How to use transform stream using request? - node.js

Question

Basically, I would like to alter the http response before sending it to the client, using transform streams, but my code below throws an error : [Error: write after end].
Documentation on http://nodejs.org/api/stream.html#stream_writable_end_chunk_encoding_callback says :
Calling write() after calling end() will raise an error.
How can I prevent write() to be called after end() in this case ?
var request = require('request');
var Transform = require('stream').Transform;
var http = require('http');
var parser = new Transform();
parser._transform = function(data, encoding, done) {
console.log(data);
this.push(data);
done();
};
parser.on('error', function(error) {
console.log(error);
});
http.createServer(function (req, resp) {
var dest = 'http://stackoverflow.com/';
var x = request({url:dest, encoding:null})
x.pipe(parser).pipe(resp)
}).listen(8000);

Answer 1

A stream is supposed to be used only once, but you're using the same transform stream for each incoming request. On the first request it will work, but when x closes, so will parser: that's why on the second client request you'll see the write after end error.
To fix this, just create a new transform stream on each use:
function createParser () {
var parser = new Transform();
parser._transform = function(data, encoding, done) {
console.log(data);
this.push(data);
done();
};
return parser;
}
http.createServer(function (req, resp) {
var dest = 'http://stackoverflow.com/';
var x = request({url:dest, encoding:null})
x.pipe(createParser()).pipe(resp)
}).listen(8000);