Refactor extension whitelist module

ext/src/background/whitelist.ts

@@ -9,27 +9,58 @@ import { CAST_FRAMEWORK_LOADER_SCRIPT_URL
        , CAST_LOADER_SCRIPT_URL } from "../lib/endpoints";
 
 
+// Missing on @types/firefox-webext-browser
+type OnBeforeSendHeadersDetails = Parameters<Parameters<
+        typeof browser.webRequest.onBeforeSendHeaders.addListener>[0]>[0] & {
+    frameAncestors?: Array<{ url: string, frameId: number }>
+};
+type OnBeforeRequestDetails = Parameters<Parameters<
+        typeof browser.webRequest.onBeforeRequest.addListener>[0]>[0] & {
+    frameAncestors?: Array<{ url: string, frameId: number }>
+};
+
+
+const originUrlCache: string[] = [];
+
+let platform: string;
+let chromeUserAgent: string | undefined;
+let chromeUserAgentHybrid: string | undefined;
+
 export async function initWhitelist () {
     logger.info("init (whitelist)");
 
-    // Missing on @types/firefox-webext-browser
-    type OnBeforeSendHeadersDetails = Parameters<Parameters<
-            typeof browser.webRequest.onBeforeSendHeaders.addListener>[0]>[0] & {
-        frameAncestors?: Array<{ url: string, frameId: number }>
-    };
-    type OnBeforeRequestDetails = Parameters<Parameters<
-            typeof browser.webRequest.onBeforeRequest.addListener>[0]>[0] & {
-        frameAncestors?: Array<{ url: string, frameId: number }>
-    };
-
-
-    const originUrlCache: string[] = [];
-
+    if (!platform) {
         // TODO: Allow hybrid UA to be configurable
-    const platform = (await browser.runtime.getPlatformInfo()).os;
-    const chromeUserAgent = getChromeUserAgent(platform);
+        platform = (await browser.runtime.getPlatformInfo()).os;
+        chromeUserAgent = getChromeUserAgent(platform);
+        chromeUserAgentHybrid = getChromeUserAgent(platform, true);
 
         /**
+         * If a UA string can't be obtained, don't bother continuing
+         * extension initialization
+         */
+        if (!chromeUserAgent) {
+            throw logger.error("Failed to get Chrome UA string");
+        }
+    }
+
+    // Register on first run
+    await registerUserAgentWhitelist();
+
+    // Re-register when options change
+    options.addEventListener("changed", ev => {
+        const alteredOpts = ev.detail;
+
+        if (alteredOpts.includes("userAgentWhitelist")
+         || alteredOpts.includes("userAgentWhitelistEnabled")) {
+            unregisterUserAgentWhitelist();
+            registerUserAgentWhitelist();
+        }
+    });
+}
+
+
+/**
  * Web apps usually only load the sender library and
  * provide cast functionality if the browser is detected
  * as Chrome, so we should rewrite the User-Agent header
@@ -52,7 +83,7 @@ export async function initWhitelist () {
     for (const header of details.requestHeaders) {
         if (header.name === "User-Agent") {
             header.value = host?.value === "www.youtube.com"
-                    ? getChromeUserAgent(platform, true)
+                ? chromeUserAgentHybrid
                 : chromeUserAgent;
             break;
         }
@@ -61,15 +92,15 @@ export async function initWhitelist () {
     return {
         requestHeaders: details.requestHeaders
     };
-    }
+}
 
-    /**
+/**
  * Requests from within child frames should also adopt
  * the modified User-Agent header to support embedded
  * players on other origins (like CDN domains) when the
  * main site is whitelisted.
  */
-    function onWhitelistedChildBeforeSendHeaders (
+function onWhitelistedChildBeforeSendHeaders (
         details: OnBeforeSendHeadersDetails) {
 
     if (!details.requestHeaders || !details.frameAncestors) {
@@ -84,7 +115,7 @@ export async function initWhitelist () {
             for (const header of details.requestHeaders) {
                 if (header.name === "User-Agent") {
                     header.value = host?.value === "www.youtube.com"
-                            ? getChromeUserAgent(platform, true)
+                        ? chromeUserAgentHybrid
                         : chromeUserAgent;
                     break;
                 }
@@ -95,10 +126,10 @@ export async function initWhitelist () {
             };
         }
     }
-    }
+}
 
 
-    /**
+/**
  * Sender applications load a cast_sender.js script that
  * functions as a loader for the internal chrome-extension:
  * hosted script.
@@ -106,7 +137,7 @@ export async function initWhitelist () {
  * We can redirect this and inject our own script to setup
  * the API shim.
  */
-    async function onBeforeCastSDKRequest (details: OnBeforeRequestDetails) {
+async function onBeforeCastSDKRequest (details: OnBeforeRequestDetails) {
     if (!details.originUrl) {
         return {};
     }
@@ -149,10 +180,10 @@ export async function initWhitelist () {
     return {
         redirectUrl: browser.runtime.getURL("shim/bundle.js")
     };
-    }
+}
 
 
-    async function registerUserAgentWhitelist () {
+async function registerUserAgentWhitelist () {
     const { userAgentWhitelist
           , userAgentWhitelistEnabled } = await options.getAll();
 
@@ -176,9 +207,9 @@ export async function initWhitelist () {
             onWhitelistedChildBeforeSendHeaders
           , { urls: [ "<all_urls>" ] }
           , [ "blocking", "requestHeaders" ]);
-    }
+}
 
-    function unregisterUserAgentWhitelist () {
+function unregisterUserAgentWhitelist () {
     originUrlCache.length = 0;
 
     browser.webRequest.onBeforeSendHeaders
@@ -187,19 +218,4 @@ export async function initWhitelist () {
             .removeListener(onWhitelistedChildBeforeSendHeaders);
     browser.webRequest.onBeforeRequest
             .removeListener(onBeforeCastSDKRequest);
-    }
-
-    // Register on first run
-    await registerUserAgentWhitelist();
-
-    // Re-register when options change
-    options.addEventListener("changed", ev => {
-        const alteredOpts = ev.detail;
-
-        if (alteredOpts.includes("userAgentWhitelist")
-         || alteredOpts.includes("userAgentWhitelistEnabled")) {
-            unregisterUserAgentWhitelist();
-            registerUserAgentWhitelist();
-        }
-    });
 }