summaryrefslogtreecommitdiff
path: root/content/fetchers/curl.c
blob: 2975f363b474c34e51696568620f757702439ae1 (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
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
/*
 * Copyright 2006 Daniel Silverstone <dsilvers@digital-scurf.org>
 * Copyright 2007 James Bursa <bursa@users.sourceforge.net>
 * Copyright 2003 Phil Mellor <monkeyson@users.sourceforge.net>
 *
 * This file is part of NetSurf.
 *
 * NetSurf is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * NetSurf 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * \file
 * implementation of fetching of data from http and https schemes.
 *
 * This implementation uses libcurl's 'multi' interface.
 *
 * The CURL handles are cached in the curl_handle_ring.
 */

/* must come first to ensure winsock2.h vs windows.h ordering issues */
#include "utils/inet.h"

#include <assert.h>
#include <errno.h>
#include <inttypes.h>
#include <stdbool.h>
#include <string.h>
#include <strings.h>
#include <time.h>
#include <sys/stat.h>
#include <openssl/ssl.h>

#include <libwapcaplet/libwapcaplet.h>
#include <nsutils/time.h>

#include "utils/corestrings.h"
#include "utils/nsoption.h"
#include "utils/log.h"
#include "utils/messages.h"
#include "utils/utils.h"
#include "utils/ring.h"
#include "utils/useragent.h"
#include "utils/file.h"
#include "utils/string.h"
#include "netsurf/fetch.h"
#include "netsurf/misc.h"
#include "desktop/gui_internal.h"

#include "content/fetch.h"
#include "content/fetchers.h"
#include "content/fetchers/curl.h"
#include "content/urldb.h"

/** maximum number of progress notifications per second */
#define UPDATES_PER_SECOND 2

/** maximum number of X509 certificates in chain for TLS connection */
#define MAX_CERTS 10

/** SSL certificate info */
struct cert_info {
	X509 *cert;		/**< Pointer to certificate */
	long err;		/**< OpenSSL error code */
};

/** Information for a single fetch. */
struct curl_fetch_info {
	struct fetch *fetch_handle; /**< The fetch handle we're parented by. */
	CURL * curl_handle;	/**< cURL handle if being fetched, or 0. */
	bool had_headers;	/**< Headers have been processed. */
	bool abort;		/**< Abort requested. */
	bool stopped;		/**< Download stopped on purpose. */
	bool only_2xx;		/**< Only HTTP 2xx responses acceptable. */
	bool downgrade_tls;	/**< Downgrade to TLS <= 1.0 */
	nsurl *url;		/**< URL of this fetch. */
	lwc_string *host;	/**< The hostname of this fetch. */
	struct curl_slist *headers;	/**< List of request headers. */
	char *location;		/**< Response Location header, or 0. */
	unsigned long content_length;	/**< Response Content-Length, or 0. */
	char *cookie_string;	/**< Cookie string for this fetch */
	char *realm;		/**< HTTP Auth Realm */
	char *post_urlenc;	/**< Url encoded POST string, or 0. */
	long http_code; /**< HTTP result code from cURL. */
	struct curl_httppost *post_multipart;	/**< Multipart post data, or 0. */
	uint64_t last_progress_update;	/**< Time of last progress update */
	int cert_depth; /**< deepest certificate in use */
	struct cert_info cert_data[MAX_CERTS];	/**< HTTPS certificate data */
};

/** curl handle cache entry */
struct cache_handle {
	CURL *handle; /**< The cached cURL handle */
	lwc_string *host; /**< The host for which this handle is cached */

	struct cache_handle *r_prev; /**< Previous cached handle in ring. */
	struct cache_handle *r_next; /**< Next cached handle in ring. */
};

/** Global cURL multi handle. */
CURLM *fetch_curl_multi;

/** Curl handle with default options set; not used for transfers. */
static CURL *fetch_blank_curl;

/** Ring of cached handles */
static struct cache_handle *curl_handle_ring = 0;

/** Count of how many schemes the curl fetcher is handling */
static int curl_fetchers_registered = 0;

/** Flag for runtime detection of openssl usage */
static bool curl_with_openssl;

/** Error buffer for cURL. */
static char fetch_error_buffer[CURL_ERROR_SIZE];

/** Proxy authentication details. */
static char fetch_proxy_userpwd[100];


/* OpenSSL 1.0.x to 1.1.0 certificate reference counting changed
 * LibreSSL declares its OpenSSL version as 2.1 but only supports the old way
 */
#if (defined(LIBRESSL_VERSION_NUMBER) || (OPENSSL_VERSION_NUMBER < 0x1010000fL))
static int ns_X509_up_ref(X509 *cert)
{
	cert->references++;
	return 1;
}

static void ns_X509_free(X509 *cert)
{
	cert->references--;
	if (cert->references == 0) {
		X509_free(cert);
	}
}
#else
#define ns_X509_up_ref X509_up_ref
#define ns_X509_free X509_free
#endif

/**
 * Initialise a cURL fetcher.
 */
static bool fetch_curl_initialise(lwc_string *scheme)
{
	LOG("Initialise cURL fetcher for %s", lwc_string_data(scheme));
	curl_fetchers_registered++;
	return true; /* Always succeeds */
}


/**
 * Finalise a cURL fetcher.
 *
 * \param scheme The scheme to finalise.
 */
static void fetch_curl_finalise(lwc_string *scheme)
{
	struct cache_handle *h;

	curl_fetchers_registered--;
	LOG("Finalise cURL fetcher %s", lwc_string_data(scheme));
	if (curl_fetchers_registered == 0) {
		CURLMcode codem;
		/* All the fetchers have been finalised. */
		LOG("All cURL fetchers finalised, closing down cURL");

		curl_easy_cleanup(fetch_blank_curl);

		codem = curl_multi_cleanup(fetch_curl_multi);
		if (codem != CURLM_OK)
			LOG("curl_multi_cleanup failed: ignoring");

		curl_global_cleanup();
	}

	/* Free anything remaining in the cached curl handle ring */
	while (curl_handle_ring != NULL) {
		h = curl_handle_ring;
		RING_REMOVE(curl_handle_ring, h);
		lwc_string_unref(h->host);
		curl_easy_cleanup(h->handle);
		free(h);
	}
}


/**
 * Check if this fetcher can fetch a url.
 *
 * \param url The url to check.
 * \return true if the fetcher supports the url else false.
 */
static bool fetch_curl_can_fetch(const nsurl *url)
{
	return nsurl_has_component(url, NSURL_HOST);
}


/**
 * Convert a list of struct ::fetch_multipart_data to a list of
 * struct curl_httppost for libcurl.
 */
static struct curl_httppost *
fetch_curl_post_convert(const struct fetch_multipart_data *control)
{
	struct curl_httppost *post = 0, *last = 0;
	CURLFORMcode code;
	nserror ret;

	for (; control; control = control->next) {
		if (control->file) {
			char *leafname = NULL;
			ret = guit->file->basename(control->value, &leafname, NULL);
			if (ret != NSERROR_OK) {
				continue;
			}

			/* We have to special case filenames of "", so curl
			 * a) actually attempts the fetch and
			 * b) doesn't attempt to open the file ""
			 */
			if (control->value[0] == '\0') {
				/* dummy buffer - needs to be static so
				 * pointer's still valid when we go out
				 * of scope (not that libcurl should be
				 * attempting to access it, of course).
				 */
				static char buf;

				code = curl_formadd(&post, &last,
					CURLFORM_COPYNAME, control->name,
					CURLFORM_BUFFER, control->value,
					/* needed, as basename("") == "." */
					CURLFORM_FILENAME, "",
					CURLFORM_BUFFERPTR, &buf,
					CURLFORM_BUFFERLENGTH, 0,
					CURLFORM_CONTENTTYPE,
						"application/octet-stream",
					CURLFORM_END);
				if (code != CURL_FORMADD_OK)
					LOG("curl_formadd: %d (%s)", code, control->name);
			} else {
				char *mimetype = guit->fetch->mimetype(control->value);
				code = curl_formadd(&post, &last,
					CURLFORM_COPYNAME, control->name,
					CURLFORM_FILE, control->rawfile,
					CURLFORM_FILENAME, leafname,
					CURLFORM_CONTENTTYPE,
					(mimetype != 0 ? mimetype : "text/plain"),
					CURLFORM_END);
				if (code != CURL_FORMADD_OK)
					LOG("curl_formadd: %d (%s=%s)", code, control->name, control->value);
				free(mimetype);
			}
			free(leafname);
		}
		else {
			code = curl_formadd(&post, &last,
					CURLFORM_COPYNAME, control->name,
					CURLFORM_COPYCONTENTS, control->value,
					CURLFORM_END);
			if (code != CURL_FORMADD_OK)
				LOG("curl_formadd: %d (%s=%s)", code, control->name, control->value);
		}
	}

	return post;
}


/**
 * Start fetching data for the given URL.
 *
 * The function returns immediately. The fetch may be queued for later
 * processing.
 *
 * A pointer to an opaque struct curl_fetch_info is returned, which can be
 * passed to fetch_abort() to abort the fetch at any time. Returns 0 if memory
 * is exhausted (or some other fatal error occurred).
 *
 * The caller must supply a callback function which is called when anything
 * interesting happens. The callback function is first called with msg
 * FETCH_HEADER, with the header in data, then one or more times
 * with FETCH_DATA with some data for the url, and finally with
 * FETCH_FINISHED. Alternatively, FETCH_ERROR indicates an error occurred:
 * data contains an error message. FETCH_REDIRECT may replace the FETCH_HEADER,
 * FETCH_DATA, FETCH_FINISHED sequence if the server sends a replacement URL.
 *
 * Some private data can be passed as the last parameter to fetch_start, and
 * callbacks will contain this.
 */
static void *
fetch_curl_setup(struct fetch *parent_fetch,
		 nsurl *url,
		 bool only_2xx,
		 bool downgrade_tls,
		 const char *post_urlenc,
		 const struct fetch_multipart_data *post_multipart,
		 const char **headers)
{
	struct curl_fetch_info *fetch;
	struct curl_slist *slist;
	int i;

	fetch = malloc(sizeof (*fetch));
	if (fetch == NULL)
		return 0;

	fetch->fetch_handle = parent_fetch;

	LOG("fetch %p, url '%s'", fetch, nsurl_access(url));

	/* construct a new fetch structure */
	fetch->curl_handle = NULL;
	fetch->had_headers = false;
	fetch->abort = false;
	fetch->stopped = false;
	fetch->only_2xx = only_2xx;
	fetch->downgrade_tls = downgrade_tls;
	fetch->headers = NULL;
	fetch->url = nsurl_ref(url);
	fetch->host = nsurl_get_component(url, NSURL_HOST);
	fetch->location = NULL;
	fetch->content_length = 0;
	fetch->http_code = 0;
	fetch->cookie_string = NULL;
	fetch->realm = NULL;
	fetch->post_urlenc = NULL;
	fetch->post_multipart = NULL;
	if (post_urlenc) {
		fetch->post_urlenc = strdup(post_urlenc);
	} else if (post_multipart) {
		fetch->post_multipart = fetch_curl_post_convert(post_multipart);
	}
	fetch->last_progress_update = 0;

	/* TLS defaults */
	memset(fetch->cert_data, 0, sizeof(fetch->cert_data));
	fetch->cert_depth = -1;

	if ((fetch->host == NULL) ||
	    (post_multipart != NULL && fetch->post_multipart == NULL) ||
	    (post_urlenc != NULL && fetch->post_urlenc == NULL)) {
		goto failed;
	}

#define APPEND(list, value) \
	slist = curl_slist_append(list, value);		\
	if (slist == NULL)				\
		goto failed;				\
	list = slist;

	/* remove curl default headers */
	APPEND(fetch->headers, "Pragma:");

	/* when doing a POST libcurl sends Expect: 100-continue" by default
	 * which fails with lighttpd, so disable it (see bug 1429054) */
	APPEND(fetch->headers, "Expect:");

	if ((nsoption_charp(accept_language) != NULL) &&
	    (nsoption_charp(accept_language)[0] != '\0')) {
		char s[80];
		snprintf(s, sizeof s, "Accept-Language: %s, *;q=0.1",
			 nsoption_charp(accept_language));
		s[sizeof s - 1] = 0;
		APPEND(fetch->headers, s);
	}

	if (nsoption_charp(accept_charset) != NULL &&
	    nsoption_charp(accept_charset)[0] != '\0') {
		char s[80];
		snprintf(s, sizeof s, "Accept-Charset: %s, *;q=0.1",
			 nsoption_charp(accept_charset));
		s[sizeof s - 1] = 0;
		APPEND(fetch->headers, s);
	}

	if (nsoption_bool(do_not_track) == true) {
		APPEND(fetch->headers, "DNT: 1");
	}

	/* And add any headers specified by the caller */
	for (i = 0; headers[i] != NULL; i++) {
		APPEND(fetch->headers, headers[i]);
	}

	return fetch;

#undef APPEND

failed:
	if (fetch->host != NULL)
		lwc_string_unref(fetch->host);

	nsurl_unref(fetch->url);
	free(fetch->post_urlenc);
	if (fetch->post_multipart)
		curl_formfree(fetch->post_multipart);
	curl_slist_free_all(fetch->headers);
	free(fetch);
	return NULL;
}


/**
 * OpenSSL Certificate verification callback
 *
 * Called for each certificate in a chain being verified. OpenSSL
 * calls this in deepest first order from the certificate authority to
 * the peer certificate at position 0.
 *
 * Each certificate is stored in the fetch context the first time it
 * is presented. If an error is encountered it is only returned for
 * the peer certificate at position 0 allowing the enumeration of the
 * entire chain not stopping early at the depth of the erroring
 * certificate.
 *
 * \param verify_ok 0 if the caller has already determined the chain
 *                   has errors else 1
 * \param x509_ctx certificate context being verified
 * \return 1 to indicate verification should continue and 0 to indicate
 *          verification should stop.
 */
static int
fetch_curl_verify_callback(int verify_ok, X509_STORE_CTX *x509_ctx)
{
	int depth;
	struct curl_fetch_info *fetch;

	depth = X509_STORE_CTX_get_error_depth(x509_ctx);
	fetch = X509_STORE_CTX_get_app_data(x509_ctx);

	/* record the max depth */
	if (depth > fetch->cert_depth) {
		fetch->cert_depth = depth;
	}

	/* certificate chain is excessively deep so fail verification */
	if (depth >= MAX_CERTS) {
		X509_STORE_CTX_set_error(x509_ctx,
					 X509_V_ERR_CERT_CHAIN_TOO_LONG);
		return 0;
	}

	/* save the certificate by incrementing the reference count and
	 * keeping a pointer.
	 */
	if (!fetch->cert_data[depth].cert) {
		fetch->cert_data[depth].cert = X509_STORE_CTX_get_current_cert(x509_ctx);
		ns_X509_up_ref(fetch->cert_data[depth].cert);
		fetch->cert_data[depth].err = X509_STORE_CTX_get_error(x509_ctx);
	}

	/* allow certificate chain to be completed */
	if (depth > 0) {
		verify_ok = 1;
	} else {
		/* search for deeper certificates in the chain with errors */
		for (depth = fetch->cert_depth; depth > 0; depth--) {
			if (fetch->cert_data[depth].err != 0) {
				/* error in previous certificate so fail verification */
				verify_ok = 0;
				X509_STORE_CTX_set_error(x509_ctx, fetch->cert_data[depth].err);
			}
		}
	}

	return verify_ok;
}


/**
 * OpenSSL certificate chain verification callback
 *
 * Verifies certificate chain by calling standard implementation after
 * setting up context for the certificate callback.
 *
 * \param x509_ctx The certificate store to validate
 * \param parm The fetch context.
 * \return 1 to indicate verification success and 0 to indicate verification failure.
 */
static int fetch_curl_cert_verify_callback(X509_STORE_CTX *x509_ctx, void *parm)
{
	int ok;

	/* Store fetch struct in context for verify callback */
	ok = X509_STORE_CTX_set_app_data(x509_ctx, parm);

	/* verify the certificate chain using standard call */
	if (ok) {
		ok = X509_verify_cert(x509_ctx);
	}

	return ok;
}


/**
 * cURL SSL setup callback
 *
 * \param curl_handle The curl handle to perform the ssl operation on.
 * \param _sslctx The ssl context.
 * \param parm The callback context.
 * \return A curl result code.
 */
static CURLcode
fetch_curl_sslctxfun(CURL *curl_handle, void *_sslctx, void *parm)
{
	struct curl_fetch_info *f = (struct curl_fetch_info *) parm;
	SSL_CTX *sslctx = _sslctx;
	long options = SSL_OP_ALL | SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3;

	/* set verify callback for each certificate in chain */
	SSL_CTX_set_verify(sslctx, SSL_VERIFY_PEER, fetch_curl_verify_callback);

	/* set callback used to verify certificate chain */
	SSL_CTX_set_cert_verify_callback(sslctx,
					 fetch_curl_cert_verify_callback,
					 parm);

	if (f->downgrade_tls) {
		/* Disable TLS 1.1/1.2 if the server can't cope with them */
#ifdef SSL_OP_NO_TLSv1_1
		options |= SSL_OP_NO_TLSv1_1;
#endif
#ifdef SSL_OP_NO_TLSv1_2
		options |= SSL_OP_NO_TLSv1_2;
#endif
#ifdef SSL_MODE_SEND_FALLBACK_SCSV
		/* Ensure server rejects the connection if downgraded too far */
		SSL_CTX_set_mode(sslctx, SSL_MODE_SEND_FALLBACK_SCSV);
#endif
	}

	SSL_CTX_set_options(sslctx, options);

	return CURLE_OK;
}


/**
 * Set options specific for a fetch.
 *
 * \param f The fetch to set options on.
 * \return A curl result code.
 */
static CURLcode fetch_curl_set_options(struct curl_fetch_info *f)
{
	CURLcode code;
	const char *auth;

#undef SETOPT
#define SETOPT(option, value) { \
	code = curl_easy_setopt(f->curl_handle, option, value);	\
	if (code != CURLE_OK)					\
		return code;					\
	}

	SETOPT(CURLOPT_URL, nsurl_access(f->url));
	SETOPT(CURLOPT_PRIVATE, f);
	SETOPT(CURLOPT_WRITEDATA, f);
	SETOPT(CURLOPT_WRITEHEADER, f);
	SETOPT(CURLOPT_PROGRESSDATA, f);
	SETOPT(CURLOPT_REFERER, fetch_get_referer_to_send(f->fetch_handle));
	SETOPT(CURLOPT_HTTPHEADER, f->headers);
	if (f->post_urlenc) {
		SETOPT(CURLOPT_HTTPPOST, NULL);
		SETOPT(CURLOPT_HTTPGET, 0L);
		SETOPT(CURLOPT_POSTFIELDS, f->post_urlenc);
	} else if (f->post_multipart) {
		SETOPT(CURLOPT_POSTFIELDS, NULL);
		SETOPT(CURLOPT_HTTPGET, 0L);
		SETOPT(CURLOPT_HTTPPOST, f->post_multipart);
	} else {
		SETOPT(CURLOPT_POSTFIELDS, NULL);
		SETOPT(CURLOPT_HTTPPOST, NULL);
		SETOPT(CURLOPT_HTTPGET, 1L);
	}

	f->cookie_string = urldb_get_cookie(f->url, true);
	if (f->cookie_string) {
		SETOPT(CURLOPT_COOKIE, f->cookie_string);
	} else {
		SETOPT(CURLOPT_COOKIE, NULL);
	}

	if ((auth = urldb_get_auth_details(f->url, NULL)) != NULL) {
		SETOPT(CURLOPT_HTTPAUTH, CURLAUTH_ANY);
		SETOPT(CURLOPT_USERPWD, auth);
	} else {
		SETOPT(CURLOPT_USERPWD, NULL);
	}

	/* set up proxy options */
	if (nsoption_bool(http_proxy) &&
	    (nsoption_charp(http_proxy_host) != NULL) &&
	    (strncmp(nsurl_access(f->url), "file:", 5) != 0)) {
		SETOPT(CURLOPT_PROXY, nsoption_charp(http_proxy_host));
		SETOPT(CURLOPT_PROXYPORT, (long) nsoption_int(http_proxy_port));

#if LIBCURL_VERSION_NUM >= 0x071304
		/* Added in 7.19.4 */
		/* setup the omission list */
		SETOPT(CURLOPT_NOPROXY, nsoption_charp(http_proxy_noproxy));
#endif

		if (nsoption_int(http_proxy_auth) != OPTION_HTTP_PROXY_AUTH_NONE) {
			SETOPT(CURLOPT_PROXYAUTH,
			       nsoption_int(http_proxy_auth) ==
					OPTION_HTTP_PROXY_AUTH_BASIC ?
					(long) CURLAUTH_BASIC :
					(long) CURLAUTH_NTLM);
			snprintf(fetch_proxy_userpwd,
					sizeof fetch_proxy_userpwd,
					"%s:%s",
				 nsoption_charp(http_proxy_auth_user),
				 nsoption_charp(http_proxy_auth_pass));
			SETOPT(CURLOPT_PROXYUSERPWD, fetch_proxy_userpwd);
		}
	} else {
		SETOPT(CURLOPT_PROXY, NULL);
	}

	/* Disable SSL session ID caching, as some servers can't cope. */
	SETOPT(CURLOPT_SSL_SESSIONID_CACHE, 0);

	if (urldb_get_cert_permissions(f->url)) {
		/* Disable certificate verification */
		SETOPT(CURLOPT_SSL_VERIFYPEER, 0L);
		SETOPT(CURLOPT_SSL_VERIFYHOST, 0L);
		if (curl_with_openssl) {
			SETOPT(CURLOPT_SSL_CTX_FUNCTION, NULL);
			SETOPT(CURLOPT_SSL_CTX_DATA, NULL);
		}
	} else {
		/* do verification */
		SETOPT(CURLOPT_SSL_VERIFYPEER, 1L);
		SETOPT(CURLOPT_SSL_VERIFYHOST, 2L);
		if (curl_with_openssl) {
			SETOPT(CURLOPT_SSL_CTX_FUNCTION, fetch_curl_sslctxfun);
			SETOPT(CURLOPT_SSL_CTX_DATA, f);
		}
	}

	return CURLE_OK;
}

/**
 * Initiate a fetch from the queue.
 *
 * \param fetch fetch to use to fetch content.
 * \param handle CURL handle to be used to fetch the content.
 * \return true if the fetch was successfully initiated else false.
 */
static bool
fetch_curl_initiate_fetch(struct curl_fetch_info *fetch, CURL *handle)
{
	CURLcode code;
	CURLMcode codem;

	fetch->curl_handle = handle;

	/* Initialise the handle */
	code = fetch_curl_set_options(fetch);
	if (code != CURLE_OK) {
		fetch->curl_handle = 0;
		return false;
	}

	/* add to the global curl multi handle */
	codem = curl_multi_add_handle(fetch_curl_multi, fetch->curl_handle);
	assert(codem == CURLM_OK || codem == CURLM_CALL_MULTI_PERFORM);

	return true;
}


/**
 * Find a CURL handle to use to dispatch a job
 */
static CURL *fetch_curl_get_handle(lwc_string *host)
{
	struct cache_handle *h;
	CURL *ret;
	RING_FINDBYLWCHOST(curl_handle_ring, h, host);
	if (h) {
		ret = h->handle;
		lwc_string_unref(h->host);
		RING_REMOVE(curl_handle_ring, h);
		free(h);
	} else {
		ret = curl_easy_duphandle(fetch_blank_curl);
	}
	return ret;
}


/**
 * Dispatch a single job
 */
static bool fetch_curl_start(void *vfetch)
{
	struct curl_fetch_info *fetch = (struct curl_fetch_info*)vfetch;
	return fetch_curl_initiate_fetch(fetch,
			fetch_curl_get_handle(fetch->host));
}

/**
 * Cache a CURL handle for the provided host (if wanted)
 */
static void fetch_curl_cache_handle(CURL *handle, lwc_string *host)
{
#if LIBCURL_VERSION_NUM >= 0x071e00
	/* 7.30.0 or later has its own connection caching; suppress ours */
	curl_easy_cleanup(handle);
	return;
#else
	struct cache_handle *h = 0;
	int c;
	RING_FINDBYLWCHOST(curl_handle_ring, h, host);
	if (h) {
		/* Already have a handle cached for this hostname */
		curl_easy_cleanup(handle);
		return;
	}
	/* We do not have a handle cached, first up determine if the cache is full */
	RING_GETSIZE(struct cache_handle, curl_handle_ring, c);
	if (c >= nsoption_int(max_cached_fetch_handles)) {
		/* Cache is full, so, we rotate the ring by one and
		 * replace the oldest handle with this one. We do this
		 * without freeing/allocating memory (except the
		 * hostname) and without removing the entry from the
		 * ring and then re-inserting it, in order to be as
		 * efficient as we can.
		 */
		if (curl_handle_ring != NULL) {
			h = curl_handle_ring;
			curl_handle_ring = h->r_next;
			curl_easy_cleanup(h->handle);
			h->handle = handle;
			lwc_string_unref(h->host);
			h->host = lwc_string_ref(host);
		} else {
			/* Actually, we don't want to cache any handles */
			curl_easy_cleanup(handle);
		}

		return;
	}
	/* The table isn't full yet, so make a shiny new handle to add to the ring */
	h = (struct cache_handle*)malloc(sizeof(struct cache_handle));
	h->handle = handle;
	h->host = lwc_string_ref(host);
	RING_INSERT(curl_handle_ring, h);
#endif
}


/**
 * Abort a fetch.
 */
static void fetch_curl_abort(void *vf)
{
	struct curl_fetch_info *f = (struct curl_fetch_info *)vf;
	assert(f);
	LOG("fetch %p, url '%s'", f, nsurl_access(f->url));
	if (f->curl_handle) {
		f->abort = true;
	} else {
		fetch_remove_from_queues(f->fetch_handle);
		fetch_free(f->fetch_handle);
	}
}


/**
 * Clean up the provided fetch object and free it.
 *
 * Will prod the queue afterwards to allow pending requests to be initiated.
 */
static void fetch_curl_stop(struct curl_fetch_info *f)
{
	CURLMcode codem;

	assert(f);
	LOG("fetch %p, url '%s'", f, nsurl_access(f->url));

	if (f->curl_handle) {
		/* remove from curl multi handle */
		codem = curl_multi_remove_handle(fetch_curl_multi,
				f->curl_handle);
		assert(codem == CURLM_OK);
		/* Put this curl handle into the cache if wanted. */
		fetch_curl_cache_handle(f->curl_handle, f->host);
		f->curl_handle = 0;
	}

	fetch_remove_from_queues(f->fetch_handle);
}


/**
 * Free a fetch structure and associated resources.
 */
static void fetch_curl_free(void *vf)
{
	struct curl_fetch_info *f = (struct curl_fetch_info *)vf;
	int i;

	if (f->curl_handle) {
		curl_easy_cleanup(f->curl_handle);
	}
	nsurl_unref(f->url);
	lwc_string_unref(f->host);
	free(f->location);
	free(f->cookie_string);
	free(f->realm);
	if (f->headers) {
		curl_slist_free_all(f->headers);
	}
	free(f->post_urlenc);
	if (f->post_multipart) {
		curl_formfree(f->post_multipart);
	}

	for (i = 0; i < MAX_CERTS && f->cert_data[i].cert; i++) {
		ns_X509_free(f->cert_data[i].cert);
	}

	free(f);
}


/**
 * Find the status code and content type and inform the caller.
 *
 * Return true if the fetch is being aborted.
 */
static bool fetch_curl_process_headers(struct curl_fetch_info *f)
{
	long http_code;
	CURLcode code;
	fetch_msg msg;

	f->had_headers = true;

	if (!f->http_code) {
		code = curl_easy_getinfo(f->curl_handle, CURLINFO_HTTP_CODE,
					 &f->http_code);
		fetch_set_http_code(f->fetch_handle, f->http_code);
		assert(code == CURLE_OK);
	}
	http_code = f->http_code;
	LOG("HTTP status code %li", http_code);

	if (http_code == 304 && !f->post_urlenc && !f->post_multipart) {
		/* Not Modified && GET request */
		msg.type = FETCH_NOTMODIFIED;
		fetch_send_callback(&msg, f->fetch_handle);
		return true;
	}

	/* handle HTTP redirects (3xx response codes) */
	if (300 <= http_code && http_code < 400 && f->location != 0) {
		LOG("FETCH_REDIRECT, '%s'", f->location);
		msg.type = FETCH_REDIRECT;
		msg.data.redirect = f->location;
		fetch_send_callback(&msg, f->fetch_handle);
		return true;
	}

	/* handle HTTP 401 (Authentication errors) */
	if (http_code == 401) {
		msg.type = FETCH_AUTH;
		msg.data.auth.realm = f->realm;
		fetch_send_callback(&msg, f->fetch_handle);
		return true;
	}

	/* handle HTTP errors (non 2xx response codes) */
	if (f->only_2xx && strncmp(nsurl_access(f->url), "http", 4) == 0 &&
			(http_code < 200 || 299 < http_code)) {
		msg.type = FETCH_ERROR;
		msg.data.error = messages_get("Not2xx");
		fetch_send_callback(&msg, f->fetch_handle);
		return true;
	}

	if (f->abort)
		return true;

	return false;
}

/**
 * setup callback to allow the user to examine certificates which have
 * failed to validate during fetch.
 */
static void
curl_start_cert_validate(struct curl_fetch_info *f,
			 struct cert_info *certs)
{
	int depth;
	BIO *mem;
	BUF_MEM *buf;
	struct ssl_cert_info ssl_certs[MAX_CERTS];
	fetch_msg msg;

	for (depth = 0; depth <= f->cert_depth; depth++) {
		assert(certs[depth].cert != NULL);

		/* get certificate version */
		ssl_certs[depth].version = X509_get_version(certs[depth].cert);

		/* not before date */
		mem = BIO_new(BIO_s_mem());
		ASN1_TIME_print(mem, X509_get_notBefore(certs[depth].cert));
		BIO_get_mem_ptr(mem, &buf);
		(void) BIO_set_close(mem, BIO_NOCLOSE);
		BIO_free(mem);
		memcpy(ssl_certs[depth].not_before,
		       buf->data,
		       min(sizeof(ssl_certs[depth].not_before) - 1,
			   (unsigned)buf->length));
		ssl_certs[depth].not_before[min(sizeof(ssl_certs[depth].not_before) - 1,
					    (unsigned)buf->length)] = 0;
		BUF_MEM_free(buf);

		/* not after date */
		mem = BIO_new(BIO_s_mem());
		ASN1_TIME_print(mem,
				X509_get_notAfter(certs[depth].cert));
		BIO_get_mem_ptr(mem, &buf);
		(void) BIO_set_close(mem, BIO_NOCLOSE);
		BIO_free(mem);
		memcpy(ssl_certs[depth].not_after,
		       buf->data,
		       min(sizeof(ssl_certs[depth].not_after) - 1,
			   (unsigned)buf->length));
		ssl_certs[depth].not_after[min(sizeof(ssl_certs[depth].not_after) - 1,
					   (unsigned)buf->length)] = 0;
		BUF_MEM_free(buf);

		/* signature type */
		ssl_certs[depth].sig_type =
			X509_get_signature_type(certs[depth].cert);

		/* serial number */
		ssl_certs[depth].serial =
			ASN1_INTEGER_get(
				X509_get_serialNumber(certs[depth].cert));

		/* issuer name */
		mem = BIO_new(BIO_s_mem());
		X509_NAME_print_ex(mem,
				   X509_get_issuer_name(certs[depth].cert),
				   0, XN_FLAG_SEP_CPLUS_SPC |
				   XN_FLAG_DN_REV | XN_FLAG_FN_NONE);
		BIO_get_mem_ptr(mem, &buf);
		(void) BIO_set_close(mem, BIO_NOCLOSE);
		BIO_free(mem);
		memcpy(ssl_certs[depth].issuer,
		       buf->data,
		       min(sizeof(ssl_certs[depth].issuer) - 1,
			   (unsigned) buf->length));
		ssl_certs[depth].issuer[min(sizeof(ssl_certs[depth].issuer) - 1,
					(unsigned) buf->length)] = 0;
		BUF_MEM_free(buf);

		/* subject */
		mem = BIO_new(BIO_s_mem());
		X509_NAME_print_ex(mem,
				   X509_get_subject_name(certs[depth].cert),
				   0,
				   XN_FLAG_SEP_CPLUS_SPC |
				   XN_FLAG_DN_REV |
				   XN_FLAG_FN_NONE);
		BIO_get_mem_ptr(mem, &buf);
		(void) BIO_set_close(mem, BIO_NOCLOSE);
		BIO_free(mem);
		memcpy(ssl_certs[depth].subject,
		       buf->data,
		       min(sizeof(ssl_certs[depth].subject) - 1,
			   (unsigned)buf->length));
		ssl_certs[depth].subject[min(sizeof(ssl_certs[depth].subject) - 1,
					 (unsigned) buf->length)] = 0;
		BUF_MEM_free(buf);

		/* type of certificate */
		ssl_certs[depth].cert_type =
			X509_certificate_type(certs[depth].cert,
					      X509_get_pubkey(certs[depth].cert));

		/* and clean up */
		ns_X509_free(certs[depth].cert);
	}

	msg.type = FETCH_CERT_ERR;
	msg.data.cert_err.certs = ssl_certs;
	msg.data.cert_err.num_certs = depth;
	fetch_send_callback(&msg, f->fetch_handle);
}

/**
 * Handle a completed fetch (CURLMSG_DONE from curl_multi_info_read()).
 *
 * \param curl_handle curl easy handle of fetch
 * \param result The result code of the completed fetch.
 */
static void fetch_curl_done(CURL *curl_handle, CURLcode result)
{
	bool finished = false;
	bool error = false;
	bool cert = false;
	bool abort_fetch;
	struct curl_fetch_info *f;
	char **_hideous_hack = (char **) (void *) &f;
	CURLcode code;
	struct cert_info certs[MAX_CERTS];

	/* find the structure associated with this fetch */
	/* For some reason, cURL thinks CURLINFO_PRIVATE should be a string?! */
	code = curl_easy_getinfo(curl_handle, CURLINFO_PRIVATE, _hideous_hack);
	assert(code == CURLE_OK);

	abort_fetch = f->abort;
	LOG("done %s", nsurl_access(f->url));

	if ((abort_fetch == false) &&
	    (result == CURLE_OK ||
	     ((result == CURLE_WRITE_ERROR) && (f->stopped == false)))) {
		/* fetch completed normally or the server fed us a junk gzip
		 * stream (usually in the form of garbage at the end of the
		 * stream). Curl will have fed us all but the last chunk of
		 * decoded data, which is sad as, if we'd received the last
		 * chunk, too, we'd be able to render the whole object.
		 * As is, we'll just have to accept that the end of the
		 * object will be truncated in this case and leave it to
		 * the content handlers to cope.
		 */
		if (f->stopped ||
		    (!f->had_headers &&	fetch_curl_process_headers(f))) {
			; /* redirect with no body or similar */
		} else {
			finished = true;
		}
	} else if (result == CURLE_PARTIAL_FILE) {
		/* CURLE_PARTIAL_FILE occurs if the received body of a
		 * response is smaller than that specified in the
		 * Content-Length header.
		 */
		if (!f->had_headers && fetch_curl_process_headers(f))
			; /* redirect with partial body, or similar */
		else {
			finished = true;
		}
	} else if (result == CURLE_WRITE_ERROR && f->stopped) {
		/* CURLE_WRITE_ERROR occurs when fetch_curl_data
		 * returns 0, which we use to abort intentionally
		 */
		;
	} else if (result == CURLE_SSL_PEER_CERTIFICATE ||
			result == CURLE_SSL_CACERT) {
		/* CURLE_SSL_PEER_CERTIFICATE renamed to
		 * CURLE_PEER_FAILED_VERIFICATION
		 */
		memset(certs, 0, sizeof(certs));
		memcpy(certs, f->cert_data, sizeof(certs));
		memset(f->cert_data, 0, sizeof(f->cert_data));
		cert = true;
	} else {
		LOG("Unknown cURL response code %d", result);
		error = true;
	}

	fetch_curl_stop(f);

	if (abort_fetch) {
		; /* fetch was aborted: no callback */
	} else if (finished) {
		fetch_msg msg;
		msg.type = FETCH_FINISHED;
		fetch_send_callback(&msg, f->fetch_handle);
	} else if (cert) {
		/* user needs to validate certificate with issue */
		curl_start_cert_validate(f, certs);
	} else if (error) {
		fetch_msg msg;
		switch (result) {
		case CURLE_SSL_CONNECT_ERROR:
			msg.type = FETCH_SSL_ERR;
			break;

		case CURLE_OPERATION_TIMEDOUT:
			msg.type = FETCH_TIMEDOUT;
			msg.data.error = curl_easy_strerror(result);
			break;

		default:
			msg.type = FETCH_ERROR;
			msg.data.error = curl_easy_strerror(result);
		}

		fetch_send_callback(&msg, f->fetch_handle);
	}

	fetch_free(f->fetch_handle);
}


/**
 * Do some work on current fetches.
 *
 * Must be called regularly to make progress on fetches.
 */
static void fetch_curl_poll(lwc_string *scheme_ignored)
{
	int running, queue;
	CURLMcode codem;
	CURLMsg *curl_msg;

	if (nsoption_bool(suppress_curl_debug) == false) {
		fd_set read_fd_set, write_fd_set, exc_fd_set;
		int max_fd = -1;
		int i;

		FD_ZERO(&read_fd_set);
		FD_ZERO(&write_fd_set);
		FD_ZERO(&exc_fd_set);

		codem = curl_multi_fdset(fetch_curl_multi,
				&read_fd_set, &write_fd_set,
				&exc_fd_set, &max_fd);
		assert(codem == CURLM_OK);

		LOG("Curl file descriptor states (maxfd=%i):", max_fd);
		for (i = 0; i <= max_fd; i++) {
			bool read = false;
			bool write = false;
			bool error = false;

			if (FD_ISSET(i, &read_fd_set)) {
				read = true;
			}
			if (FD_ISSET(i, &write_fd_set)) {
				write = true;
			}
			if (FD_ISSET(i, &exc_fd_set)) {
				error = true;
			}
			if (read || write || error) {
				LOG("  fd %i: %s %s %s", i,
						read  ? "read" : "    ",
						write ? "write" : "     ",
						error ? "error" : "     ");
			}
		}
	}

	/* do any possible work on the current fetches */
	do {
		codem = curl_multi_perform(fetch_curl_multi, &running);
		if (codem != CURLM_OK && codem != CURLM_CALL_MULTI_PERFORM) {
			LOG("curl_multi_perform: %i %s", codem, curl_multi_strerror(codem));
			guit->misc->warning("MiscError", curl_multi_strerror(codem));
			return;
		}
	} while (codem == CURLM_CALL_MULTI_PERFORM);

	/* process curl results */
	curl_msg = curl_multi_info_read(fetch_curl_multi, &queue);
	while (curl_msg) {
		switch (curl_msg->msg) {
			case CURLMSG_DONE:
				fetch_curl_done(curl_msg->easy_handle,
						curl_msg->data.result);
				break;
			default:
				break;
		}
		curl_msg = curl_multi_info_read(fetch_curl_multi, &queue);
	}
}




/**
 * Callback function for fetch progress.
 */
static int
fetch_curl_progress(void *clientp,
		    double dltotal,
		    double dlnow,
		    double ultotal,
		    double ulnow)
{
	static char fetch_progress_buffer[256]; /**< Progress buffer for cURL */
	struct curl_fetch_info *f = (struct curl_fetch_info *) clientp;
	uint64_t time_now_ms;
	fetch_msg msg;

	if (f->abort) {
		return 0;
        }

	msg.type = FETCH_PROGRESS;
	msg.data.progress = fetch_progress_buffer;

	/* Rate limit each fetch's progress notifications */
        nsu_getmonotonic_ms(&time_now_ms);
#define UPDATE_DELAY_MS (1000 / UPDATES_PER_SECOND)
	if (time_now_ms - f->last_progress_update < UPDATE_DELAY_MS) {
		return 0;
        }
#undef UPDATE_DELAY_MS
	f->last_progress_update = time_now_ms;

	if (dltotal > 0) {
		snprintf(fetch_progress_buffer, 255,
				messages_get("Progress"),
				human_friendly_bytesize(dlnow),
				human_friendly_bytesize(dltotal));
		fetch_send_callback(&msg, f->fetch_handle);
	} else {
		snprintf(fetch_progress_buffer, 255,
				messages_get("ProgressU"),
				human_friendly_bytesize(dlnow));
		fetch_send_callback(&msg, f->fetch_handle);
	}

	return 0;
}


/**
 * Ignore everything given to it.
 *
 * Used to ignore cURL debug.
 */
static int fetch_curl_ignore_debug(CURL *handle,
			    curl_infotype type,
			    char *data,
			    size_t size,
			    void *userptr)
{
	return 0;
}


/**
 * Callback function for cURL.
 */
static size_t fetch_curl_data(char *data, size_t size, size_t nmemb, void *_f)
{
	struct curl_fetch_info *f = _f;
	CURLcode code;
	fetch_msg msg;

	/* ensure we only have to get this information once */
	if (!f->http_code) {
		code = curl_easy_getinfo(f->curl_handle, CURLINFO_HTTP_CODE,
					 &f->http_code);
		fetch_set_http_code(f->fetch_handle, f->http_code);
		assert(code == CURLE_OK);
	}

	/* ignore body if this is a 401 reply by skipping it and reset
	 * the HTTP response code to enable follow up fetches.
	 */
	if (f->http_code == 401) {
		f->http_code = 0;
		return size * nmemb;
	}

	if (f->abort || (!f->had_headers && fetch_curl_process_headers(f))) {
		f->stopped = true;
		return 0;
	}

	/* send data to the caller */
	msg.type = FETCH_DATA;
	msg.data.header_or_data.buf = (const uint8_t *) data;
	msg.data.header_or_data.len = size * nmemb;
	fetch_send_callback(&msg, f->fetch_handle);

	if (f->abort) {
		f->stopped = true;
		return 0;
	}

	return size * nmemb;
}


/**
 * Callback function for headers.
 *
 * See RFC 2616 4.2.
 */
static size_t
fetch_curl_header(char *data, size_t size, size_t nmemb, void *_f)
{
	struct curl_fetch_info *f = _f;
	int i;
	fetch_msg msg;
	size *= nmemb;

	if (f->abort) {
		f->stopped = true;
		return 0;
	}

	msg.type = FETCH_HEADER;
	msg.data.header_or_data.buf = (const uint8_t *) data;
	msg.data.header_or_data.len = size;
	fetch_send_callback(&msg, f->fetch_handle);

#define SKIP_ST(o) for (i = (o); i < (int) size && (data[i] == ' ' || data[i] == '\t'); i++)

	if (12 < size && strncasecmp(data, "Location:", 9) == 0) {
		/* extract Location header */
		free(f->location);
		f->location = malloc(size);
		if (!f->location) {
			LOG("malloc failed");
			return size;
		}
		SKIP_ST(9);
		strncpy(f->location, data + i, size - i);
		f->location[size - i] = '\0';
		for (i = size - i - 1; i >= 0 &&
				(f->location[i] == ' ' ||
				f->location[i] == '\t' ||
				f->location[i] == '\r' ||
				f->location[i] == '\n'); i--)
			f->location[i] = '\0';
	} else if (15 < size && strncasecmp(data, "Content-Length:", 15) == 0) {
		/* extract Content-Length header */
		SKIP_ST(15);
		if (i < (int)size && '0' <= data[i] && data[i] <= '9')
			f->content_length = atol(data + i);
	} else if (17 < size && strncasecmp(data, "WWW-Authenticate:", 17) == 0) {
		/* extract the first Realm from WWW-Authenticate header */
		SKIP_ST(17);

		while (i < (int) size - 5 &&
				strncasecmp(data + i, "realm", 5))
			i++;
		while (i < (int) size - 1 && data[++i] != '"')
			/* */;
		i++;

		if (i < (int) size) {
			size_t end = i;

			while (end < size && data[end] != '"')
				++end;

			if (end < size) {
				free(f->realm);
				f->realm = malloc(end - i + 1);
				if (f->realm != NULL) {
					strncpy(f->realm, data + i, end - i);
					f->realm[end - i] = '\0';
				}
			}
		}
	} else if (11 < size && strncasecmp(data, "Set-Cookie:", 11) == 0) {
		/* extract Set-Cookie header */
		SKIP_ST(11);

		fetch_set_cookie(f->fetch_handle, &data[i]);
	}

	return size;
#undef SKIP_ST
}

static int fetch_curl_fdset(lwc_string *scheme, fd_set *read_set,
			    fd_set *write_set, fd_set *error_set)
{
	CURLMcode code;
	int maxfd = -1;

	code = curl_multi_fdset(fetch_curl_multi,
				read_set,
				write_set,
				error_set,
				&maxfd);
	assert(code == CURLM_OK);

	return maxfd;
}



/* exported function documented in content/fetchers/curl.h */
nserror fetch_curl_register(void)
{
	CURLcode code;
	curl_version_info_data *data;
	int i;
	lwc_string *scheme;
	const struct fetcher_operation_table fetcher_ops = {
		.initialise = fetch_curl_initialise,
		.acceptable = fetch_curl_can_fetch,
		.setup = fetch_curl_setup,
		.start = fetch_curl_start,
		.abort = fetch_curl_abort,
		.ffree = fetch_curl_free,
		.poll = fetch_curl_poll,
		.fdset = fetch_curl_fdset,
		.finalise = fetch_curl_finalise
	};

	LOG("curl_version %s", curl_version());

	code = curl_global_init(CURL_GLOBAL_ALL);
	if (code != CURLE_OK) {
		LOG("curl_global_init failed.");
		return NSERROR_INIT_FAILED;
	}

	fetch_curl_multi = curl_multi_init();
	if (!fetch_curl_multi) {
		LOG("curl_multi_init failed.");
		return NSERROR_INIT_FAILED;
	}

#if LIBCURL_VERSION_NUM >= 0x071e00
	/* built against 7.30.0 or later: configure caching */
	{
		CURLMcode mcode;
		int maxconnects = nsoption_int(max_fetchers) +
				nsoption_int(max_cached_fetch_handles);

#undef SETOPT
#define SETOPT(option, value) \
	mcode = curl_multi_setopt(fetch_curl_multi, option, value);	\
	if (mcode != CURLM_OK)						\
		goto curl_multi_setopt_failed;

		SETOPT(CURLMOPT_MAXCONNECTS, maxconnects);
		SETOPT(CURLMOPT_MAX_TOTAL_CONNECTIONS, maxconnects);
		SETOPT(CURLMOPT_MAX_HOST_CONNECTIONS, nsoption_int(max_fetchers_per_host));
	}
#endif

	/* Create a curl easy handle with the options that are common to all
	 *  fetches.
	 */
	fetch_blank_curl = curl_easy_init();
	if (!fetch_blank_curl) {
		LOG("curl_easy_init failed");
		return NSERROR_INIT_FAILED;
	}

#undef SETOPT
#define SETOPT(option, value) \
	code = curl_easy_setopt(fetch_blank_curl, option, value);	\
	if (code != CURLE_OK)						\
		goto curl_easy_setopt_failed;

	if (verbose_log) {
	    SETOPT(CURLOPT_VERBOSE, 1);
	} else {
	    SETOPT(CURLOPT_VERBOSE, 0);
	}
	SETOPT(CURLOPT_ERRORBUFFER, fetch_error_buffer);
	if (nsoption_bool(suppress_curl_debug)) {
		SETOPT(CURLOPT_DEBUGFUNCTION, fetch_curl_ignore_debug);
	}
	SETOPT(CURLOPT_WRITEFUNCTION, fetch_curl_data);
	SETOPT(CURLOPT_HEADERFUNCTION, fetch_curl_header);
	SETOPT(CURLOPT_PROGRESSFUNCTION, fetch_curl_progress);
	SETOPT(CURLOPT_NOPROGRESS, 0);
	SETOPT(CURLOPT_USERAGENT, user_agent_string());
	SETOPT(CURLOPT_ENCODING, "gzip");
	SETOPT(CURLOPT_LOW_SPEED_LIMIT, 1L);
	SETOPT(CURLOPT_LOW_SPEED_TIME, 180L);
	SETOPT(CURLOPT_NOSIGNAL, 1L);
	SETOPT(CURLOPT_CONNECTTIMEOUT, nsoption_uint(curl_fetch_timeout));

	if (nsoption_charp(ca_bundle) &&
	    strcmp(nsoption_charp(ca_bundle), "")) {
		LOG("ca_bundle: '%s'", nsoption_charp(ca_bundle));
		SETOPT(CURLOPT_CAINFO, nsoption_charp(ca_bundle));
	}
	if (nsoption_charp(ca_path) && strcmp(nsoption_charp(ca_path), "")) {
		LOG("ca_path: '%s'", nsoption_charp(ca_path));
		SETOPT(CURLOPT_CAPATH, nsoption_charp(ca_path));
	}

	/* Detect whether the SSL CTX function API works */
	curl_with_openssl = true;
	code = curl_easy_setopt(fetch_blank_curl,
			CURLOPT_SSL_CTX_FUNCTION, NULL);
	if (code != CURLE_OK) {
		curl_with_openssl = false;
	}

	LOG("cURL %slinked against openssl", curl_with_openssl ? "" : "not ");

	/* cURL initialised okay, register the fetchers */

	data = curl_version_info(CURLVERSION_NOW);

	for (i = 0; data->protocols[i]; i++) {
		if (strcmp(data->protocols[i], "http") == 0) {
			scheme = lwc_string_ref(corestring_lwc_http);

		} else if (strcmp(data->protocols[i], "https") == 0) {
			scheme = lwc_string_ref(corestring_lwc_https);

		} else {
			/* Ignore non-http(s) protocols */
			continue;
		}

		if (fetcher_add(scheme, &fetcher_ops) != NSERROR_OK) {
			LOG("Unable to register cURL fetcher for %s", data->protocols[i]);
		}
	}

	return NSERROR_OK;

curl_easy_setopt_failed:
	LOG("curl_easy_setopt failed.");
	return NSERROR_INIT_FAILED;

#if LIBCURL_VERSION_NUM >= 0x071e00
curl_multi_setopt_failed:
	LOG("curl_multi_setopt failed.");
	return NSERROR_INIT_FAILED;
#endif
}