How to use pipe in levelup (node.js)? http://stackoverflow.com/questions/20293286/how-to-use-pipe-in-levelup-node-js

stream_leveldb.js

#!/usr/bin/nodejs

var levelup        = require('levelup');
var http           = require("http");

var stream = require('stream');
var util = require('util');
var Transform = stream.Transform || require('readable-stream').Transform;

var server = http.createServer(onRequest);

var db = levelup('db',{"valueEncoding": "json"});

//save something in db
db.put("1",{"leo":1});
db.put("2",{"nardo":2});
db.put("3",{"LEONARDO":3});


var stringifier = new stream.Transform();
stringifier._readableState.objectMode = true;
stringifier._transform = function (data, encoding, done) {
    this.push(JSON.stringify(data));
    this.push('\n');
    done();
}

server.listen(9090, function() { //'listening' listener
	console.log("Server has started --- " + (new Date).toJSON());
});

server.on('error', function (e) {
	if (e.code == 'EADDRINUSE') {
		console.error('Error: address in use');
	}
	else {
		console.error(e + '. Error code: ' + e.code);
	}
});

function onRequest(request, response) {
	response.setHeader("Content-Type", "application/json; charset=utf-8");
	var rs = db.createReadStream();

	request.on('close', function(){
		rs.destroy();
		response.end();
	});

	rs.on('end', function(){
		response.end();
	});
	rs.on('error', function(err){
		console.log('ERROR-RS',err);
		rs.destroy();
	});

	//this way works, but increases memory with large bases, because of event emmiting: http://stackoverflow.com/questions/19550180/memory-leak-when-using-streams-in-node-js
	//rs.on('data', function(data){
	//	response.write(JSON.stringify(data)+"\n");
	//});
	
	//This is the way suggested by Paul Mougel
	rs.pipe(stringifier).pipe(response);
	
	
}

/*
I've got this error:
events.js:72
        throw er; // Unhandled 'error' event
              ^
TypeError: Invalid non-string/buffer chunk
    at validChunk (_stream_writable.js:150:14)
    at Transform.Writable.write (_stream_writable.js:179:12)
    at write (_stream_readable.js:573:24)
    at flow (_stream_readable.js:582:7)
    at ReadStream.pipeOnReadable (_stream_readable.js:614:5)
    at ReadStream.EventEmitter.emit (events.js:92:17)
    at emitReadable_ (_stream_readable.js:408:10)
    at emitReadable (_stream_readable.js:404:5)
    at readableAddChunk (_stream_readable.js:165:9)
    at ReadStream.Readable.push (_stream_readable.js:127:10)

*/