How to modify websocket message using fiddler

[Bruce Han]

Hi,

I am using the latest version of fiddler in my window.  I manage to intercept the websocket SEND message which my browser had sent to the server.

I want to modify the json value, such as from DEV to PROD....but is there any UI to do that easily?

SEND

destination:/websocketApp/ws/genAppList/CD944B73007E008E9B03ADD2F3D2A67E

content-length:99

{"environment":"DEV","appVersionNum":"1.1","startViewLabel":"Label1","endViewLabel":"Label2"}

[EricLaw]

Fiddler's WebSocket View tab does not presently offer the ability to modify the contents of WebSocket Messages as you can with normal HTTP messages in the other inspectors. Instead, you must use the OnWebSocketMessage event handler within your FiddlerScript. E.g. in Rules > Customize Rules you want something like:

static function OnWebSocketMessage(oMsg: WebSocketMessage) {

// Modify a message's content
var sPayload = oMsg.PayloadAsString();
if (sPayload.Contains('"DEV"')) {
    oMsg.SetPayload(sPayload.Replace('"DEV"', '"PROD"');

}                            

}

[Gerald Song]

I wonder where can I find these documents.

It seems I can't find these on official doc site.

[EricLaw]

What "documents" are you asking about?

[Gerald Song]

Fiddler Script.

I can't find things about onWebSocketMessage and WebSocketMessage in http://docs.telerik.com/fiddler/KnowledgeBase/FiddlerScript/ModifyRequestOrResponse or FiddlerScript's ClassView

[Eric Lawrence]

Unfortunately, the documentation on the docs.telerik.com site hasn't been updated in a long time. It should be present in FiddlerScript's classview; if not, please file an issue in https://fiddler.ideas.aha.io

The FiddlerBook (www.fiddlerbook.com) has the most comprehensive documentation on Fiddler; this forum also has a number of useful threads. The FiddlerCore documentation files are somewhat outdated but you may find them useful anyway; see e.g. https://fiddlerbook.com/om/html/F8192318.htm