gistfile1.js

var express = require('express');
var Promise = require("bluebird");
var fs = Promise.promisifyAll(require('fs'));  
var app = express();

function pipe() {
  return [].reduce.call(arguments, function(red, p) {
    return red.then(p);
  }
}

app.post('/process-file', function(req, res) {  
  var inputFile = 'input.txt';
  var outputFile = 'output.txt';

  pipe( fs.readFileAsync(inputFile),
        process1,
        process2,
        process3,
        fs.writeFileAsync.bind(fs, outputFile),
        function(data) {
          res.status(200).send('processed successfully using bluebird promises');
        }
  ).catch(function(err) {
    res.status(500).send(err);
  });
});