Redirect cast extension chrome-extension:// URLs to regular API URL

ext/src/compat/youtube.js

@@ -8,3 +8,53 @@ document.addEventListener("beforescriptexecute", function onBeforeScriptExecute
     scriptElement.src = browser.runtime.getURL("vendor/webcomponents-lite.min.js");
     document.head.prepend(scriptElement);
 });
+
+
+const EXT_SENDER_SCRIPT_URLS = [
+    "chrome-extension://pkedcjkdefgpdelpbcmbmeomcjbeemfm/cast_sender.js"
+  , "chrome-extension://enhhojjnijigcajfphajepfemndkmdlo/cast_sender.js"
+];
+
+const SENDER_SCRIPT_URL = "https://www.gstatic.com/cv/js/sender/v1/cast_sender.js";
+
+
+// Store reference to original function
+const _createElement = document.createElement;
+
+function createElement () {
+    // Call original function
+    const element = _createElement.apply(this, arguments);
+
+    /**
+     * If the new element being created is a <script> element,
+     * replace the src property setter to intercept the new value.
+     *
+     * If it matches Chrome's cast extension sender script URL,
+     * replace it with the standard API URL, the request for which
+     * is handled in the main script.
+     */
+    if (element.nodeName === "SCRIPT") {
+        const { get, set } = Reflect.getOwnPropertyDescriptor(
+                Reflect.getPrototypeOf(element.wrappedJSObject), "src");
+
+        Reflect.defineProperty(element.wrappedJSObject, "src", {
+            configurable: true
+          , enumerable: true          
+          , get
+
+          , set: exportFunction(function (value) {
+                if (EXT_SENDER_SCRIPT_URLS.includes(value)) {
+                    return set.call(this, SENDER_SCRIPT_URL);
+                }
+                return set.call(this, value);
+            }, window)
+        });
+    }
+
+    return element;
+}
+
+// Redefine page's document.createElement function
+exportFunction(createElement, document, {
+    defineAs: "createElement"
+});

ext/src/lib/userAgents.ts

@@ -7,18 +7,28 @@ const PLATFORM_LINUX = "Mozilla/5.0 (X11; Linux x86_64";
 const UA_PREFIX = "Mozilla/5.0";
 
 const UA_CHROME = "AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.67 Safari/537.36";
+const UA_CHROME_LEGACY = "AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2883.87 Safari/537.36";
 const UA_SAFARI = "AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Safari/605.1.15";
 
 
-export function getChromeUserAgent (platform: string): string {
+function getPlatformComponent (platform: string) {
-    let platformComponent: string;
     switch (platform) {
-        case "mac": platformComponent = PLATFORM_MAC; break;
+        case "mac": return PLATFORM_MAC; break;
-        case "win": platformComponent = PLATFORM_WIN; break;
+        case "win": return PLATFORM_WIN; break;
-        case "linux": platformComponent = PLATFORM_LINUX; break;
+        case "linux": return PLATFORM_LINUX; break;
     }
+}
 
-    return `${UA_PREFIX} (${platformComponent}) ${UA_CHROME}`;
+export function getChromeUserAgent (
+        platform: string
+      , legacy: boolean = false): string {
+
+    const platformComponent = getPlatformComponent(platform);
+    const browserComponent = legacy
+        ? UA_CHROME_LEGACY
+        : UA_CHROME;
+
+    return `${UA_PREFIX} (${platformComponent}) ${browserComponent}`;
 }
 
 export function getSafariUserAgent (platform: string): string {

ext/src/main.ts

@@ -173,10 +173,19 @@ async function onBeforeSendHeaders (
         currentUAString = getChromeUserAgent(os);
     }
 
+    const host = details.requestHeaders.find(
+            (header: any) => header.name === "Host");
+
     // Find and rewrite the User-Agent header
     for (const header of details.requestHeaders) {
         if (header.name.toLowerCase() === "user-agent") {
+            // TODO: Move this somewhere else
+            if (host.value === "www.youtube.com") {
+                header.value = getChromeUserAgent(os, true);
+            } else {
                 header.value = currentUAString;
+            }
+
             break;
         }
     }

ext/src/shim/contentSetup.ts

@@ -1,3 +1,6 @@
 "use strict";
 
-(window.wrappedJSObject as any).chrome = cloneInto({}, window);
+const _window = (window.wrappedJSObject as any);
+
+_window.chrome = cloneInto({}, window);
+_window.navigator.presentation = cloneInto({}, window);