Inspecting websocket traffic with proxy

Question

I'm using Charles Proxy to inspect traffic from my Android apps. I have the phone configured to proxy all traffic through Charles, which is installed on my PC.

Everything has worked thus far (HTTP/HTTPS traffic) except for websocket traffic. I have been unable to inspect it in Charles and Fiddler. First, the CONNECT request fails as follows:

URL https://184.73.XX.XX/
Status  Failed
Failure Invalid first line in request
Response Code   -
Protocol    HTTP/1.0
Method  CONNECT
Content-Type    -
Client Address  /192.168.0.10
Remote Address  184.73.XX.XX/184.73.XX.XX

And right after this request, there is an additional request sent to upgrade the connection, which appears to be successful as seen in the response:

HTTP/1.1 101 Switching Protocols
Server: nginx
Date: Sun, 16 Feb 2014 02:04:33 GMT
Connection: upgrade
Upgrade: websocket
Sec-WebSocket-Accept: CKm+rgmiltNrbQvwU2HzKHzr2eM=

After that, traffic from the app stops appearing even though activity continues. So, what is it about websocket traffic that it isn't captured by the proxy? Also, how can I capture it to see what is being sent back and forth?

I have tried Wireshark and I see TLS traffic continuing after the CONNECT/upgrade request, but I don't know how to reconstruct the packets into something I can understand, and to decrypt the TLS encrypted traffic.

Answer 1

Found the answer myself in case anyone is interested (source is blogs.telerik.com)

WebSockets

Fiddler’s HTML5 WebSockets support continues to grow; Fiddler extensions can now capture and manipulate WebSocket messages by handling the FiddlerApplication.OnWebSocketMessage event.

In preparation for a full-featured WebSockets UI, Fiddler no longer spews WebSocket messages to the Log tab. If you’d like to re-enable that behavior until the full UI is available, you can do so using FiddlerScript. Simply click Rules > Customize Rules and add the following function inside your Handlers class.

static function OnWebSocketMessage(oMsg: WebSocketMessage) {

// Log Message to the LOG tab
FiddlerApplication.Log.LogString(oMsg.ToString());

/*
// Modify a message's content
var sPayload = oMsg.PayloadAsString();
if (sPayload.Contains("time")) {
    oMsg.SetPayload(sPayload + "... bazinga!");
}                            
*/
}