svinja svinja - 6 months ago 53
Node.js Question

Receiving WebSocket ArrayBuffer data in the browser - receiving string instead

I have a node.js server application and a browser client. Sending

ArrayBuffer
data browser -> server works perfectly, but server -> browser results in a string
"[object ArrayBuffer]"
being received. This happens in the latest versions of both Chrome and Firefox.

Server:

var serverPort = 9867;

// dependencies
var webSocketServer = require('websocket').server;
var http = require('http');
var players = {};
var nextPlayerId = 0;

// create http server
var server = http.createServer(function(request, response) { });
server.listen(serverPort, function() {
console.log((new Date()) + " Server is listening on port " + serverPort);
});

// create websocket server
var wServer = new webSocketServer({ httpServer: server });
// connection request callback
wServer.on('request', function(request) {
var connection = request.accept(null, request.origin);
connection.binaryType = "arraybuffer";
var player = {};
player.connection = connection;
player.id = nextPlayerId;
nextPlayerId++;
players[player.id] = player;
console.log((new Date()) + ' connect: ' + player.id);

// message received callback
connection.on('message', function(message) {
if (message.type == 'binary' && 'binaryData' in message && message.binaryData instanceof Buffer) {
// this works!
console.log('received:');
console.log(message);

}
});

// connection closed callback
connection.on('close', function(connection) {
console.log((new Date()) + ' disconnect: ' + player.id);
delete players[player.id];
});
});

function loop() {
var byteArray = new Uint8Array(2);
byteArray[0] = 1;
byteArray[0] = 2;
for (var index in players) {
var player = players[index];
console.log('sending: ');
console.log(byteArray.buffer);
player.connection.send(byteArray.buffer);
}
}

timerId = setInterval(loop, 500);


Client:

<!DOCTYPE html>
<html>
<head>
</head>
<body>
<script type="text/javascript">

window.WebSocket = window.WebSocket || window.MozWebSocket;
var connection = new WebSocket('ws://127.0.0.1:9867');
connection.binaryType = "arraybuffer";

// most important part - incoming messages
connection.onmessage = function (event) {
document.getElementById("log").innerHTML += typeof(event.data) + ' ';
document.getElementById("log").innerHTML += event.data + ' ';
if (event.data instanceof ArrayBuffer) {
// string received instead of a buffer
}
};

window.onkeydown = function(e) {
var byteArray = new Uint8Array(2);
byteArray[0] = 1;
byteArray[1] = e.keyCode;
connection.send(byteArray.buffer);
};
</script>

<div id='log'>Log: </div>
</body>
</html>


What am I doing wrong?

Edit:

From the node.js websocket source:

WebSocketConnection.prototype.send = function(data, cb) {
if (Buffer.isBuffer(data)) {
this.sendBytes(data, cb);
}
else if (typeof(data['toString']) === 'function') {
this.sendUTF(data, cb);
}


So if you use an
Uint8Array
, it sends the data as a string, instead of using
sendBytes
, as
sendBytes
needs a
Buffer
object. As in the answer below, I need
sendBytes
. As I can't pass an
ArrayBuffer
to
sendBytes
, I did this on the server:

function loop() {
var buffer = new Buffer(2);
buffer[0] = 1;
buffer[1] = 2;
for (var index in players) {
var player = players[index];
console.log('sending: ');
console.log(buffer);
player.connection.send(buffer);
}
}


Now it works.

Conclusion:

While Chrome and Firefox websockets
.send()
a
Uint8Array
buffer as binary data, it seems node.js websockets send it as
string
data, and you need a
Buffer
buffer to send binary.

Answer

send binary data use sendBytes() method.

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