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
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
|
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
<!--
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
This file is generated from xml source: DO NOT EDIT
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-->
<title>Developing modules for the Apache HTTP Server 2.4 - Apache HTTP Server Version 2.4</title>
<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" />
<script src="../style/scripts/prettify.min.js" type="text/javascript">
</script>
<link href="../images/favicon.ico" rel="shortcut icon" /></head>
<body id="manual-page"><div id="page-header">
<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.4</p>
<img alt="" src="../images/feather.png" /></div>
<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
<div id="path">
<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.4</a> > <a href="./">Developer</a></div><div id="page-content"><div id="preamble"><h1>Developing modules for the Apache HTTP Server 2.4</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
</div>
<p>This document explains how you can develop modules for the Apache HTTP
Server 2.4</p>
</div>
<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#basics">Defining a module</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#hooking">Getting started: Hooking into the server</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#handling">Building a handler</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#configuration">Adding configuration options</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#context">Context aware configurations</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#summary">Summing up</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#snippets">Some useful snippets of code</a></li>
</ul><h3>See also</h3><ul class="seealso"><li><a href="request.html">Request Processing in Apache 2.4</a></li><li><a href="hooks.html">Apache 2.x Hook Functions</a></li><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="introduction" id="introduction">Introduction</a></h2>
<h3><a name="what" id="what">What we will be discussing in this document</a></h3>
<p>
This document will discuss how you can create modules for the Apache
HTTP Server 2.4, by exploring an example module called
<code>mod_example</code>. In the first part of this document, the purpose
of this module will be to calculate and print out various digest values for
existing files on your web server, whenever we access the URL <code>
http://hostname/filename.sum</code>. For instance, if we want to know the
MD5 digest value of the file located at <code>
http://www.example.com/index.html</code>, we would visit <code>
http://www.example.com/index.html.sum</code>.
</p>
<p>
In the second part of this document, which deals with configuration
directive and context awareness, we will be looking at a module that simply
writes out its own configuration to the client.
</p>
<h3><a name="prerequisites" id="prerequisites">Prerequisites</a></h3>
<p>
First and foremost, you are expected to have a basic knowledge of how the C
programming language works. In most cases, we will try to be as pedagogical
as possible and link to documents describing the functions used in the
examples, but there are also many cases where it is necessary to either
just assume that "it works" or do some digging yourself into what the hows
and whys of various function calls.
</p>
<p>
Lastly, you will need to have a basic understanding of how modules are
loaded and configured in the Apache HTTP Server, as well as how to get the headers for
Apache if you do not have them already, as these are needed for compiling
new modules.
</p>
<h3><a name="compiling" id="compiling">Compiling your module</a></h3>
<p>
To compile the source code we are building in this document, we will be
using <a href="../programs/apxs.html">APXS</a>. Assuming your source file
is called mod_example.c, compiling, installing and activating the module is
as simple as:
</p>
<div class="example"><pre>apxs -i -a -c mod_example.c</pre></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="basics" id="basics">Defining a module</a></h2>
<p>
<img src="../images/build_a_mod_3.png" alt="Module name tags" /><br />
Every module starts with the same declaration, or name tag if you will,
that defines a module as <em>a separate entity within Apache</em>:</p>
<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
create_dir_conf, /* Per-directory configuration handler */
merge_dir_conf, /* Merge handler for per-directory configurations */
create_svr_conf, /* Per-server configuration handler */
merge_svr_conf, /* Merge handler for per-server configurations */
directives, /* Any directives we may have for httpd */
register_hooks /* Our hook registering function */
};</pre>
<p>
This bit of code lets the server know that we have now registered a new module
in the system, and that its name is <code>example_module</code>. The name
of the module is used primarily for two things:<br />
</p>
<ul>
<li>Letting the server know how to load the module using the LoadModule</li>
<li>Setting up a namespace for the module to use in configurations</li>
</ul>
<p>
For now, we're only concerned with the first purpose of the module name,
which comes into play when we need to load the module:
</p>
<pre class="prettyprint lang-config">LoadModule example_module modules/mod_example.so</pre>
<p>
In essence, this tells the server to open up <code>mod_example.so</code> and look for a module
called <code>example_module</code>.
</p>
<p>
Within this name tag of ours is also a bunch of references to how we would
like to handle things: Which directives do we respond to in a configuration
file or .htaccess, how do we operate within specific contexts, and what
handlers are we interested in registering with the Apache HTTP service. We'll
return to all these elements later in this document.
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="hooking" id="hooking">Getting started: Hooking into the server</a></h2>
<h3><a name="hook_intro" id="hook_intro">An introduction to hooks</a></h3>
<p>
When handling requests in Apache HTTP Server 2.4, the first thing you will need to do is
create a hook into the request handling process. A hook is essentially a
message telling the server that you are willing to either serve or at least
take a glance at certain requests given by clients. All handlers, whether
it's mod_rewrite, mod_authn_*, mod_proxy and so on, are hooked into
specific parts of the request process. As you are probably aware, modules
serve different purposes; Some are authentication/authorization handlers,
others are file or script handlers while some third modules rewrite URIs or
proxies content. Furthermore, in the end, it is up to the user of the server
how and when each module will come into place. Thus, the server itself does not
presume to know which module is responsible for handling a specific
request, and will ask each module whether they have an interest in a given
request or not. It is then up to each module to either gently decline
serving a request, accept serving it or flat out deny the request from
being served, as authentication/authorization modules do: <br />
<img src="../images/build_a_mod_2.png" alt="Hook handling in httpd" /><br />
To make it a bit easier for handlers such as our mod_example to know
whether the client is requesting content we should handle or not, the server
has directives for hinting to modules whether their assistance is needed or
not. Two of these are <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>
and <code class="directive"><a href="../mod/core.html#sethandler">SetHandler</a></code>. Let's take a look at
an example using <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>. In
our example case, we want every request ending with .sum to be served by
<code>mod_example</code>, so we'll add a configuration directive that tells
the server to do just that:
</p>
<pre class="prettyprint lang-config">AddHandler example-handler .sum</pre>
<p>
What this tells the server is the following: <em>Whenever we receive a request
for a URI ending in .sum, we are to let all modules know that we are
looking for whoever goes by the name of "example-handler" </em>.
Thus, when a request is being served that ends in .sum, the server will let all
modules know, that this request should be served by "example-handler
". As you will see later, when we start building mod_example, we will
check for this handler tag relayed by <code>AddHandler</code> and reply to
the server based on the value of this tag.
</p>
<h3><a name="hook_declaration" id="hook_declaration">Hooking into httpd</a></h3>
<p>
To begin with, we only want to create a simple handler that replies to the
client browser when a specific URL is requested, so we won't bother setting
up configuration handlers and directives just yet. Our initial module
definition will look like this:</p>
<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
NULL,
NULL,
NULL,
NULL,
NULL,
register_hooks /* Our hook registering function */
};</pre>
<p>This lets the server know that we are not interested in anything fancy, we
just want to hook onto the requests and possibly handle some of them. </p>
<p> The reference in our example declaration, <code>register_hooks</code>
is the name of a function we will create to manage how we hook onto the
request process. In this example module, the function has just one purpose;
To create a simple hook that gets called after all the rewrites, access
control etc has been handled. Thus, we will let the server know that we want
to hook into its process as one of the last modules:
</p>
<pre class="prettyprint lang-c">static void register_hooks(apr_pool_t *pool)
{
/* Create a hook in the request handler, so we get called when a request arrives */
ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
}</pre>
<p>
The <code>example_handler</code> reference is the function that will handle
the request. We will discuss how to create a handler in the next chapter.
</p>
<h3><a name="hook_others" id="hook_others">Other useful hooks</a></h3>
<p>
Hooking into the request handling phase is but one of many hooks that you
can create. Some other ways of hooking are:
</p>
<ul>
<li><code>ap_hook_child_init</code>: Place a hook that executes when a child process is spawned (commonly used for initializing modules after the server has forked)</li>
<li><code>ap_hook_pre_config</code>: Place a hook that executes before any configuration data has been read (very early hook)</li>
<li><code>ap_hook_post_config</code>: Place a hook that executes after configuration has been parsed, but before the server has forked</li>
<li><code>ap_hook_pre_translate_name</code>: Place a hook that executes when a URI needs to be translated into a filename on the server, before decoding</li>
<li><code>ap_hook_translate_name</code>: Place a hook that executes when a URI needs to be translated into a filename on the server (think <code>mod_rewrite</code>)</li>
<li><code>ap_hook_quick_handler</code>: Similar to <code>ap_hook_handler</code>, except it is run before any other request hooks (translation, auth, fixups etc)</li>
<li><code>ap_hook_log_transaction</code>: Place a hook that executes when the server is about to add a log entry of the current request</li>
</ul>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="handling" id="handling">Building a handler</a></h2>
<p>
A handler is essentially a function that receives a callback when a request
to the server is made. It is passed a record of the current request (how it was
made, which headers and requests were passed along, who's giving the
request and so on), and is put in charge of either telling the server that it's
not interested in the request or handle the request with the tools provided.
</p>
<h3><a name="simple_handler" id="simple_handler">A simple "Hello, world!"
handler</a></h3>
<p>Let's start off by making a very simple request handler
that does the following:
</p>
<ol>
<li>Check that this is a request that should be served by "example-handler"</li>
<li>Set the content type of our output to <code>text/html</code></li>
<li>Write "Hello, world!" back to the client browser</li>
<li>Let the server know that we took care of this request and everything went fine</li>
</ol>
<p>
In C code, our example handler will now look like this:
</p>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
/* First off, we need to check if this is a call for the "example-handler" handler.
* If it is, we accept it and do our things, if not, we simply return DECLINED,
* and the server will try somewhere else.
*/
if (!r->handler || strcmp(r->handler, "example-handler")) return (DECLINED);
/* Now that we are handling this request, we'll write out "Hello, world!" to the client.
* To do so, we must first set the appropriate content type, followed by our output.
*/
ap_set_content_type(r, "text/html");
ap_rprintf(r, "Hello, world!");
/* Lastly, we must tell the server that we took care of this request and everything went fine.
* We do so by simply returning the value OK to the server.
*/
return OK;
}</pre>
<p>
Now, we put all we have learned together and end up with a program that
looks like
<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_1.c">mod_example_1.c</a>
. The functions used in this example will be explained later in the section
<a href="#functions">"Some useful functions you should know"</a>.
</p>
<h3><a name="request_rec" id="request_rec">The request_rec structure</a></h3>
<p>The most essential part of any request is the <em>request record
</em>. In a call to a handler function, this is represented by the <code>
request_rec* </code> structure passed along with every call that is made.
This struct, typically just referred to as <code>r</code> in modules,
contains all the information you need for your module to fully process any
HTTP request and respond accordingly.</p> <p>Some key elements of the <code>
request_rec </code> structure are:
</p>
<ul>
<li><code>r->handler (char*):</code> Contains the name of the handler the server is currently asking to do the handling of this request</li>
<li><code>r->method (char*):</code> Contains the HTTP method being used, f.x. GET or POST</li>
<li><code>r->filename (char*):</code> Contains the translated filename the client is requesting</li>
<li><code>r->args (char*):</code> Contains the query string of the request, if any</li>
<li><code>r->headers_in (apr_table_t*):</code> Contains all the headers sent by the client</li>
<li><code>r->connection (conn_rec*):</code> A record containing information about the current connection</li>
<li><code>r->user (char*):</code> If the URI requires authentication, this is set to the username provided</li>
<li><code>r->useragent_ip (char*):</code> The IP address of the client connecting to us</li>
<li><code>r->pool (apr_pool_t*)</code>: The memory pool of this request. We'll discuss this in the
"<a href="#memory">Memory management</a>" chapter.</li>
</ul>
<p>
A complete list of all the values contained within the <code>request_rec</code> structure can be found in
the <a href="http://svn.apache.org/repos/asf/httpd/httpd/trunk/include/httpd.h"><code>httpd.h</code></a> header
file or at <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html">http://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html</a>.
</p>
<p>
Let's try out some of these variables in another example handler:<br />
</p>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
/* Set the appropriate content type */
ap_set_content_type(r, "text/html");
/* Print out the IP address of the client connecting to us: */
ap_rprintf(r, "<h2>Hello, %s!</h2>", r->useragent_ip);
/* If we were reached through a GET or a POST request, be happy, else sad. */
if ( !strcmp(r->method, "POST") || !strcmp(r->method, "GET") ) {
ap_rputs("You used a GET or a POST method, that makes us happy!<br/>", r);
}
else {
ap_rputs("You did not use POST or GET, that makes us sad :(<br/>", r);
}
/* Lastly, if there was a query string, let's print that too! */
if (r->args) {
ap_rprintf(r, "Your query string was: %s", r->args);
}
return OK;
}</pre>
<h3><a name="return_value" id="return_value">Return values</a></h3>
<p>
Apache relies on return values from handlers to signify whether a request
was handled or not, and if so, whether the request went well or not. If a
module is not interested in handling a specific request, it should always
return the value <code>DECLINED</code>. If it is handling a request, it
should either return the generic value <code>OK</code>, or a specific HTTP
status code, for example:
</p>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
/* Return 404: Not found */
return HTTP_NOT_FOUND;
}</pre>
<p>
Returning <code>OK</code> or a HTTP status code does not necessarily mean
that the request will end. The server may still have other handlers that are
interested in this request, for instance the logging modules which, upon a
successful request, will write down a summary of what was requested and how
it went. To do a full stop and prevent any further processing after your
module is done, you can return the value <code>DONE</code> to let the server
know that it should cease all activity on this request and carry on with
the next, without informing other handlers.
<br />
<strong>General response codes:</strong>
</p>
<ul>
<li><code>DECLINED</code>: We are not handling this request</li>
<li><code>OK</code>: We handled this request and it went well</li>
<li><code>DONE</code>: We handled this request and the server should just close this thread without further processing</li>
</ul>
<p>
<strong>HTTP specific return codes (excerpt):</strong>
</p>
<ul>
<li><code>HTTP_OK (200)</code>: Request was okay</li>
<li><code>HTTP_MOVED_PERMANENTLY (301)</code>: The resource has moved to a new URL</li>
<li><code>HTTP_UNAUTHORIZED (401)</code>: Client is not authorized to visit this page</li>
<li><code>HTTP_FORBIDDEN (403)</code>: Permission denied</li>
<li><code>HTTP_NOT_FOUND (404)</code>: File not found</li>
<li><code>HTTP_INTERNAL_SERVER_ERROR (500)</code>: Internal server error (self explanatory)</li>
</ul>
<h3><a name="functions" id="functions">Some useful functions you should know</a></h3>
<ul>
<li>
<code>ap_rputs(const char *string, request_rec *r)</code>: <br />
Sends a string of text to the client. This is a shorthand version of <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gac827cd0537d2b6213a7c06d7c26cc36e">
ap_rwrite</a>.
<pre class="prettyprint lang-c">ap_rputs("Hello, world!", r);</pre>
</li>
<li>
<code>
<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a></code>: <br />
This function works just like <code>printf</code>, except it sends the result to the client.
<pre class="prettyprint lang-c">ap_rprintf(r, "Hello, %s!", r->useragent_ip);</pre>
</li>
<li>
<code>
<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a>(request_rec *r, const char *type)</code>: <br />
Sets the content type of the output you are sending.
<pre class="prettyprint lang-c">ap_set_content_type(r, "text/plain"); /* force a raw text output */</pre>
</li>
</ul>
<h3><a name="memory" id="memory">Memory management</a></h3>
<p>
Managing your resources in Apache HTTP Server 2.4 is quite easy, thanks to the memory pool
system. In essence, each server, connection and request have their own
memory pool that gets cleaned up when its scope ends, e.g. when a request
is done or when a server process shuts down. All your module needs to do is
latch onto this memory pool, and you won't have to worry about having to
clean up after yourself - pretty neat, huh?
</p>
<p>
In our module, we will primarily be allocating memory for each request, so
it's appropriate to use the <code>r->pool</code>
reference when creating new objects. A few of the functions for allocating
memory within a pool are:
</p>
<ul>
<li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#ga85f1e193c31d109affda72f9a92c6915">apr_palloc</a>(
apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you</li>
<li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#gaf61c098ad258069d64cdf8c0a9369f9e">apr_pcalloc</a>(
apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you and sets all bytes to 0</li>
<li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#gabc79e99ff19abbd7cfd18308c5f85d47">apr_pstrdup</a>(
apr_pool_t *p, const char *s)</code>: Creates a duplicate of the string <code>s</code>. This is useful for copying constant values so you can edit them</li>
<li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#ga3eca76b8d293c5c3f8021e45eda813d8">apr_psprintf</a>(
apr_pool_t *p, const char *fmt, ...)</code>: Similar to <code>sprintf</code>, except the server supplies you with an appropriately allocated target variable</li>
</ul>
<p>Let's put these functions into an example handler:</p>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
const char *original = "You can't edit this!";
char *copy;
int *integers;
/* Allocate space for 10 integer values and set them all to zero. */
integers = apr_pcalloc(r->pool, sizeof(int)*10);
/* Create a copy of the 'original' variable that we can edit. */
copy = apr_pstrdup(r->pool, original);
return OK;
}</pre>
<p>
This is all well and good for our module, which won't need any
pre-initialized variables or structures. However, if we wanted to
initialize something early on, before the requests come rolling in, we
could simply add a call to a function in our <code>register_hooks</code>
function to sort it out:
</p>
<pre class="prettyprint lang-c">static void register_hooks(apr_pool_t *pool)
{
/* Call a function that initializes some stuff */
example_init_function(pool);
/* Create a hook in the request handler, so we get called when a request arrives */
ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
}</pre>
<p>
In this pre-request initialization function we would not be using the
same pool as we did when allocating resources for request-based functions.
Instead, we would use the pool given to us by the server for allocating memory
on a per-process based level.
</p>
<h3><a name="parsing" id="parsing">Parsing request data</a></h3>
<p>
In our example module, we would like to add a feature, that checks which
type of digest, MD5 or SHA1 the client would like to see. This could be
solved by adding a query string to the request. A query string is typically
comprised of several keys and values put together in a string, for instance
<code>valueA=yes&valueB=no&valueC=maybe</code>. It is up to the
module itself to parse these and get the data it requires. In our example,
we'll be looking for a key called <code>digest</code>, and if set to <code>
md5</code>, we'll produce an MD5 digest, otherwise we'll produce a SHA1
digest.
</p>
<p>
Since the introduction of Apache HTTP Server 2.4, parsing request data from GET and
POST requests have never been easier. All we require to parse both GET and
POST data is four simple lines:
</p>
<pre class="prettyprint lang-c">
<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__apr__tables.html#gad7ea82d6608a4a633fc3775694ab71e4">apr_table_t</a> *GET; <em>
</em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structapr__array__header__t.html">apr_array_header_t</a>*POST;
<em>
</em>
<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__SCRIPT.html#gaed25877b529623a4d8f99f819ba1b7bd">
ap_args_to_table</a>(r, &GET); <em>
</em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__DAEMON.html#ga9d426b6382b49754d4f87c55f65af202">
ap_parse_form_data</a>(r, NULL, &POST, -1, 8192);</pre>
<p>
In our specific example module, we're looking for the <code>digest</code>
value from the query string, which now resides inside a table called <code>
GET</code>. To extract this value, we need only perform a simple operation:
</p>
<pre class="prettyprint lang-c">/* Get the "digest" key from the query string, if any. */
const char *digestType = apr_table_get(GET, "digest");
/* If no key was returned, we will set a default value instead. */
if (!digestType) digestType = "sha1";</pre>
<p>
The structures used for the POST and GET data are not exactly the same, so
if we were to fetch a value from POST data instead of the query string, we
would have to resort to a few more lines, as outlined in <a href="#get_post">this example</a> in the last chapter of this document.
</p>
<h3><a name="advanced_handler" id="advanced_handler">Making an advanced handler</a></h3>
<p>
Now that we have learned how to parse form data and manage our resources,
we can move on to creating an advanced version of our module, that spits
out the MD5 or SHA1 digest of files:
</p>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
int rc, exists;
apr_finfo_t finfo;
apr_file_t *file;
char *filename;
char buffer[256];
apr_size_t readBytes;
int n;
apr_table_t *GET;
apr_array_header_t *POST;
const char *digestType;
/* Check that the "example-handler" handler is being called. */
if (!r->handler || strcmp(r->handler, "example-handler")) return (DECLINED);
/* Figure out which file is being requested by removing the .sum from it */
filename = apr_pstrdup(r->pool, r->filename);
filename[strlen(filename)-4] = 0; /* Cut off the last 4 characters. */
/* Figure out if the file we request a sum on exists and isn't a directory */
rc = apr_stat(&finfo, filename, APR_FINFO_MIN, r->pool);
if (rc == APR_SUCCESS) {
exists =
(
(finfo.filetype != APR_NOFILE)
&& !(finfo.filetype & APR_DIR)
);
if (!exists) return HTTP_NOT_FOUND; /* Return a 404 if not found. */
}
/* If apr_stat failed, we're probably not allowed to check this file. */
else return HTTP_FORBIDDEN;
/* Parse the GET and, optionally, the POST data sent to us */
ap_args_to_table(r, &GET);
ap_parse_form_data(r, NULL, &POST, -1, 8192);
/* Set the appropriate content type */
ap_set_content_type(r, "text/html");
/* Print a title and some general information */
ap_rprintf(r, "<h2>Information on %s:</h2>", filename);
ap_rprintf(r, "<b>Size:</b> %u bytes<br/>", finfo.size);
/* Get the digest type the client wants to see */
digestType = apr_table_get(GET, "digest");
if (!digestType) digestType = "MD5";
rc = apr_file_open(&file, filename, APR_READ, APR_OS_DEFAULT, r->pool);
if (rc == APR_SUCCESS) {
/* Are we trying to calculate the MD5 or the SHA1 digest? */
if (!strcasecmp(digestType, "md5")) {
/* Calculate the MD5 sum of the file */
union {
char chr[16];
uint32_t num[4];
} digest;
apr_md5_ctx_t md5;
apr_md5_init(&md5);
readBytes = 256;
while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) {
apr_md5_update(&md5, buffer, readBytes);
}
apr_md5_final(digest.chr, &md5);
/* Print out the MD5 digest */
ap_rputs("<b>MD5: </b><code>", r);
for (n = 0; n < APR_MD5_DIGESTSIZE/4; n++) {
ap_rprintf(r, "%08x", digest.num[n]);
}
ap_rputs("</code>", r);
/* Print a link to the SHA1 version */
ap_rputs("<br/><a href='?digest=sha1'>View the SHA1 hash instead</a>", r);
}
else {
/* Calculate the SHA1 sum of the file */
union {
char chr[20];
uint32_t num[5];
} digest;
apr_sha1_ctx_t sha1;
apr_sha1_init(&sha1);
readBytes = 256;
while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) {
apr_sha1_update(&sha1, buffer, readBytes);
}
apr_sha1_final(digest.chr, &sha1);
/* Print out the SHA1 digest */
ap_rputs("<b>SHA1: </b><code>", r);
for (n = 0; n < APR_SHA1_DIGESTSIZE/4; n++) {
ap_rprintf(r, "%08x", digest.num[n]);
}
ap_rputs("</code>", r);
/* Print a link to the MD5 version */
ap_rputs("<br/><a href='?digest=md5'>View the MD5 hash instead</a>", r);
}
apr_file_close(file);
}
/* Let the server know that we responded to this request. */
return OK;
}</pre>
<p>
This version in its entirety can be found here:
<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_2.c">mod_example_2.c</a>.
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="configuration" id="configuration">Adding configuration options</a></h2>
<p>
In this next segment of this document, we will turn our eyes away from the
digest module and create a new example module, whose only function is to
write out its own configuration. The purpose of this is to examine how
the server works with configuration, and what happens when you start writing
advanced configurations
for your modules.
</p>
<h3><a name="config_intro" id="config_intro">An introduction to configuration
directives</a></h3>
<p>
If you are reading this, then you probably already know
what a configuration directive is. Simply put, a directive is a way of
telling an individual module (or a set of modules) how to behave, such as
these directives control how <code>mod_rewrite</code> works:
</p>
<pre class="prettyprint lang-config">RewriteEngine On
RewriteCond "%{REQUEST_URI}" "^/foo/bar"
RewriteRule "^/foo/bar/(.*)$" "/foobar?page=$1"</pre>
<p>
Each of these configuration directives are handled by a separate function,
that parses the parameters given and sets up a configuration accordingly.
</p>
<h3><a name="config_simple" id="config_simple">Making an example configuration</a></h3>
<p>To begin with, we'll create a basic configuration in C-space:</p>
<pre class="prettyprint lang-c">typedef struct {
int enabled; /* Enable or disable our module */
const char *path; /* Some path to...something */
int typeOfAction; /* 1 means action A, 2 means action B and so on */
} example_config;</pre>
<p>
Now, let's put this into perspective by creating a very small module that
just prints out a hard-coded configuration. You'll notice that we use the
<code>register_hooks</code> function for initializing the configuration
values to their defaults:
</p>
<pre class="prettyprint lang-c">typedef struct {
int enabled; /* Enable or disable our module */
const char *path; /* Some path to...something */
int typeOfAction; /* 1 means action A, 2 means action B and so on */
} example_config;
static example_config config;
static int example_handler(request_rec *r)
{
if (!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
ap_set_content_type(r, "text/plain");
ap_rprintf(r, "Enabled: %u\n", config.enabled);
ap_rprintf(r, "Path: %s\n", config.path);
ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
return OK;
}
static void register_hooks(apr_pool_t *pool)
{
config.enabled = 1;
config.path = "/foo/bar";
config.typeOfAction = 0x00;
ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
}
/* Define our module as an entity and assign a function for registering hooks */
module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
NULL, /* Per-directory configuration handler */
NULL, /* Merge handler for per-directory configurations */
NULL, /* Per-server configuration handler */
NULL, /* Merge handler for per-server configurations */
NULL, /* Any directives we may have for httpd */
register_hooks /* Our hook registering function */
};</pre>
<p>
So far so good. To access our new handler, we could add the following to
our configuration:
</p>
<pre class="prettyprint lang-config"><Location "/example">
SetHandler example-handler
</Location></pre>
<p>
When we visit, we'll see our current configuration being spit out by our
module.
</p>
<h3><a name="register_directive" id="register_directive">Registering directives with the server</a></h3>
<p>
What if we want to change our configuration, not by hard-coding new values
into the module, but by using either the httpd.conf file or possibly a
.htaccess file? It's time to let the server know that we want this to be
possible. To do so, we must first change our <em>name tag</em> to include a
reference to the configuration directives we want to register with the server:
</p>
<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
NULL, /* Per-directory configuration handler */
NULL, /* Merge handler for per-directory configurations */
NULL, /* Per-server configuration handler */
NULL, /* Merge handler for per-server configurations */
example_directives, /* Any directives we may have for httpd */
register_hooks /* Our hook registering function */
};</pre>
<p>
This will tell the server that we are now accepting directives from the
configuration files, and that the structure called <code>example_directives
</code> holds information on what our directives are and how they work.
Since we have three different variables in our module configuration, we
will add a structure with three directives and a NULL at the end:
</p>
<pre class="prettyprint lang-c">static const command_rec example_directives[] =
{
AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
{ NULL }
};</pre>
<p>
<img src="../images/build_a_mod_4.png" alt="Directives structure" /><br />
As you can see, each directive needs at least 5 parameters set:
</p>
<ol>
<li><code><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a></code>: This is a macro that tells the server that this directive takes one and only one argument.
If we required two arguments, we could use the macro <code><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#gafaec43534fcf200f37d9fecbf9247c21">AP_INIT_TAKE2</a></code> and so on (refer to httpd_conf.h
for more macros).</li>
<li><code>exampleEnabled</code>: This is the name of our directive. More precisely, it is what the user must put in his/her
configuration in order to invoke a configuration change in our module.</li>
<li><code>example_set_enabled</code>: This is a reference to a C function that parses the directive and sets the configuration
accordingly. We will discuss how to make this in the following paragraph.</li>
<li><code>RSRC_CONF</code>: This tells the server where the directive is permitted. We'll go into details on this value in the
later chapters, but for now, <code>RSRC_CONF</code> means that the server will only accept these directives in a server context.</li>
<li><code>"Enable or disable...."</code>: This is simply a brief description of what the directive does.</li>
</ol>
<p>
(<em>The "missing" parameter in our definition, which is usually set to
<code>NULL</code>, is an optional function that can be run after the
initial function to parse the arguments have been run. This is usually
omitted, as the function for verifying arguments might as well be used to
set them.</em>)
</p>
<h3><a name="directive_handler" id="directive_handler">The directive handler function</a></h3>
<p>
Now that we have told the server to expect some directives for our module, it's
time to make a few functions for handling these. What the server reads in the
configuration file(s) is text, and so naturally, what it passes along to
our directive handler is one or more strings, that we ourselves need to
recognize and act upon. You'll notice, that since we set our <code>
exampleAction</code> directive to accept two arguments, its C function also
has an additional parameter defined:</p>
<pre class="prettyprint lang-c">/* Handler for the "exampleEnabled" directive */
const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
{
if(!strcasecmp(arg, "on")) config.enabled = 1;
else config.enabled = 0;
return NULL;
}
/* Handler for the "examplePath" directive */
const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
{
config.path = arg;
return NULL;
}
/* Handler for the "exampleAction" directive */
/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
/* and we store it in a bit-wise manner. */
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
else config.typeOfAction = 0x02;
if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
else config.typeOfAction += 0x20;
return NULL;
}</pre>
<h3><a name="directive_complete" id="directive_complete">Putting it all together</a></h3>
<p>
Now that we have our directives set up, and handlers configured for them,
we can assemble our module into one big file:
</p>
<pre class="prettyprint lang-c">/* mod_example_config_simple.c: */
#include <stdio.h>
#include "apr_hash.h"
#include "ap_config.h"
#include "ap_provider.h"
#include "httpd.h"
#include "http_core.h"
#include "http_config.h"
#include "http_log.h"
#include "http_protocol.h"
#include "http_request.h"
/*
==============================================================================
Our configuration prototype and declaration:
==============================================================================
*/
typedef struct {
int enabled; /* Enable or disable our module */
const char *path; /* Some path to...something */
int typeOfAction; /* 1 means action A, 2 means action B and so on */
} example_config;
static example_config config;
/*
==============================================================================
Our directive handlers:
==============================================================================
*/
/* Handler for the "exampleEnabled" directive */
const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
{
if(!strcasecmp(arg, "on")) config.enabled = 1;
else config.enabled = 0;
return NULL;
}
/* Handler for the "examplePath" directive */
const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
{
config.path = arg;
return NULL;
}
/* Handler for the "exampleAction" directive */
/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
/* and we store it in a bit-wise manner. */
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
else config.typeOfAction = 0x02;
if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
else config.typeOfAction += 0x20;
return NULL;
}
/*
==============================================================================
The directive structure for our name tag:
==============================================================================
*/
static const command_rec example_directives[] =
{
AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
{ NULL }
};
/*
==============================================================================
Our module handler:
==============================================================================
*/
static int example_handler(request_rec *r)
{
if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
ap_set_content_type(r, "text/plain");
ap_rprintf(r, "Enabled: %u\n", config.enabled);
ap_rprintf(r, "Path: %s\n", config.path);
ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
return OK;
}
/*
==============================================================================
The hook registration function (also initializes the default config values):
==============================================================================
*/
static void register_hooks(apr_pool_t *pool)
{
config.enabled = 1;
config.path = "/foo/bar";
config.typeOfAction = 3;
ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
}
/*
==============================================================================
Our module name tag:
==============================================================================
*/
module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
NULL, /* Per-directory configuration handler */
NULL, /* Merge handler for per-directory configurations */
NULL, /* Per-server configuration handler */
NULL, /* Merge handler for per-server configurations */
example_directives, /* Any directives we may have for httpd */
register_hooks /* Our hook registering function */
};</pre>
<p>
In our httpd.conf file, we can now change the hard-coded configuration by
adding a few lines:
</p>
<pre class="prettyprint lang-config">ExampleEnabled On
ExamplePath "/usr/bin/foo"
ExampleAction file allow</pre>
<p>
And thus we apply the configuration, visit <code>/example</code> on our
web site, and we see the configuration has adapted to what we wrote in our
configuration file.
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="context" id="context">Context aware configurations</a></h2>
<h3><a name="context_intro" id="context_intro">Introduction to context aware configurations</a></h3>
<p>
In Apache HTTP Server 2.4, different URLs, virtual hosts, directories etc can have very
different meanings to the user of the server, and thus different contexts
within which modules must operate. For example, let's assume you have this
configuration set up for mod_rewrite:
</p>
<pre class="prettyprint lang-config"><Directory "/var/www">
RewriteCond "%{HTTP_HOST}" "^example.com$"
RewriteRule "(.*)" "http://www.example.com/$1"
</Directory>
<Directory "/var/www/sub">
RewriteRule "^foobar$" "index.php?foobar=true"
</Directory></pre>
<p>
In this example, you will have set up two different contexts for
mod_rewrite:</p>
<ol>
<li>Inside <code>/var/www</code>, all requests for <code>http://example.com</code> must go to <code>http://www.example.com</code></li>
<li>Inside <code>/var/www/sub</code>, all requests for <code>foobar</code> must go to <code>index.php?foobar=true</code></li>
</ol>
<p>
If mod_rewrite (or the entire server for that matter) wasn't context aware, then
these rewrite rules would just apply to every and any request made,
regardless of where and how they were made, but since the module can pull
the context specific configuration straight from the server, it does not need
to know itself, which of the directives are valid in this context, since
the server takes care of this.</p>
<p>
So how does a module get the specific configuration for the server,
directory or location in question? It does so by making one simple call:
</p>
<pre class="prettyprint lang-c">example_config *config = (example_config*) <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga1093a5908a384eacc929b028c79f2a02">ap_get_module_config</a>(r->per_dir_config, &example_module);</pre>
<p>
That's it! Of course, a whole lot goes on behind the scenes, which we will
discuss in this chapter, starting with how the server came to know what our
configuration looks like, and how it came to be set up as it is in the
specific context.
</p>
<h3><a name="context_base" id="context_base">Our basic configuration setup</a></h3>
<p>In this chapter, we will be working with a slightly modified version of
our previous context structure. We will set a <code>context</code>
variable that we can use to track which context configuration is being
used by the server in various places:
</p>
<pre class="prettyprint lang-c">typedef struct {
char context[256];
char path[256];
int typeOfAction;
int enabled;
} example_config;</pre>
<p>Our handler for requests will also be modified, yet still very simple:</p>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
example_config *config = (example_config*) ap_get_module_config(r->per_dir_config, &example_module);
ap_set_content_type(r, "text/plain");
ap_rprintf("Enabled: %u\n", config->enabled);
ap_rprintf("Path: %s\n", config->path);
ap_rprintf("TypeOfAction: %x\n", config->typeOfAction);
ap_rprintf("Context: %s\n", config->context);
return OK;
}</pre>
<h3><a name="context_which" id="context_which">Choosing a context</a></h3>
<p>
Before we can start making our module context aware, we must first define,
which contexts we will accept. As we saw in the previous chapter, defining
a directive required five elements be set:</p>
<pre class="prettyprint lang-c">AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),</pre>
<p>The <code>RSRC_CONF</code> definition told the server that we would only allow
this directive in a global server context, but since we are now trying out
a context aware version of our module, we should set this to something
more lenient, namely the value <code>ACCESS_CONF</code>, which lets us use
the directive inside <Directory> and <Location> blocks. For more
control over the placement of your directives, you can combine the following
restrictions together to form a specific rule:
</p>
<ul>
<li><code>RSRC_CONF</code>: Allow in .conf files (not .htaccess) outside <Directory> or <Location></li>
<li><code>ACCESS_CONF</code>: Allow in .conf files (not .htaccess) inside <Directory> or <Location></li>
<li><code>OR_OPTIONS</code>: Allow in .conf files and .htaccess when <code>AllowOverride Options</code> is set</li>
<li><code>OR_FILEINFO</code>: Allow in .conf files and .htaccess when <code>AllowOverride FileInfo</code> is set</li>
<li><code>OR_AUTHCFG</code>: Allow in .conf files and .htaccess when <code>AllowOverride AuthConfig</code> is set</li>
<li><code>OR_INDEXES</code>: Allow in .conf files and .htaccess when <code>AllowOverride Indexes</code> is set</li>
<li><code>OR_ALL</code>: Allow anywhere in .conf files and .htaccess</li>
</ul>
<h3><a name="context_pool" id="context_pool">Using the server to allocate configuration slots</a></h3>
<p> A much smarter way to manage your configurations is by letting the server
help you create them. To do so, we must first start off by changing our
<em>name tag</em> to let the server know, that it should assist us in creating
and managing our configurations. Since we have chosen the per-directory
(or per-location) context for our module configurations, we'll add a
per-directory creator and merger function reference in our tag:</p>
<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
create_dir_conf, /* Per-directory configuration handler */
merge_dir_conf, /* Merge handler for per-directory configurations */
NULL, /* Per-server configuration handler */
NULL, /* Merge handler for per-server configurations */
directives, /* Any directives we may have for httpd */
register_hooks /* Our hook registering function */
};</pre>
<h3><a name="context_new" id="context_new">Creating new context configurations</a></h3>
<p>
Now that we have told the server to help us create and manage configurations,
our first step is to make a function for creating new, blank
configurations. We do so by creating the function we just referenced in
our name tag as the Per-directory configuration handler:</p>
<pre class="prettyprint lang-c">void *create_dir_conf(apr_pool_t *pool, char *context) {
context = context ? context : "(undefined context)";
example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
if(cfg) {
/* Set some default values */
strcpy(cfg->context, context);
cfg->enabled = 0;
cfg->path = "/foo/bar";
cfg->typeOfAction = 0x11;
}
return cfg;
}</pre>
<h3><a name="context_merge" id="context_merge">Merging configurations</a></h3>
<p>
Our next step in creating a context aware configuration is merging
configurations. This part of the process particularly applies to scenarios
where you have a parent configuration and a child, such as the following:
</p>
<pre class="prettyprint lang-config"><Directory "/var/www">
ExampleEnabled On
ExamplePath "/foo/bar"
ExampleAction file allow
</Directory>
<Directory "/var/www/subdir">
ExampleAction file deny
</Directory></pre>
<p>
In this example, it is natural to assume that the directory <code>
/var/www/subdir</code> should inherit the values set for the <code>/var/www
</code> directory, as we did not specify an <code>ExampleEnabled</code> nor
an <code>ExamplePath</code> for this directory. The server does not presume to
know if this is true, but cleverly does the following:
</p>
<ol>
<li>Creates a new configuration for <code>/var/www</code></li>
<li>Sets the configuration values according to the directives given for <code>/var/www</code></li>
<li>Creates a new configuration for <code>/var/www/subdir</code></li>
<li>Sets the configuration values according to the directives given for <code>/var/www/subdir</code></li>
<li><strong>Proposes a merge</strong> of the two configurations into a new configuration for <code>/var/www/subdir</code></li>
</ol>
<p>
This proposal is handled by the <code>merge_dir_conf</code> function we
referenced in our name tag. The purpose of this function is to assess the
two configurations and decide how they are to be merged:</p>
<pre class="prettyprint lang-c">void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD) {
example_config *base = (example_config *) BASE ; /* This is what was set in the parent context */
example_config *add = (example_config *) ADD ; /* This is what is set in the new context */
example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration"); /* This will be the merged configuration */
/* Merge configurations */
conf->enabled = ( add->enabled == 0 ) ? base->enabled : add->enabled ;
conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
strcpy(conf->path, strlen(add->path) ? add->path : base->path);
return conf ;
}</pre>
<h3><a name="context_example" id="context_example">Trying out our new context aware configurations</a></h3>
<p>
Now, let's try putting it all together to create a new module that is
context aware. First off, we'll create a configuration that lets us test
how the module works:
</p>
<pre class="prettyprint lang-config"><Location "/a">
SetHandler example-handler
ExampleEnabled on
ExamplePath "/foo/bar"
ExampleAction file allow
</Location>
<Location "/a/b">
ExampleAction file deny
ExampleEnabled off
</Location>
<Location "/a/b/c">
ExampleAction db deny
ExamplePath "/foo/bar/baz"
ExampleEnabled on
</Location></pre>
<p>
Then we'll assemble our module code. Note, that since we are now using our
name tag as reference when fetching configurations in our handler, I have
added some prototypes to keep the compiler happy:
</p>
<pre class="prettyprint lang-c">/*$6
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
* mod_example_config.c
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*/
#include <stdio.h>
#include "apr_hash.h"
#include "ap_config.h"
#include "ap_provider.h"
#include "httpd.h"
#include "http_core.h"
#include "http_config.h"
#include "http_log.h"
#include "http_protocol.h"
#include "http_request.h"
/*$1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Configuration structure
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
typedef struct
{
char context[256];
char path[256];
int typeOfAction;
int enabled;
} example_config;
/*$1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prototypes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
static int example_handler(request_rec *r);
const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg);
const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg);
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2);
void *create_dir_conf(apr_pool_t *pool, char *context);
void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD);
static void register_hooks(apr_pool_t *pool);
/*$1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Configuration directives
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
static const command_rec directives[] =
{
AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, ACCESS_CONF, "Enable or disable mod_example"),
AP_INIT_TAKE1("examplePath", example_set_path, NULL, ACCESS_CONF, "The path to whatever"),
AP_INIT_TAKE2("exampleAction", example_set_action, NULL, ACCESS_CONF, "Special action value!"),
{ NULL }
};
/*$1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Our name tag
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*/
module AP_MODULE_DECLARE_DATA example_module =
{
STANDARD20_MODULE_STUFF,
create_dir_conf, /* Per-directory configuration handler */
merge_dir_conf, /* Merge handler for per-directory configurations */
NULL, /* Per-server configuration handler */
NULL, /* Merge handler for per-server configurations */
directives, /* Any directives we may have for httpd */
register_hooks /* Our hook registering function */
};
/*
=======================================================================================================================
Hook registration function
=======================================================================================================================
*/
static void register_hooks(apr_pool_t *pool)
{
ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
}
/*
=======================================================================================================================
Our example web service handler
=======================================================================================================================
*/
static int example_handler(request_rec *r)
{
if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
example_config *config = (example_config *) ap_get_module_config(r->per_dir_config, &example_module);
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
ap_set_content_type(r, "text/plain");
ap_rprintf(r, "Enabled: %u\n", config->enabled);
ap_rprintf(r, "Path: %s\n", config->path);
ap_rprintf(r, "TypeOfAction: %x\n", config->typeOfAction);
ap_rprintf(r, "Context: %s\n", config->context);
return OK;
}
/*
=======================================================================================================================
Handler for the "exampleEnabled" directive
=======================================================================================================================
*/
const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
{
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
example_config *conf = (example_config *) cfg;
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
if(conf)
{
if(!strcasecmp(arg, "on"))
conf->enabled = 1;
else
conf->enabled = 0;
}
return NULL;
}
/*
=======================================================================================================================
Handler for the "examplePath" directive
=======================================================================================================================
*/
const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
{
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
example_config *conf = (example_config *) cfg;
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
if(conf)
{
strcpy(conf->path, arg);
}
return NULL;
}
/*
=======================================================================================================================
Handler for the "exampleAction" directive ;
Let's pretend this one takes one argument (file or db), and a second (deny or allow), ;
and we store it in a bit-wise manner.
=======================================================================================================================
*/
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
example_config *conf = (example_config *) cfg;
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
if(conf)
{
{
if(!strcasecmp(arg1, "file"))
conf->typeOfAction = 0x01;
else
conf->typeOfAction = 0x02;
if(!strcasecmp(arg2, "deny"))
conf->typeOfAction += 0x10;
else
conf->typeOfAction += 0x20;
}
}
return NULL;
}
/*
=======================================================================================================================
Function for creating new configurations for per-directory contexts
=======================================================================================================================
*/
void *create_dir_conf(apr_pool_t *pool, char *context)
{
context = context ? context : "Newly created configuration";
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
if(cfg)
{
{
/* Set some default values */
strcpy(cfg->context, context);
cfg->enabled = 0;
memset(cfg->path, 0, 256);
cfg->typeOfAction = 0x00;
}
}
return cfg;
}
/*
=======================================================================================================================
Merging function for configurations
=======================================================================================================================
*/
void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD)
{
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
example_config *base = (example_config *) BASE;
example_config *add = (example_config *) ADD;
example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration");
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
conf->enabled = (add->enabled == 0) ? base->enabled : add->enabled;
conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
strcpy(conf->path, strlen(add->path) ? add->path : base->path);
return conf;
}</pre>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="summary" id="summary">Summing up</a></h2>
<p>
We have now looked at how to create simple modules for Apache HTTP Server 2.4 and
configuring them. What you do next is entirely up to you, but it is my
hope that something valuable has come out of reading this documentation.
If you have questions on how to further develop modules, you are welcome
to join our <a href="http://httpd.apache.org/lists.html">mailing lists</a>
or check out the rest of our documentation for further tips.
</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="snippets" id="snippets">Some useful snippets of code</a></h2>
<h3><a name="get_post" id="get_post">Retrieve variables from POST form data</a></h3>
<pre class="prettyprint lang-c">typedef struct {
const char *key;
const char *value;
} keyValuePair;
keyValuePair *readPost(request_rec *r) {
apr_array_header_t *pairs = NULL;
apr_off_t len;
apr_size_t size;
int res;
int i = 0;
char *buffer;
keyValuePair *kvp;
res = ap_parse_form_data(r, NULL, &pairs, -1, HUGE_STRING_LEN);
if (res != OK || !pairs) return NULL; /* Return NULL if we failed or if there are is no POST data */
kvp = apr_pcalloc(r->pool, sizeof(keyValuePair) * (pairs->nelts + 1));
while (pairs && !apr_is_empty_array(pairs)) {
ap_form_pair_t *pair = (ap_form_pair_t *) apr_array_pop(pairs);
apr_brigade_length(pair->value, 1, &len);
size = (apr_size_t) len;
buffer = apr_palloc(r->pool, size + 1);
apr_brigade_flatten(pair->value, buffer, &size);
buffer[len] = 0;
kvp[i].key = apr_pstrdup(r->pool, pair->name);
kvp[i].value = buffer;
i++;
}
return kvp;
}
static int example_handler(request_rec *r)
{
/*~~~~~~~~~~~~~~~~~~~~~~*/
keyValuePair *formData;
/*~~~~~~~~~~~~~~~~~~~~~~*/
formData = readPost(r);
if (formData) {
int i;
for (i = 0; &formData[i]; i++) {
if (formData[i].key && formData[i].value) {
ap_rprintf(r, "%s = %s\n", formData[i].key, formData[i].value);
} else if (formData[i].key) {
ap_rprintf(r, "%s\n", formData[i].key);
} else if (formData[i].value) {
ap_rprintf(r, "= %s\n", formData[i].value);
} else {
break;
}
}
}
return OK;
}</pre>
<h3><a name="headers_out" id="headers_out">Printing out every HTTP header received</a></h3>
<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
{
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
const apr_array_header_t *fields;
int i;
apr_table_entry_t *e = 0;
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
fields = apr_table_elts(r->headers_in);
e = (apr_table_entry_t *) fields->elts;
for(i = 0; i < fields->nelts; i++) {
ap_rprintf(r, "%s: %s\n", e[i].key, e[i].val);
}
return OK;
}</pre>
<h3><a name="request_body" id="request_body">Reading the request body into memory</a></h3>
<pre class="prettyprint lang-c">static int util_read(request_rec *r, const char **rbuf, apr_off_t *size)
{
/*~~~~~~~~*/
int rc = OK;
/*~~~~~~~~*/
if((rc = ap_setup_client_block(r, REQUEST_CHUNKED_ERROR))) {
return(rc);
}
if(ap_should_client_block(r)) {
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
char argsbuffer[HUGE_STRING_LEN];
apr_off_t rsize, len_read, rpos = 0;
apr_off_t length = r->remaining;
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
*rbuf = (const char *) apr_pcalloc(r->pool, (apr_size_t) (length + 1));
*size = length;
while((len_read = ap_get_client_block(r, argsbuffer, sizeof(argsbuffer))) > 0) {
if((rpos + len_read) > length) {
rsize = length - rpos;
}
else {
rsize = len_read;
}
memcpy((char *) *rbuf + rpos, argsbuffer, (size_t) rsize);
rpos += rsize;
}
}
return(rc);
}
static int example_handler(request_rec *r)
{
/*~~~~~~~~~~~~~~~~*/
apr_off_t size;
const char *buffer;
/*~~~~~~~~~~~~~~~~*/
if(util_read(r, &buffer, &size) == OK) {
ap_rprintf(r, "We read a request body that was %" APR_OFF_T_FMT " bytes long", size);
}
return OK;
}</pre>
</div></div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
<script type="text/javascript"><!--//--><![CDATA[//><!--
var comments_shortname = 'httpd';
var comments_identifier = 'http://httpd.apache.org/docs/2.4/developer/modguide.html';
(function(w, d) {
if (w.location.hostname.toLowerCase() == "httpd.apache.org") {
d.write('<div id="comments_thread"><\/div>');
var s = d.createElement('script');
s.type = 'text/javascript';
s.async = true;
s.src = 'https://comments.apache.org/show_comments.lua?site=' + comments_shortname + '&page=' + comments_identifier;
(d.getElementsByTagName('head')[0] || d.getElementsByTagName('body')[0]).appendChild(s);
}
else {
d.write('<div id="comments_thread">Comments are disabled for this page at the moment.<\/div>');
}
})(window, document);
//--><!]]></script></div><div id="footer">
<p class="apache">Copyright 2024 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div><script type="text/javascript"><!--//--><![CDATA[//><!--
if (typeof(prettyPrint) !== 'undefined') {
prettyPrint();
}
//--><!]]></script>
</body></html>
|
