WebSocket always sending stringified JSON object as buffer

Question

I have a node/ws WebSocket server listening for messages on a Redis backplane, and then forwards it on to any client that is listening:

sub.on("message", function(channel, message) {
    console.log('received message from redis: ' + message);
    console.log('message is type ' + typeof(message));
    var stringified = JSON.stringify(message);
    console.log('stringified is type ' + typeof(stringified));

    wss.clients.forEach(function each(client) {
      client.send(stringified);
    });
});

message is a JSON object. The log output is:

received message from redis: {"temp":81}
message is type object
stringified is type string

On the client, I have:

socket.onmessage = function(e) {
  console.log(e.data)
  ...
};

The log output is:

{"type":"Buffer","data":[123,34,116,101,109,112,34,58,53,52,125]}

Why am I not receiving a string?

If on the server I hardcode:

client.send('foobar');

then the client code will log out:

foobar

Your whole log output could be a JSON string. Try console.log(typeof e.data) in the client and see if it tells you it is a string. Also, please make the title of your question more meaningful. — jfriend00
– jfriend00, Commented Dec 26, 2016 at 20:06
@jfriend00 Indeed typeof e.data is a string. I'm unclear how I should be processing this. Why the discrepancy between a stringified JSON object and a basic string? Cheers. — Mister Epic
– Mister Epic, Commented Dec 26, 2016 at 20:13
My issue is message from Redis isn't a string, but when I call console.log('received message from redis: ' + message); then toString() was being called implicitly. I was being lazy and didn't hook up a proper inspector so console.log wasn't showing me what I needed to see. — Mister Epic
– Mister Epic, Commented Dec 26, 2016 at 20:55
In the future, you can do: console.log('received message from redis: ', message); instead of console.log('received message from redis: ' + message); and you will see the whole object instead of only a .toString() conversion. — jfriend00
– jfriend00, Commented Dec 26, 2016 at 20:59

Mister Spock · Accepted Answer · 2016-12-26 20:30:11Z

8

This is due to the fact that any kind of socket-based communication in Node is based on Buffers (more precisely, on Unit8Array, a kind of TypedArray).

You can safely call toString on a Buffer to get a string, or use Streams to make any kind of desired transformations on received data.

Edit: BTW, when you try to console.log a Buffer, it's toString method will be called implicitly.

edited Dec 26, 2016 at 20:30

answered Dec 26, 2016 at 20:17

Mister Spock

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1 Comment

Mister Epic Over a year ago

Looks like this was user error on my part, but I have no doubt you are indeed correct!

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