Chrome extension API for intercepting/modifying websockets UA

Question

I'm trying to write an extension that will modify the User-Agent on all outgoing requests from Chrome.

For http://, https://, ftp://, file://, or chrome-extension:// I can use the chrome.webRequest API and onBeforeSendHeaders. However, this does not work for ws:// or wss://.

Is there some other API that allows me to set/modify headers on these requests?

Answer 1

I was googling for an answer to this question, and since it now, three years later, is possible, I'll document it here.

According to https://developer.chrome.com/extensions/webRequest, it should work from Chrome 58. But there were several configurations required in order to make it work.

• In the manifest permissions must be requested for webRequest and webRequestBlocking
• Permissions must also be requested for the web socket URLs, like "wss://*/" and "ws://*/"
• In the request filters (in the addListener function calls) the urls must be declared with wss or ws scheme. Using * as scheme resolves as http and https only
• In the request filters, websocket has to be declared in types. (I'm not sure if this is required, I don't have time to verify that)

And remember, webRequest is only available in background scripts, and not in content scripts.

Example (changing the Origin header, changing User Agent should be similar)

In manifest.json:

"permissions": [
"storage",
"tabs",
"activeTab",
"webRequest",
"webRequestBlocking",
"webNavigation",
"debugger",
"https://*/",
"wss://*/"
],

In the background script

// origin is defined somewhere above
chrome.webRequest.onBeforeSendHeaders.addListener((details) => {
      if (origin) {
        const headers = details.requestHeaders;
        for (let i = 0; i < headers.length; i++) {
          if (headers[i].name === 'Origin') {
            headers[i].value = origin;
          }
        }
        return { requestHeaders: headers };
      }
    }, { urls: ['wss://server.example.com/*', 'https://server.example.com/*'],
         types: ['xmlhttprequest', 'websocket'] },
       ['requestHeaders', 'blocking']);