feat: add Android browser preset for companion device registration (#248)

* feat: add Android browser preset for companion device registration

Add Browsers.android(apiLevel) preset that identifies as an Android
companion device (SMB_ANDROID platform, ANDROID_PHONE device type).
Validated against Frida captures of real WhatsApp Android protocol.


* feat: support BAILEYS_BROWSER env var for browser selection

Allows selecting Android companion mode via environment variable
without code changes. Set BAILEYS_BROWSER=android (or android:15
for a specific API level) to register as an Android device.

* fix: auto-detect Android browser in pair code and fall back to Chrome

Pair code companion registration fails with Android browser because the
WA server rejects the ANDROID_PHONE companion_platform_id over the web
Noise protocol. When Android is detected, requestPairingCode() now
transparently uses Chrome/macOS platform values for the pair code stanza
while QR code pairing continues to work as Android (SMB_ANDROID).

* docs: add android to isValidBrowserPreset JSDoc

src/Defaults/index.ts

@@ -56,10 +56,26 @@ export const PROCESSABLE_HISTORY_TYPES = [
 // 6 hours in milliseconds
 const SIX_HOURS_MS = 6 * 60 * 60 * 1000
 
+/**
+ * Resolves the default browser tuple from the BAILEYS_BROWSER env var.
+ *   'android'    → Browsers.android('14')
+ *   'android:15' → Browsers.android('15')
+ *   unset / other → Browsers.macOS('Chrome')
+ */
+const resolveDefaultBrowser = (): [string, string, string] => {
+	const env = process.env.BAILEYS_BROWSER?.trim().toLowerCase()
+	if (env?.startsWith('android')) {
+		const apiLevel = env.split(':')[1] || '14'
+		return Browsers.android(apiLevel)
+	}
+
+	return Browsers.macOS('Chrome')
+}
+
 export const DEFAULT_CONNECTION_CONFIG: SocketConfig = {
 	version: version as WAVersion,
 	versionCheckIntervalMs: SIX_HOURS_MS,
-	browser: Browsers.macOS('Chrome'),
+	browser: resolveDefaultBrowser(),
 	waWebSocketUrl: 'wss://web.whatsapp.com/ws/chat',
 	connectTimeoutMs: 20_000,
 	keepAliveIntervalMs: 15_000,

src/Socket/socket.ts

@@ -38,7 +38,7 @@ import {
 	signedKeyPair,
 	xmppSignedPreKey
 } from '../Utils'
-import { getPlatformId } from '../Utils/browser-utils'
+import { getPlatformId, isAndroidBrowser } from '../Utils/browser-utils'
 import {
 	CircuitBreaker,
 	CircuitOpenError,
@@ -1352,6 +1352,14 @@ export const makeSocket = (config: SocketConfig) => {
 			id: jidEncode(phoneNumber, 's.whatsapp.net'),
 			name: '~'
 		}
+
+		// Pair code with Android browser doesn't work (WA server rejects the
+		// companion registration). When Android is detected, fall back to the
+		// Chrome/macOS platform values that are known to work.
+		const isAndroid = isAndroidBrowser(browser)
+		const pairPlatformId = isAndroid ? getPlatformId('Chrome') : getPlatformId(browser[1])
+		const pairPlatformDisplay = isAndroid ? 'Chrome (Mac OS)' : `${browser[1]} (${browser[0]})`
+
 		ev.emit('creds.update', authState.creds)
 		await sendNode({
 			tag: 'iq',
@@ -1384,12 +1392,12 @@ export const makeSocket = (config: SocketConfig) => {
 						{
 							tag: 'companion_platform_id',
 							attrs: {},
-							content: getPlatformId(browser[1])
+							content: pairPlatformId
 						},
 						{
 							tag: 'companion_platform_display',
 							attrs: {},
-							content: `${browser[1]} (${browser[0]})`
+							content: pairPlatformDisplay
 						},
 						{
 							tag: 'link_code_pairing_nonce',

src/Types/index.ts

@@ -23,6 +23,7 @@ export type BrowsersMap = {
 	baileys(browser: string): [string, string, string]
 	windows(browser: string): [string, string, string]
 	appropriate(browser: string): [string, string, string]
+	android(apiLevel: string): [string, string, string]
 }
 
 export enum DisconnectReason {

src/Utils/browser-utils.ts

@@ -94,7 +94,13 @@ const BROWSER_TO_PLATFORM_ID: ReadonlyMap<string, string> = (() => {
 		}
 	}
 
-	return new Map(entries)
+	const map = new Map(entries)
+	// ANDROID → ANDROID_PHONE alias (DeviceProps.PlatformType has ANDROID_PHONE but not ANDROID)
+	if (!map.has('ANDROID') && map.has('ANDROID_PHONE')) {
+		map.set('ANDROID', map.get('ANDROID_PHONE')!)
+	}
+
+	return map
 })()
 
 // ============================================================
@@ -331,7 +337,8 @@ export const Browsers: BrowsersMap = {
 	macOS: (browser: string): [string, string, string] => ['Mac OS', browser, OS_VERSIONS.macOS],
 	windows: (browser: string): [string, string, string] => ['Windows', browser, OS_VERSIONS.windows],
 	baileys: (browser: string): [string, string, string] => ['Baileys', browser, OS_VERSIONS.baileys],
-	appropriate: (browser: string): [string, string, string] => [getPlatformName(), browser, getAppropriateVersion()]
+	appropriate: (browser: string): [string, string, string] => [getPlatformName(), browser, getAppropriateVersion()],
+	android: (apiLevel: string): [string, string, string] => [apiLevel, 'Android', '']
 } as const
 
 /**
@@ -378,7 +385,7 @@ export const getPlatformId = (browser: unknown): string => {
  * properties like 'toString' or 'constructor'.
  *
  * @param value - Value to check
- * @returns True if value is a valid browser preset key ('ubuntu', 'macOS', 'windows', 'baileys', 'appropriate')
+ * @returns True if value is a valid browser preset key ('ubuntu', 'macOS', 'windows', 'baileys', 'appropriate', 'android')
  *
  * @example
  * isValidBrowserPreset('ubuntu')      // true
@@ -391,6 +398,16 @@ export const getPlatformId = (browser: unknown): string => {
  *   const config = Browsers[userInput]('MyApp')
  * }
  */
+/**
+ * Checks if the browser tuple represents an Android companion device.
+ *
+ * @param browser - Browser tuple [os, platform, version]
+ * @returns True if platform is 'Android' (case-insensitive)
+ */
+export const isAndroidBrowser = (browser: [string, string, string]): boolean => {
+	return browser[1]?.toUpperCase() === 'ANDROID'
+}
+
 export const isValidBrowserPreset = (value: unknown): value is keyof BrowsersMap => {
 	return typeof value === 'string' && Object.prototype.hasOwnProperty.call(Browsers, value)
 }

src/Utils/validate-connection.ts

@@ -9,24 +9,27 @@ import {
 } from '../Defaults'
 import type { AuthenticationCreds, SignalCreds, SocketConfig } from '../Types'
 import { type BinaryNode, getBinaryNodeChild, jidDecode, S_WHATSAPP_NET } from '../WABinary'
+import { isAndroidBrowser } from './browser-utils'
 import { Curve, hmacSign } from './crypto'
 import { encodeBigEndian } from './generics'
 import { createSignalIdentity } from './signal'
 
 const getUserAgent = (config: SocketConfig): proto.ClientPayload.IUserAgent => {
+	const isAndroid = isAndroidBrowser(config.browser)
 	return {
 		appVersion: {
 			primary: config.version[0],
 			secondary: config.version[1],
 			tertiary: config.version[2]
 		},
-		platform: proto.ClientPayload.UserAgent.Platform.MACOS,
+		platform: isAndroid
+			? proto.ClientPayload.UserAgent.Platform.SMB_ANDROID
+			: proto.ClientPayload.UserAgent.Platform.MACOS,
 		releaseChannel: proto.ClientPayload.UserAgent.ReleaseChannel.RELEASE,
-		osVersion: '0.1',
-		device: 'Desktop',
+		osVersion: isAndroid ? config.browser[0] : '0.1',
+		device: isAndroid ? 'Android' : 'Desktop',
 		osBuildNumber: '0.1',
 		localeLanguageIso6391: 'en',
-
 		mnc: '000',
 		mcc: '000',
 		localeCountryIso31661Alpha2: config.countryCode
@@ -58,7 +61,9 @@ const getClientPayload = (config: SocketConfig) => {
 		userAgent: getUserAgent(config)
 	}
 
-	payload.webInfo = getWebInfo(config)
+	if (!isAndroidBrowser(config.browser)) {
+		payload.webInfo = getWebInfo(config)
+	}
 
 	return payload
 }
@@ -84,6 +89,10 @@ export const generateLoginNode = (userJid: string, config: SocketConfig): proto.
 
 const getPlatformType = (platform: string): proto.DeviceProps.PlatformType => {
 	const platformType = platform.toUpperCase()
+	if (platformType === 'ANDROID') {
+		return proto.DeviceProps.PlatformType.ANDROID_PHONE
+	}
+
 	return (
 		proto.DeviceProps.PlatformType[platformType as keyof typeof proto.DeviceProps.PlatformType] ||
 		proto.DeviceProps.PlatformType.CHROME