Chrome Extension
The Chrome extension allows for snooping on two-way traffic between the diep.io client
(written in Javascript, primarily in d.js) and the server (written in an unknown language,
most likely node.js or C/C++).
All packets and protocol information so far has been discovered by using this extension.
To set up this extension and modify it, go to chrome://extensions and click "Load
Unpacked Extension", then navigate to this directory (you will need to clone this
project first).
The file modifier.js contains a framework for handling communications to/from
the server.
To intercept packets sent by the client, modify the function handleSendData(data). If you
would like to modify the packet sent to the server, simply modify data, which is then
returned by the function and sent to the server.
Similarly, to intercept/modify packets sent by the server, use the function handleRecvData(event, proxiedRecv).
The event variable is simply the Javascript WebSocket event; to access the data, use event.data.
For altering the data, all you have to do is modify event.data.
If you would like to send the client custom packets or such in order to observe the client's response, etc., use proxiedRecv.call(this, customEvent).
Remember to navigate to chrome://extensions and click "Reload" after any changes to the code!