Detect when WebView is broken and return null poToken

Some old Android devices have a broken WebView implementation, that can't execute the poToken code. This is now detected and the getWebClientPoToken return null instead of throwing an error in such a case, to allow the extractor to try to extract the video data even without a poToken.

app/src/main/java/org/schabi/newpipe/util/potoken/PoTokenException.kt

@@ -1,3 +1,13 @@
 package org.schabi.newpipe.util.potoken
 
 class PoTokenException(message: String) : Exception(message)
+
+// to be thrown if the WebView provided by the system is broken
+class BadWebViewException(message: String) : Exception(message)
+
+fun buildExceptionForJsError(error: String): Exception {
+    return if (error.contains("SyntaxError"))
+        BadWebViewException(error)
+    else
+        PoTokenException(error)
+}

app/src/main/java/org/schabi/newpipe/util/potoken/PoTokenProviderImpl.kt

@@ -15,6 +15,7 @@ import org.schabi.newpipe.util.DeviceUtils
 object PoTokenProviderImpl : PoTokenProvider {
     val TAG = PoTokenProviderImpl::class.simpleName
     private val webViewSupported by lazy { DeviceUtils.supportsWebView() }
+    private var webViewBadImpl = false // whether the system has a bad WebView implementation
 
     private object WebPoTokenGenLock
     private var webPoTokenVisitorData: String? = null
@@ -22,11 +23,24 @@ object PoTokenProviderImpl : PoTokenProvider {
     private var webPoTokenGenerator: PoTokenGenerator? = null
 
     override fun getWebClientPoToken(videoId: String): PoTokenResult? {
-        if (!webViewSupported) {
+        if (!webViewSupported || webViewBadImpl) {
             return null
         }
 
-        return getWebClientPoToken(videoId = videoId, forceRecreate = false)
+        try {
+            return getWebClientPoToken(videoId = videoId, forceRecreate = false)
+        } catch (e: RuntimeException) {
+            // RxJava's Single wraps exceptions into RuntimeErrors, so we need to unwrap them here
+            when (val cause = e.cause) {
+                is BadWebViewException -> {
+                    Log.e(TAG, "Could not obtain poToken because WebView is broken", e)
+                    webViewBadImpl = true
+                    return null
+                }
+                null -> throw e
+                else -> throw cause // includes PoTokenException
+            }
+        }
     }
 
     /**

app/src/main/java/org/schabi/newpipe/util/potoken/PoTokenWebView.kt

@@ -5,7 +5,9 @@ import android.os.Build
 import android.os.Handler
 import android.os.Looper
 import android.util.Log
+import android.webkit.ConsoleMessage
 import android.webkit.JavascriptInterface
+import android.webkit.WebChromeClient
 import android.webkit.WebView
 import androidx.annotation.MainThread
 import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
@@ -40,6 +42,24 @@ class PoTokenWebView private constructor(
 
         // so that we can run async functions and get back the result
         webView.addJavascriptInterface(this, JS_INTERFACE)
+
+        webView.webChromeClient = object : WebChromeClient() {
+            override fun onConsoleMessage(m: ConsoleMessage): Boolean {
+                if (m.message().contains("Uncaught")) {
+                    // There should not be any uncaught errors while executing the code, because
+                    // everything that can fail is guarded by try-catch. Therefore, this likely
+                    // indicates that there was a syntax error in the code, i.e. the WebView only
+                    // supports a really old version of JS.
+
+                    val fmt = "\"${m.message()}\", source: ${m.sourceId()} (${m.lineNumber()})"
+                    Log.e(TAG, "This WebView implementation is broken: $fmt")
+
+                    // This can only happen during initialization, where there is no try-catch
+                    onInitializationErrorCloseAndCancel(BadWebViewException(fmt))
+                }
+                return super.onConsoleMessage(m)
+            }
+        }
     }
 
     /**
@@ -117,7 +137,7 @@ class PoTokenWebView private constructor(
         if (BuildConfig.DEBUG) {
             Log.e(TAG, "Initialization error from JavaScript: $error")
         }
-        onInitializationErrorCloseAndCancel(PoTokenException(error))
+        onInitializationErrorCloseAndCancel(buildExceptionForJsError(error))
     }
 
     /**
@@ -223,7 +243,7 @@ class PoTokenWebView private constructor(
         if (BuildConfig.DEBUG) {
             Log.e(TAG, "obtainPoToken error from JavaScript: $error")
         }
-        popPoTokenEmitter(identifier)?.onError(PoTokenException(error))
+        popPoTokenEmitter(identifier)?.onError(buildExceptionForJsError(error))
     }
 
     /**