Add a dialogue for when custom tab fallback fails. (#575)

This applies when there is no package available for any of the
options (browser, trusted web activity, or custom tab). When the
custom tab fallback itself fails because there is no provider
available, there is currently an exception thrown somewhere in
the Android package management code. Visually, the user sees
a window open, there's some flickering from lots of retries to
launch a custom tab, and then it gives up and fails.

The most prominent case for this is when Android's parental
controls are active and they have blocked Chrome (or whichever
browser is installed on the device). To make this case clearer
to the user, this introduces a dialogue telling the user that
their browser is blocked and provides a link to parental controls
in settings. There are admittedly some use cases where this can
happen for reasons other than parental controls, but this was
deemed not worth the complexity since this is a short term
solution for a very niche case.

* Create a constant for the parental control action.

* Revert fallsBackToCustomTab_whenSessionCreationFails accidental change.

* More clean up of TwaLauncher.

* Remove neutral button and its associated string from TwaLauncher

Author: ericsum26

androidbrowserhelper/src/androidTest/java/com/google/androidbrowserhelper/trusted/TwaLauncherTest.java

@@ -22,8 +22,10 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doAnswer;
+import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.spy;
@@ -33,6 +35,7 @@
 
 import android.content.Context;
 import android.content.Intent;
+import android.content.pm.PackageManager;
 import android.net.Uri;
 
 import com.google.androidbrowserhelper.trusted.splashscreens.SplashScreenStrategy;
@@ -57,6 +60,7 @@
 import androidx.test.rule.ActivityTestRule;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 
+import java.util.Collections;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -100,6 +104,7 @@ public void setUp() {
     @After
     public void tearDown() {
         TwaProviderPicker.restrictToPackageForTesting(null);
+        TwaLauncher.setDialogStrategyForTesting(null);
         mTwaLauncher.destroy();
     }
 
@@ -278,6 +283,35 @@ public void cancelsLaunch_IfSplashScreenStrategyFinishes_AfterDestroy() throws E
         verify(builder, never()).build(any());
     }
 
+    @Test
+    public void showsBrowserUnavailableDialog() throws Exception {
+        // Disable all browsers and services in the test package.
+        mEnableComponents.manuallyDisable(TestBrowser.class);
+        mEnableComponents.manuallyDisable(TestCustomTabsServiceSupportsTwas.class);
+        mEnableComponents.manuallyDisable(TestCustomTabsService.class);
+
+        // Mock PackageManager to return no Custom Tabs providers and no browsers.
+        // This forces CustomTabsClient.getPackageName to return null.
+        PackageManager pmSpy = spy(mContext.getPackageManager());
+        doReturn(Collections.emptyList()).when(pmSpy).queryIntentServices(any(), anyInt());
+        doReturn(Collections.emptyList()).when(pmSpy).queryIntentActivities(any(), anyInt());
+        doReturn(null).when(pmSpy).resolveActivity(any(), anyInt());
+        TestActivity activitySpy = spy(mActivity);
+        doReturn(pmSpy).when(activitySpy).getPackageManager();
+        doReturn(activitySpy).when(activitySpy).getApplicationContext();
+        TwaLauncher.BrowserUnavailableDialogStrategy mockStrategy =
+                mock(TwaLauncher.BrowserUnavailableDialogStrategy.class);
+        TwaLauncher.setDialogStrategyForTesting(mockStrategy);
+        TwaLauncher launcher = new TwaLauncher(activitySpy);
+
+        mActivity.runOnUiThread(() -> launcher.launch(new TrustedWebActivityIntentBuilder(URL),
+                mCustomTabsCallback, null, null, TwaLauncher.CCT_FALLBACK_STRATEGY));
+
+        InstrumentationRegistry.getInstrumentation().waitForIdleSync();
+        verify(mockStrategy).show(any());
+        assertNotNull(launcher);
+    }
+
     private TrustedWebActivityIntentBuilder makeBuilder() {
         return new TrustedWebActivityIntentBuilder(URL);
     }

androidbrowserhelper/src/main/java/com/google/androidbrowserhelper/trusted/TwaLauncher.java

@@ -14,9 +14,15 @@
 
 package com.google.androidbrowserhelper.trusted;
 
+
+import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.ActivityNotFoundException;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
+import android.content.pm.PackageManager;
+import android.content.pm.ResolveInfo;
 import android.net.Uri;
 import android.util.Log;
 
@@ -34,8 +40,11 @@
 import androidx.browser.trusted.TokenStore;
 import androidx.browser.trusted.TrustedWebActivityIntent;
 import androidx.browser.trusted.TrustedWebActivityIntentBuilder;
+import com.google.androidbrowserhelper.R;
+import java.util.List;
 
 import com.google.androidbrowserhelper.BuildConfig;
+import androidx.annotation.VisibleForTesting;
 
 /**
  * Encapsulates the steps necessary to launch a Trusted Web Activity, such as establishing a
@@ -52,8 +61,38 @@ public class TwaLauncher {
     private static final String EXTRA_ANDROID_BROWSER_HELPER_VERSION =
             "org.chromium.chrome.browser.ANDROID_BROWSER_HELPER_VERSION";
 
+
+
+    /** 
+     * Strategy for showing a dialog when no browser is available. Interface exists just to
+     * facilitate unit testing.
+     */
+    public interface BrowserUnavailableDialogStrategy {
+        void show(Activity activity);
+    }
+
+    private static BrowserUnavailableDialogStrategy sDialogStrategy =
+            TwaLauncher::showBrowserUnavailableDialog;
+
+    /** For testing: allows mocking the dialog show. */
+    @VisibleForTesting
+    public static void setDialogStrategyForTesting(BrowserUnavailableDialogStrategy strategy) {
+        sDialogStrategy = strategy;
+    }
+
     public static final FallbackStrategy CCT_FALLBACK_STRATEGY =
             (context, twaBuilder, providerPackage, completionCallback) -> {
+        if (providerPackage == null) {
+            providerPackage = CustomTabsClient.getPackageName(context, null);
+        }
+        if (providerPackage == null) {
+            if (context instanceof Activity) {
+                sDialogStrategy.show((Activity) context);
+            } else {
+                Log.e(TAG, "Cannot show browser unavailable dialog without an Activity context.");
+            }
+            return;
+        }
         // CustomTabsIntent will fall back to launching the Browser if there are no Custom Tabs
         // providers installed.
         CustomTabsIntent intent = twaBuilder.buildCustomTabsIntent();
@@ -338,6 +377,39 @@ public void setStartupUptimeMillis(long startupUptimeMillis) {
         mStartupUptimeMillis = startupUptimeMillis;
     }
 
+    /**
+     * Shows a dialog explaining that no browser is available to open the URL.
+     *
+     * @param activity The {@link Activity} used to show the dialog.
+     */
+    private static void showBrowserUnavailableDialog(Activity activity) {
+        PackageManager pm = activity.getPackageManager();
+
+        // Query for all browsers that can handle a standard URL. This allows us to find the
+        // user's preferred browser to provide a helpful name in the dialog.
+        Intent queryBrowsersIntent = new Intent()
+                .setAction(Intent.ACTION_VIEW)
+                .addCategory(Intent.CATEGORY_BROWSABLE)
+                .setData(Uri.fromParts("http", "", null));
+
+        List<ResolveInfo> allBrowsers = pm.queryIntentActivities(queryBrowsersIntent,
+                PackageManager.MATCH_DEFAULT_ONLY | PackageManager.MATCH_UNINSTALLED_PACKAGES);
+
+        String browserName = activity.getString(R.string.provider_unavailable_default_browser);
+        if (!allBrowsers.isEmpty()) {
+            // The list is ordered from best to worst match, so we pick the first one.
+            browserName = allBrowsers.get(0).loadLabel(pm).toString();
+        }
+
+        AlertDialog.Builder builder = new AlertDialog.Builder(activity);
+        builder.setTitle(R.string.provider_unavailable_title)
+                .setMessage(activity.getString(R.string.provider_unavailable_message, browserName))
+                .setPositiveButton(R.string.provider_unavailable_button_ok, (dialog, which) -> dialog.dismiss())
+                .setCancelable(true);
+        builder.setOnDismissListener(dialog -> activity.finish());
+        builder.show();
+    }
+
     private class TwaCustomTabsServiceConnection extends CustomTabsServiceConnection {
         private Runnable mOnSessionCreatedRunnable;
         private Runnable mOnSessionCreationFailedRunnable;

androidbrowserhelper/src/main/res/values/strings.xml

@@ -4,4 +4,8 @@
     <string name="no_provider_toast">Please install Chrome Stable 72 or later.</string>
     <string name="manage_space_not_supported_toast">This app\'s data is stored in %1$s.</string>
     <string name="manage_space_no_data_toast">This app holds no browsing data.</string>
+    <string name="provider_unavailable_title">App Unavailable</string>
+    <string name="provider_unavailable_message">This app is unavailable because %1$s is blocked</string>
+    <string name="provider_unavailable_button_ok">OK</string>
+    <string name="provider_unavailable_default_browser">Chrome</string>
 </resources>