JavaScript double backslash in WebSocket messages

Question

I'm sending binary data over WebSocket to a Python application. This binary data is decoded by calling struct.unpack("BH", data") on it, requiring a 4-long bytes object.
The problem I'm currently facing is, that all data contains duplicate backslashes, even in arraybuffer mode and is therefor 16 bytes long. I can't detect the varying size because there is data appended to the back of it (irrelevant for this question) and even if I could, I also couldn't find a way to strip the backslashes in Python.

How the data is sent:

// this.webSocket.binaryType = "arraybuffer";   
var message = "\\x05\\x00\\x00\\x00"; // escaping required
var buffer = new Int8Array(message.length);
for (var i = 0; i < message.length; i++) {
    buffer[i] = message.charCodeAt(i);
}
this.webSocket.send(buffer.buffer);

In comparison, this is how said data looks when defined in Python:

b'\x05\x00\x00\x00'

And this is how it looks as a received message:

b'\\x05\\x00\\x00\\x00'

The ideal solution for this issue would be on the JavaScript-side because I can't really change the implementation of the Python application without breaking Python-based clients.

Daniel · Accepted Answer · 2016-10-19 21:09:56Z

1

You should define the message as bytes and not as string:

var buffer = new Int8Array([5,0,0,0])
this.webSocket.send(buffer.buffer)

answered Oct 19, 2016 at 21:09

Daniel

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7 Comments

guest271314 Over a year ago

Is 5 equivalent to "\\x05"?

Daniel Over a year ago

No, "\\x05" are 4 bytes, but 5 is equal to the byte \x05.

Daniel Over a year ago

What do you mean with «format»? This is a string with a backslash, x 0 and 5.

guest271314 Over a year ago

Why are "\\" included in original string? Is "\\x05" intended to be the literal string x05? Why are \`, x, 0` not included at first element of Uint8Array? For example using approach described at stackoverflow.com/questions/17204912/…, +parseInt("0x05", 16).toString(2) returns 101, String.fromCodePoint(101) returns "e". Is this not incorrect conversion? Can ask a Question if that would be more appropriate.

Daniel Over a year ago

the decimal number 5 as a number to the base of 2 is 101. That is not the decimal number 101.

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