Want to build a chrome extension that can intercept network request and rewrite the response body

[Long]

Hey ya'll,

I am currently looking for a way to build a chrome extension that can rewrite the response of certain network calls (like how we have it in the network tab -> override content). Is there a chrome extension that is best suited for that?

Is it possible to intercept the request with chrome.declarativeNetworkRequest and then use the redirect api to a server on a background script to return json?

i.e Browser calls get fakeSite/items -> chrome extension intercepts it and redirects the response to myBackgroundScript -> myBackgroundSCript returns mockedItem payload.

I've been reading mixed replies on google if this is possible or not, want to double check before going down this route.

[Long]

or in another words, how does requestly.io does it 

[woxxom]

Only Firefox implements this functionality properly.

In Chrome there are limited workarounds:

1. The declarativeNetworkRequest API can redirect to data:text/html,foo
2. A script in the MAIN world can spoof XMLHttpRequest.prototype, Response.prototype, window.fetch. It won't work for requests made inside a worker or service worker of a site or when the site intentionally exploits https://crbug.com/40202434, preventing which requires spoofing dozens of methods, which might cause problems by itself.
3. The chrome.debugger API can be used to implement what devtools does: send Fetch.enable, listen to Fetch.requestPaused event, send Fetch.takeResponseBodyAsStream, see https://chromedevtools.github.io/devtools-protocol/tot/Fetch/ and inspect example extensions. Using this API displays a warning above all tabs that annoyingly flickers on every navigation in the tab.