# EventStream
[Streams](http://nodejs.org/api/streams.html "Stream") are nodes best and most misunderstood idea, and
_<em>EventStream</em>_ is a toolkit to make creating and working with streams <em>easy</em>.
Normally, streams are only used of IO,
but in event stream we send all kinds of objects down the pipe.
If your application's <em>input</em> and <em>output</em> are streams,
shouldn't the <em>throughput</em> be a stream too?
The *EventStream* functions resemble the array functions,
because Streams are like Arrays, but laid out in time, rather than in memory.
<em>All the `event-stream` functions return instances of `Stream`</em>.
Stream API docs: [nodejs.org/api/streams](http://nodejs.org/api/streams.html "Stream")
NOTE: I shall use the term <em>"through stream"</em> to refer to a stream that is writable <em>and</em> readable.
###[simple example](https://github.com/dominictarr/event-stream/blob/master/examples/pretty.js):
``` js
//pretty.js
if(!module.parent) {
var es = require('event-stream')
es.connect( //connect streams together with `pipe`
process.openStdin(), //open stdin
es.split(), //split stream to break on newlines
es.map(function (data, callback) {//turn this async function into a stream
callback(null
, inspect(JSON.parse(data))) //render it nicely
}),
process.stdout // pipe it to stdout !
)
}
```
run it ...
``` bash
curl -sS registry.npmjs.org/event-stream | node pretty.js
```
[test are in event-stream_tests](https://github.com/dominictarr/event-stream_tests)
[node Stream documentation](http://nodejs.org/api/streams.html)
##map (asyncFunction)
Create a through stream from an asyncronous function.
``` js
var es = require('event-stream')
es.map(function (data, callback) {
//transform data
// ...
callback(null, data)
})
```
Each map MUST call the callback. It may callback with data, with an error or with no arguments,
* `callback()` drop this data.
this makes the map work like `filter`,
note:`callback(null,null)` is not the same, and will emit `null`
* `callback(null, newData)` turn data into newData
* `callback(error)` emit an error for this item.
>Note: if a callback is not called, `map` will think that it is still being processed,
>every call must be answered or the stream will not know when to end.
>
>Also, if the callback is called more than once, every call but the first will be ignored.
##readable (asyncFunction)
create a readable stream (that respects pause) from an async function.
while the stream is not paused,
the function will be polled with `(count, callback)`,
and `this` will be the readable stream.
``` js
es.readable(function (count, callback) {
if(streamHasEnded)
return this.emit('end')
//...
this.emit('data', data) //use this way to emit multiple chunks per call.
callback() // you MUST always call the callback eventually.
// the function will not be called again until you do this.
})
```
you can also pass the data and the error to the callback.
you may only call the callback once.
calling the same callback more than once will have no effect.
##readArray (array)
Create a readable stream from an Array.
Just emit each item as a data event, respecting `pause` and `resume`.
``` js
var es = require('event-stream')
, reader = es.readArray([1,2,3])
reader.pipe(...)
```
## writeArray (callback)
create a writeable stream from a callback,
all `data` events are stored in an array, which is passed to the callback when the stream ends.
``` js
var es = require('event-stream')
, reader = es.readArray([1, 2, 3])
, writer = es.writeArray(function (err, array){
//array deepEqual [1, 2, 3]
})
reader.pipe(writer)
```
## split ()
Break up a stream and reassemble it so that each line is a chunk.
Example, read every line in a file ...
``` js
es.connect(
fs.createReadStream(file, {flags: 'r'}),
es.split(),
es.map(function (line, cb) {
//do something with the line
cb(null, line)
})
)
```
## connect (stream1,...,streamN)
Connect multiple Streams together into one stream.
`connect` will return a Stream. This stream will write to the first stream,
and will emit data from the last stream.
Listening for 'error' will recieve errors from all streams inside the pipe.
``` js
es.connect( //connect streams together with `pipe`
process.openStdin(), //open stdin
es.split(), //split stream to break on newlines
es.map(function (data, callback) {//turn this async function into a stream
callback(null
, inspect(JSON.parse(data))) //render it nicely
}),
process.stdout // pipe it to stdout !
)
```
## gate (isShut=true)
If the gate is `shut`, buffer the stream.
All calls to write will return false (pause upstream),
and end will not be sent downstream.
If the gate is open, let the stream through.
Named `shut` instead of close, because close is already kinda meaningful with streams.
Gate is useful for holding off processing a stream until some resource (i.e. a database, or network connection) is ready.
``` js
var gate = es.gate()
gate.open() //allow the gate to stream
gate.close() //buffer the stream, also do not allow 'end'
```
## duplex
Takes a writable stream and a readable stream and makes them appear as a readable writable stream.
It is assumed that the two streams are connected to each other in some way.
(This is used by `connect` and `child`.)
``` js
var grep = cp.exec('grep Stream')
es.duplex(grep.stdin, grep.stdout)
```
## child (child_process)
Create a through stream from a child process ...
``` js
var cp = require('child_process')
es.child(cp.exec('grep Stream')) // a through stream
```
## pipeable (streamCreatorFunction,...)
The arguments to pipable must be functions that return
instances of Stream or async functions.
(If a function is returned, it will be turned into a Stream
with `es.map`.)
Here is the first example rewritten to use `pipeable`.
``` js
//examples/pretty_pipeable.js
var inspect = require('util').inspect
if(!module.parent)
require('event-stream').pipeable(function () {
return function (data, callback) {
try {
data = JSON.parse(data)
} catch (err) {} //pass non JSON straight through!
callback(null, inspect(data))
}
})
})
```
``` bash
curl -sS registry.npmjs.org/event-stream | node pipeable_pretty.js
## or, turn the pipe into a server!
node pipeable_pretty.js --port 4646
curl -sS registry.npmjs.org/event-stream | curl -sSNT- localhost:4646
```
## compatible modules:
* https://github.com/felixge/node-growing-file
stream changes on file that is being appended to. just like `tail -f`
* https://github.com/isaacs/sax-js
streaming xml parser
* https://github.com/mikeal/request
make http requests. request() returns a through stream!
* https://github.com/TooTallNate/node-throttle
throttle streams on a bytes per second basis (binary streams only, of course)
* https://github.com/mikeal/morestreams
buffer input until connected to a pipe.
* https://github.com/TooTallNate/node-gzip-stack
compress and decompress raw streams.
* https://github.com/Floby/node-json-streams
parse json without buffering it first
* https://github.com/floby/node-tokenizer
tokenizer
* https://github.com/floby/node-parser
general mechanisms for custom parsers
* https://github.com/dodo/node-bufferstream
buffer streams until you say (written in C)
* https://github.com/tim-smart/node-filter
`filter` pipeable string.replace
## almost compatible modules: (1+ these issues)
* https://github.com/fictorial/json-line-protocol/issues/1
line reader
* https://github.com/jahewson/node-byline/issues/1
line reader
* https://github.com/AvianFlu/ntwitter/issues/3
twitter client
* https://github.com/swdyh/node-chirpstream/issues/1
twitter client
* https://github.com/polotek/evented-twitter/issues/22
twitter client
<!--
TODO, the following methods are not implemented yet.
## sidestream (stream1,...,streamN)
Pipes the incoming stream to many writable streams.
remits the input stream.
``` js
es.sidestream( //will log the stream to a file
es.connect(
es.mapSync(function (j) {return JSON.stringify(j) + '/n'}),
fs.createWruteStream(file, {flags: 'a'})
)
```
## merge (stream1,...,streamN)
Create a readable stream that merges many streams into one.
(Not implemented yet.)
### another pipe example
SEARCH SUBDIRECTORIES FROM CWD
FILTER IF NOT A GIT REPO
MAP TO GIT STATUS --porclean + the directory
FILTER IF EMPTY STATUS
process.stdout
that will show all the repos which have unstaged changes
## TODO & applications
* buffer -- buffer items
* rate limiter
* save to database
* couch
* redis
* mongo
* file(s)
* read from database
* couch
* redis
* mongo
* file(s)
* recursive
* search filesystem
* scrape web pages (load pages, parse for links, etc)
* module dependencies
-->
