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diff --git a/background/policy_injector.js b/background/policy_injector.js
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+++ b/background/policy_injector.js
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+/**
+ * Myext injecting policy to page using webRequest
+ *
+ * Copyright (C) 2021 Wojtek Kosior
+ *
+ * This code is dual-licensed under:
+ * - Asshole license 1.0,
+ * - GPLv3 or (at your option) any later version
+ *
+ * "dual-licensed" means you can choose the license you prefer.
+ *
+ * This code is released under a permissive license because I disapprove of
+ * copyright and wouldn't be willing to sue a violator. Despite not putting
+ * this code under copyleft (which is also kind of copyright), I do not want
+ * it to be made proprietary. Hence, the permissive alternative to GPL is the
+ * Asshole license 1.0 that allows me to call you an asshole if you use it.
+ * This means you're legally ok regardless of how you utilize this code but if
+ * you make it into something nonfree, you're an asshole.
+ *
+ * You should have received a copy of both GPLv3 and Asshole license 1.0
+ * together with this code. If not, please see:
+ * - https://www.gnu.org/licenses/gpl-3.0.en.html
+ * - https://koszko.org/asshole-license.txt
+ */
+
+"use strict";
+
+(() => {
+    const TYPE_PREFIX = window.TYPE_PREFIX;
+    const get_storage = window.get_storage;
+    const browser = window.browser;
+    const is_chrome = window.is_chrome;
+    const gen_unique = window.gen_unique;
+    const url_item = window.url_item;
+    const get_query_best = window.get_query_best;
+
+    var storage;
+    var query_best;
+
+    let csp_header_names = {
+	"content-security-policy" : true,
+	"x-webkit-csp" : true,
+	"x-content-security-policy" : true
+    };
+
+    function is_noncsp_header(header)
+    {
+	return !csp_header_names[header.name.toLowerCase()];
+    }
+
+    function inject(details)
+    {
+	let url = url_item(details.url);
+
+	let [pattern, settings] = query_best(url);
+
+	if (settings !== undefined && settings.allow) {
+	    console.log("allowing", url);
+	    return {cancel : false};
+	}
+
+	let nonce = gen_unique(url).substring(1);
+	let headers = details.responseHeaders.filter(is_noncsp_header);
+	headers.push({
+	    name : "content-security-policy",
+	    value : `script-src 'nonce-${nonce}'; script-src-elem 'nonce-${nonce}';`
+	});
+
+	console.log("modified headers", url, headers);
+
+	return {responseHeaders: headers};
+    }
+
+    async function start() {
+	storage = await get_storage();
+	query_best = await get_query_best();
+
+	let extra_opts = ["blocking", "responseHeaders"];
+	if (is_chrome)
+	    extra_opts.push("extraHeaders");
+
+	browser.webRequest.onHeadersReceived.addListener(
+	    inject,
+	    {
+		urls: ["<all_urls>"],
+		types: ["main_frame", "sub_frame"]
+	    },
+	    extra_opts
+	);
+    }
+
+    window.start_policy_injector = start;
+})();