pressure-stream

pressure-stream

call an async function for each data event into through stream. manage concurrency as back pressure.

var pressure = require('pressure-stream');
var split = require('split');
var request = require('request');


// reading urls from stdin only do 2 requests at a time

var options = {
  high:50, // if i get to 50 concurrent requests become paused
  low:25,  // if i was paused wait until i am down to at least 25 concurrent requests before resuming again
  max:100  // never ever do more than 100 requests at a time. when someone doesn't care if you are paused and keeps writing.
};

process.stdin.pipe(split())
.pipe(pressure(function(data,cb){
  request(data,function(err,res,body){
    cb(err,body)
  });
},options)).pipe(process.stdout);

API

pressure(fn,opts)

• fn is the data handler it is always called with 2 arguments
  • fn(data,cb)
• when you are done with the the handler call cb(err,data)
  • if err is passed back with cb "error" will be emitted on the stream
  • data passed back on this stream will be emited as data

options

• max
  • the maximum number of concurrent data handlers the stream will execute.
  • defaults to no limit
• high
  • the number of concurrent data handlers in progress before the stream will emit pause
• low
  • the number of data handlers in progress the stream will wait for before resuming.
  • defaults to the same value as high