Eventual Pony

Process streams with generators and co.

• Write code and handle exceptions in sync style.
• Stream2 readables, writables and transforms.
• Has pipe()ing and backpressure.
• Works natively on io.js. Works on node with --harmony.
• Backed by co so do any co stuff.
• Great name.

Install

npm install eventual-pony

Silly example

var pony = require('eventual-pony')

var upperify = pony.transform(function*(input, output){
  while (true) {
    var chunk = yield input('utf8')
    chunk = chunk.toUpperCase()
    yield output(chunk, 'utf8')
  }
})

fs.createReadStream('./foo')
.pipe(upperify)
.pipe(fs.createWriteStream('./foo-upper'))

API Documentation

pony.writable([opts], genFunc(input))

Create a writable stream.

• opts - Options object passed to native Writable constructor. (optional)
• input([encoding]) - Returns yieldable for next available upstream value. If not in object mode and encoding is provided, produces string, otherwise a buffer.

// consume a stream of numbers to produce a sum
var sum = 0
pony.writable({
  objectMode: true
}, function* (input){
  while (true) {
    sum += yield input()
  }
}).on('end', function(){
  console.log(sum)
})

pony.readable([opts], genFunc(output))

Create a readable stream.

• opts - Options object passed to native Readable constructor. (optional)
• output(value, [encoding]) - Sends a value downstream. Returns a yieldable that resolves more or less quickly depending on how fast downstream is accepting data.

// stream of fibonacci numbers
pony.readable({
  objectMode: true
}, function* (output){
  var f1 = 1
    , f2 = 1
  while (true) {
    let result = f2
    f2 = f1
    f1 = f1 + result
    yield output(result)
  }
}).pipe(downstream)

pony.transform([opts], genFunc(input, output))

Create a transform stream.

• opts - Options object passed to native Transform constructor. (optional)
• input([encoding]) - Returns a yieldable on next available upstream value. If not in object mode and encoding is provided, produces string, otherwise a buffer.
• input.ended() - Once this returns true the input is ended, so output() any remaining stuff.
• output(value, [encoding]) - Sends a value downstream. Returns a yieldable that resolves more or less quickly depending on how fast downstream is accepting data.

// dedupe an object stream
upstream.pipe(pony.transform({
  objectMode: true
}, function* (inp, out){
  var uniq = new Set()
  var chunk = yield inp()
  if (!uniq.has(chunk)) {
    uniq.add(chunk)
    yield out(chunk)
  }
})).pipe(downstream)

Change log

• 0.0.2 - Updated header comments in code files.
• 0.0.1 - Added a repository field in package.json.
• 0.0.0 - First version. Has readables, writables and transforms.

Why "Eventual Pony"?

If you're good little boys and girls, eventually you'll get a pony.