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
|
# delayed-stream
Buffers events from a stream until you are ready to handle them.
## Installation
``` bash
npm install delayed-stream
```
## Usage
The following example shows how to write a http echo server that delays its
response by 1000 ms.
``` javascript
var DelayedStream = require('delayed-stream');
var http = require('http');
http.createServer(function(req, res) {
var delayed = DelayedStream.create(req);
setTimeout(function() {
res.writeHead(200);
delayed.pipe(res);
}, 1000);
});
```
If you are not using `Stream#pipe`, you can also manually release the buffered
events by calling `delayedStream.resume()`:
``` javascript
var delayed = DelayedStream.create(req);
setTimeout(function() {
// Emit all buffered events and resume underlaying source
delayed.resume();
}, 1000);
```
## Implementation
In order to use this meta stream properly, here are a few things you should
know about the implementation.
### Event Buffering / Proxying
All events of the `source` stream are hijacked by overwriting the `source.emit`
method. Until node implements a catch-all event listener, this is the only way.
However, delayed-stream still continues to emit all events it captures on the
`source`, regardless of whether you have released the delayed stream yet or
not.
Upon creation, delayed-stream captures all `source` events and stores them in
an internal event buffer. Once `delayedStream.release()` is called, all
buffered events are emitted on the `delayedStream`, and the event buffer is
cleared. After that, delayed-stream merely acts as a proxy for the underlaying
source.
### Error handling
Error events on `source` are buffered / proxied just like any other events.
However, `delayedStream.create` attaches a no-op `'error'` listener to the
`source`. This way you only have to handle errors on the `delayedStream`
object, rather than in two places.
### Buffer limits
delayed-stream provides a `maxDataSize` property that can be used to limit
the amount of data being buffered. In order to protect you from bad `source`
streams that don't react to `source.pause()`, this feature is enabled by
default.
## API
### DelayedStream.create(source, [options])
Returns a new `delayedStream`. Available options are:
* `pauseStream`
* `maxDataSize`
The description for those properties can be found below.
### delayedStream.source
The `source` stream managed by this object. This is useful if you are
passing your `delayedStream` around, and you still want to access properties
on the `source` object.
### delayedStream.pauseStream = true
Whether to pause the underlaying `source` when calling
`DelayedStream.create()`. Modifying this property afterwards has no effect.
### delayedStream.maxDataSize = 1024 * 1024
The amount of data to buffer before emitting an `error`.
If the underlaying source is emitting `Buffer` objects, the `maxDataSize`
refers to bytes.
If the underlaying source is emitting JavaScript strings, the size refers to
characters.
If you know what you are doing, you can set this property to `Infinity` to
disable this feature. You can also modify this property during runtime.
### delayedStream.dataSize = 0
The amount of data buffered so far.
### delayedStream.readable
An ECMA5 getter that returns the value of `source.readable`.
### delayedStream.resume()
If the `delayedStream` has not been released so far, `delayedStream.release()`
is called.
In either case, `source.resume()` is called.
### delayedStream.pause()
Calls `source.pause()`.
### delayedStream.pipe(dest)
Calls `delayedStream.resume()` and then proxies the arguments to `source.pipe`.
### delayedStream.release()
Emits and clears all events that have been buffered up so far. This does not
resume the underlaying source, use `delayedStream.resume()` instead.
## License
delayed-stream is licensed under the MIT license.
|
