Issue 4399 - Add WebView inheritor with ad blocking

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

+/*
+ * 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.libadblockplus.android.webview;
+
+import android.annotation.TargetApi;
+import android.content.Context;
+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.JavascriptInterface;  // makes android min version to be 17
+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.WebViewClient;
+
+import org.adblockplus.libadblockplus.FilterEngine;
+import org.adblockplus.libadblockplus.Subscription;
+import org.adblockplus.libadblockplus.android.AdblockEngine;
+import org.adblockplus.libadblockplus.android.Utils;
+
+import java.io.IOException;
+import java.lang.reflect.Proxy;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+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);
+
+  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();
+  }
+
+  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)
+  {
+    d("addDomListener=" + value);
+    this.addDomListener = value;
+  }
+
+  @JavascriptInterface
+  public boolean getAddDomListener()
+  {
+    return addDomListener;
+  }
+
+  private boolean adblockEnabled = true;
+
+  public boolean isAdblockEnabled()
+  {
+    return adblockEnabled;
+  }
+
+  private void applyAdblockEnabled()
+  {
+    super.setWebViewClient(adblockEnabled ? intWebViewClient : extWebViewClient);
+    super.setWebChromeClient(adblockEnabled ? intWebChromeClient : extWebChromeClient);
+  }
+
+  public void setAdblockEnabled(boolean adblockEnabled)
+  {
+    this.adblockEnabled = adblockEnabled;
+    applyAdblockEnabled();
+  }
+
+  private WebChromeClient extWebChromeClient;
+
+  @Override
+  public void setWebChromeClient(WebChromeClient client)
+  {
+    extWebChromeClient = client;
+    applyAdblockEnabled();
+  }
+
+  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)
+  {
+    d("runScript started");
+    if (Build.VERSION.SDK_INT >= 19)
+    {
+      evaluateJavascript(script, null);
+    }
+    else
+    {
+      loadUrl("javascript:" + script);
+    }
+    d("runScript finished");
+  }
+
+  private AdblockEngine adblockEngine;
+
+  public AdblockEngine getAdblockEngine()
+  {
+    return adblockEngine;
+  }
+
+  private boolean disposeEngine;
+  private Integer loadError;
+
+  /**
+   * Set external adblockEngine. A new (internal) is created automatically if not set
+   * Don't forget to invoke {@link #dispose(Runnable)} later and dispose external adblockEngine
+   * @param adblockEngine external adblockEngine
+   */
+  public void setAdblockEngine(final AdblockEngine adblockEngine)
+  {
+    if (this.adblockEngine != null && adblockEngine != null && this.adblockEngine == adblockEngine)
+    {
+      return;
+    }
+
+    final Runnable setRunnable = new Runnable()
+    {
+      @Override
+      public void run()
+      {
+        AdblockWebView.this.adblockEngine = adblockEngine;
+        AdblockWebView.this.disposeEngine = false;
+      }
+    };
+
+    if (this.adblockEngine != null && disposeEngine)
+    {
+      // as adblockEngine can be busy with elemhide thread we need to use callback
+      this.dispose(setRunnable);
+    }
+    else
+    {
+      setRunnable.run();
+    }
+  }
+
+  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)
+    {
+      d("JS: level=" + consoleMessage.messageLevel()
+        + ", message=\"" + consoleMessage.message() + "\""
+        + ", sourceId=\"" + consoleMessage.sourceId() + "\""
+        + ", line=" + consoleMessage.lineNumber());
+
+      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;
+    applyAdblockEnabled();
+  }
+
+  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 Referrers information)
+   */
+  private 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);
+      }
+    }
+
+    protected WebResourceResponse shouldInterceptRequest(
+      WebView webview, String url, boolean isMainFrame,
+      boolean isXmlHttpRequest, String[] referrerChainArray)
+    {
+      // if dispose() was invoke, but the page is still loading then just let it go
+      if (adblockEngine == null)
+      {
+        e("FilterEngine already disposed, allow loading");
+
+        // allow loading by returning null
+        return null;
+      }
+
+      if (isMainFrame)
+      {
+        // never blocking main frame requests, just subrequests
+        w(url + " is main frame, allow loading");
+
+        // allow loading by returning null
+        return null;
+      }
+
+      // whitelisted
+      if (adblockEngine.isDomainWhitelisted(url, referrerChainArray))
+      {
+        w(url + " domain is whitelisted, allow loading");
+
+        // allow loading by returning null
+        return null;
+      }
+
+      if (adblockEngine.isDocumentWhitelisted(url, referrerChainArray))
+      {
+        w(url + " document is whitelisted, allow loading");
+
+        // allow loading by returning null
+        return null;
+      }
+
+      // determine the content
+      FilterEngine.ContentType contentType;
+      if (isXmlHttpRequest)
+      {
+        contentType = FilterEngine.ContentType.XMLHTTPREQUEST;
+      }
+      else
+      {
+        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
+      if (adblockEngine.matches(url, contentType, referrerChainArray))
+      {
+        w("Blocked loading " + url);
+
+        // if we should block, return empty response which results in 'errorLoading' callback
+        return new WebResourceResponse("text/plain", "UTF-8", null);
+      }
+
+      d("Allowed loading " + url);
+
+      // continue by returning null
+      return null;
+    }
+
+    @Override
+    public WebResourceResponse shouldInterceptRequest(WebView view, String url)
+    {
+      /*
+        we use hack - injecting Proxy instance instead of IoThreadClient and intercepting
+        `isForMainFrame` argument value, see `initIoThreadClient()`.
+
+        it's expected to be not `null` as first invocation goes to
+        https://android.googlesource.com/platform/external/chromium_org/+/android-4.4_r1/android_webview/java/src/org/chromium/android_webview/AwContents.java#235
+        and we intercept it by injecting our proxy instead of `IoThreadClientImpl`
+        and then it goes here
+        https://android.googlesource.com/platform/external/chromium_org/+/android-4.4_r1/android_webview/java/src/org/chromium/android_webview/AwContents.java#242
+      */
+      Boolean isMainFrame = IoThreadClientInvocationHandler.isMainFrame;
+      if (isMainFrame == null)
+      {
+        // the only reason for having null here is probably it failed to inject IoThreadClient proxy
+        isMainFrame = false;
+      }
+
+      // sadly we don't have request headers
+      // (referrer and x-requested until android-21 and new callback with request (instead of just url) argument)
+      String[] referrers = null;
+      boolean isXmlHttpRequest = false;
+
+      return shouldInterceptRequest(view, url, isMainFrame, isXmlHttpRequest, referrers);
+    }
+  }
+
+  private void clearReferrers()
+  {
+    d("Clearing referrers");
+    url2Referrer.clear();
+  }
+
+  protected static final String HEADER_REFERRER = "Referer";
+  protected static final String HEADER_REQUESTED_WITH = "X-Requested-With";
+  protected static final String HEADER_REQUESTED_WITH_XMLHTTPREQUEST = "XMLHttpRequest";
+
+
+  /**
+   * WebViewClient for API 21 and newer
+   * (has Referrer since it overrides `shouldInterceptRequest(..., request)` with referrer)
+   */
+  private class AdblockWebViewClient21 extends AdblockWebViewClient
+  {
+    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
+    @Override
+    public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request)
+    {
+      // here we just trying to fill url -> referrer map
+      // blocking/allowing loading will happen in `shouldInterceptRequest(WebView,String)`
+      String url = request.getUrl().toString();
+
+      boolean isXmlHttpRequest =
+        request.getRequestHeaders().containsKey(HEADER_REQUESTED_WITH) &&
+        HEADER_REQUESTED_WITH_XMLHTTPREQUEST.equals(
+          request.getRequestHeaders().get(HEADER_REQUESTED_WITH));
+
+      String referrer = request.getRequestHeaders().get(HEADER_REFERRER);
+      String[] referrers;
+
+      if (referrer != null)
+      {
+        d("Header referrer for " + url + " is " + referrer);
+        url2Referrer.put(url, referrer);
+
+        referrers = new String[]
+        {
+          referrer
+        };
+      }
+      else
+      {
+        w("No referrer header for " + url);
+        referrers = EMPTY_ARRAY;
+      }
+
+      return shouldInterceptRequest(view, url, request.isForMainFrame(), isXmlHttpRequest, referrers);
+    }
+  }
+
+  private Map<String, String> url2Referrer = Collections.synchronizedMap(new HashMap<String, String>());
+
+  private void initAbp()
+  {
+    addJavascriptInterface(this, BRIDGE);
+    initClients();
+
+    if (Build.VERSION.SDK_INT < 21)
+    {
+      // we need to inject proxy to hijack `isMainFrame` argument value at pre-android-21
+      initIoThreadClient();
+    }
+  }
+
+  private synchronized void initIoThreadClient()
+  {
+    final Object awContents = ReflectionUtils.extractProperty(this, new String[]
+    {
+      "mProvider",
+      "mAwContents"
+    });
+
+    final String ioThreadClientProperty = "mIoThreadClient";
+    final Object originalClient = ReflectionUtils.extractProperty(
+      awContents,
+      new String[]
+      {
+        ioThreadClientProperty
+      });
+
+    // avoid injecting twice (already injected Proxy instance has another class name)
+    if (!originalClient.getClass().getSimpleName().startsWith("$Proxy"))
+    {
+      Object proxyClient = Proxy.newProxyInstance(
+        originalClient.getClass().getClassLoader(),
+        originalClient.getClass().getInterfaces(),
+        new IoThreadClientInvocationHandler(originalClient));
+
+      // inject proxy instead of original client
+      boolean injected = ReflectionUtils.injectProperty(awContents, ioThreadClientProperty,
+        proxyClient);
+      if (injected)
+      {
+        // after we injected it as field we should pass it to native code as invocation comes from it
+        Integer mNativeAwContents = (Integer) ReflectionUtils.extractProperty(awContents,
+          "mNativeAwContents");
+        Object mWebContentsDelegate = ReflectionUtils.extractProperty(awContents,
+          "mWebContentsDelegate");
+        Object mContentsClientBridge = ReflectionUtils.extractProperty(awContents,
+          "mContentsClientBridge");
+        Object mInterceptNavigationDelegate = ReflectionUtils.extractProperty(awContents,
+          "mInterceptNavigationDelegate");
+
+        boolean invoked = ReflectionUtils.invokeMethod(awContents, "nativeSetJavaPeers", new Object[]
+        {
+          mNativeAwContents, awContents, mWebContentsDelegate,
+          mContentsClientBridge, proxyClient, mInterceptNavigationDelegate
+        });
+        if (!invoked)
+        {
+          e("Failed to inject IoThreadClient proxy");
+        }
+      }
+    }
+  }
+
+  private void initClients()
+  {
+    if (Build.VERSION.SDK_INT >= 21)
+    {
+      intWebViewClient = new AdblockWebViewClient21();
+    }
+    else
+    {
+      intWebViewClient = new AdblockWebViewClient();
+    }
+    applyAdblockEnabled();
+  }
+
+  private void createAdblockEngine()
+  {
+    w("Creating AdblockEngine");
+
+    // assuming `this.debugMode` can be used as `developmentBuild` value
+    adblockEngine = AdblockEngine.create(
+      this.getContext(),
+      AdblockEngine.generateAppInfo(this.getContext(), debugMode),
+      this.getContext().getCacheDir().getAbsolutePath(),
+      true);
+  }
+
+  private String url;
+  private String domain;
+  private String injectJs;
+  private CountDownLatch elemHideLatch;
+  private String elemHideSelectorsString;
+  private Object elemHideThreadLockObject = new Object();

[diegocarloslima, 2016/11/29 17:47:45]

Lock objects for synchronized statements should be final

[anton, 2016/11/30 06:34:43]

Acknowledged.

+  private ElemHideThread elemHideThread;
+
+  private static final String[] EMPTY_ARRAY = {};
+
+  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);
+    }
+
+    @Override
+    public void run()
+    {
+      try
+      {
+        if (adblockEngine == null)
+        {
+          w("FilterEngine already disposed");
+          selectorsString = EMPTY_ELEMHIDE_ARRAY_STRING;
+        }
+        else
+        {
+          String[] referrers = new String[]
+          {
+            url
+          };
+
+          List<Subscription> subscriptions = adblockEngine.getFilterEngine().getListedSubscriptions();
+          d("Listed subscriptions: " + subscriptions.size());
+          if (debugMode)
+          {
+            for (Subscription eachSubscription : subscriptions)
+            {
+              d("Subscribed to " + eachSubscription);
+            }
+          }
+
+          d("Requesting elemhide selectors from AdblockEngine for " + url + " in " + this);
+          List<String> selectors = adblockEngine.getElementHidingSelectors(url, domain, referrers);
+          d("Finished requesting elemhide selectors, got " + selectors.size() + " in " + this);
+          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 final 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 (adblockEngine == null)
+    {
+      createAdblockEngine();
+      disposeEngine = true;
+    }
+  }
+
+  private void startAbpLoading(String newUrl)
+  {
+    d("Start loading " + newUrl);
+
+    loading = true;
+    addDomListener = true;
+    elementsHidden = false;
+    loadError = null;
+    url = newUrl;
+
+    if (url != null && adblockEngine != null)
+    {
+      try
+      {
+        domain = adblockEngine.getFilterEngine().getHostFromURL(url);
+        if (domain == null)
+        {
+          throw new RuntimeException("Failed to extract domain from " + url);
+        }
+
+        d("Extracted domain " + domain + " from " + url);
+      }
+      catch (Throwable t)
+      {
+        e("Failed to extract domain from " + url, t);
+      }
+
+      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 reload()
+  {
+    initAbpLoading();
+
+    if (loading)
+    {
+      stopAbpLoading();
+    }
+
+    super.reload();
+  }
+
+  @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();
+    clearReferrers();
+
+    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();
+  }
+
+  // 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");
+
+        clearReferrers();
+
+        return elemHideSelectorsString;
+      }
+      catch (InterruptedException e)
+      {
+        w("Interrupted, returning empty selectors list");
+        return EMPTY_ELEMHIDE_ARRAY_STRING;
+      }
+    }
+  }
+
+  private void doDispose()
+  {
+    w("Disposing AdblockEngine");
+    adblockEngine.dispose();
+    adblockEngine = null;
+
+    disposeEngine = false;
+  }
+
+  private class DisposeRunnable implements Runnable
+  {
+    private Runnable disposeFinished;
+
+    private DisposeRunnable(Runnable disposeFinished)
+    {
+      this.disposeFinished = disposeFinished;
+    }
+
+    @Override
+    public void run()
+    {
+      if (disposeEngine)
+      {
+        doDispose();
+      }
+
+      if (disposeFinished != null)
+      {
+        disposeFinished.run();
+      }
+    }
+  }
+
+  /**
+   * Dispose AdblockWebView and internal adblockEngine if it was created
+   * If external AdblockEngine was passed using `setAdblockEngine()` it should be disposed explicitly
+   * Warning: runnable can be invoked from background thread
+   * @param disposeFinished runnable to run when AdblockWebView is disposed
+   */
+  public void dispose(final Runnable disposeFinished)
+  {
+    d("Dispose invoked");
+
+    stopLoading();
+
+    removeJavascriptInterface(BRIDGE);
+    if (!disposeEngine)
+    {
+      adblockEngine = null;
+    }
+
+    DisposeRunnable disposeRunnable = new DisposeRunnable(disposeFinished);
+    synchronized (elemHideThreadLockObject)
+    {
+      if (elemHideThread != null)
+      {
+        w("Busy with elemhide selectors, delayed disposing scheduled");
+        elemHideThread.setFinishedRunnable(disposeRunnable);
+      }
+      else
+      {
+        disposeRunnable.run();
+      }
+    }
+  }
+}