How to inspect websocket traffic with charlesproxy

Question

I would like to inspect network traffic going through web sockets, I have no control over the networking code as this is a binary lib for which I do not have the source code, so I cannot do any log/breakpoint in the networking part of the code.

I have tried using the latest version of CharlesProxy which claim to be able to sniff websockets however when I tried the url and apis using websockets were not even mentionned in the list of endpoints called from my iPhone.

I have verified that CharlesProxy is configured correctly as I am able to inspect non-websocket traffic even under SSL.

So my question is: did anyone find a solution to inspect traffic going through websockets with CharlesProxy?

Note: I have ATS disabled when using iOS9

Thanks!

Answer 1

I finally found the answer.

Charles 3.11.2 works perfectly with WebSocket.

I use socketIO, so I've already seen http requests sent during the negotiation phase, but I missed websockets traffic.

In the beginning, socketIO try to use polling then switches to use websockets.

The websocket traffic is visible when you go to the request with status: "Sending request body" which is actually wss:// request.

You even have a dedicated tab for this kind of traffic. The rest of messages will appear right there.

PS1. Ensure you're connected to socket properly then it appears in Charles.
PS2. I suggest using socketIO it's a great enhancement for full-duplex traffic like websockets.