Add periodic user agent string updates

docs/ua.json

@@ -0,0 +1,9 @@
+{
+    "$schema": "./ua.schema.json",
+    "version": 1,
+    "platforms": {
+        "win": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/143.0.0.0 Safari/537.36",
+        "mac": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/143.0.0.0 Safari/537.36",
+        "linux": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/143.0.0.0 Safari/537.36"
+    }
+}

docs/ua.schema.json

@@ -0,0 +1,22 @@
+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$defs": {
+        "ua_string": { "type": "string", "minLength": 1 }
+    },
+    "properties": {
+        "$schema": { "type": "string" },
+        "version": { "type": "integer", "const": 1 },
+        "platforms": {
+            "type": "object",
+            "properties": {
+                "win": { "$ref": "#/$defs/ua_string" },
+                "mac": { "$ref": "#/$defs/ua_string" },
+                "linux": { "$ref": "#/$defs/ua_string" }
+            },
+            "required": ["win", "mac", "linux"],
+            "additionalProperties": false
+        }
+    },
+    "required": ["version", "platforms"],
+    "additionalProperties": false
+}

extension/src/background/background.ts

@@ -12,6 +12,7 @@ import deviceManager from "./deviceManager";
 import { initAction } from "./action";
 import { initMenus } from "./menus";
 import { initWhitelist } from "./whitelist";
+import { cacheUaInfo, getChromeUserAgentString } from "../lib/userAgents";
 
 const _ = browser.i18n.getMessage;
 
@@ -143,5 +144,6 @@ async function init() {
     });
 }
 
+cacheUaInfo();
 cacheBaseConfig();
 init();

extension/src/background/whitelist.ts

@@ -1,7 +1,7 @@
 import logger from "../lib/logger";
 import options from "../lib/options";
 
-import { getChromeUserAgent } from "../lib/userAgents";
+import { cacheUaInfo, getChromeUserAgentString } from "../lib/userAgents";
 import { RemoteMatchPattern } from "../lib/matchPattern";
 
 import {
@@ -41,11 +41,17 @@ let customUserAgent: string | undefined;
 export async function initWhitelist() {
     logger.info("init (whitelist)");
 
+    await cacheUaInfo();
+
     if (!platform) {
+        const browserInfo = await browser.runtime.getBrowserInfo();
+
         // TODO: Allow hybrid UA to be configurable
         platform = (await browser.runtime.getPlatformInfo()).os;
-        chromeUserAgent = getChromeUserAgent(platform);
-        chromeUserAgentHybrid = getChromeUserAgent(platform, true);
+        chromeUserAgent = await getChromeUserAgentString(platform);
+        chromeUserAgentHybrid = await getChromeUserAgentString(platform, {
+            hybridFirefoxVersion: browserInfo.version
+        });
         if (!chromeUserAgent) {
             throw logger.error("Failed to get Chrome UA string");
         }

extension/src/defaultOptions.ts

@@ -106,4 +106,4 @@ export default {
     siteWhitelistCustomUserAgent: "",
 
     showAdvancedOptions: false
-} as Options;
+} satisfies Options as Options;

extension/src/lib/userAgents.ts

@@ -1,25 +1,90 @@
-const PLATFORM_MAC = "Macintosh; Intel Mac OS X 12_5";
-const PLATFORM_MAC_HYBRID = "Macintosh; Intel Mac OS X 12_5; rv:103.0";
-const PLATFORM_WIN = "Windows NT 10.0; Win64; x64";
-const PLATFORM_LINUX = "X11; Linux x86_64";
+import logger from "./logger";
+import { TypedStorageArea } from "./TypedStorageArea";
 
-const UA_CHROME =
-    "AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36";
-const UA_HYBRID = "Chrome/104.0.0.0 Gecko/20100101 Firefox/103.0";
+// Bundle UA info at time of build (as a fallback)
+import bundledUaInfo from "../../../docs/ua.json";
 
-export function getChromeUserAgent(platform: string, hybrid = false) {
-    let platformComponent: string;
-    if (platform === "mac") {
-        platformComponent = hybrid ? PLATFORM_MAC_HYBRID : PLATFORM_MAC;
-    } else if (platform === "win") {
-        platformComponent = PLATFORM_WIN;
-    } else if (platform === "linux") {
-        platformComponent = PLATFORM_LINUX;
-    } else {
-        return;
-    }
+const UA_INFO_ENDPOINT = "https://hensm.github.io/fx_cast/ua.json";
 
-    const browserComponent = hybrid ? UA_HYBRID : UA_CHROME;
-
-    return `Mozilla/5.0 (${platformComponent}) ${browserComponent}`;
+interface UaInfo {
+    version: 1;
+    platforms: {
+        [key: string]: string;
+    };
+}
+
+const uaInfoStorage = new TypedStorageArea<{
+    uaInfo: UaInfo | undefined;
+    uaInfoUpdated: number | undefined;
+}>(browser.storage.local);
+
+async function fetchUaInfo(): Promise<UaInfo | null> {
+    try {
+        const res: UaInfo = await fetch(UA_INFO_ENDPOINT).then(r => r.json());
+        if (typeof res.version !== "number" || res.version !== 1) {
+            throw logger.error(
+                `UA info version mismatch (got ${res.version}, expected 1)`
+            );
+        } else if (
+            typeof res.platforms !== "object" ||
+            res.platforms === null
+        ) {
+            throw logger.error("UA info platforms missing or invalid");
+        }
+        return res;
+    } catch (err) {
+        logger.error("Failed to fetch UA info:", err);
+        return null;
+    }
+}
+
+export async function cacheUaInfo() {
+    const { uaInfoUpdated } = await uaInfoStorage.get("uaInfoUpdated");
+
+    // If never updated or updated more than 24 hours ago
+    if (!uaInfoUpdated || (Date.now() - uaInfoUpdated) / 1000 >= 86400) {
+        logger.info("Fetching updated Chrome User-Agent strings...");
+        const uaInfo = await fetchUaInfo();
+        if (uaInfo) {
+            await uaInfoStorage.set({ uaInfo, uaInfoUpdated: Date.now() });
+        }
+    }
+}
+
+/** Get a chrome user */
+export async function getChromeUserAgentString(
+    platform: string,
+    opts?: { hybridFirefoxVersion?: string }
+) {
+    const { uaInfo } = await uaInfoStorage.get("uaInfo");
+    if (!uaInfo) {
+        logger.warn("UA info not cached (using bundled version)");
+    }
+    const maybeBundledUaInfo = uaInfo ?? (bundledUaInfo as UaInfo);
+    const userAgentString = maybeBundledUaInfo.platforms[platform];
+    if (userAgentString) {
+        // Return hybrid UA (mostly Firefox UA) if requested
+        if (opts?.hybridFirefoxVersion) {
+            // Sans-patch (e.g. "145.0.1" -> "145.0")
+            const firefoxMajorMinorVersionMatch =
+                opts.hybridFirefoxVersion.match(/^\d+\.\d+/);
+            const componentMatch = userAgentString.match(
+                /Mozilla\/5.0 \(([^\(]+)\) (.+)/
+            );
+            if (firefoxMajorMinorVersionMatch && componentMatch) {
+                const [rv] = firefoxMajorMinorVersionMatch;
+                const [, platformComponent, browserComponent] = componentMatch;
+                // Extract Chrome/xxx part
+                const chromeVersionMatch = browserComponent.match(
+                    /(?<= )Chrome\/[^ ]+(?= )/
+                );
+                if (chromeVersionMatch) {
+                    const [chromeVersion] = chromeVersionMatch;
+                    return `Mozilla/5.0 (${platformComponent}; rv:${rv}) ${chromeVersion} Gecko/20100101 Firefox/${rv}`;
+                }
+            }
+        } else {
+            return userAgentString;
+        }
+    }
 }

extension/src/ui/options/Options.svelte

@@ -10,7 +10,7 @@
     import options, { Options } from "../../lib/options";
     import defaultOptions from "../../defaultOptions";
 
-    import { getChromeUserAgent } from "../../lib/userAgents";
+    import { getChromeUserAgentString } from "../../lib/userAgents";
 
     const _ = browser.i18n.getMessage;
 
@@ -23,7 +23,7 @@
     let opts: Options | undefined;
     onMount(async () => {
         const platform = (await browser.runtime.getPlatformInfo()).os;
-        defaultUserAgent = getChromeUserAgent(platform);
+        defaultUserAgent = await getChromeUserAgentString(platform);
 
         opts = await options.getAll();
         options.addEventListener("changed", async () => {