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
|
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Stream Node.js v0.10.29 Manual & Documentation</title>
<link rel="stylesheet" href="assets/style.css">
<link rel="stylesheet" href="assets/sh.css">
<link rel="canonical" href="http://nodejs.org/api/stream.html">
</head>
<body class="alt apidoc" id="api-section-stream">
<div id="intro" class="interior">
<a href="/" title="Go back to the home page">
<img id="logo" src="http://nodejs.org/images/logo-light.png" alt="node.js">
</a>
</div>
<div id="content" class="clearfix">
<div id="column2" class="interior">
<ul>
<li><a href="/" class="home">Home</a></li>
<li><a href="/download/" class="download">Download</a></li>
<li><a href="/about/" class="about">About</a></li>
<li><a href="http://npmjs.org/" class="npm">npm Registry</a></li>
<li><a href="http://nodejs.org/api/" class="docs current">Docs</a></li>
<li><a href="http://blog.nodejs.org" class="blog">Blog</a></li>
<li><a href="/community/" class="community">Community</a></li>
<li><a href="/logos/" class="logos">Logos</a></li>
<li><a href="http://jobs.nodejs.org/" class="jobs">Jobs</a></li>
</ul>
<p class="twitter"><a href="http://twitter.com/nodejs">@nodejs</a></p>
</div>
<div id="column1" class="interior">
<header>
<h1>Node.js v0.10.29 Manual & Documentation</h1>
<div id="gtoc">
<p>
<a href="index.html" name="toc">Index</a> |
<a href="all.html">View on single page</a> |
<a href="stream.json">View as JSON</a>
</p>
</div>
<hr>
</header>
<div id="toc">
<h2>Table of Contents</h2>
<ul>
<li><a href="#stream_stream">Stream</a><ul>
<li><a href="#stream_api_for_stream_consumers">API for Stream Consumers</a><ul>
<li><a href="#stream_class_stream_readable">Class: stream.Readable</a><ul>
<li><a href="#stream_event_readable">Event: 'readable'</a></li>
<li><a href="#stream_event_data">Event: 'data'</a></li>
<li><a href="#stream_event_end">Event: 'end'</a></li>
<li><a href="#stream_event_close">Event: 'close'</a></li>
<li><a href="#stream_event_error">Event: 'error'</a></li>
<li><a href="#stream_readable_read_size">readable.read([size])</a></li>
<li><a href="#stream_readable_setencoding_encoding">readable.setEncoding(encoding)</a></li>
<li><a href="#stream_readable_resume">readable.resume()</a></li>
<li><a href="#stream_readable_pause">readable.pause()</a></li>
<li><a href="#stream_readable_pipe_destination_options">readable.pipe(destination, [options])</a></li>
<li><a href="#stream_readable_unpipe_destination">readable.unpipe([destination])</a></li>
<li><a href="#stream_readable_unshift_chunk">readable.unshift(chunk)</a></li>
<li><a href="#stream_readable_wrap_stream">readable.wrap(stream)</a></li>
</ul>
</li>
<li><a href="#stream_class_stream_writable">Class: stream.Writable</a><ul>
<li><a href="#stream_writable_write_chunk_encoding_callback">writable.write(chunk, [encoding], [callback])</a></li>
<li><a href="#stream_event_drain">Event: 'drain'</a></li>
<li><a href="#stream_writable_end_chunk_encoding_callback">writable.end([chunk], [encoding], [callback])</a></li>
<li><a href="#stream_event_finish">Event: 'finish'</a></li>
<li><a href="#stream_event_pipe">Event: 'pipe'</a></li>
<li><a href="#stream_event_unpipe">Event: 'unpipe'</a></li>
<li><a href="#stream_event_error_1">Event: 'error'</a></li>
</ul>
</li>
<li><a href="#stream_class_stream_duplex">Class: stream.Duplex</a></li>
<li><a href="#stream_class_stream_transform">Class: stream.Transform</a></li>
</ul>
</li>
<li><a href="#stream_api_for_stream_implementors">API for Stream Implementors</a><ul>
<li><a href="#stream_class_stream_readable_1">Class: stream.Readable</a><ul>
<li><a href="#stream_example_a_counting_stream">Example: A Counting Stream</a></li>
<li><a href="#stream_example_simpleprotocol_v1_sub_optimal">Example: SimpleProtocol v1 (Sub-optimal)</a></li>
<li><a href="#stream_new_stream_readable_options">new stream.Readable([options])</a></li>
<li><a href="#stream_readable_read_size_1">readable._read(size)</a></li>
<li><a href="#stream_readable_push_chunk_encoding">readable.push(chunk, [encoding])</a></li>
</ul>
</li>
<li><a href="#stream_class_stream_writable_1">Class: stream.Writable</a><ul>
<li><a href="#stream_new_stream_writable_options">new stream.Writable([options])</a></li>
<li><a href="#stream_writable_write_chunk_encoding_callback_1">writable._write(chunk, encoding, callback)</a></li>
</ul>
</li>
<li><a href="#stream_class_stream_duplex_1">Class: stream.Duplex</a><ul>
<li><a href="#stream_new_stream_duplex_options">new stream.Duplex(options)</a></li>
</ul>
</li>
<li><a href="#stream_class_stream_transform_1">Class: stream.Transform</a><ul>
<li><a href="#stream_new_stream_transform_options">new stream.Transform([options])</a></li>
<li><a href="#stream_transform_transform_chunk_encoding_callback">transform._transform(chunk, encoding, callback)</a></li>
<li><a href="#stream_transform_flush_callback">transform._flush(callback)</a></li>
<li><a href="#stream_events_finish_and_end">Events: 'finish' and 'end'</a></li>
<li><a href="#stream_example_simpleprotocol_parser_v2">Example: <code>SimpleProtocol</code> parser v2</a></li>
</ul>
</li>
<li><a href="#stream_class_stream_passthrough">Class: stream.PassThrough</a></li>
</ul>
</li>
<li><a href="#stream_streams_under_the_hood">Streams: Under the Hood</a><ul>
<li><a href="#stream_buffering">Buffering</a></li>
<li><a href="#stream_stream_read_0"><code>stream.read(0)</code></a></li>
<li><a href="#stream_stream_push"><code>stream.push('')</code></a></li>
<li><a href="#stream_compatibility_with_older_node_versions">Compatibility with Older Node Versions</a></li>
<li><a href="#stream_object_mode">Object Mode</a></li>
<li><a href="#stream_state_objects">State Objects</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div id="apicontent">
<h1>Stream<span><a class="mark" href="#stream_stream" id="stream_stream">#</a></span></h1>
<pre class="api_stability_2">Stability: 2 - Unstable</pre><p>A stream is an abstract interface implemented by various objects in
Node. For example a <a href="http.html#http_http_incomingmessage">request to an HTTP
server</a> is a stream, as is
<a href="process.html#process_process_stdout">stdout</a>. Streams are readable, writable, or both. All streams are
instances of <a href="events.html#events_class_events_eventemitter">EventEmitter</a>
</p>
<p>You can load the Stream base classes by doing <code>require('stream')</code>.
There are base classes provided for <a href="#stream_class_stream_readable">Readable</a> streams, <a href="#stream_class_stream_writable">Writable</a>
streams, <a href="#stream_class_stream_duplex">Duplex</a> streams, and <a href="#stream_class_stream_transform">Transform</a> streams.
</p>
<p>This document is split up into 3 sections. The first explains the
parts of the API that you need to be aware of to use streams in your
programs. If you never implement a streaming API yourself, you can
stop there.
</p>
<p>The second section explains the parts of the API that you need to use
if you implement your own custom streams yourself. The API is
designed to make this easy for you to do.
</p>
<p>The third section goes into more depth about how streams work,
including some of the internal mechanisms and functions that you
should probably not modify unless you definitely know what you are
doing.
</p>
<h2>API for Stream Consumers<span><a class="mark" href="#stream_api_for_stream_consumers" id="stream_api_for_stream_consumers">#</a></span></h2>
<!--type=misc-->
<p>Streams can be either <a href="#stream_class_stream_readable">Readable</a>, <a href="#stream_class_stream_writable">Writable</a>, or both (<a href="#stream_class_stream_duplex">Duplex</a>).
</p>
<p>All streams are EventEmitters, but they also have other custom methods
and properties depending on whether they are Readable, Writable, or
Duplex.
</p>
<p>If a stream is both Readable and Writable, then it implements all of
the methods and events below. So, a <a href="#stream_class_stream_duplex">Duplex</a> or <a href="#stream_class_stream_transform">Transform</a> stream is
fully described by this API, though their implementation may be
somewhat different.
</p>
<p>It is not necessary to implement Stream interfaces in order to consume
streams in your programs. If you <strong>are</strong> implementing streaming
interfaces in your own program, please also refer to
<a href="#stream_api_for_stream_implementors">API for Stream Implementors</a> below.
</p>
<p>Almost all Node programs, no matter how simple, use Streams in some
way. Here is an example of using Streams in a Node program:
</p>
<pre><code class="javascript">var http = require('http');
var server = http.createServer(function (req, res) {
// req is an http.IncomingMessage, which is a Readable Stream
// res is an http.ServerResponse, which is a Writable Stream
var body = '';
// we want to get the data as utf8 strings
// If you don't set an encoding, then you'll get Buffer objects
req.setEncoding('utf8');
// Readable streams emit 'data' events once a listener is added
req.on('data', function (chunk) {
body += chunk;
})
// the end event tells you that you have entire body
req.on('end', function () {
try {
var data = JSON.parse(body);
} catch (er) {
// uh oh! bad json!
res.statusCode = 400;
return res.end('error: ' + er.message);
}
// write back something interesting to the user:
res.write(typeof data);
res.end();
})
})
server.listen(1337);
// $ curl localhost:1337 -d '{}'
// object
// $ curl localhost:1337 -d '"foo"'
// string
// $ curl localhost:1337 -d 'not json'
// error: Unexpected token o</code></pre>
<h3>Class: stream.Readable<span><a class="mark" href="#stream_class_stream_readable" id="stream_class_stream_readable">#</a></span></h3>
<!--type=class-->
<p>The Readable stream interface is the abstraction for a <em>source</em> of
data that you are reading from. In other words, data comes <em>out</em> of a
Readable stream.
</p>
<p>A Readable stream will not start emitting data until you indicate that
you are ready to receive it.
</p>
<p>Readable streams have two "modes": a <strong>flowing mode</strong> and a <strong>non-flowing
mode</strong>. When in flowing mode, data is read from the underlying system
and provided to your program as fast as possible. In non-flowing
mode, you must explicitly call <code>stream.read()</code> to get chunks of data
out.
</p>
<p>Examples of readable streams include:
</p>
<ul>
<li><a href="http.html#http_http_incomingmessage">http responses, on the client</a></li>
<li><a href="http.html#http_http_incomingmessage">http requests, on the server</a></li>
<li><a href="fs.html#fs_class_fs_readstream">fs read streams</a></li>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
<li><a href="net.html#net_class_net_socket">tcp sockets</a></li>
<li><a href="child_process.html#child_process_child_stdout">child process stdout and stderr</a></li>
<li><a href="process.html#process_process_stdin">process.stdin</a></li>
</ul>
<h4>Event: 'readable'<span><a class="mark" href="#stream_event_readable" id="stream_event_readable">#</a></span></h4>
<p>When a chunk of data can be read from the stream, it will emit a
<code>'readable'</code> event.
</p>
<p>In some cases, listening for a <code>'readable'</code> event will cause some data
to be read into the internal buffer from the underlying system, if it
hadn't already.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.on('readable', function() {
// there is some data to read now
})</code></pre>
<p>Once the internal buffer is drained, a <code>readable</code> event will fire
again when more data is available.
</p>
<h4>Event: 'data'<span><a class="mark" href="#stream_event_data" id="stream_event_data">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">Buffer | String</span> The chunk of data.</li>
</div></ul>
<p>If you attach a <code>data</code> event listener, then it will switch the stream
into flowing mode, and data will be passed to your handler as soon as
it is available.
</p>
<p>If you just want to get all the data out of the stream as fast as
possible, this is the best way to do so.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.on('data', function(chunk) {
console.log('got %d bytes of data', chunk.length);
})</code></pre>
<h4>Event: 'end'<span><a class="mark" href="#stream_event_end" id="stream_event_end">#</a></span></h4>
<p>This event fires when there will be no more data to read.
</p>
<p>Note that the <code>end</code> event <strong>will not fire</strong> unless the data is
completely consumed. This can be done by switching into flowing mode,
or by calling <code>read()</code> repeatedly until you get to the end.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.on('data', function(chunk) {
console.log('got %d bytes of data', chunk.length);
})
readable.on('end', function() {
console.log('there will be no more data.');
});</code></pre>
<h4>Event: 'close'<span><a class="mark" href="#stream_event_close" id="stream_event_close">#</a></span></h4>
<p>Emitted when the underlying resource (for example, the backing file
descriptor) has been closed. Not all streams will emit this.
</p>
<h4>Event: 'error'<span><a class="mark" href="#stream_event_error" id="stream_event_error">#</a></span></h4>
<p>Emitted if there was an error receiving data.
</p>
<h4>readable.read([size])<span><a class="mark" href="#stream_readable_read_size" id="stream_readable_read_size">#</a></span></h4>
<div class="signature"><ul>
<li><code>size</code> <span class="type">Number</span> Optional argument to specify how much data to read.</li>
<li>Return <span class="type">String | Buffer | null</span></li>
</div></ul>
<p>The <code>read()</code> method pulls some data out of the internal buffer and
returns it. If there is no data available, then it will return
<code>null</code>.
</p>
<p>If you pass in a <code>size</code> argument, then it will return that many
bytes. If <code>size</code> bytes are not available, then it will return <code>null</code>.
</p>
<p>If you do not specify a <code>size</code> argument, then it will return all the
data in the internal buffer.
</p>
<p>This method should only be called in non-flowing mode. In
flowing-mode, this method is called automatically until the internal
buffer is drained.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.on('readable', function() {
var chunk;
while (null !== (chunk = readable.read())) {
console.log('got %d bytes of data', chunk.length);
}
});</code></pre>
<h4>readable.setEncoding(encoding)<span><a class="mark" href="#stream_readable_setencoding_encoding" id="stream_readable_setencoding_encoding">#</a></span></h4>
<div class="signature"><ul>
<li><code>encoding</code> <span class="type">String</span> The encoding to use.</li>
</div></ul>
<p>Call this function to cause the stream to return strings of the
specified encoding instead of Buffer objects. For example, if you do
<code>readable.setEncoding('utf8')</code>, then the output data will be
interpreted as UTF-8 data, and returned as strings. If you do
<code>readable.setEncoding('hex')</code>, then the data will be encoded in
hexadecimal string format.
</p>
<p>This properly handles multi-byte characters that would otherwise be
potentially mangled if you simply pulled the Buffers directly and
called <code>buf.toString(encoding)</code> on them. If you want to read the data
as strings, always use this method.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', function(chunk) {
assert.equal(typeof chunk, 'string');
console.log('got %d characters of string data', chunk.length);
})</code></pre>
<h4>readable.resume()<span><a class="mark" href="#stream_readable_resume" id="stream_readable_resume">#</a></span></h4>
<p>This method will cause the readable stream to resume emitting <code>data</code>
events.
</p>
<p>This method will switch the stream into flowing-mode. If you do <em>not</em>
want to consume the data from a stream, but you <em>do</em> want to get to
its <code>end</code> event, you can call <code>readable.resume()</code> to open the flow of
data.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.resume();
readable.on('end', function(chunk) {
console.log('got to the end, but did not read anything');
})</code></pre>
<h4>readable.pause()<span><a class="mark" href="#stream_readable_pause" id="stream_readable_pause">#</a></span></h4>
<p>This method will cause a stream in flowing-mode to stop emitting
<code>data</code> events. Any data that becomes available will remain in the
internal buffer.
</p>
<p>This method is only relevant in flowing mode. When called on a
non-flowing stream, it will switch into flowing mode, but remain
paused.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
readable.on('data', function(chunk) {
console.log('got %d bytes of data', chunk.length);
readable.pause();
console.log('there will be no more data for 1 second');
setTimeout(function() {
console.log('now data will start flowing again');
readable.resume();
}, 1000);
})</code></pre>
<h4>readable.pipe(destination, [options])<span><a class="mark" href="#stream_readable_pipe_destination_options" id="stream_readable_pipe_destination_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>destination</code> <span class="type"><a href="#stream_class_stream_writable">Writable</a> Stream</span> The destination for writing data</li>
<li><code>options</code> <span class="type">Object</span> Pipe options<ul>
<li><code>end</code> <span class="type">Boolean</span> End the writer when the reader ends. Default = <code>true</code></li>
</ul>
</li>
</div></ul>
<p>This method pulls all the data out of a readable stream, and writes it
to the supplied destination, automatically managing the flow so that
the destination is not overwhelmed by a fast readable stream.
</p>
<p>Multiple destinations can be piped to safely.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt'
readable.pipe(writable);</code></pre>
<p>This function returns the destination stream, so you can set up pipe
chains like so:
</p>
<pre><code class="javascript">var r = fs.createReadStream('file.txt');
var z = zlib.createGzip();
var w = fs.createWriteStream('file.txt.gz');
r.pipe(z).pipe(w);</code></pre>
<p>For example, emulating the Unix <code>cat</code> command:
</p>
<pre><code class="javascript">process.stdin.pipe(process.stdout);</code></pre>
<p>By default <a href="#stream_writable_end_chunk_encoding_callback"><code>end()</code></a> is called on the destination when the source stream
emits <code>end</code>, so that <code>destination</code> is no longer writable. Pass <code>{ end:
false }</code> as <code>options</code> to keep the destination stream open.
</p>
<p>This keeps <code>writer</code> open so that "Goodbye" can be written at the
end.
</p>
<pre><code class="javascript">reader.pipe(writer, { end: false });
reader.on('end', function() {
writer.end('Goodbye\n');
});</code></pre>
<p>Note that <code>process.stderr</code> and <code>process.stdout</code> are never closed until
the process exits, regardless of the specified options.
</p>
<h4>readable.unpipe([destination])<span><a class="mark" href="#stream_readable_unpipe_destination" id="stream_readable_unpipe_destination">#</a></span></h4>
<div class="signature"><ul>
<li><code>destination</code> <span class="type"><a href="#stream_class_stream_writable">Writable</a> Stream</span> Optional specific stream to unpipe</li>
</div></ul>
<p>This method will remove the hooks set up for a previous <code>pipe()</code> call.
</p>
<p>If the destination is not specified, then all pipes are removed.
</p>
<p>If the destination is specified, but no pipe is set up for it, then
this is a no-op.
</p>
<pre><code class="javascript">var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second
readable.pipe(writable);
setTimeout(function() {
console.log('stop writing to file.txt');
readable.unpipe(writable);
console.log('manually close the file stream');
writable.end();
}, 1000);</code></pre>
<h4>readable.unshift(chunk)<span><a class="mark" href="#stream_readable_unshift_chunk" id="stream_readable_unshift_chunk">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">Buffer | String</span> Chunk of data to unshift onto the read queue</li>
</div></ul>
<p>This is useful in certain cases where a stream is being consumed by a
parser, which needs to "un-consume" some data that it has
optimistically pulled out of the source, so that the stream can be
passed on to some other party.
</p>
<p>If you find that you must often call <code>stream.unshift(chunk)</code> in your
programs, consider implementing a <a href="#stream_class_stream_transform">Transform</a> stream instead. (See API
for Stream Implementors, below.)
</p>
<pre><code class="javascript">// Pull off a header delimited by \n\n
// use unshift() if we get too much
// Call the callback with (error, header, stream)
var StringDecoder = require('string_decoder').StringDecoder;
function parseHeader(stream, callback) {
stream.on('error', callback);
stream.on('readable', onReadable);
var decoder = new StringDecoder('utf8');
var header = '';
function onReadable() {
var chunk;
while (null !== (chunk = stream.read())) {
var str = decoder.write(chunk);
if (str.match(/\n\n/)) {
// found the header boundary
var split = str.split(/\n\n/);
header += split.shift();
var remaining = split.join('\n\n');
var buf = new Buffer(remaining, 'utf8');
if (buf.length)
stream.unshift(buf);
stream.removeListener('error', callback);
stream.removeListener('readable', onReadable);
// now the body of the message can be read from the stream.
callback(null, header, stream);
} else {
// still reading the header.
header += str;
}
}
}
}</code></pre>
<h4>readable.wrap(stream)<span><a class="mark" href="#stream_readable_wrap_stream" id="stream_readable_wrap_stream">#</a></span></h4>
<div class="signature"><ul>
<li><code>stream</code> <span class="type">Stream</span> An "old style" readable stream</li>
</div></ul>
<p>Versions of Node prior to v0.10 had streams that did not implement the
entire Streams API as it is today. (See "Compatibility" below for
more information.)
</p>
<p>If you are using an older Node library that emits <code>'data'</code> events and
has a <code>pause()</code> method that is advisory only, then you can use the
<code>wrap()</code> method to create a <a href="#stream_class_stream_readable">Readable</a> stream that uses the old stream
as its data source.
</p>
<p>You will very rarely ever need to call this function, but it exists
as a convenience for interacting with old Node programs and libraries.
</p>
<p>For example:
</p>
<pre><code class="javascript">var OldReader = require('./old-api-module.js').OldReader;
var oreader = new OldReader;
var Readable = require('stream').Readable;
var myReader = new Readable().wrap(oreader);
myReader.on('readable', function() {
myReader.read(); // etc.
});</code></pre>
<h3>Class: stream.Writable<span><a class="mark" href="#stream_class_stream_writable" id="stream_class_stream_writable">#</a></span></h3>
<!--type=class-->
<p>The Writable stream interface is an abstraction for a <em>destination</em>
that you are writing data <em>to</em>.
</p>
<p>Examples of writable streams include:
</p>
<ul>
<li><a href="http.html#http_class_http_clientrequest">http requests, on the client</a></li>
<li><a href="http.html#http_class_http_serverresponse">http responses, on the server</a></li>
<li><a href="fs.html#fs_class_fs_writestream">fs write streams</a></li>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
<li><a href="net.html#net_class_net_socket">tcp sockets</a></li>
<li><a href="child_process.html#child_process_child_stdin">child process stdin</a></li>
<li><a href="process.html#process_process_stdout">process.stdout</a>, <a href="process.html#process_process_stderr">process.stderr</a></li>
</ul>
<h4>writable.write(chunk, [encoding], [callback])<span><a class="mark" href="#stream_writable_write_chunk_encoding_callback" id="stream_writable_write_chunk_encoding_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">String | Buffer</span> The data to write</li>
<li><code>encoding</code> <span class="type">String</span> The encoding, if <code>chunk</code> is a String</li>
<li><code>callback</code> <span class="type">Function</span> Callback for when this chunk of data is flushed</li>
<li>Returns: <span class="type">Boolean</span> True if the data was handled completely.</li>
</div></ul>
<p>This method writes some data to the underlying system, and calls the
supplied callback once the data has been fully handled.
</p>
<p>The return value indicates if you should continue writing right now.
If the data had to be buffered internally, then it will return
<code>false</code>. Otherwise, it will return <code>true</code>.
</p>
<p>This return value is strictly advisory. You MAY continue to write,
even if it returns <code>false</code>. However, writes will be buffered in
memory, so it is best not to do this excessively. Instead, wait for
the <code>drain</code> event before writing more data.
</p>
<h4>Event: 'drain'<span><a class="mark" href="#stream_event_drain" id="stream_event_drain">#</a></span></h4>
<p>If a <a href="#stream_writable_write_chunk_encoding_callback"><code>writable.write(chunk)</code></a> call returns false, then the <code>drain</code>
event will indicate when it is appropriate to begin writing more data
to the stream.
</p>
<pre><code class="javascript">// Write the data to the supplied writable stream 1MM times.
// Be attentive to back-pressure.
function writeOneMillionTimes(writer, data, encoding, callback) {
var i = 1000000;
write();
function write() {
var ok = true;
do {
i -= 1;
if (i === 0) {
// last time!
writer.write(data, encoding, callback);
} else {
// see if we should continue, or wait
// don't pass the callback, because we're not done yet.
ok = writer.write(data, encoding);
}
} while (i > 0 && ok);
if (i > 0) {
// had to stop early!
// write some more once it drains
writer.once('drain', write);
}
}
}</code></pre>
<h4>writable.end([chunk], [encoding], [callback])<span><a class="mark" href="#stream_writable_end_chunk_encoding_callback" id="stream_writable_end_chunk_encoding_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">String | Buffer</span> Optional data to write</li>
<li><code>encoding</code> <span class="type">String</span> The encoding, if <code>chunk</code> is a String</li>
<li><code>callback</code> <span class="type">Function</span> Optional callback for when the stream is finished</li>
</div></ul>
<p>Call this method when no more data will be written to the stream. If
supplied, the callback is attached as a listener on the <code>finish</code> event.
</p>
<p>Calling <a href="#stream_writable_write_chunk_encoding_callback"><code>write()</code></a> after calling <a href="#stream_writable_end_chunk_encoding_callback"><code>end()</code></a> will raise an error.
</p>
<pre><code class="javascript">// write 'hello, ' and then end with 'world!'
http.createServer(function (req, res) {
res.write('hello, ');
res.end('world!');
// writing more now is not allowed!
});</code></pre>
<h4>Event: 'finish'<span><a class="mark" href="#stream_event_finish" id="stream_event_finish">#</a></span></h4>
<p>When the <a href="#stream_writable_end_chunk_encoding_callback"><code>end()</code></a> method has been called, and all data has been flushed
to the underlying system, this event is emitted.
</p>
<pre><code class="javascript">var writer = getWritableStreamSomehow();
for (var i = 0; i < 100; i ++) {
writer.write('hello, #' + i + '!\n');
}
writer.end('this is the end\n');
writer.on('finish', function() {
console.error('all writes are now complete.');
});</code></pre>
<h4>Event: 'pipe'<span><a class="mark" href="#stream_event_pipe" id="stream_event_pipe">#</a></span></h4>
<div class="signature"><ul>
<li><code>src</code> <span class="type"><a href="#stream_class_stream_readable">Readable</a> Stream</span> source stream that is piping to this writable</li>
</div></ul>
<p>This is emitted whenever the <code>pipe()</code> method is called on a readable
stream, adding this writable to its set of destinations.
</p>
<pre><code class="javascript">var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('pipe', function(src) {
console.error('something is piping into the writer');
assert.equal(src, reader);
});
reader.pipe(writer);</code></pre>
<h4>Event: 'unpipe'<span><a class="mark" href="#stream_event_unpipe" id="stream_event_unpipe">#</a></span></h4>
<div class="signature"><ul>
<li><code>src</code> <span class="type"><a href="#stream_class_stream_readable">Readable</a> Stream</span> The source stream that <a href="#stream_readable_unpipe_destination">unpiped</a> this writable</li>
</div></ul>
<p>This is emitted whenever the <a href="#stream_readable_unpipe_destination"><code>unpipe()</code></a> method is called on a
readable stream, removing this writable from its set of destinations.
</p>
<pre><code class="javascript">var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('unpipe', function(src) {
console.error('something has stopped piping into the writer');
assert.equal(src, reader);
});
reader.pipe(writer);
reader.unpipe(writer);</code></pre>
<h4>Event: 'error'<span><a class="mark" href="#stream_event_error_1" id="stream_event_error_1">#</a></span></h4>
<p>Emitted if there was an error when writing or piping data.
</p>
<h3>Class: stream.Duplex<span><a class="mark" href="#stream_class_stream_duplex" id="stream_class_stream_duplex">#</a></span></h3>
<p>Duplex streams are streams that implement both the <a href="#stream_class_stream_readable">Readable</a> and
<a href="#stream_class_stream_writable">Writable</a> interfaces. See above for usage.
</p>
<p>Examples of Duplex streams include:
</p>
<ul>
<li><a href="net.html#net_class_net_socket">tcp sockets</a></li>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
</ul>
<h3>Class: stream.Transform<span><a class="mark" href="#stream_class_stream_transform" id="stream_class_stream_transform">#</a></span></h3>
<p>Transform streams are <a href="#stream_class_stream_duplex">Duplex</a> streams where the output is in some way
computed from the input. They implement both the <a href="#stream_class_stream_readable">Readable</a> and
<a href="#stream_class_stream_writable">Writable</a> interfaces. See above for usage.
</p>
<p>Examples of Transform streams include:
</p>
<ul>
<li><a href="zlib.html">zlib streams</a></li>
<li><a href="crypto.html">crypto streams</a></li>
</ul>
<h2>API for Stream Implementors<span><a class="mark" href="#stream_api_for_stream_implementors" id="stream_api_for_stream_implementors">#</a></span></h2>
<!--type=misc-->
<p>To implement any sort of stream, the pattern is the same:
</p>
<ol>
<li>Extend the appropriate parent class in your own subclass. (The
<a href="util.html#util_util_inherits_constructor_superconstructor"><code>util.inherits</code></a> method is particularly helpful for this.)</li>
<li>Call the appropriate parent class constructor in your constructor,
to be sure that the internal mechanisms are set up properly.</li>
<li>Implement one or more specific methods, as detailed below.</li>
</ol>
<p>The class to extend and the method(s) to implement depend on the sort
of stream class you are writing:
</p>
<table>
<thead>
<tr>
<th>
<p>Use-case</p>
</th>
<th>
<p>Class</p>
</th>
<th>
<p>Method(s) to implement</p>
</th>
</tr>
</thead>
<tr>
<td>
<p>Reading only</p>
</td>
<td>
<p><a href="#stream_class_stream_readable_1">Readable</a></p>
</td>
<td>
<p><code><a href="#stream_readable_read_size_1">_read</a></code></p>
</td>
</tr>
<tr>
<td>
<p>Writing only</p>
</td>
<td>
<p><a href="#stream_class_stream_writable_1">Writable</a></p>
</td>
<td>
<p><code><a href="#stream_writable_write_chunk_encoding_callback_1">_write</a></code></p>
</td>
</tr>
<tr>
<td>
<p>Reading and writing</p>
</td>
<td>
<p><a href="#stream_class_stream_duplex_1">Duplex</a></p>
</td>
<td>
<p><code><a href="#stream_readable_read_size_1">_read</a></code>, <code><a href="#stream_writable_write_chunk_encoding_callback_1">_write</a></code></p>
</td>
</tr>
<tr>
<td>
<p>Operate on written data, then read the result</p>
</td>
<td>
<p><a href="#stream_class_stream_transform_1">Transform</a></p>
</td>
<td>
<p><code>_transform</code>, <code>_flush</code></p>
</td>
</tr>
</table>
<p>In your implementation code, it is very important to never call the
methods described in <a href="#stream_api_for_stream_consumers">API for Stream Consumers</a> above. Otherwise, you
can potentially cause adverse side effects in programs that consume
your streaming interfaces.
</p>
<h3>Class: stream.Readable<span><a class="mark" href="#stream_class_stream_readable_1" id="stream_class_stream_readable_1">#</a></span></h3>
<!--type=class-->
<p><code>stream.Readable</code> is an abstract class designed to be extended with an
underlying implementation of the <a href="#stream_readable_read_size_1"><code>_read(size)</code></a> method.
</p>
<p>Please see above under <a href="#stream_api_for_stream_consumers">API for Stream Consumers</a> for how to consume
streams in your programs. What follows is an explanation of how to
implement Readable streams in your programs.
</p>
<h4>Example: A Counting Stream<span><a class="mark" href="#stream_example_a_counting_stream" id="stream_example_a_counting_stream">#</a></span></h4>
<!--type=example-->
<p>This is a basic example of a Readable stream. It emits the numerals
from 1 to 1,000,000 in ascending order, and then ends.
</p>
<pre><code class="javascript">var Readable = require('stream').Readable;
var util = require('util');
util.inherits(Counter, Readable);
function Counter(opt) {
Readable.call(this, opt);
this._max = 1000000;
this._index = 1;
}
Counter.prototype._read = function() {
var i = this._index++;
if (i > this._max)
this.push(null);
else {
var str = '' + i;
var buf = new Buffer(str, 'ascii');
this.push(buf);
}
};</code></pre>
<h4>Example: SimpleProtocol v1 (Sub-optimal)<span><a class="mark" href="#stream_example_simpleprotocol_v1_sub_optimal" id="stream_example_simpleprotocol_v1_sub_optimal">#</a></span></h4>
<p>This is similar to the <code>parseHeader</code> function described above, but
implemented as a custom stream. Also, note that this implementation
does not convert the incoming data to a string.
</p>
<p>However, this would be better implemented as a <a href="#stream_class_stream_transform">Transform</a> stream. See
below for a better implementation.
</p>
<pre><code class="javascript">// A parser for a simple data protocol.
// The "header" is a JSON object, followed by 2 \n characters, and
// then a message body.
//
// NOTE: This can be done more simply as a Transform stream!
// Using Readable directly for this is sub-optimal. See the
// alternative example below under the Transform section.
var Readable = require('stream').Readable;
var util = require('util');
util.inherits(SimpleProtocol, Readable);
function SimpleProtocol(source, options) {
if (!(this instanceof SimpleProtocol))
return new SimpleProtocol(source, options);
Readable.call(this, options);
this._inBody = false;
this._sawFirstCr = false;
// source is a readable stream, such as a socket or file
this._source = source;
var self = this;
source.on('end', function() {
self.push(null);
});
// give it a kick whenever the source is readable
// read(0) will not consume any bytes
source.on('readable', function() {
self.read(0);
});
this._rawHeader = [];
this.header = null;
}
SimpleProtocol.prototype._read = function(n) {
if (!this._inBody) {
var chunk = this._source.read();
// if the source doesn't have data, we don't have data yet.
if (chunk === null)
return this.push('');
// check if the chunk has a \n\n
var split = -1;
for (var i = 0; i < chunk.length; i++) {
if (chunk[i] === 10) { // '\n'
if (this._sawFirstCr) {
split = i;
break;
} else {
this._sawFirstCr = true;
}
} else {
this._sawFirstCr = false;
}
}
if (split === -1) {
// still waiting for the \n\n
// stash the chunk, and try again.
this._rawHeader.push(chunk);
this.push('');
} else {
this._inBody = true;
var h = chunk.slice(0, split);
this._rawHeader.push(h);
var header = Buffer.concat(this._rawHeader).toString();
try {
this.header = JSON.parse(header);
} catch (er) {
this.emit('error', new Error('invalid simple protocol data'));
return;
}
// now, because we got some extra data, unshift the rest
// back into the read queue so that our consumer will see it.
var b = chunk.slice(split);
this.unshift(b);
// and let them know that we are done parsing the header.
this.emit('header', this.header);
}
} else {
// from there on, just provide the data to our consumer.
// careful not to push(null), since that would indicate EOF.
var chunk = this._source.read();
if (chunk) this.push(chunk);
}
};
// Usage:
// var parser = new SimpleProtocol(source);
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.</code></pre>
<h4>new stream.Readable([options])<span><a class="mark" href="#stream_new_stream_readable_options" id="stream_new_stream_readable_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <span class="type">Object</span><ul>
<li><code>highWaterMark</code> <span class="type">Number</span> The maximum number of bytes to store in
the internal buffer before ceasing to read from the underlying
resource. Default=16kb</li>
<li><code>encoding</code> <span class="type">String</span> If specified, then buffers will be decoded to
strings using the specified encoding. Default=null</li>
<li><code>objectMode</code> <span class="type">Boolean</span> Whether this stream should behave
as a stream of objects. Meaning that stream.read(n) returns
a single value instead of a Buffer of size n. Default=false</li>
</ul>
</li>
</div></ul>
<p>In classes that extend the Readable class, make sure to call the
Readable constructor so that the buffering settings can be properly
initialized.
</p>
<h4>readable._read(size)<span><a class="mark" href="#stream_readable_read_size_1" id="stream_readable_read_size_1">#</a></span></h4>
<div class="signature"><ul>
<li><code>size</code> <span class="type">Number</span> Number of bytes to read asynchronously</li>
</div></ul>
<p>Note: <strong>Implement this function, but do NOT call it directly.</strong>
</p>
<p>This function should NOT be called directly. It should be implemented
by child classes, and only called by the internal Readable class
methods.
</p>
<p>All Readable stream implementations must provide a <code>_read</code> method to
fetch data from the underlying resource.
</p>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.
</p>
<p>When data is available, put it into the read queue by calling
<code>readable.push(chunk)</code>. If <code>push</code> returns false, then you should stop
reading. When <code>_read</code> is called again, you should start pushing more
data.
</p>
<p>The <code>size</code> argument is advisory. Implementations where a "read" is a
single call that returns data can use this to know how much data to
fetch. Implementations where that is not relevant, such as TCP or
TLS, may ignore this argument, and simply provide data whenever it
becomes available. There is no need, for example to "wait" until
<code>size</code> bytes are available before calling <a href="#stream_readable_push_chunk_encoding"><code>stream.push(chunk)</code></a>.
</p>
<h4>readable.push(chunk, [encoding])<span><a class="mark" href="#stream_readable_push_chunk_encoding" id="stream_readable_push_chunk_encoding">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">Buffer | null | String</span> Chunk of data to push into the read queue</li>
<li><code>encoding</code> <span class="type">String</span> Encoding of String chunks. Must be a valid
Buffer encoding, such as <code>'utf8'</code> or <code>'ascii'</code></li>
<li>return <span class="type">Boolean</span> Whether or not more pushes should be performed</li>
</div></ul>
<p>Note: <strong>This function should be called by Readable implementors, NOT
by consumers of Readable streams.</strong>
</p>
<p>The <code>_read()</code> function will not be called again until at least one
<code>push(chunk)</code> call is made.
</p>
<p>The <code>Readable</code> class works by putting data into a read queue to be
pulled out later by calling the <code>read()</code> method when the <code>'readable'</code>
event fires.
</p>
<p>The <code>push()</code> method will explicitly insert some data into the read
queue. If it is called with <code>null</code> then it will signal the end of the
data (EOF).
</p>
<p>This API is designed to be as flexible as possible. For example,
you may be wrapping a lower-level source which has some sort of
pause/resume mechanism, and a data callback. In those cases, you
could wrap the low-level source object by doing something like this:
</p>
<pre><code class="javascript">// source is an object with readStop() and readStart() methods,
// and an `ondata` member that gets called when it has data, and
// an `onend` member that gets called when the data is over.
util.inherits(SourceWrapper, Readable);
function SourceWrapper(options) {
Readable.call(this, options);
this._source = getLowlevelSourceObject();
var self = this;
// Every time there's data, we push it into the internal buffer.
this._source.ondata = function(chunk) {
// if push() returns false, then we need to stop reading from source
if (!self.push(chunk))
self._source.readStop();
};
// When the source ends, we push the EOF-signalling `null` chunk
this._source.onend = function() {
self.push(null);
};
}
// _read will be called when the stream wants to pull more data in
// the advisory size argument is ignored in this case.
SourceWrapper.prototype._read = function(size) {
this._source.readStart();
};</code></pre>
<h3>Class: stream.Writable<span><a class="mark" href="#stream_class_stream_writable_1" id="stream_class_stream_writable_1">#</a></span></h3>
<!--type=class-->
<p><code>stream.Writable</code> is an abstract class designed to be extended with an
underlying implementation of the <a href="#stream_writable_write_chunk_encoding_callback_1"><code>_write(chunk, encoding, callback)</code></a> method.
</p>
<p>Please see above under <a href="#stream_api_for_stream_consumers">API for Stream Consumers</a> for how to consume
writable streams in your programs. What follows is an explanation of
how to implement Writable streams in your programs.
</p>
<h4>new stream.Writable([options])<span><a class="mark" href="#stream_new_stream_writable_options" id="stream_new_stream_writable_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <span class="type">Object</span><ul>
<li><code>highWaterMark</code> <span class="type">Number</span> Buffer level when <a href="#stream_writable_write_chunk_encoding_callback"><code>write()</code></a> starts
returning false. Default=16kb</li>
<li><code>decodeStrings</code> <span class="type">Boolean</span> Whether or not to decode strings into
Buffers before passing them to <a href="#stream_writable_write_chunk_encoding_callback_1"><code>_write()</code></a>. Default=true</li>
<li><code>objectMode</code> <span class="type">Boolean</span> Whether or not the <code>write(anyObj)</code> is
a valid operation. If set you can write arbitrary data instead
of only <code>Buffer</code> / <code>String</code> data. Default=false</li>
</ul>
</li>
</div></ul>
<p>In classes that extend the Writable class, make sure to call the
constructor so that the buffering settings can be properly
initialized.
</p>
<h4>writable._write(chunk, encoding, callback)<span><a class="mark" href="#stream_writable_write_chunk_encoding_callback_1" id="stream_writable_write_chunk_encoding_callback_1">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">Buffer | String</span> The chunk to be written. Will always
be a buffer unless the <code>decodeStrings</code> option was set to <code>false</code>.</li>
<li><code>encoding</code> <span class="type">String</span> If the chunk is a string, then this is the
encoding type. Ignore chunk is a buffer. Note that chunk will
<strong>always</strong> be a buffer unless the <code>decodeStrings</code> option is
explicitly set to <code>false</code>.</li>
<li><code>callback</code> <span class="type">Function</span> Call this function (optionally with an error
argument) when you are done processing the supplied chunk.</li>
</div></ul>
<p>All Writable stream implementations must provide a <a href="#stream_writable_write_chunk_encoding_callback_1"><code>_write()</code></a>
method to send data to the underlying resource.
</p>
<p>Note: <strong>This function MUST NOT be called directly.</strong> It should be
implemented by child classes, and called by the internal Writable
class methods only.
</p>
<p>Call the callback using the standard <code>callback(error)</code> pattern to
signal that the write completed successfully or with an error.
</p>
<p>If the <code>decodeStrings</code> flag is set in the constructor options, then
<code>chunk</code> may be a string rather than a Buffer, and <code>encoding</code> will
indicate the sort of string that it is. This is to support
implementations that have an optimized handling for certain string
data encodings. If you do not explicitly set the <code>decodeStrings</code>
option to <code>false</code>, then you can safely ignore the <code>encoding</code> argument,
and assume that <code>chunk</code> will always be a Buffer.
</p>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.
</p>
<h3>Class: stream.Duplex<span><a class="mark" href="#stream_class_stream_duplex_1" id="stream_class_stream_duplex_1">#</a></span></h3>
<!--type=class-->
<p>A "duplex" stream is one that is both Readable and Writable, such as a
TCP socket connection.
</p>
<p>Note that <code>stream.Duplex</code> is an abstract class designed to be extended
with an underlying implementation of the <code>_read(size)</code> and
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>_write(chunk, encoding, callback)</code></a> methods as you would with a
Readable or Writable stream class.
</p>
<p>Since JavaScript doesn't have multiple prototypal inheritance, this
class prototypally inherits from Readable, and then parasitically from
Writable. It is thus up to the user to implement both the lowlevel
<code>_read(n)</code> method as well as the lowlevel
<a href="#stream_writable_write_chunk_encoding_callback_1"><code>_write(chunk, encoding, callback)</code></a> method on extension duplex classes.
</p>
<h4>new stream.Duplex(options)<span><a class="mark" href="#stream_new_stream_duplex_options" id="stream_new_stream_duplex_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <span class="type">Object</span> Passed to both Writable and Readable
constructors. Also has the following fields:<ul>
<li><code>allowHalfOpen</code> <span class="type">Boolean</span> Default=true. If set to <code>false</code>, then
the stream will automatically end the readable side when the
writable side ends and vice versa.</li>
</ul>
</li>
</div></ul>
<p>In classes that extend the Duplex class, make sure to call the
constructor so that the buffering settings can be properly
initialized.
</p>
<h3>Class: stream.Transform<span><a class="mark" href="#stream_class_stream_transform_1" id="stream_class_stream_transform_1">#</a></span></h3>
<p>A "transform" stream is a duplex stream where the output is causally
connected in some way to the input, such as a <a href="zlib.html">zlib</a> stream or a
<a href="crypto.html">crypto</a> stream.
</p>
<p>There is no requirement that the output be the same size as the input,
the same number of chunks, or arrive at the same time. For example, a
Hash stream will only ever have a single chunk of output which is
provided when the input is ended. A zlib stream will produce output
that is either much smaller or much larger than its input.
</p>
<p>Rather than implement the <a href="#stream_readable_read_size_1"><code>_read()</code></a> and <a href="#stream_writable_write_chunk_encoding_callback_1"><code>_write()</code></a> methods, Transform
classes must implement the <code>_transform()</code> method, and may optionally
also implement the <code>_flush()</code> method. (See below.)
</p>
<h4>new stream.Transform([options])<span><a class="mark" href="#stream_new_stream_transform_options" id="stream_new_stream_transform_options">#</a></span></h4>
<div class="signature"><ul>
<li><code>options</code> <span class="type">Object</span> Passed to both Writable and Readable
constructors.</li>
</div></ul>
<p>In classes that extend the Transform class, make sure to call the
constructor so that the buffering settings can be properly
initialized.
</p>
<h4>transform._transform(chunk, encoding, callback)<span><a class="mark" href="#stream_transform_transform_chunk_encoding_callback" id="stream_transform_transform_chunk_encoding_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>chunk</code> <span class="type">Buffer | String</span> The chunk to be transformed. Will always
be a buffer unless the <code>decodeStrings</code> option was set to <code>false</code>.</li>
<li><code>encoding</code> <span class="type">String</span> If the chunk is a string, then this is the
encoding type. (Ignore if <code>decodeStrings</code> chunk is a buffer.)</li>
<li><code>callback</code> <span class="type">Function</span> Call this function (optionally with an error
argument) when you are done processing the supplied chunk.</li>
</div></ul>
<p>Note: <strong>This function MUST NOT be called directly.</strong> It should be
implemented by child classes, and called by the internal Transform
class methods only.
</p>
<p>All Transform stream implementations must provide a <code>_transform</code>
method to accept input and produce output.
</p>
<p><code>_transform</code> should do whatever has to be done in this specific
Transform class, to handle the bytes being written, and pass them off
to the readable portion of the interface. Do asynchronous I/O,
process things, and so on.
</p>
<p>Call <code>transform.push(outputChunk)</code> 0 or more times to generate output
from this input chunk, depending on how much data you want to output
as a result of this chunk.
</p>
<p>Call the callback function only when the current chunk is completely
consumed. Note that there may or may not be output as a result of any
particular input chunk.
</p>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.
</p>
<h4>transform._flush(callback)<span><a class="mark" href="#stream_transform_flush_callback" id="stream_transform_flush_callback">#</a></span></h4>
<div class="signature"><ul>
<li><code>callback</code> <span class="type">Function</span> Call this function (optionally with an error
argument) when you are done flushing any remaining data.</li>
</div></ul>
<p>Note: <strong>This function MUST NOT be called directly.</strong> It MAY be implemented
by child classes, and if so, will be called by the internal Transform
class methods only.
</p>
<p>In some cases, your transform operation may need to emit a bit more
data at the end of the stream. For example, a <code>Zlib</code> compression
stream will store up some internal state so that it can optimally
compress the output. At the end, however, it needs to do the best it
can with what is left, so that the data will be complete.
</p>
<p>In those cases, you can implement a <code>_flush</code> method, which will be
called at the very end, after all the written data is consumed, but
before emitting <code>end</code> to signal the end of the readable side. Just
like with <code>_transform</code>, call <code>transform.push(chunk)</code> zero or more
times, as appropriate, and call <code>callback</code> when the flush operation is
complete.
</p>
<p>This method is prefixed with an underscore because it is internal to
the class that defines it, and should not be called directly by user
programs. However, you <strong>are</strong> expected to override this method in
your own extension classes.
</p>
<h4>Events: 'finish' and 'end'<span><a class="mark" href="#stream_events_finish_and_end" id="stream_events_finish_and_end">#</a></span></h4>
<p>The <a href="#stream_event_finish"><code>finish</code></a> and <a href="#stream_event_end"><code>end</code></a> events are from the parent Writable
and Readable classes respectively. The <code>finish</code> event is fired after
<code>.end()</code> is called and all chunks have been processed by <code>_transform</code>,
<code>end</code> is fired after all data has been output which is after the callback
in <code>_flush</code> has been called.
</p>
<h4>Example: <code>SimpleProtocol</code> parser v2<span><a class="mark" href="#stream_example_simpleprotocol_parser_v2" id="stream_example_simpleprotocol_parser_v2">#</a></span></h4>
<p>The example above of a simple protocol parser can be implemented
simply by using the higher level <a href="#stream_class_stream_transform">Transform</a> stream class, similar to
the <code>parseHeader</code> and <code>SimpleProtocol v1</code> examples above.
</p>
<p>In this example, rather than providing the input as an argument, it
would be piped into the parser, which is a more idiomatic Node stream
approach.
</p>
<pre><code class="javascript">var util = require('util');
var Transform = require('stream').Transform;
util.inherits(SimpleProtocol, Transform);
function SimpleProtocol(options) {
if (!(this instanceof SimpleProtocol))
return new SimpleProtocol(options);
Transform.call(this, options);
this._inBody = false;
this._sawFirstCr = false;
this._rawHeader = [];
this.header = null;
}
SimpleProtocol.prototype._transform = function(chunk, encoding, done) {
if (!this._inBody) {
// check if the chunk has a \n\n
var split = -1;
for (var i = 0; i < chunk.length; i++) {
if (chunk[i] === 10) { // '\n'
if (this._sawFirstCr) {
split = i;
break;
} else {
this._sawFirstCr = true;
}
} else {
this._sawFirstCr = false;
}
}
if (split === -1) {
// still waiting for the \n\n
// stash the chunk, and try again.
this._rawHeader.push(chunk);
} else {
this._inBody = true;
var h = chunk.slice(0, split);
this._rawHeader.push(h);
var header = Buffer.concat(this._rawHeader).toString();
try {
this.header = JSON.parse(header);
} catch (er) {
this.emit('error', new Error('invalid simple protocol data'));
return;
}
// and let them know that we are done parsing the header.
this.emit('header', this.header);
// now, because we got some extra data, emit this first.
this.push(chunk.slice(split));
}
} else {
// from there on, just provide the data to our consumer as-is.
this.push(chunk);
}
done();
};
// Usage:
// var parser = new SimpleProtocol();
// source.pipe(parser)
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.</code></pre>
<h3>Class: stream.PassThrough<span><a class="mark" href="#stream_class_stream_passthrough" id="stream_class_stream_passthrough">#</a></span></h3>
<p>This is a trivial implementation of a <a href="#stream_class_stream_transform">Transform</a> stream that simply
passes the input bytes across to the output. Its purpose is mainly
for examples and testing, but there are occasionally use cases where
it can come in handy as a building block for novel sorts of streams.
</p>
<h2>Streams: Under the Hood<span><a class="mark" href="#stream_streams_under_the_hood" id="stream_streams_under_the_hood">#</a></span></h2>
<!--type=misc-->
<h3>Buffering<span><a class="mark" href="#stream_buffering" id="stream_buffering">#</a></span></h3>
<!--type=misc-->
<p>Both Writable and Readable streams will buffer data on an internal
object called <code>_writableState.buffer</code> or <code>_readableState.buffer</code>,
respectively.
</p>
<p>The amount of data that will potentially be buffered depends on the
<code>highWaterMark</code> option which is passed into the constructor.
</p>
<p>Buffering in Readable streams happens when the implementation calls
<a href="#stream_readable_push_chunk_encoding"><code>stream.push(chunk)</code></a>. If the consumer of the Stream does not call
<code>stream.read()</code>, then the data will sit in the internal queue until it
is consumed.
</p>
<p>Buffering in Writable streams happens when the user calls
<a href="#stream_writable_write_chunk_encoding_callback"><code>stream.write(chunk)</code></a> repeatedly, even when <code>write()</code> returns <code>false</code>.
</p>
<p>The purpose of streams, especially with the <code>pipe()</code> method, is to
limit the buffering of data to acceptable levels, so that sources and
destinations of varying speed will not overwhelm the available memory.
</p>
<h3><code>stream.read(0)</code><span><a class="mark" href="#stream_stream_read_0" id="stream_stream_read_0">#</a></span></h3>
<p>There are some cases where you want to trigger a refresh of the
underlying readable stream mechanisms, without actually consuming any
data. In that case, you can call <code>stream.read(0)</code>, which will always
return null.
</p>
<p>If the internal read buffer is below the <code>highWaterMark</code>, and the
stream is not currently reading, then calling <code>read(0)</code> will trigger
a low-level <code>_read</code> call.
</p>
<p>There is almost never a need to do this. However, you will see some
cases in Node's internals where this is done, particularly in the
Readable stream class internals.
</p>
<h3><code>stream.push('')</code><span><a class="mark" href="#stream_stream_push" id="stream_stream_push">#</a></span></h3>
<p>Pushing a zero-byte string or Buffer (when not in <a href="#stream_object_mode">Object mode</a>) has an
interesting side effect. Because it <em>is</em> a call to
<a href="#stream_readable_push_chunk_encoding"><code>stream.push()</code></a>, it will end the <code>reading</code> process. However, it
does <em>not</em> add any data to the readable buffer, so there's nothing for
a user to consume.
</p>
<p>Very rarely, there are cases where you have no data to provide now,
but the consumer of your stream (or, perhaps, another bit of your own
code) will know when to check again, by calling <code>stream.read(0)</code>. In
those cases, you <em>may</em> call <code>stream.push('')</code>.
</p>
<p>So far, the only use case for this functionality is in the
<a href="tls.html#tls_class_cryptostream">tls.CryptoStream</a> class, which is deprecated in Node v0.12. If you
find that you have to use <code>stream.push('')</code>, please consider another
approach, because it almost certainly indicates that something is
horribly wrong.
</p>
<h3>Compatibility with Older Node Versions<span><a class="mark" href="#stream_compatibility_with_older_node_versions" id="stream_compatibility_with_older_node_versions">#</a></span></h3>
<!--type=misc-->
<p>In versions of Node prior to v0.10, the Readable stream interface was
simpler, but also less powerful and less useful.
</p>
<ul>
<li>Rather than waiting for you to call the <code>read()</code> method, <code>'data'</code>
events would start emitting immediately. If you needed to do some
I/O to decide how to handle data, then you had to store the chunks
in some kind of buffer so that they would not be lost.</li>
<li>The <code>pause()</code> method was advisory, rather than guaranteed. This
meant that you still had to be prepared to receive <code>'data'</code> events
even when the stream was in a paused state.</li>
</ul>
<p>In Node v0.10, the Readable class described below was added. For
backwards compatibility with older Node programs, Readable streams
switch into "flowing mode" when a <code>'data'</code> event handler is added, or
when the <code>pause()</code> or <code>resume()</code> methods are called. The effect is
that, even if you are not using the new <code>read()</code> method and
<code>'readable'</code> event, you no longer have to worry about losing <code>'data'</code>
chunks.
</p>
<p>Most programs will continue to function normally. However, this
introduces an edge case in the following conditions:
</p>
<ul>
<li>No <code>'data'</code> event handler is added.</li>
<li>The <code>pause()</code> and <code>resume()</code> methods are never called.</li>
</ul>
<p>For example, consider the following code:
</p>
<pre><code class="javascript">// WARNING! BROKEN!
net.createServer(function(socket) {
// we add an 'end' method, but never consume the data
socket.on('end', function() {
// It will never get here.
socket.end('I got your message (but didnt read it)\n');
});
}).listen(1337);</code></pre>
<p>In versions of node prior to v0.10, the incoming message data would be
simply discarded. However, in Node v0.10 and beyond, the socket will
remain paused forever.
</p>
<p>The workaround in this situation is to call the <code>resume()</code> method to
trigger "old mode" behavior:
</p>
<pre><code class="javascript">// Workaround
net.createServer(function(socket) {
socket.on('end', function() {
socket.end('I got your message (but didnt read it)\n');
});
// start the flow of data, discarding it.
socket.resume();
}).listen(1337);</code></pre>
<p>In addition to new Readable streams switching into flowing-mode, pre-v0.10
style streams can be wrapped in a Readable class using the <code>wrap()</code>
method.
</p>
<h3>Object Mode<span><a class="mark" href="#stream_object_mode" id="stream_object_mode">#</a></span></h3>
<!--type=misc-->
<p>Normally, Streams operate on Strings and Buffers exclusively.
</p>
<p>Streams that are in <strong>object mode</strong> can emit generic JavaScript values
other than Buffers and Strings.
</p>
<p>A Readable stream in object mode will always return a single item from
a call to <code>stream.read(size)</code>, regardless of what the size argument
is.
</p>
<p>A Writable stream in object mode will always ignore the <code>encoding</code>
argument to <code>stream.write(data, encoding)</code>.
</p>
<p>The special value <code>null</code> still retains its special value for object
mode streams. That is, for object mode readable streams, <code>null</code> as a
return value from <code>stream.read()</code> indicates that there is no more
data, and <a href="#stream_readable_push_chunk_encoding"><code>stream.push(null)</code></a> will signal the end of stream data
(<code>EOF</code>).
</p>
<p>No streams in Node core are object mode streams. This pattern is only
used by userland streaming libraries.
</p>
<p>You should set <code>objectMode</code> in your stream child class constructor on
the options object. Setting <code>objectMode</code> mid-stream is not safe.
</p>
<h3>State Objects<span><a class="mark" href="#stream_state_objects" id="stream_state_objects">#</a></span></h3>
<p><a href="#stream_class_stream_readable">Readable</a> streams have a member object called <code>_readableState</code>.
<a href="#stream_class_stream_writable">Writable</a> streams have a member object called <code>_writableState</code>.
<a href="#stream_class_stream_duplex">Duplex</a> streams have both.
</p>
<p><strong>These objects should generally not be modified in child classes.</strong>
However, if you have a Duplex or Transform stream that should be in
<code>objectMode</code> on the readable side, and not in <code>objectMode</code> on the
writable side, then you may do this in the constructor by setting the
flag explicitly on the appropriate state object.
</p>
<pre><code class="javascript">var util = require('util');
var StringDecoder = require('string_decoder').StringDecoder;
var Transform = require('stream').Transform;
util.inherits(JSONParseStream, Transform);
// Gets \n-delimited JSON string data, and emits the parsed objects
function JSONParseStream(options) {
if (!(this instanceof JSONParseStream))
return new JSONParseStream(options);
Transform.call(this, options);
this._writableState.objectMode = false;
this._readableState.objectMode = true;
this._buffer = '';
this._decoder = new StringDecoder('utf8');
}
JSONParseStream.prototype._transform = function(chunk, encoding, cb) {
this._buffer += this._decoder.write(chunk);
// split on newlines
var lines = this._buffer.split(/\r?\n/);
// keep the last partial line buffered
this._buffer = lines.pop();
for (var l = 0; l < lines.length; l++) {
var line = lines[l];
try {
var obj = JSON.parse(line);
} catch (er) {
this.emit('error', er);
return;
}
// push the parsed object out to the readable consumer
this.push(obj);
}
cb();
};
JSONParseStream.prototype._flush = function(cb) {
// Just handle any leftover
var rem = this._buffer.trim();
if (rem) {
try {
var obj = JSON.parse(rem);
} catch (er) {
this.emit('error', er);
return;
}
// push the parsed object out to the readable consumer
this.push(obj);
}
cb();
};</code></pre>
<p>The state objects contain other useful information for debugging the
state of streams in your programs. It is safe to look at them, but
beyond setting option flags in the constructor, it is <strong>not</strong> safe to
modify them.
</p>
</div>
</div>
</div>
<div id="footer">
<a href="http://joyent.com" class="joyent-logo">Joyent</a>
<ul class="clearfix">
<li><a href="/">Node.js</a></li>
<li><a href="/download/">Download</a></li>
<li><a href="/about/">About</a></li>
<li><a href="http://npmjs.org/">npm Registry</a></li>
<li><a href="http://nodejs.org/api/">Docs</a></li>
<li><a href="http://blog.nodejs.org">Blog</a></li>
<li><a href="/community/">Community</a></li>
<li><a href="/logos/">Logos</a></li>
<li><a href="http://jobs.nodejs.org/">Jobs</a></li>
<li><a href="http://twitter.com/nodejs" class="twitter">@nodejs</a></li>
</ul>
<p>Copyright <a href="http://joyent.com/">Joyent, Inc</a>, Node.js is a <a href="/trademark-policy.pdf">trademark</a> of Joyent, Inc. View <a href="https://raw.github.com/joyent/node/v0.10.29/LICENSE">license</a>.</p>
</div>
<script src="../sh_main.js"></script>
<script src="../sh_javascript.min.js"></script>
<script>highlight(undefined, undefined, 'pre');</script>
<script>
window._gaq = [['_setAccount', 'UA-10874194-2'], ['_trackPageview']];
(function(d, t) {
var g = d.createElement(t),
s = d.getElementsByTagName(t)[0];
g.src = '//www.google-analytics.com/ga.js';
s.parentNode.insertBefore(g, s);
}(document, 'script'));
</script>
</body>
</html>
|
