DuckDuckGo .Onion redirect

main.js

const DDG_ONION = browser.runtime.getManifest().permissions.find(p =>
	p.match(/duckduckgo.*\.onion/));
const DDG_CLEARNET = browser.runtime.getManifest().permissions.find(p =>
	p.match(/duckduckgo(?!.*\.onion)/))
const DDG_ONION_HOST = DDG_ONION.match(/^\*:\/\/(.+)\/\*$/)[1];

function injectOnionHeader(details) {
	let u = new URL(details.url);
	let h = details.responseHeaders;
	u.host = DDG_ONION_HOST;
	h.push({name: 'Onion-Location', value: u.toString()});
	return {responseHeaders: h};
}

browser.webRequest.onHeadersReceived.addListener(
	injectOnionHeader,
	{urls: [DDG_CLEARNET]},
	["blocking", "responseHeaders"]
);

function redirectToOnion(details) {
	let u = new URL(details.url);
	u.host = DDG_ONION_HOST;
	return {redirectUrl: u.toString()};
}

function enableOnionRedirect(details) {
	if( details.statusCode != 200 ) return;
	browser.webRequest.onBeforeRequest.addListener(
		redirectToOnion,
		{urls: [DDG_CLEARNET]},
		["blocking"]
	);
	console.info('browser.webRequest.onBeforeRequest.removeListener(redirectToOnion);');
	browser.webRequest.onCompleted.removeListener(enableOnionRedirect);
}

browser.webRequest.onCompleted.addListener(
	enableOnionRedirect,
	{urls: [DDG_ONION]}
);

manifest.json

{
	"manifest_version": 2,
	"name": "DuckDuckGo .Onion redirect",
	"version": "0",

	"permissions": [
		"webRequest","webRequestBlocking",
		"*://duckduckgo.com/*",
		"*://duckduckgogg42xjoc72x3sjasowoarfbgcmvfimaftt6twagswzczad.onion/*"
	],

	"background": {
		"scripts": ["main.js"]
	}
}