How can i temporarily disable websocket in Google Chrome?

To begin, I'd say that there are better mechanisms to test your JavaScript in a websocketless environment. You could run your JavaScript in IE9, for instance, which doesn't implement the protocol. They're still disabled for the moment in Firefox 4 as well, if that's more your style.

Assuming that there's some good reason that you need to test in a websocketless Chromium, I think you're out of luck. There's not a trivial mechanism to disable WebSockets in Chromium. It's not built in as a command-line switch, nor is there a configurable flag. Since there's no mechanism to make this happen natively, I wouldn't suggest spending time testing the scenario. Every version of Chromium that your users use (e.g. 9+) has websockets enabled.

All that said, if you really need to disable websockets, the closest you can get without recompiling the browser would be to drop the relevant variables in your test code:

WebSocket = undefined;

would be relatively brute force, but should work. You could even create an extension to inject that JavaScript into every page you visit, for a truly websocketless experience (assuming, again, that that's somehow valuable for your use case).

I was able to block WebSockets with Fiddler.

Go to Rules / Customize Rules... in the Fiddler menu

Add this code to class Handlers (I put it after the existing RulesOption items):

    // Block Websocketspublic static RulesOption("Block Websockets")BindPref("fiddlerscript.rules.BlockWebsockets")var m_BlockWebsockets: boolean = false; 

Add this code in OnBeforeRequest:

    if (m_BlockWebsockets && oSession.oRequest.headers.Exists("Connection") && oSession.oRequest["Connection"] == "Upgrade") {                oSession.oRequest.FailSession(502, "Blocked", "Fiddler blocked websocket connection");                return;            }

This adds a menu option Block Websockets to the Rules menu. When it is toggled on, ws connections should be blocked based on the Connection: Upgrade header.

After seeing @user3661841's answer on another question, I created a GreaseMonkey/TamperMonkey script that will allow you to disable WebSockets in a similar way.

Here's instructions for Chromium based browsers (Chrome, Brave, Sidekick, etc.):

1. Download the TamperMonkey extension from the Chrome Store
2. Install this script from GreasyFork. By default, installing this script will disable WebSockets on every site you visit. If you don't want to block WebSockets immediately, click on the TamperMonkey icon and the toggle switch to disable blocking.
3. When you want to turn off WebSockets, click on the TamperMonkey icon and the toggle switch to enable blocking. Refresh the page.
4. Disable the script when you no longer want to block WebSockets.

Here's the switch you want to click to disable/enable WebSocket blocking:

NOTE 1: You should be able to see output in your console marking that the WebSocket connection was attempted to be opened, but blocked.

NOTE 2: Make sure to disable this when you're done disabling WebSockets for development. If you only use TamperMonkey to disable WebSockets, You'll want your TamperMonkey to look like this most of the time:

And like this when you want to block: