stream.Readable returns data on first read call even it first should buffer

stream.js

var util = require('util');
var http = require('http');
var stream = require('stream');
var crypto = require('crypto');

var server = http.createServer();

server.on('request', function(request, response) {
    response.writeHead(200, { "Content-Type": "text/plain" });
    response.end('Hello World\n');
});

server.on('upgrade', function(request, socket) {
    var key = request.headers['sec-websocket-key'];
    var accept = generateAccept(key);
        
    socket.write(util.format(
        'HTTP/1.1 101 Switching Protocols\r\n' +
        'Upgrade: websocket\r\n' +
        'Connection: upgrade\r\n' +
        'Sec-WebSocket-Accept: %s\r\n' +
        'Sec-WebSocket-Version: 13\r\n' +
    '\r\n', accept));

    var wsstream = new stream.Readable();

    console.log(wsstream);

    wsstream._read = function() {
        var chunk = socket.read();

        if (chunk === null)
            return this.push('');

        this.push(chunk);
    };

    wsstream.on('readable', function() {
        console.log('stream', wsstream.read());
    });

    console.log(wsstream);

    socket.on('readable', function() {
        // using wsstream.read() would return all data here
        console.log('socket', wsstream.read(0));
    });
});

server.listen(3000);

function generateAccept(key) {
    var GUID = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11';

    return crypto.createHash('sha1').update(key.trim() + GUID).digest('base64');
}

To use it run node stream.js and open a WebBrowser with console. In the console you type in:

var ws = new WebSocket('ws://localhost:3000');

now you can send frames as you like with:

ws.send('some text message');