Merge pull request #16146 from keymanapp/fix/android/16096_blankKeyboard

fix(android): use `WebViewAssetLoader` for loading assets on Android (address regression in 19.0.242)

This PR migrates the Android WebView from loading local files via file:// URLs to using `WebViewAssetLoader`, which serves internal storage files through a magic HTTPS domain (https://appassets.androidplatform.net). This fixes the blank keyboard problem reported in #16096 for Android.

Core pattern of the change:

```
// Before:
"file://" + context.getDir("data", ...)
  + "/" + filename
// After:
"https://appassets.androidplatform.net"
  + "/data/" + filename
```

The `WebViewAssetLoader` in `KMKeyboardWebViewClient` intercepts requests to this domain and serves files from internal storage. Since the domain is a constant, `Context` is no longer needed to construct URLs, simplifying several method signatures.

Also this PR makes `KMKeyboard.getKeyboardRoot()` private, and renames public `Keyboard.getKeyboardPath()` to private `Keyboard.getKeyboardUrl()`.

Part-of: #16096
Replaces: #16132

Author: ermshiperete

android/KMAPro/kMAPro/build.gradle

@@ -173,10 +173,11 @@ dependencies {
     implementation 'androidx.constraintlayout:constraintlayout:2.2.1'
     implementation 'com.google.android.material:material:1.12.0'
     implementation 'com.stepstone.stepper:material-stepper:4.3.1'
+    implementation 'androidx.webkit:webkit:1.14.0'
     implementation files('libs/keyman-engine.aar')
     implementation 'io.sentry:sentry-android:8.19.1'
     implementation 'androidx.preference:preference:1.2.1'
-    implementation "com.android.installreferrer:installreferrer:2.2"
+    implementation 'com.android.installreferrer:installreferrer:2.2'
 
     // Add dependency for generating QR Codes
     // (Even though it's embedded in KMEA, because we're manually copying keyman-engine.aar,

android/KMEA/app/build.gradle

@@ -72,6 +72,7 @@ dependencies {
     implementation 'commons-io:commons-io:2.16.1'
     implementation 'io.sentry:sentry-android:8.19.1'
     implementation 'androidx.preference:preference:1.2.1'
+    implementation 'androidx.webkit:webkit:1.14.0'
 
     // Robolectric
     testImplementation 'androidx.test.ext:junit:1.2.1'

android/KMEA/app/src/main/java/com/keyman/engine/KMKeyboard.java

@@ -1,5 +1,5 @@
-/**
- * Copyright (C) 2017-2018 SIL International. All rights reserved.
+/*
+ * Keyman is copyright (C) SIL Global. MIT License.
  */
 
 package com.keyman.engine;
@@ -23,6 +23,7 @@
 import com.keyman.engine.util.FileUtils;
 import com.keyman.engine.util.KMLog;
 import com.keyman.engine.util.KMString;
+import com.keyman.engine.util.WebViewUtils;
 
 import android.annotation.SuppressLint;
 import android.content.Context;
@@ -85,7 +86,8 @@ final class KMKeyboard extends WebView {
 
   private static String txtFont = "";
   private static String oskFont = null;
-  private static String keyboardRoot = "";
+  private static String dataRoot = "";
+  private static String packageRoot = "";
   private final String fontUndefined = "undefined";
   private GestureDetector gestureDetector;
   private static ArrayList<OnKeyboardEventListener> kbEventListeners = null;
@@ -366,8 +368,7 @@ public void loadKeyboard() {
     } else {
       KMManager.SystemKeyboardWebViewClient.setKeyboardLoaded(false);
     }
-
-    String htmlPath = "file://" + getContext().getDir("data", Context.MODE_PRIVATE) + "/" + KMManager.KMFilename_KeyboardHtml;
+    String htmlPath = WebViewUtils.buildAssetUrl(KMManager.KMFilename_KeyboardHtml);
     loadUrl(htmlPath);
     setBackgroundColor(0);
   }
@@ -561,6 +562,7 @@ public static String oskFontFilename() {
     return oskFont;
   }
 
+  // REVIEW: this method seems to be unused
   /**
    * Return the full path to the special OSK font,
    * which is with all the keyboard assets at the root app_data folder
@@ -646,7 +648,7 @@ public boolean prepareKeyboardSwitch(String packageID, String keyboardID, String
     }
     String kbKey = KMString.format("%s_%s", languageID, keyboardID);
 
-    setKeyboardRoot(packageID);
+    setPackageRoot(packageID);
 
     // Escape single-quoted names for javascript call
     keyboardName = keyboardName.replaceAll("\'", "\\\\'"); // Double-escaped-backslash b/c regex.
@@ -702,28 +704,28 @@ public boolean setKeyboard(String packageID, String keyboardID, String languageI
         KMManager.getLatestKeyboardFileVersion(getContext(), packageID, keyboardID) : null;
     }
 
-    setKeyboardRoot(packageID);
+    setPackageRoot(packageID);
 
     if(kOskFont == null || kOskFont.isEmpty())
       kOskFont = kFont;
 
-    JSONObject jDisplayFont = makeFontPaths(kFont);
-    JSONObject jOskFont = makeFontPaths(kOskFont);
+    JSONObject jDisplayFont = makeFontObject(kFont);
+    JSONObject jOskFont = makeFontObject(kOskFont);
 
     txtFont = getFontFilename(jDisplayFont);
     oskFont = getFontFilename(jOskFont);
 
     String kbKey = KMString.format("%s_%s", languageID, keyboardID);
 
-    String keyboardPath = makeKeyboardPath(packageID, keyboardID, keyboardVersion);
+    String keyboardUrl = makeKeyboardUrl(packageID, keyboardID, keyboardVersion);
 
     JSONObject reg = new JSONObject();
     try {
       reg.put("KN", keyboardName);
       reg.put("KI", "Keyboard_" + keyboardID);
       reg.put("KLC", languageID);
       reg.put("KL", languageName);
-      reg.put("KF", keyboardPath);
+      reg.put("KF", keyboardUrl);
       reg.put("KP", packageID);
 
       if (jDisplayFont != null) reg.put("KFont", jDisplayFont);
@@ -809,28 +811,31 @@ private void sendError(String packageID, String keyboardID, String languageID, b
   }
 
   // Set the base path of the keyboard depending on the package ID
-  private void setKeyboardRoot(String packageID) {
+  private void setPackageRoot(String packageID) {
+    this.dataRoot = WebViewUtils.buildAssetUrl("");
     if (packageID.equals(KMManager.KMDefault_UndefinedPackageID)) {
-      this.keyboardRoot = (context.getDir("data", Context.MODE_PRIVATE).toString() +
-        File.separator + KMManager.KMDefault_UndefinedPackageID + File.separator);
+      this.packageRoot = this.dataRoot + KMManager.KMDefault_UndefinedPackageID + "/";
     } else {
-      this.keyboardRoot = (context.getDir("data", Context.MODE_PRIVATE).toString() +
-        File.separator + KMManager.KMDefault_AssetPackages + File.separator + packageID + File.separator);
+      this.packageRoot = this.dataRoot + KMManager.KMDefault_AssetPackages + "/" + packageID + "/";
     }
   }
 
-  public String getKeyboardRoot() {
-    return this.keyboardRoot;
+  private String getDataRoot() {
+    return this.dataRoot;
+  }
+
+  private String getPackageRoot() {
+    return this.packageRoot;
   }
 
-  private String makeKeyboardPath(String packageID, String keyboardID, String keyboardVersion) {
-    String keyboardPath;
+  private String makeKeyboardUrl(String packageID, String keyboardID, String keyboardVersion) {
+    String keyboardUrl = getPackageRoot();
     if (packageID.equals(KMManager.KMDefault_UndefinedPackageID)) {
-      keyboardPath = getKeyboardRoot() + keyboardID + "-" + keyboardVersion + ".js";
+      keyboardUrl += keyboardID + "-" + keyboardVersion + ".js";
     } else {
-      keyboardPath = getKeyboardRoot() + keyboardID + ".js";
+      keyboardUrl += keyboardID + ".js";
     }
-    return keyboardPath;
+    return keyboardUrl;
   }
 
   private void sendKMWError(int lineNumber, String sourceId, String message) {
@@ -1042,13 +1047,26 @@ public void onDismiss() {
   }
 
   /**
-   * Take a font JSON object and adjust to pass to JS
-   * 1. Replace "source" keys for "files" keys
-   * 2. Create full font paths for .ttf or .svg
-   * @param font String font JSON object as a string
-   * @return JSONObject of modified font information with full paths. If font is invalid, return `null`
+   * Create a JSON object consisting of the font family and the URLs of the
+   * font files on the local device.
+   *
+   * The `font` parameter can either be the filename of the font (with an
+   * extension recognized as font), or a Font object or JSON string.
+   * In the former case a new JSON object is created with the font family
+   * derived from the filename, and the font filename prefixed with path
+   * to the fonts.
+   * In the latter case the legacy `sources` key is renamed to `files`.
+   * If `files` is a single string it will be prefixed with the path to the
+   * fonts. If `files` is an array, the array is iterated until finding
+   * the first file with a font extension which is then prefixed with the
+   * path to the fonts.
+   *
+   * @param font  A string containing either the font filename or a font JSON
+   *              object as a string
+   * @return JSONObject of modified font information with full paths. If font
+   *         is invalid, return `null`.
    */
-  private JSONObject makeFontPaths(String font) {
+  private JSONObject makeFontObject(String font) {
 
     if(font == null || font.equals("")) {
       return null;
@@ -1059,14 +1077,13 @@ private JSONObject makeFontPaths(String font) {
         JSONObject jfont = new JSONObject();
         jfont.put(KMManager.KMKey_FontFamily, font.substring(0, font.length()-4));
         JSONArray jfiles = new JSONArray();
-        jfiles.put(keyboardRoot + font);
+        String fontRoot = KMManager.isDefaultFont(font) ? getDataRoot() : getPackageRoot();
+        jfiles.put(fontRoot + font);
         jfont.put(KMManager.KMKey_FontFiles, jfiles);
         return jfont;
       }
 
       JSONObject fontObj = new JSONObject(font);
-      JSONArray sourceArray;
-      String fontFile;
 
       // Replace "sources" key with "files"
       if (fontObj.has(KMManager.KMKey_FontSource)) {
@@ -1076,16 +1093,18 @@ private JSONObject makeFontPaths(String font) {
 
       Object obj = fontObj.get(KMManager.KMKey_FontFiles);
       if (obj instanceof String) {
-        fontFile = fontObj.getString(KMManager.KMKey_FontFiles);
-        fontObj.put(KMManager.KMKey_FontFiles, keyboardRoot + obj);
+        String fontFile = fontObj.getString(KMManager.KMKey_FontFiles);
+        String fontRoot = KMManager.isDefaultFont(fontFile) ? getDataRoot() : getPackageRoot();
+        fontObj.put(KMManager.KMKey_FontFiles, fontRoot + obj);
         return fontObj;
       } else if (obj instanceof JSONArray) {
-        sourceArray = fontObj.optJSONArray(KMManager.KMKey_FontFiles);
+        JSONArray sourceArray = fontObj.optJSONArray(KMManager.KMKey_FontFiles);
         if (sourceArray != null) {
           for (int i = 0; i < sourceArray.length(); i++) {
-            fontFile = sourceArray.getString(i);
+            String fontFile = sourceArray.getString(i);
             if (FileUtils.hasFontExtension(fontFile)) {
-              fontObj.put(KMManager.KMKey_FontFiles, keyboardRoot + fontFile);
+              String fontRoot = KMManager.isDefaultFont(fontFile) ? getDataRoot() : getPackageRoot();
+              fontObj.put(KMManager.KMKey_FontFiles, fontRoot + fontFile);
               fontObj.remove(KMManager.KMKey_FontSource);
               return fontObj;
             }
@@ -1094,7 +1113,6 @@ private JSONObject makeFontPaths(String font) {
       }
     } catch (JSONException e) {
       KMLog.LogException(TAG, "Failed to make font for '"+font+"'", e);
-      return null;
     }
 
     return null;

android/KMEA/app/src/main/java/com/keyman/engine/KMKeyboardWebViewClient.java

@@ -1,5 +1,5 @@
-/**
- * Copyright (C) 2023 SIL International. All rights reserved.
+/*
+ * Keyman is copyright (C) SIL Global. MIT License.
  */
 package com.keyman.engine;
 
@@ -9,16 +9,21 @@
 import android.graphics.RectF;
 import android.net.Uri;
 import android.util.Log;
+import android.webkit.WebResourceRequest;
+import android.webkit.WebResourceResponse;
 import android.webkit.WebView;
 import android.webkit.WebViewClient;
 import android.widget.RelativeLayout;
+import androidx.webkit.WebViewAssetLoader;
+import androidx.webkit.WebViewAssetLoader.InternalStoragePathHandler;
 
 import com.keyman.engine.KeyboardEventHandler.EventType;
 import com.keyman.engine.KMManager;
 import com.keyman.engine.KMManager.KeyboardType;
 import com.keyman.engine.KMManager.SuggestionType;
 import com.keyman.engine.util.KMLog;
 import com.keyman.engine.data.Keyboard;
+import com.keyman.engine.util.WebViewUtils;
 
 import org.json.JSONObject;
 
@@ -31,11 +36,16 @@ public final class KMKeyboardWebViewClient extends WebViewClient {
   public Context context;
   private KeyboardType keyboardType;
   private boolean keyboardLoaded;
+  private WebViewAssetLoader assetLoader;
 
   KMKeyboardWebViewClient(Context context, KeyboardType keyboardType) {
     this.context = context;
     this.keyboardType = keyboardType;
     this.keyboardLoaded = false;
+    this.assetLoader = new WebViewAssetLoader.Builder()
+      .addPathHandler(WebViewUtils.ASSET_DATA_PATH,
+        new InternalStoragePathHandler(context, context.getDir("data", Context.MODE_PRIVATE)))
+      .build();
 
     if (keyboardType != KeyboardType.KEYBOARD_TYPE_INAPP && keyboardType != KeyboardType.KEYBOARD_TYPE_SYSTEM) {
       KMLog.LogError(TAG, String.format("Cannot initialize: Invalid keyboard type: %s", keyboardType.toString()));
@@ -58,6 +68,11 @@ public void setKeyboardLoaded(boolean keyboardLoaded) {
   public void onPageStarted(WebView view, String url, Bitmap favicon) {
   }
 
+  @Override
+  public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) {
+    return this.assetLoader.shouldInterceptRequest(request.getUrl());
+  }
+
   @Override
   public void onPageFinished(WebView view, String url) {
     Log.d("KMEA", String.format("onPageFinished: [%s] %s", keyboardType.toString(), url));
@@ -74,46 +89,44 @@ private void pageLoaded(WebView view, String url) {
     kmKeyboard.keyboardSet = false;
     KMManager.currentLexicalModel = null;
 
-    if (url.startsWith("file")) { // TODO: is this test necessary?
-      this.keyboardLoaded = true;
+    this.keyboardLoaded = true;
 
-      SharedPreferences prefs = context.getSharedPreferences(context.getString(R.string.kma_prefs_name), Context.MODE_PRIVATE);
-      int index = prefs.getInt(KMManager.KMKey_UserKeyboardIndex, 0);
-      if (index < 0) {
-        index = 0;
+    SharedPreferences prefs = context.getSharedPreferences(context.getString(R.string.kma_prefs_name), Context.MODE_PRIVATE);
+    int index = prefs.getInt(KMManager.KMKey_UserKeyboardIndex, 0);
+    Keyboard keyboardInfo = null;
+    if (index >= 0) {
+      keyboardInfo = KMManager.getKeyboardInfo(context, index);
+    }
+    String langId = null;
+    if (keyboardInfo != null) {
+      langId = keyboardInfo.getLanguageID();
+      kmKeyboard.setKeyboard(keyboardInfo);
+    } else {
+      // Revert to default (index 0) or fallback keyboard
+      keyboardInfo = KMManager.getKeyboardInfo(context, 0);
+      if (keyboardInfo == null) {
+        // Don't log to Sentry because some keyboard apps like FV don't install keyboards until the user chooses
+        keyboardInfo = KMManager.getDefaultKeyboard(context);
       }
-      Keyboard keyboardInfo = KMManager.getKeyboardInfo(context, index);
-      String langId = null;
       if (keyboardInfo != null) {
         langId = keyboardInfo.getLanguageID();
         kmKeyboard.setKeyboard(keyboardInfo);
-      } else {
-        // Revert to default (index 0) or fallback keyboard
-        keyboardInfo = KMManager.getKeyboardInfo(context, 0);
-        if (keyboardInfo == null) {
-          // Don't log to Sentry because some keyboard apps like FV don't install keyboards until the user chooses
-          keyboardInfo = KMManager.getDefaultKeyboard(context);
-        }
-        if (keyboardInfo != null) {
-          langId = keyboardInfo.getLanguageID();
-          kmKeyboard.setKeyboard(keyboardInfo);
-        }
       }
+    }
 
-      KMManager.registerAssociatedLexicalModel(langId);
+    KMManager.registerAssociatedLexicalModel(langId);
 
-      kmKeyboard.showHelpBubbleAfterDelay(2000, true); // check if it should be shown at that time!
+    kmKeyboard.showHelpBubbleAfterDelay(2000, true); // check if it should be shown at that time!
 
-      kmKeyboard.callJavascriptAfterLoad();
-      kmKeyboard.setSpacebarText(KMManager.getSpacebarText());
+    kmKeyboard.callJavascriptAfterLoad();
+    kmKeyboard.setSpacebarText(KMManager.getSpacebarText());
 
-      KeyboardEventHandler.notifyListeners(KMTextView.kbEventListeners, keyboardType, EventType.KEYBOARD_LOADED, null);
+    KeyboardEventHandler.notifyListeners(KMTextView.kbEventListeners, keyboardType, EventType.KEYBOARD_LOADED, null);
 
-      // Special handling for in-app TextView context keymanapp/keyman#3809
-      if (keyboardType == KeyboardType.KEYBOARD_TYPE_INAPP &&
-          KMTextView.activeView != null && KMTextView.activeView.getClass() == KMTextView.class) {
-        KMTextView.updateTextContext();
-      }
+    // Special handling for in-app TextView context keymanapp/keyman#3809
+    if (keyboardType == KeyboardType.KEYBOARD_TYPE_INAPP &&
+        KMTextView.activeView != null && KMTextView.activeView.getClass() == KMTextView.class) {
+      KMTextView.updateTextContext();
     }
   }