kubernetes-handbook/delayed-stream/Readme.md

# 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.