Array being sent as String on node.js

Question

I am doing some experimenting with socket.io. I have a canvas that successfully sends data to the server which receives it fine.

It receives a Uint8ClampedArray which is correct because that is what is being sent.

When I then .send this message from the server to the client, I get a string: [object Object]. Again I have checked! Am I missing something, the code for the server is below:

var fs, http, io, server;
fs = require('fs');
http = require('http');
server = http.createServer(function(req, res) {
    return fs.readFile("" + __dirname + "/front.html", function(err, data) {
        res.writeHead(200, {
            'Content-Type': 'text/html'
        });
        return res.end(data, 'utf8');
    });
});
server.listen(1337);
io = require('socket.io').listen(server);
io.sockets.on('connection', function(socket) {
    socket.on('publish', function(message) {
         return io.sockets.send(message);
    });
});

did you tried serializing data before send - JSON.stringify ? — Damian Krawczyk
– Damian Krawczyk, Commented May 13, 2013 at 7:11
Ah thank you! JSON.stringify sends the data! Just need to figure out how to convert it back! — Antony D'Andrea
– Antony D'Andrea, Commented May 13, 2013 at 7:14
Thanks, how do I convert it back to Uint8ClampedArray, that is all Canvas seems to accept. — Antony D'Andrea
– Antony D'Andrea, Commented May 13, 2013 at 8:05

Waqar Alamgir · Accepted Answer · 2015-11-19 10:41:57Z

9

On Client:

var dataStr = JSON.stringify(data); // converts object to string

On Server:

var dataObj = JSON.parse(data); // converts string to object

edited Nov 19, 2015 at 10:41

answered May 13, 2013 at 7:14

Waqar Alamgir

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5 Comments

Antony D'Andrea Over a year ago

I have to do the JSON.parse on the client when it receives the data because when I do it on the server, I get the same problem as before.

Waqar Alamgir Over a year ago

JSON.parse will convert back string to array so you can use at any place where you need this type of conversion. server will always return string so you will need to parse it with these two options I mentioned.

Waqar Alamgir Over a year ago

JSON.parse uses eval at the back, so I prefer using eval.

Bret Copeland Over a year ago

Waqar, sorry, eval is a security risk. Just to echo Christoph's outrage, running eval('client submitted data') is equivalent to saying, "hey, run any code you want on my server." It opens you up to every security hole imaginable. Don't do it!

Waqar Alamgir Over a year ago

You are right in that case... its just a matter of conversion. For security concerns I would only use JSON.parse

ikaruss · Accepted Answer · 2014-03-26 10:34:30Z

2

The only way is to reuse Uint8ClampedArray in your client size. If you have this on your server-side

var x = new Uint8ClampedArray(3);
x[0] = -17;
x[1] = 93;
x[2] = 350;
var dataThatWillBeSent = JSON.stringify(x);
// '{"0":0,"1":93,"2":255,"length":3,"byteLength":3,"byteOffset":0,"buffer":{"byteLength":3}}'

In your client side, assume that you have included Uint8ClampedArray, you can do this

var dataReceived = '{"0":0,"1":93,"2":255,"length":3,"byteLength":3,"byteOffset":0,"buffer":{"byteLength":3}}';
dataReceived = JSON.parse(dataReceived);
// reconstruct Uint8ClampedArray object

I have not used Uint8ClampedArray before, so I dont know exactly how you can recover a Uint8ClampedArray object from a JSON data, but if you read the document you might be able to figure something out

edited Mar 26, 2014 at 10:34

ikaruss

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answered May 15, 2013 at 6:53

Tan Nguyen

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