hash table (Bug!)");
          return circ;
        }
      }
      if (circ->n_conn == conn && circ->n_circ_id == circ_id) {
        log_warn(LD_BUG,
                 "circuit matches n_conn, but not in hash table (Bug!)");
        return circ;
      }
    }
    return NULL;
  } */
}

/** Return a circ such that:
 *  - circ-\>n_circ_id or circ-\>p_circ_id is equal to <b>circ_id</b>, and
 *  - circ is attached to <b>conn</b>, either as p_conn or n_conn.
 *  - circ is not marked for close.
 * Return NULL if no such circuit exists.
 */
circuit_t *
circuit_get_by_circid_orconn(circid_t circ_id, or_connection_t *conn)
{
  circuit_t *circ = circuit_get_by_circid_orconn_impl(circ_id, conn);
  if (!circ || circ->marked_for_close)
    return NULL;
  else
    return circ;
}

/** Return true iff the circuit ID <b>circ_id</b> is currently used by a
 * circuit, marked or not, on <b>conn</b>. */
int
circuit_id_in_use_on_orconn(circid_t circ_id, or_connection_t *conn)
{
  return circuit_get_by_circid_orconn_impl(circ_id, conn) != NULL;
}

/** Return the circuit that a given edge connection is using. */
circuit_t *
circuit_get_by_edge_conn(edge_connection_t *conn)
{
  circuit_t *circ;

  circ = conn->on_circuit;
  tor_assert(!circ ||
             (CIRCUIT_IS_ORIGIN(circ) ? circ->magic == ORIGIN_CIRCUIT_MAGIC
                                      : circ->magic == OR_CIRCUIT_MAGIC));

  return circ;
}

/** For each circuit that has <b>conn</b> as n_conn or p_conn, unlink the
 * circuit from the orconn,circid map, and mark it for close if it hasn't
 * been marked already.
 */
void
circuit_unlink_all_from_or_conn(or_connection_t *conn, int reason)
{
  circuit_t *circ;

  connection_or_unlink_all_active_circs(conn);

  for (circ = global_circuitlist; circ; circ = circ->next) {
    int mark = 0;
    if (circ->n_conn == conn) {
        circuit_set_n_circid_orconn(circ, 0, NULL);
        mark = 1;
    }
    if (! CIRCUIT_IS_ORIGIN(circ)) {
      or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
      if (or_circ->p_conn == conn) {
        circuit_set_p_circid_orconn(or_circ, 0, NULL);
        mark = 1;
      }
    }
    if (mark && !circ->marked_for_close)
      circuit_mark_for_close(circ, reason);
  }
}

/** Return a circ such that
 *  - circ-\>rend_data-\>onion_address is equal to
 *    <b>rend_data</b>-\>onion_address,
 *  - circ-\>rend_data-\>rend_cookie is equal to
 *    <b>rend_data</b>-\>rend_cookie, and
 *  - circ-\>purpose is equal to CIRCUIT_PURPOSE_C_REND_READY.
 *
 * Return NULL if no such circuit exists.
 */
origin_circuit_t *
circuit_get_ready_rend_circ_by_rend_data(const rend_data_t *rend_data)
{
  circuit_t *circ;

  for (circ = global_circuitlist; circ; circ = circ->next) {
    if (!circ->marked_for_close &&
        circ->purpose == CIRCUIT_PURPOSE_C_REND_READY) {
      origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
      if (ocirc->rend_data &&
          !rend_cmp_service_ids(rend_data->onion_address,
                                ocirc->rend_data->onion_address) &&
          tor_memeq(ocirc->rend_data->rend_cookie,
                    rend_data->rend_cookie,
                    REND_COOKIE_LEN))
        return ocirc;
    }
  }
  return NULL;
}

/** Return the first circuit originating here in global_circuitlist after
 * <b>start</b> whose purpose is <b>purpose</b>, and where
 * <b>digest</b> (if set) matches the rend_pk_digest field. Return NULL if no
 * circuit is found.  If <b>start</b> is NULL, begin at the start of the list.
 */
origin_circuit_t *
circuit_get_next_by_pk_and_purpose(origin_circuit_t *start,
                                   const char *digest, uint8_t purpose)
{
  circuit_t *circ;
  tor_assert(CIRCUIT_PURPOSE_IS_ORIGIN(purpose));
  if (start == NULL)
    circ = global_circuitlist;
  else
    circ = TO_CIRCUIT(start)->next;

  for ( ; circ; circ = circ->next) {
    if (circ->marked_for_close)
      continue;
    if (circ->purpose != purpose)
      continue;
    if (!digest)
      return TO_ORIGIN_CIRCUIT(circ);
    else if (TO_ORIGIN_CIRCUIT(circ)->rend_data &&
             tor_memeq(TO_ORIGIN_CIRCUIT(circ)->rend_data->rend_pk_digest,
                     digest, DIGEST_LEN))
      return TO_ORIGIN_CIRCUIT(circ);
  }
  return NULL;
}

/** Return the first OR circuit in the global list whose purpose is
 * <b>purpose</b>, and whose rend_token is the <b>len</b>-byte
 * <b>token</b>. */
static or_circuit_t *
circuit_get_by_rend_token_and_purpose(uint8_t purpose, const char *token,
                                      size_t len)
{
  circuit_t *circ;
  for (circ = global_circuitlist; circ; circ = circ->next) {
    if (! circ->marked_for_close &&
        circ->purpose == purpose &&
        tor_memeq(TO_OR_CIRCUIT(circ)->rend_token, token, len))
      return TO_OR_CIRCUIT(circ);
  }
  return NULL;
}

/** Return the circuit waiting for a rendezvous with the provided cookie.
 * Return NULL if no such circuit is found.
 */
or_circuit_t *
circuit_get_rendezvous(const char *cookie)
{
  return circuit_get_by_rend_token_and_purpose(
                                     CIRCUIT_PURPOSE_REND_POINT_WAITING,
                                     cookie, REND_COOKIE_LEN);
}

/** Return the circuit waiting for intro cells of the given digest.
 * Return NULL if no such circuit is found.
 */
or_circuit_t *
circuit_get_intro_point(const char *digest)
{
  return circuit_get_by_rend_token_and_purpose(
                                     CIRCUIT_PURPOSE_INTRO_POINT, digest,
                                     DIGEST_LEN);
}

/** Return a circuit that is open, is CIRCUIT_PURPOSE_C_GENERAL,
 * has a timestamp_dirty value of 0, has flags matching the CIRCLAUNCH_*
 * flags in <b>flags</b>, and if info is defined, does not already use info
 * as any of its hops; or NULL if no circuit fits this description.
 *
 * The <b>purpose</b> argument (currently ignored) refers to the purpose of
 * the circuit we want to create, not the purpose of the circuit we want to
 * cannibalize.
 *
 * If !CIRCLAUNCH_NEED_UPTIME, prefer returning non-uptime circuits.
 */
origin_circuit_t *
circuit_find_to_cannibalize(uint8_t purpose, extend_info_t *info,
                            int flags)
{
  circuit_t *_circ;
  origin_circuit_t *best=NULL;
  int need_uptime = (flags & CIRCLAUNCH_NEED_UPTIME) != 0;
  int need_capacity = (flags & CIRCLAUNCH_NEED_CAPACITY) != 0;
  int internal = (flags & CIRCLAUNCH_IS_INTERNAL) != 0;
  const or_options_t *options = get_options();

  /* Make sure we're not trying to create a onehop circ by
   * cannibalization. */
  tor_assert(!(flags & CIRCLAUNCH_ONEHOP_TUNNEL));

  log_debug(LD_CIRC,
            "Hunting for a circ to cannibalize: purpose %d, uptime %d, "
            "capacity %d, internal %d",
            purpose, need_uptime, need_capacity, internal);

  for (_circ=global_circuitlist; _circ; _circ = _circ->next) {
    if (CIRCUIT_IS_ORIGIN(_circ) &&
        _circ->state == CIRCUIT_STATE_OPEN &&
        !_circ->marked_for_close &&
        _circ->purpose == CIRCUIT_PURPOSE_C_GENERAL &&
        !_circ->timestamp_dirty) {
      origin_circuit_t *circ = TO_ORIGIN_CIRCUIT(_circ);
      if ((!need_uptime || circ->build_state->need_uptime) &&
          (!need_capacity || circ->build_state->need_capacity) &&
          (internal == circ->build_state->is_internal) &&
          circ->remaining_relay_early_cells &&
          circ->build_state->desired_path_len == DEFAULT_ROUTE_LEN &&
          !circ->build_state->onehop_tunnel &&
          !circ->isolation_values_set) {
        if (info) {
          /* need to make sure we don't duplicate hops */
          crypt_path_t *hop = circ->cpath;
          const node_t *ri1 = node_get_by_id(info->identity_digest);
          do {
            const node_t *ri2;
            if (tor_memeq(hop->extend_info->identity_digest,
                        info->identity_digest, DIGEST_LEN))
              goto next;
            if (ri1 &&
                (ri2 = node_get_by_id(hop->extend_info->identity_digest))
                && nodes_in_same_family(ri1, ri2))
              goto next;
            hop=hop->next;
          } while (hop!=circ->cpath);
        }
        if (options->ExcludeNodes) {
          /* Make sure no existing nodes in the circuit are excluded for
           * general use.  (This may be possible if StrictNodes is 0, and we
           * thought we needed to use an otherwise excluded node for, say, a
           * directory operation.) */
          crypt_path_t *hop = circ->cpath;
          do {
            if (routerset_contains_extendinfo(options->ExcludeNodes,
                                              hop->extend_info))
              goto next;
            hop = hop->next;
          } while (hop != circ->cpath);
        }
        if (!best || (best->build_state->need_uptime && !need_uptime))
          best = circ;
      next: ;
      }
    }
  }
  return best;
}

/** Return the number of hops in circuit's path. */
int
circuit_get_cpath_len(origin_circuit_t *circ)
{
  int n = 0;
  if (circ && circ->cpath) {
    crypt_path_t *cpath, *cpath_next = NULL;
    for (cpath = circ->cpath; cpath_next != circ->cpath; cpath = cpath_next) {
      cpath_next = cpath->next;
      ++n;
    }
  }
  return n;
}

/** Return the <b>hopnum</b>th hop in <b>circ</b>->cpath, or NULL if there
 * aren't that many hops in the list. */
crypt_path_t *
circuit_get_cpath_hop(origin_circuit_t *circ, int hopnum)
{
  if (circ && circ->cpath && hopnum > 0) {
    crypt_path_t *cpath, *cpath_next = NULL;
    for (cpath = circ->cpath; cpath_next != circ->cpath; cpath = cpath_next) {
      cpath_next = cpath->next;
      if (--hopnum <= 0)
        return cpath;
    }
  }
  return NULL;
}

/** Go through the circuitlist; mark-for-close each circuit that starts
 *  at us but has not yet been used. */
void
circuit_mark_all_unused_circs(void)
{
  circuit_t *circ;

  for (circ=global_circuitlist; circ; circ = circ->next) {
    if (CIRCUIT_IS_ORIGIN(circ) &&
        !circ->marked_for_close &&
        !circ->timestamp_dirty)
      circuit_mark_for_close(circ, END_CIRC_REASON_FINISHED);
  }
}

/** Go through the circuitlist; for each circuit that starts at us
 * and is dirty, frob its timestamp_dirty so we won't use it for any
 * new streams.
 *
 * This is useful for letting the user change pseudonyms, so new
 * streams will not be linkable to old streams.
 */
/* XXX023 this is a bad name for what this function does */
void
circuit_expire_all_dirty_circs(void)
{
  circuit_t *circ;
  const or_options_t *options = get_options();

  for (circ=global_circuitlist; circ; circ = circ->next) {
    if (CIRCUIT_IS_ORIGIN(circ) &&
        !circ->marked_for_close &&
        circ->timestamp_dirty)
      /* XXXX023 This is a screwed-up way to say "This is too dirty
       * for new circuits. */
      circ->timestamp_dirty -= options->MaxCircuitDirtiness;
  }
}

/** Mark <b>circ</b> to be closed next time we call
 * circuit_close_all_marked(). Do any cleanup needed:
 *   - If state is onionskin_pending, remove circ from the onion_pending
 *     list.
 *   - If circ isn't open yet: call circuit_build_failed() if we're
 *     the origin, and in either case call circuit_rep_hist_note_result()
 *     to note stats.
 *   - If purpose is C_INTRODUCE_ACK_WAIT, report the intro point
 *     failure we just had to the hidden service client module.
 *   - If purpose is C_INTRODUCING and <b>reason</b> isn't TIMEOUT,
 *     report to the hidden service client module that the intro point
 *     we just tried may be unreachable.
 *   - Send appropriate destroys and edge_destroys for conns and
 *     streams attached to circ.
 *   - If circ->rend_splice is set (we are the midpoint of a joined
 *     rendezvous stream), then mark the other circuit to close as well.
 */
void
_circuit_mark_for_close(circuit_t *circ, int reason, int line,
                        const char *file)
{
  int orig_reason = reason; /* Passed to the controller */
  assert_circuit_ok(circ);
  tor_assert(line);
  tor_assert(file);

  if (circ->marked_for_close) {
    log(LOG_WARN,LD_BUG,
        "Duplicate call to circuit_mark_for_close at %s:%d"
        " (first at %s:%d)", file, line,
        circ->marked_for_close_file, circ->marked_for_close);
    return;
  }
  if (reason == END_CIRC_AT_ORIGIN) {
    if (!CIRCUIT_IS_ORIGIN(circ)) {
      log_warn(LD_BUG, "Specified 'at-origin' non-reason for ending circuit, "
               "but circuit was not at origin. (called %s:%d, purpose=%d)",
               file, line, circ->purpose);
    }
    reason = END_CIRC_REASON_NONE;
  }
  if (CIRCUIT_IS_ORIGIN(circ)) {
    /* We don't send reasons when closing circuits at the origin. */
    reason = END_CIRC_REASON_NONE;
  }

  if (reason & END_CIRC_REASON_FLAG_REMOTE)
    reason &= ~END_CIRC_REASON_FLAG_REMOTE;

  if (reason < _END_CIRC_REASON_MIN || reason > _END_CIRC_REASON_MAX) {
    if (!(orig_reason & END_CIRC_REASON_FLAG_REMOTE))
      log_warn(LD_BUG, "Reason %d out of range at %s:%d", reason, file, line);
    reason = END_CIRC_REASON_NONE;
  }

  if (circ->state == CIRCUIT_STATE_ONIONSKIN_PENDING) {
    onion_pending_remove(TO_OR_CIRCUIT(circ));
  }
  /* If the circuit ever became OPEN, we sent it to the reputation history
   * module then.  If it isn't OPEN, we send it there now to remember which
   * links worked and which didn't.
   */
  if (circ->state != CIRCUIT_STATE_OPEN) {
    if (CIRCUIT_IS_ORIGIN(circ)) {
      origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
      circuit_build_failed(ocirc); /* take actions if necessary */
      circuit_rep_hist_note_result(ocirc);
    }
  }
  if (circ->state == CIRCUIT_STATE_OR_WAIT) {
    if (circuits_pending_or_conns)
      smartlist_remove(circuits_pending_or_conns, circ);
  }
  if (CIRCUIT_IS_ORIGIN(circ)) {
    control_event_circuit_status(TO_ORIGIN_CIRCUIT(circ),
     (circ->state == CIRCUIT_STATE_OPEN)?CIRC_EVENT_CLOSED:CIRC_EVENT_FAILED,
     orig_reason);
  }
  if (circ->purpose == CIRCUIT_PURPOSE_C_INTRODUCE_ACK_WAIT) {
    origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
    int timed_out = (reason == END_CIRC_REASON_TIMEOUT);
    tor_assert(circ->state == CIRCUIT_STATE_OPEN);
    tor_assert(ocirc->build_state->chosen_exit);
    tor_assert(ocirc->rend_data);
    /* treat this like getting a nack from it */
    log_info(LD_REND, "Failed intro circ %s to %s (awaiting ack). %s",
           safe_str_client(ocirc->rend_data->onion_address),
           safe_str_client(build_state_get_exit_nickname(ocirc->build_state)),
           timed_out ? "Recording timeout." : "Removing from descriptor.");
    rend_client_report_intro_point_failure(ocirc->build_state->chosen_exit,
                                           ocirc->rend_data,
                                           timed_out ?
                                           INTRO_POINT_FAILURE_TIMEOUT :
                                           INTRO_POINT_FAILURE_GENERIC);
  } else if (circ->purpose == CIRCUIT_PURPOSE_C_INTRODUCING &&
             reason != END_CIRC_REASON_TIMEOUT) {
    origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
    if (ocirc->build_state->chosen_exit && ocirc->rend_data) {
      log_info(LD_REND, "Failed intro circ %s to %s "
               "(building circuit to intro point). "
               "Marking intro point as possibly unreachable.",
               safe_str_client(ocirc->rend_data->onion_address),
           safe_str_client(build_state_get_exit_nickname(ocirc->build_state)));
      rend_client_report_intro_point_failure(ocirc->build_state->chosen_exit,
                                             ocirc->rend_data,
                                             INTRO_POINT_FAILURE_UNREACHABLE);
    }
  }
  if (circ->n_conn) {
    circuit_clear_cell_queue(circ, circ->n_conn);
    connection_or_send_destroy(circ->n_circ_id, circ->n_conn, reason);
  }

  if (! CIRCUIT_IS_ORIGIN(circ)) {
    or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
    edge_connection_t *conn;
    for (conn=or_circ->n_streams; conn; conn=conn->next_stream)
      connection_edge_destroy(or_circ->p_circ_id, conn);
    or_circ->n_streams = NULL;

    while (or_circ->resolving_streams) {
      conn = or_circ->resolving_streams;
      or_circ->resolving_streams = conn->next_stream;
      if (!conn->_base.marked_for_close) {
        /* The client will see a DESTROY, and infer that the connections
         * are closing because the circuit is getting torn down.  No need
         * to send an end cell. */
        conn->edge_has_sent_end = 1;
        conn->end_reason = END_STREAM_REASON_DESTROY;
        conn->end_reason |= END_STREAM_REASON_FLAG_ALREADY_SENT_CLOSED;
        connection_mark_for_close(TO_CONN(conn));
      }
      conn->on_circuit = NULL;
    }

    if (or_circ->p_conn) {
      circuit_clear_cell_queue(circ, or_circ->p_conn);
      connection_or_send_destroy(or_circ->p_circ_id, or_circ->p_conn, reason);
    }
  } else {
    origin_circuit_t *ocirc = TO_ORIGIN_CIRCUIT(circ);
    edge_connection_t *conn;
    for (conn=ocirc->p_streams; conn; conn=conn->next_stream)
      connection_edge_destroy(circ->n_circ_id, conn);
    ocirc->p_streams = NULL;
  }

  circ->marked_for_close = line;
  circ->marked_for_close_file = file;

  if (!CIRCUIT_IS_ORIGIN(circ)) {
    or_circuit_t *or_circ = TO_OR_CIRCUIT(circ);
    if (or_circ->rend_splice) {
      if (!or_circ->rend_splice->_base.marked_for_close) {
        /* do this after marking this circuit, to avoid infinite recursion. */
        circuit_mark_for_close(TO_CIRCUIT(or_circ->rend_splice), reason);
      }
      or_circ->rend_splice = NULL;
    }
  }
}

/** Verify that cpath layer <b>cp</b> has all of its invariants
 * correct. Trigger an assert if anything is invalid.
 */
void
assert_cpath_layer_ok(const crypt_path_t *cp)
{
//  tor_assert(cp->addr); /* these are zero for rendezvous extra-hops */
//  tor_assert(cp->port);
  tor_assert(cp);
  tor_assert(cp->magic == CRYPT_PATH_MAGIC);
  switch (cp->state)
    {
    case CPATH_STATE_OPEN:
      tor_assert(cp->f_crypto);
      tor_assert(cp->b_crypto);
      /* fall through */
    case CPATH_STATE_CLOSED:
      tor_assert(!cp->dh_handshake_state);
      break;
    case CPATH_STATE_AWAITING_KEYS:
      /* tor_assert(cp->dh_handshake_state); */
      break;
    default:
      log_fn(LOG_ERR, LD_BUG, "Unexpected state %d", cp->state);
      tor_assert(0);
    }
  tor_assert(cp->package_window >= 0);
  tor_assert(cp->deliver_window >= 0);
}

/** Verify that cpath <b>cp</b> has all of its invariants
 * correct. Trigger an assert if anything is invalid.
 */
static void
assert_cpath_ok(const crypt_path_t *cp)
{
  const crypt_path_t *start = cp;

  do {
    assert_cpath_layer_ok(cp);
    /* layers must be in sequence of: "open* awaiting? closed*" */
    if (cp != start) {
      if (cp->state == CPATH_STATE_AWAITING_KEYS) {
        tor_assert(cp->prev->state == CPATH_STATE_OPEN);
      } else if (cp->state == CPATH_STATE_OPEN) {
        tor_assert(cp->prev->state == CPATH_STATE_OPEN);
      }
    }
    cp = cp->next;
    tor_assert(cp);
  } while (cp != start);
}

/** Verify that circuit <b>c</b> has all of its invariants
 * correct. Trigger an assert if anything is invalid.
 */
void
assert_circuit_ok(const circuit_t *c)
{
  edge_connection_t *conn;
  const or_circuit_t *or_circ = NULL;
  const origin_circuit_t *origin_circ = NULL;

  tor_assert(c);
  tor_assert(c->magic == ORIGIN_CIRCUIT_MAGIC || c->magic == OR_CIRCUIT_MAGIC);
  tor_assert(c->purpose >= _CIRCUIT_PURPOSE_MIN &&
             c->purpose <= _CIRCUIT_PURPOSE_MAX);

  {
    /* Having a separate variable for this pleases GCC 4.2 in ways I hope I
     * never understand. -NM. */
    circuit_t *nonconst_circ = (circuit_t*) c;
    if (CIRCUIT_IS_ORIGIN(c))
      origin_circ = TO_ORIGIN_CIRCUIT(nonconst_circ);
    else
      or_circ = TO_OR_CIRCUIT(nonconst_circ);
  }

  if (c->n_conn) {
    tor_assert(!c->n_hop);

    if (c->n_circ_id) {
      /* We use the _impl variant here to make sure we don't fail on marked
       * circuits, which would not be returned by the regular function. */
      circuit_t *c2 = circuit_get_by_circid_orconn_impl(c->n_circ_id,
                                                        c->n_conn);
      tor_assert(c == c2);
    }
  }
  if (or_circ && or_circ->p_conn) {
    if (or_circ->p_circ_id) {
      /* ibid */
      circuit_t *c2 = circuit_get_by_circid_orconn_impl(or_circ->p_circ_id,
                                                        or_circ->p_conn);
      tor_assert(c == c2);
    }
  }
  if (or_circ)
    for (conn = or_circ->n_streams; conn; conn = conn->next_stream)
      tor_assert(conn->_base.type == CONN_TYPE_EXIT);

  tor_assert(c->deliver_window >= 0);
  tor_assert(c->package_window >= 0);
  if (c->state == CIRCUIT_STATE_OPEN) {
    tor_assert(!c->n_conn_onionskin);
    if (or_circ) {
      tor_assert(or_circ->n_crypto);
      tor_assert(or_circ->p_crypto);
      tor_assert(or_circ->n_digest);
      tor_assert(or_circ->p_digest);
    }
  }
  if (c->state == CIRCUIT_STATE_OR_WAIT && !c->marked_for_close) {
    tor_assert(circuits_pending_or_conns &&
               smartlist_isin(circuits_pending_or_conns, c));
  } else {
    tor_assert(!circuits_pending_or_conns ||
               !smartlist_isin(circuits_pending_or_conns, c));
  }
  if (origin_circ && origin_circ->cpath) {
    assert_cpath_ok(origin_circ->cpath);
  }
  if (c->purpose == CIRCUIT_PURPOSE_REND_ESTABLISHED) {
    tor_assert(or_circ);
    if (!c->marked_for_close) {
      tor_assert(or_circ->rend_splice);
      tor_assert(or_circ->rend_splice->rend_splice == or_circ);
    }
    tor_assert(or_circ->rend_splice != or_circ);
  } else {
    tor_assert(!or_circ || !or_circ->rend_splice);
  }
}