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# 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.