4.2 KiB
delayed-stream
Buffers events from a stream until you are ready to handle them.
Installation
npm install delayed-stream
Usage
The following example shows how to write a http echo server that delays its response by 1000 ms.
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():
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:
pauseStreammaxDataSize
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.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.
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.