Issue 4399 - Add WebView inheritor with ad blocking

libadblockplus-android-webview/src/org/adblockplus/android/AdblockWebView.java

Index: libadblockplus-android-webview/src/org/adblockplus/android/AdblockWebView.java
diff --git a/libadblockplus-android-webview/src/org/adblockplus/android/AdblockWebView.java b/libadblockplus-android-webview/src/org/adblockplus/android/AdblockWebView.java
new file mode 100644
index 0000000000000000000000000000000000000000..ce120fc6fcad4c717614b705571e06b4882c7896
--- /dev/null
+++ b/libadblockplus-android-webview/src/org/adblockplus/android/AdblockWebView.java
@@ -0,0 +1,1474 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-2016 Eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.adblockplus.android;
+
+import org.adblockplus.libadblockplus.AppInfo;
+import org.adblockplus.libadblockplus.Filter;
+import org.adblockplus.libadblockplus.FilterEngine;
+import org.adblockplus.libadblockplus.JsEngine;
+import org.adblockplus.libadblockplus.Subscription;
+
+import android.content.Context;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.net.http.SslError;
+import android.os.Build;
+import android.os.Handler;
+import android.os.Message;
+import android.util.AttributeSet;
+import android.util.Log;
+import android.view.KeyEvent;
+import android.view.View;
+import android.webkit.ConsoleMessage;
+import android.webkit.GeolocationPermissions;
+import android.webkit.HttpAuthHandler;
+import android.webkit.JsPromptResult;
+import android.webkit.JsResult;
+import android.webkit.SslErrorHandler;
+import android.webkit.ValueCallback;
+import android.webkit.WebChromeClient;
+import android.webkit.WebResourceRequest;  // makes android min version to be 21
+import android.webkit.WebResourceResponse;
+import android.webkit.WebStorage;
+import android.webkit.WebView;
+import android.webkit.JavascriptInterface; // makes android min version to be 17
+import android.webkit.WebViewClient;
+
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.regex.Pattern;
+
+/**
+ * WebView with ad blocking
+ */
+public class AdblockWebView extends WebView
+{
+  private static final String TAG = Utils.getTag(AdblockWebView.class);
+
+  private volatile boolean addDomListener = true;
+
+  /**
+   * Warning: do not rename (used in injected JS by method name)
+   * @param value set if one need to set DOM listener
+   */
+  @JavascriptInterface
+  public void setAddDomListener(boolean value)
+  {
+    this.addDomListener = value;
+  }
+
+  @JavascriptInterface
+  public boolean getAddDomListener()
+  {
+    return addDomListener;
+  }
+
+  private WebChromeClient extWebChromeClient;
+
+  @Override
+  public void setWebChromeClient(WebChromeClient client)
+  {
+    extWebChromeClient = client;
+  }
+
+  private boolean debugMode;
+
+  public boolean isDebugMode()
+  {
+    return debugMode;
+  }
+
+  /**
+   * Set to true to see debug log output int AdblockWebView and JS console
+   * @param debugMode is debug mode
+   */
+  public void setDebugMode(boolean debugMode)
+  {
+    this.debugMode = debugMode;
+  }
+
+  private void d(String message)
+  {
+    if (debugMode)
+    {
+      Log.d(TAG, message);
+    }
+  }
+
+  private void w(String message)
+  {
+    if (debugMode)
+    {
+      Log.w(TAG, message);
+    }
+  }
+
+  private void e(String message, Throwable t)
+  {
+    Log.e(TAG, message, t);
+  }
+
+  private void e(String message)
+  {
+    Log.e(TAG, message);
+  }
+
+  private static final String BRIDGE_TOKEN = "{{BRIDGE}}";
+  private static final String DEBUG_TOKEN = "{{DEBUG}}";
+  private static final String HIDE_TOKEN = "{{HIDE}}";
+  private static final String BRIDGE = "jsBridge";
+
+  private String readScriptFile(String filename) throws IOException
+  {
+    return Utils
+      .readAssetAsString(getContext(), filename)
+      .replace(BRIDGE_TOKEN, BRIDGE)
+      .replace(DEBUG_TOKEN, (debugMode ? "" : "//"));
+  }
+
+  private void runScript(String script)
+  {
+    if (Build.VERSION.SDK_INT >= 19)
+    {
+      evaluateJavascript(script, null);
+    }
+    else
+    {
+      loadUrl("javascript:" + script);
+    }
+  }
+
+  private Subscription acceptableAdsSubscription;
+
+  private boolean acceptableAdsEnabled = true;
+
+  public boolean isAcceptableAdsEnabled()
+  {
+    return acceptableAdsEnabled;
+  }
+
+  /**
+   * Enable or disable Acceptable Ads
+   * @param enabled enabled
+   */
+  public void setAcceptableAdsEnabled(boolean enabled)
+  {
+    this.acceptableAdsEnabled = enabled;
+
+    if (filterEngine != null)
+    {
+      applyAcceptableAds();
+    }
+  }
+
+  private final static String EXCEPTIONS_URL = "subscriptions_exceptionsurl";
+
+  private void applyAcceptableAds()
+  {
+    if (acceptableAdsEnabled)
+    {
+      if (acceptableAdsSubscription == null)
+      {
+        String url = filterEngine.getPref(EXCEPTIONS_URL).toString();
+        if (url == null)
+        {
+          w("no AA subscription url");
+          return;
+        }
+
+        acceptableAdsSubscription = filterEngine.getSubscription(url);
+        acceptableAdsSubscription.addToList();
+        d("AA subscription added (" + url + ")");
+      }
+    }
+    else
+    {
+      if (acceptableAdsSubscription != null)
+      {
+        removeAcceptableAdsSubscription();
+      }
+    }
+  }
+
+  private void removeAcceptableAdsSubscription()
+  {
+    acceptableAdsSubscription.removeFromList();
+    acceptableAdsSubscription = null;
+    d("AA subscription removed");
+  }
+
+  private boolean disposeFilterEngine;
+
+  private JsEngine jsEngine;
+
+  public JsEngine getJsEngine()
+  {
+    return jsEngine;
+  }
+
+  private FilterEngine filterEngine;
+
+  public FilterEngine getFilterEngine()
+  {
+    return filterEngine;
+  }
+
+  private Integer loadError;
+
+  /**
+   * Set external filter engine. A new (internal) is created automatically if not set
+   * Don't forget to invoke {@link #dispose()} if not using external filter engine
+   * @param newFilterEngine external filter engine
+   */
+  public void setFilterEngine(FilterEngine newFilterEngine)
+  {
+    if (filterEngine != null && newFilterEngine != null && newFilterEngine == filterEngine)
+    {
+      return;
+    }
+
+    if (filterEngine != null)
+    {
+      if (acceptableAdsEnabled && acceptableAdsSubscription != null)
+      {
+        removeAcceptableAdsSubscription();
+      }
+
+      if (disposeFilterEngine)
+      {
+        filterEngine.dispose();
+      }
+    }
+
+    filterEngine = newFilterEngine;
+    disposeFilterEngine = false;
+
+    if (filterEngine != null)
+    {
+      applyAcceptableAds();
+
+      if (jsEngine != null)
+      {
+        jsEngine.dispose();
+      }
+    }
+
+    jsEngine = null;
+  }
+
+  private WebChromeClient intWebChromeClient = new WebChromeClient()
+  {
+    @Override
+    public void onReceivedTitle(WebView view, String title)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onReceivedTitle(view, title);
+      }
+    }
+
+    @Override
+    public void onReceivedIcon(WebView view, Bitmap icon)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onReceivedIcon(view, icon);
+      }
+    }
+
+    @Override
+    public void onReceivedTouchIconUrl(WebView view, String url, boolean precomposed)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onReceivedTouchIconUrl(view, url, precomposed);
+      }
+    }
+
+    @Override
+    public void onShowCustomView(View view, CustomViewCallback callback)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onShowCustomView(view, callback);
+      }
+    }
+
+    @Override
+    public void onShowCustomView(View view, int requestedOrientation, CustomViewCallback callback)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onShowCustomView(view, requestedOrientation, callback);
+      }
+    }
+
+    @Override
+    public void onHideCustomView()
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onHideCustomView();
+      }
+    }
+
+    @Override
+    public boolean onCreateWindow(WebView view, boolean isDialog, boolean isUserGesture,
+                                  Message resultMsg)
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onCreateWindow(view, isDialog, isUserGesture, resultMsg);
+      }
+      else
+      {
+        return super.onCreateWindow(view, isDialog, isUserGesture, resultMsg);
+      }
+    }
+
+    @Override
+    public void onRequestFocus(WebView view)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onRequestFocus(view);
+      }
+    }
+
+    @Override
+    public void onCloseWindow(WebView window)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onCloseWindow(window);
+      }
+    }
+
+    @Override
+    public boolean onJsAlert(WebView view, String url, String message, JsResult result)
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onJsAlert(view, url, message, result);
+      }
+      else
+      {
+        return super.onJsAlert(view, url, message, result);
+      }
+    }
+
+    @Override
+    public boolean onJsConfirm(WebView view, String url, String message, JsResult result)
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onJsConfirm(view, url, message, result);
+      }
+      else
+      {
+        return super.onJsConfirm(view, url, message, result);
+      }
+    }
+
+    @Override
+    public boolean onJsPrompt(WebView view, String url, String message, String defaultValue,
+                              JsPromptResult result)
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onJsPrompt(view, url, message, defaultValue, result);
+      }
+      else
+      {
+        return super.onJsPrompt(view, url, message, defaultValue, result);
+      }
+    }
+
+    @Override
+    public boolean onJsBeforeUnload(WebView view, String url, String message, JsResult result)
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onJsBeforeUnload(view, url, message, result);
+      }
+      else
+      {
+        return super.onJsBeforeUnload(view, url, message, result);
+      }
+    }
+
+    @Override
+    public void onExceededDatabaseQuota(String url, String databaseIdentifier, long quota,
+                                        long estimatedDatabaseSize, long totalQuota,
+                                        WebStorage.QuotaUpdater quotaUpdater)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onExceededDatabaseQuota(url, databaseIdentifier, quota,
+          estimatedDatabaseSize, totalQuota, quotaUpdater);
+      }
+      else
+      {
+        super.onExceededDatabaseQuota(url, databaseIdentifier, quota,
+          estimatedDatabaseSize, totalQuota, quotaUpdater);
+      }
+    }
+
+    @Override
+    public void onReachedMaxAppCacheSize(long requiredStorage, long quota,
+                                         WebStorage.QuotaUpdater quotaUpdater)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onReachedMaxAppCacheSize(requiredStorage, quota, quotaUpdater);
+      }
+      else
+      {
+        super.onReachedMaxAppCacheSize(requiredStorage, quota, quotaUpdater);
+      }
+    }
+
+    @Override
+    public void onGeolocationPermissionsShowPrompt(String origin,
+                                                   GeolocationPermissions.Callback callback)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onGeolocationPermissionsShowPrompt(origin, callback);
+      }
+      else
+      {
+        super.onGeolocationPermissionsShowPrompt(origin, callback);
+      }
+    }
+
+    @Override
+    public void onGeolocationPermissionsHidePrompt()
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onGeolocationPermissionsHidePrompt();
+      }
+      else
+      {
+        super.onGeolocationPermissionsHidePrompt();
+      }
+    }
+
+    @Override
+    public boolean onJsTimeout()
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onJsTimeout();
+      }
+      else
+      {
+        return super.onJsTimeout();
+      }
+    }
+
+    @Override
+    public void onConsoleMessage(String message, int lineNumber, String sourceID)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onConsoleMessage(message, lineNumber, sourceID);
+      }
+      else
+      {
+        super.onConsoleMessage(message, lineNumber, sourceID);
+      }
+    }
+
+    @Override
+    public boolean onConsoleMessage(ConsoleMessage consoleMessage)
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.onConsoleMessage(consoleMessage);
+      }
+      else
+      {
+        return super.onConsoleMessage(consoleMessage);
+      }
+    }
+
+    @Override
+    public Bitmap getDefaultVideoPoster()
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.getDefaultVideoPoster();
+      }
+      else
+      {
+        return super.getDefaultVideoPoster();
+      }
+    }
+
+    @Override
+    public View getVideoLoadingProgressView()
+    {
+      if (extWebChromeClient != null)
+      {
+        return extWebChromeClient.getVideoLoadingProgressView();
+      }
+      else
+      {
+        return super.getVideoLoadingProgressView();
+      }
+    }
+
+    @Override
+    public void getVisitedHistory(ValueCallback<String[]> callback)
+    {
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.getVisitedHistory(callback);
+      }
+      else
+      {
+        super.getVisitedHistory(callback);
+      }
+    }
+
+    @Override
+    public void onProgressChanged(WebView view, int newProgress)
+    {
+      d("Loading progress=" + newProgress + "%");
+
+      // addDomListener is changed to 'false' in `setAddDomListener` invoked from injected JS
+      if (getAddDomListener() && loadError == null && injectJs != null)
+      {
+        d("Injecting script");
+        runScript(injectJs);
+
+        if (allowDraw && loading)
+        {
+          startPreventDrawing();
+        }
+      }
+
+      if (extWebChromeClient != null)
+      {
+        extWebChromeClient.onProgressChanged(view, newProgress);
+      }
+    }
+  };
+
+  /**
+   * Default (in some conditions) start redraw delay after DOM modified with injected JS (millis)
+   */
+  public static final int ALLOW_DRAW_DELAY = 200;
+  /*
+     The value could be different for devices and completely unclear why we need it and
+     how to measure actual value
+  */
+
+  private int allowDrawDelay = ALLOW_DRAW_DELAY;
+
+  public int getAllowDrawDelay()
+  {
+    return allowDrawDelay;
+  }
+
+  /**
+   * Set start redraw delay after DOM modified with injected JS
+   * (used to prevent flickering after 'DOM ready')
+   * @param allowDrawDelay delay (in millis)
+   */
+  public void setAllowDrawDelay(int allowDrawDelay)
+  {
+    if (allowDrawDelay < 0)
+      throw new IllegalArgumentException("Negative value is not allowed");
+
+    this.allowDrawDelay = allowDrawDelay;
+  }
+
+  private WebViewClient extWebViewClient;
+
+  @Override
+  public void setWebViewClient(WebViewClient client)
+  {
+    extWebViewClient = client;
+  }
+
+  private static final Pattern RE_JS = Pattern.compile("\\.js$", Pattern.CASE_INSENSITIVE);
+  private static final Pattern RE_CSS = Pattern.compile("\\.css$", Pattern.CASE_INSENSITIVE);
+  private static final Pattern RE_IMAGE = Pattern.compile("\\.(?:gif|png|jpe?g|bmp|ico)$", Pattern.CASE_INSENSITIVE);
+  private static final Pattern RE_FONT = Pattern.compile("\\.(?:ttf|woff)$", Pattern.CASE_INSENSITIVE);
+  private static final Pattern RE_HTML = Pattern.compile("\\.html?$", Pattern.CASE_INSENSITIVE);
+
+  private WebViewClient intWebViewClient;
+
+  /**
+   * WebViewClient for API pre 21
+   * (does not have Referers information)
+   */
+  class AdblockWebViewClient extends WebViewClient
+  {
+    @Override
+    public boolean shouldOverrideUrlLoading(WebView view, String url)
+    {
+      if (extWebViewClient != null)
+      {
+        return extWebViewClient.shouldOverrideUrlLoading(view, url);
+      }
+      else
+      {
+        return super.shouldOverrideUrlLoading(view, url);
+      }
+    }
+
+    @Override
+    public void onPageStarted(WebView view, String url, Bitmap favicon)
+    {
+      if (loading)
+      {
+        stopAbpLoading();
+      }
+
+      startAbpLoading(url);
+
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onPageStarted(view, url, favicon);
+      }
+      else
+      {
+        super.onPageStarted(view, url, favicon);
+      }
+    }
+
+    @Override
+    public void onPageFinished(WebView view, String url)
+    {
+      loading = false;
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onPageFinished(view, url);
+      }
+      else
+      {
+        super.onPageFinished(view, url);
+      }
+    }
+
+    @Override
+    public void onLoadResource(WebView view, String url)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onLoadResource(view, url);
+      }
+      else
+      {
+        super.onLoadResource(view, url);
+      }
+    }
+
+    @Override
+    public void onTooManyRedirects(WebView view, Message cancelMsg, Message continueMsg)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onTooManyRedirects(view, cancelMsg, continueMsg);
+      }
+      else
+      {
+        super.onTooManyRedirects(view, cancelMsg, continueMsg);
+      }
+    }
+
+    @Override
+    public void onReceivedError(WebView view, int errorCode, String description, String failingUrl)
+    {
+      e("Load error:" +
+        " code=" + errorCode +
+        " with description=" + description +
+        " for url=" + failingUrl);
+      loadError = errorCode;
+
+      stopAbpLoading();
+
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onReceivedError(view, errorCode, description, failingUrl);
+      }
+      else
+      {
+        super.onReceivedError(view, errorCode, description, failingUrl);
+      }
+    }
+
+    @Override
+    public void onFormResubmission(WebView view, Message dontResend, Message resend)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onFormResubmission(view, dontResend, resend);
+      }
+      else
+      {
+        super.onFormResubmission(view, dontResend, resend);
+      }
+    }
+
+    @Override
+    public void doUpdateVisitedHistory(WebView view, String url, boolean isReload)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.doUpdateVisitedHistory(view, url, isReload);
+      }
+      else
+      {
+        super.doUpdateVisitedHistory(view, url, isReload);
+      }
+    }
+
+    @Override
+    public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onReceivedSslError(view, handler, error);
+      }
+      else
+      {
+        super.onReceivedSslError(view, handler, error);
+      }
+    }
+
+    @Override
+    public void onReceivedHttpAuthRequest(WebView view, HttpAuthHandler handler, String host, String realm)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onReceivedHttpAuthRequest(view, handler, host, realm);
+      }
+      else
+      {
+        super.onReceivedHttpAuthRequest(view, handler, host, realm);
+      }
+    }
+
+    @Override
+    public boolean shouldOverrideKeyEvent(WebView view, KeyEvent event)
+    {
+      if (extWebViewClient != null)
+      {
+        return extWebViewClient.shouldOverrideKeyEvent(view, event);
+      }
+      else
+      {
+        return super.shouldOverrideKeyEvent(view, event);
+      }
+    }
+
+    @Override
+    public void onUnhandledKeyEvent(WebView view, KeyEvent event)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onUnhandledKeyEvent(view, event);
+      }
+      else
+      {
+        super.onUnhandledKeyEvent(view, event);
+      }
+    }
+
+    @Override
+    public void onScaleChanged(WebView view, float oldScale, float newScale)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onScaleChanged(view, oldScale, newScale);
+      }
+      else
+      {
+        super.onScaleChanged(view, oldScale, newScale);
+      }
+    }
+
+    @Override
+    public void onReceivedLoginRequest(WebView view, String realm, String account, String args)
+    {
+      if (extWebViewClient != null)
+      {
+        extWebViewClient.onReceivedLoginRequest(view, realm, account, args);
+      }
+      else
+      {
+        super.onReceivedLoginRequest(view, realm, account, args);
+      }
+    }
+
+    @Override
+    public WebResourceResponse shouldInterceptRequest(WebView view, String url)
+    {
+      // if dispose() was invoke, but the page is still loading then just let it go
+      if (filterEngine == null)
+      {
+        e("FilterEngine already disposed");
+        return null;
+      }
+
+      // Determine the content
+      FilterEngine.ContentType contentType = null;
+      if (RE_JS.matcher(url).find())
+      {
+        contentType = FilterEngine.ContentType.SCRIPT;
+      }
+      else if (RE_CSS.matcher(url).find())
+      {
+        contentType = FilterEngine.ContentType.STYLESHEET;
+      }
+      else if (RE_IMAGE.matcher(url).find())
+      {
+        contentType = FilterEngine.ContentType.IMAGE;
+      }
+      else if (RE_FONT.matcher(url).find())
+      {
+        contentType = FilterEngine.ContentType.FONT;
+      }
+      else if (RE_HTML.matcher(url).find())
+      {
+        contentType = FilterEngine.ContentType.SUBDOCUMENT;
+      }
+      else
+      {
+        contentType = FilterEngine.ContentType.OTHER;
+      }
+      // Check if we should block ... we sadly do not have the referrer chain here,
+      // might also be hard to get as we do not have HTTP headers here
+      Filter filter = filterEngine.matches(url, contentType, new String[0]);
+      if (filter != null && filter.getType().equals(Filter.Type.BLOCKING))
+      {
+        w("Blocked loading " + url);
+        // If we should block, return empty response which results in a 404
+        return new WebResourceResponse("text/plain", "UTF-8", null);
+      }
+
+      d("Allowed loading " + url);
+
+      // Otherwise, continue by returning null
+      return null;
+    }
+  }
+
+  private void clearReferers()
+  {
+    d("Clearing referers");
+    url2Referer.clear();
+  }
+
+  /**
+   * WebViewClient for API 21 and newer
+   * (has Referer since it overrides `shouldInterceptRequest(..., request)` with referer)
+   */
+  class AdblockWebViewClient21 extends AdblockWebViewClient
+  {
+    @Override
+    // makes android min version to be 21
+    public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request)
+    {
+      // here we just trying to fill url -> referer map
+      // blocking/allowing loading will happen in `shouldInterceptRequest(WebView,String)`
+
+      String url = request.getUrl().toString();
+      String referer = request.getRequestHeaders().get("Referer");
+
+      if (referer != null)
+      {
+        d("Remember referer " + referer + " for " + url);
+        url2Referer.put(url, referer);
+      }
+      else
+      {
+        w("No referer for " + url);
+
+        if (request.isForMainFrame() && AdblockWebView.this.url != null)
+        {
+          d("Request is for main frame, adding current url " + AdblockWebView.this.url + " as referer");
+          url2Referer.put(url, AdblockWebView.this.url);
+        }
+      }
+
+      return super.shouldInterceptRequest(view, request);
+    }
+  }
+
+  private Map<String, String> url2Referer = Collections.synchronizedMap(new HashMap<String, String>());
+
+  private void initAbp()
+  {
+    addJavascriptInterface(this, BRIDGE);
+
+    if (Build.VERSION.SDK_INT >= 21)
+    {
+      intWebViewClient = new AdblockWebViewClient21();
+    }
+    else
+    {
+      intWebViewClient = new AdblockWebViewClient();
+    }
+
+    super.setWebChromeClient(intWebChromeClient);
+    super.setWebViewClient(intWebViewClient);
+  }
+
+  /**
+   * Build app info using Android package information
+   * @param context context
+   * @param developmentBuild if it's dev build
+   * @return app info required to build JsEngine
+   */
+  public static AppInfo buildAppInfo(final Context context, boolean developmentBuild)
+  {
+    String version = "0";
+    try
+    {
+      final PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
+      version = info.versionName;
+      if (developmentBuild)
+        version += "." + info.versionCode;
+    }
+    catch (final PackageManager.NameNotFoundException e)
+    {
+      Log.e(TAG, "Failed to get the application version number", e);
+    }
+    final String sdkVersion = String.valueOf(Build.VERSION.SDK_INT);
+    final String locale = Locale.getDefault().toString().replace('_', '-');
+
+    return AppInfo.builder()
+      .setVersion(version)
+      .setApplicationVersion(sdkVersion)
+      .setLocale(locale)
+      .setDevelopmentBuild(developmentBuild)
+      .build();
+  }
+
+  /**
+   * Build JsEngine required to build FilterEngine
+   * @param context context
+   * @param developmentBuild if it's dev build
+   * @return JsEngine
+   */
+  public static JsEngine buildJsEngine(Context context, boolean developmentBuild)
+  {
+    JsEngine jsEngine = new JsEngine(buildAppInfo(context, developmentBuild));
+    jsEngine.setDefaultFileSystem(context.getCacheDir().getAbsolutePath());
+    jsEngine.setWebRequest(new AndroidWebRequest(true)); // 'true' because we need element hiding
+    return jsEngine;
+  }
+
+  private void createFilterEngine()
+  {
+    w("Creating FilterEngine");
+    jsEngine = buildJsEngine(getContext(), debugMode);
+    filterEngine = new FilterEngine(jsEngine);
+    applyAcceptableAds();
+    d("FilterEngine created");
+  }
+
+  private String url;
+  private String domain;
+  private String injectJs;
+  private CountDownLatch elemHideLatch;
+  private String elemHideSelectorsString;
+  private Object elemHideThreadLockObject = new Object();
+  private ElemHideThread elemHideThread;
+
+  private class ElemHideThread extends Thread
+  {
+    private String selectorsString;
+    private CountDownLatch finishedLatch;
+    private AtomicBoolean isCancelled;
+
+    public ElemHideThread(CountDownLatch finishedLatch)
+    {
+      this.finishedLatch = finishedLatch;
+      isCancelled = new AtomicBoolean(false);
+    }
+
+    private String[] EMPTY_ARRAY = new String[] {};
+
+    @Override
+    public void run()
+    {
+      try
+      {
+        if (filterEngine == null)
+        {
+          w("FilterEngine already disposed");
+          selectorsString = EMPTY_ELEMHIDE_ARRAY_STRING;
+        }
+        else
+        {
+
+          String[] referers = EMPTY_ARRAY;
+          if (url != null)
+          {
+            String referer = url2Referer.get(url);
+            if (referer != null)
+            {
+              referers = new String[] { referer };
+            }
+          }
+
+          d("Check whitelisting for " + url + " with " +
+            (referers.length > 0
+              ? "referer " + referers[0]
+              : "no referer"));
+
+          if (filterEngine.isDocumentWhitelisted(url, referers) ||
+            filterEngine.isElemhideWhitelisted(url, referers))
+          {
+            w("Whitelisted " + url);
+            selectorsString = EMPTY_ELEMHIDE_ARRAY_STRING;
+          }
+          else
+          {
+            d("Listed subscriptions: " + filterEngine.getListedSubscriptions().size());
+
+            d("Requesting elemhide selectors from FilterEngine for " + domain);
+            List<String> selectors = filterEngine.getElementHidingSelectors(domain);
+            d("Finished requesting elemhide selectors, got " + selectors.size());
+            selectorsString = Utils.stringListToJsonArray(selectors);
+          }
+        }
+      }
+      finally
+      {
+        if (!isCancelled.get())
+        {
+          finish(selectorsString);
+        }
+        else
+        {
+          w("This thread is cancelled, exiting silently " + this);
+        }
+      }
+    }
+
+    private void onFinished()
+    {
+      finishedLatch.countDown();
+      synchronized (finishedRunnableLockObject)
+      {
+        if (finishedRunnable != null)
+        {
+          finishedRunnable.run();
+        }
+      }
+    }
+
+    private void finish(String result)
+    {
+      d("Setting elemhide string " + result.length() + " bytes");
+      elemHideSelectorsString = result;
+      onFinished();
+    }
+
+    private Object finishedRunnableLockObject = new Object();
+    private Runnable finishedRunnable;
+
+    public void setFinishedRunnable(Runnable runnable)
+    {
+      synchronized (finishedRunnableLockObject)
+      {
+        this.finishedRunnable = runnable;
+      }
+    }
+
+    public void cancel()
+    {
+      w("Cancelling elemhide thread " + this);
+      isCancelled.set(true);
+
+      finish(EMPTY_ELEMHIDE_ARRAY_STRING);
+    }
+  }
+
+  private Runnable elemHideThreadFinishedRunnable = new Runnable()
+  {
+    @Override
+    public void run()
+    {
+      synchronized (elemHideThreadLockObject)
+      {
+        w("elemHideThread set to null");
+        elemHideThread = null;
+      }
+    }
+  };
+
+  private boolean loading;
+
+  private void initAbpLoading()
+  {
+    getSettings().setJavaScriptEnabled(true);
+    buildInjectJs();
+
+    if (filterEngine == null)
+    {
+      createFilterEngine();
+      disposeFilterEngine = true;
+    }
+  }
+
+  private void startAbpLoading(String newUrl)
+  {
+    d("Start loading " + newUrl);
+
+    loading = true;
+    addDomListener = true;
+    elementsHidden = false;
+    loadError = null;
+    url = newUrl;
+
+    if (url != null)
+    {
+      try
+      {
+        domain = Utils.getDomain(url);
+      }
+      catch (URISyntaxException e)
+      {
+        domain = null;
+        e("Failed to extract domain for " + url);
+      }
+
+      elemHideLatch = new CountDownLatch(1);
+      elemHideThread = new ElemHideThread(elemHideLatch);
+      elemHideThread.setFinishedRunnable(elemHideThreadFinishedRunnable);
+      elemHideThread.start();
+    }
+    else
+    {
+      elemHideLatch = null;
+    }
+  }
+
+  private void buildInjectJs()
+  {
+    try
+    {
+      if (injectJs == null)
+      {
+        injectJs = readScriptFile("inject.js").replace(HIDE_TOKEN, readScriptFile("css.js"));
+      }
+    }
+    catch (IOException e)
+    {
+      e("Failed to read script", e);
+    }
+  }
+
+  @Override
+  public void goBack()
+  {
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.goBack();
+  }
+
+  @Override
+  public void goForward()
+  {
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.goForward();
+  }
+
+  @Override
+  public void loadUrl(String url)
+  {
+    initAbpLoading();
+
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.loadUrl(url);
+  }
+
+  @Override
+  public void loadUrl(String url, Map<String, String> additionalHttpHeaders)
+  {
+    initAbpLoading();
+
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.loadUrl(url, additionalHttpHeaders);
+  }
+
+  @Override
+  public void loadData(String data, String mimeType, String encoding)
+  {
+    initAbpLoading();
+
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.loadData(data, mimeType, encoding);
+  }
+
+  @Override
+  public void loadDataWithBaseURL(String baseUrl, String data, String mimeType, String encoding,
+                                  String historyUrl)
+  {
+    initAbpLoading();
+
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.loadDataWithBaseURL(baseUrl, data, mimeType, encoding, historyUrl);
+  }
+
+  @Override
+  public void stopLoading()
+  {
+    stopAbpLoading();
+    super.stopLoading();
+  }
+
+  private void stopAbpLoading()
+  {
+    d("Stop abp loading");
+
+    loading = false;
+    stopPreventDrawing();
+    clearReferers();
+
+    synchronized (elemHideThreadLockObject)
+    {
+      if (elemHideThread != null)
+      {
+        elemHideThread.cancel();
+      }
+    }
+  }
+
+  private volatile boolean elementsHidden = false;
+
+  // warning: do not rename (used in injected JS by method name)
+  @JavascriptInterface
+  public void setElementsHidden(boolean value)
+  {
+    // invoked with 'true' by JS callback when DOM is loaded
+    elementsHidden = value;
+
+    // fired on worker thread, but needs to be invoked on main thread
+    if (value)
+    {
+//     handler.post(allowDrawRunnable);
+//     should work, but it's not working:
+//     the user can see element visible even though it was hidden on dom event
+
+      if (allowDrawDelay > 0)
+      {
+        d("Scheduled 'allow drawing' invocation in " + allowDrawDelay + " ms");
+      }
+      handler.postDelayed(allowDrawRunnable, allowDrawDelay);
+    }
+  }
+
+  // warning: do not rename (used in injected JS by method name)
+  @JavascriptInterface
+  public boolean isElementsHidden()
+  {
+    return elementsHidden;
+  }
+
+  @Override
+  public void onPause()
+  {
+    handler.removeCallbacks(allowDrawRunnable);
+    super.onPause();
+  }
+
+  public AdblockWebView(Context context)
+  {
+    super(context);
+    initAbp();
+  }
+
+  public AdblockWebView(Context context, AttributeSet attrs)
+  {
+    super(context, attrs);
+    initAbp();
+  }
+
+  public AdblockWebView(Context context, AttributeSet attrs, int defStyle)
+  {
+    super(context, attrs, defStyle);
+    initAbp();
+  }
+
+  // used to prevent user see flickering for elements to hide
+  // for some reason it's rendered even if element is hidden on 'dom ready' event
+  private volatile boolean allowDraw = true;
+
+  @Override
+  protected void onDraw(Canvas canvas)
+  {
+    if (allowDraw)
+    {
+      super.onDraw(canvas);
+    }
+    else
+    {
+      w("Prevent drawing");
+      drawEmptyPage(canvas);
+    }
+  }
+
+  private void drawEmptyPage(Canvas canvas)
+  {
+    // assuming default color is WHITE
+    canvas.drawColor(Color.WHITE);
+  }
+
+  private Handler handler = new Handler();
+
+  protected void startPreventDrawing()
+  {
+    w("Start prevent drawing");
+
+    allowDraw = false;
+  }
+
+  protected void stopPreventDrawing()
+  {
+    d("Stop prevent drawing, invalidating");
+
+    allowDraw = true;
+    invalidate();
+  }
+
+  private Runnable allowDrawRunnable = new Runnable()
+  {
+    @Override
+    public void run()
+    {
+      stopPreventDrawing();
+    }
+  };
+
+  private static final String EMPTY_ELEMHIDE_ARRAY_STRING = "[]";
+
+  // warning: do not rename (used in injected JS by method name)
+  @JavascriptInterface
+  public String getElemhideSelectors()
+  {
+    if (elemHideLatch == null)
+    {
+      return EMPTY_ELEMHIDE_ARRAY_STRING;
+    }
+    else
+    {
+      try
+      {
+        // elemhide selectors list getting is started in startAbpLoad() in background thread
+        d("Waiting for elemhide selectors to be ready");
+        elemHideLatch.await();
+        d("Elemhide selectors ready, " + elemHideSelectorsString.length() + " bytes");
+
+        clearReferers();
+
+        return elemHideSelectorsString;
+      }
+      catch (InterruptedException e)
+      {
+        w("Interrupted, returning empty selectors list");
+        return EMPTY_ELEMHIDE_ARRAY_STRING;
+      }
+    }
+  }
+
+  private void doDispose()
+  {
+    w("Disposing jsEngine");
+    jsEngine.dispose();
+    jsEngine = null;
+
+    w("Disposing filterEngine");
+    filterEngine.dispose();
+    filterEngine = null;
+
+    disposeFilterEngine = false;
+  }
+
+  public void dispose()
+  {
+    d("Dispose invoked");
+
+    removeJavascriptInterface(BRIDGE);
+
+    if (disposeFilterEngine)
+    {
+      synchronized (elemHideThreadLockObject)
+      {
+        if (elemHideThread != null)
+        {
+          w("Busy with elemhide selectors, delayed disposing scheduled");
+          elemHideThread.setFinishedRunnable(new Runnable()
+          {
+            @Override
+            public void run()
+            {
+              doDispose();
+            }
+          });
+        }
+        else
+        {
+          doDispose();
+        }
+      }
+    }
+  }
+}