| [d565449] | 1 | # delayed-stream
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| 2 |
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| 3 | Buffers events from a stream until you are ready to handle them.
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| 4 |
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| 5 | ## Installation
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| 6 |
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| 7 | ``` bash
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| 8 | npm install delayed-stream
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| 9 | ```
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| 10 |
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| 11 | ## Usage
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| 12 |
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| 13 | The following example shows how to write a http echo server that delays its
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| 14 | response by 1000 ms.
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| 15 |
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| 16 | ``` javascript
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| 17 | var DelayedStream = require('delayed-stream');
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| 18 | var http = require('http');
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| 19 |
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| 20 | http.createServer(function(req, res) {
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| 21 | var delayed = DelayedStream.create(req);
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| 22 |
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| 23 | setTimeout(function() {
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| 24 | res.writeHead(200);
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| 25 | delayed.pipe(res);
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| 26 | }, 1000);
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| 27 | });
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| 28 | ```
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| 29 |
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| 30 | If you are not using `Stream#pipe`, you can also manually release the buffered
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| 31 | events by calling `delayedStream.resume()`:
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| 32 |
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| 33 | ``` javascript
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| 34 | var delayed = DelayedStream.create(req);
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| 35 |
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| 36 | setTimeout(function() {
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| 37 | // Emit all buffered events and resume underlaying source
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| 38 | delayed.resume();
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| 39 | }, 1000);
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| 40 | ```
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| 41 |
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| 42 | ## Implementation
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| 43 |
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| 44 | In order to use this meta stream properly, here are a few things you should
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| 45 | know about the implementation.
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| 46 |
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| 47 | ### Event Buffering / Proxying
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| 48 |
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| 49 | All events of the `source` stream are hijacked by overwriting the `source.emit`
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| 50 | method. Until node implements a catch-all event listener, this is the only way.
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| 51 |
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| 52 | However, delayed-stream still continues to emit all events it captures on the
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| 53 | `source`, regardless of whether you have released the delayed stream yet or
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| 54 | not.
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| 55 |
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| 56 | Upon creation, delayed-stream captures all `source` events and stores them in
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| 57 | an internal event buffer. Once `delayedStream.release()` is called, all
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| 58 | buffered events are emitted on the `delayedStream`, and the event buffer is
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| 59 | cleared. After that, delayed-stream merely acts as a proxy for the underlaying
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| 60 | source.
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| 61 |
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| 62 | ### Error handling
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| 63 |
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| 64 | Error events on `source` are buffered / proxied just like any other events.
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| 65 | However, `delayedStream.create` attaches a no-op `'error'` listener to the
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| 66 | `source`. This way you only have to handle errors on the `delayedStream`
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| 67 | object, rather than in two places.
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| 68 |
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| 69 | ### Buffer limits
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| 70 |
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| 71 | delayed-stream provides a `maxDataSize` property that can be used to limit
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| 72 | the amount of data being buffered. In order to protect you from bad `source`
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| 73 | streams that don't react to `source.pause()`, this feature is enabled by
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| 74 | default.
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| 75 |
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| 76 | ## API
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| 77 |
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| 78 | ### DelayedStream.create(source, [options])
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| 79 |
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| 80 | Returns a new `delayedStream`. Available options are:
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| 81 |
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| 82 | * `pauseStream`
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| 83 | * `maxDataSize`
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| 84 |
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| 85 | The description for those properties can be found below.
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| 86 |
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| 87 | ### delayedStream.source
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| 88 |
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| 89 | The `source` stream managed by this object. This is useful if you are
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| 90 | passing your `delayedStream` around, and you still want to access properties
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| 91 | on the `source` object.
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| 92 |
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| 93 | ### delayedStream.pauseStream = true
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| 94 |
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| 95 | Whether to pause the underlaying `source` when calling
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| 96 | `DelayedStream.create()`. Modifying this property afterwards has no effect.
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| 97 |
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| 98 | ### delayedStream.maxDataSize = 1024 * 1024
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| 99 |
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| 100 | The amount of data to buffer before emitting an `error`.
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| 101 |
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| 102 | If the underlaying source is emitting `Buffer` objects, the `maxDataSize`
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| 103 | refers to bytes.
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| 104 |
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| 105 | If the underlaying source is emitting JavaScript strings, the size refers to
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| 106 | characters.
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| 107 |
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| 108 | If you know what you are doing, you can set this property to `Infinity` to
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| 109 | disable this feature. You can also modify this property during runtime.
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| 110 |
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| 111 | ### delayedStream.dataSize = 0
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| 112 |
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| 113 | The amount of data buffered so far.
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| 114 |
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| 115 | ### delayedStream.readable
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| 116 |
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| 117 | An ECMA5 getter that returns the value of `source.readable`.
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| 118 |
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| 119 | ### delayedStream.resume()
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| 120 |
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| 121 | If the `delayedStream` has not been released so far, `delayedStream.release()`
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| 122 | is called.
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| 123 |
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| 124 | In either case, `source.resume()` is called.
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| 125 |
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| 126 | ### delayedStream.pause()
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| 127 |
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| 128 | Calls `source.pause()`.
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| 129 |
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| 130 | ### delayedStream.pipe(dest)
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| 131 |
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| 132 | Calls `delayedStream.resume()` and then proxies the arguments to `source.pipe`.
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| 133 |
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| 134 | ### delayedStream.release()
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| 135 |
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| 136 | Emits and clears all events that have been buffered up so far. This does not
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| 137 | resume the underlaying source, use `delayedStream.resume()` instead.
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| 138 |
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| 139 | ## License
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| 140 |
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| 141 | delayed-stream is licensed under the MIT license.
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