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