Added: Add isTermuxAppInstalled() and isTermuxAppAccessible() functions to TermuxUtils

The `TermuxUtils.isTermuxAppInstalled()` function can be used by external apps to check if termux app is installed and enabled.

The `TermuxUtils.isTermuxAppAccessible()` function can be used by termux plugin apps to check if termux app is installed, enabled, accessible as per `sharedUserId` and `TERMUX_PREFIX_DIR_PATH` is accessible and has read, write and execute permission.

termux-shared/src/main/java/com/termux/shared/termux/TermuxUtils.java

@@ -3,11 +3,14 @@ package com.termux.shared.termux;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
+import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageManager;
 import android.content.pm.ResolveInfo;
 
 import androidx.annotation.NonNull;
 
 import com.termux.shared.R;
+import com.termux.shared.file.FileUtils;
 import com.termux.shared.file.TermuxFileUtils;
 import com.termux.shared.logger.Logger;
 import com.termux.shared.markdown.MarkdownUtils;
@@ -101,6 +104,90 @@ public class TermuxUtils {
 
 
 
+    /**
+     * Check if Termux app is installed and enabled. This can be used by external apps that don't
+     * share `sharedUserId` with the Termux app.
+     *
+     * If your third-party app is targeting sdk `30` (android `11`), then it needs to add `com.termux`
+     * package to the `queries` element or request `QUERY_ALL_PACKAGES` permission in its
+     * `AndroidManifest.xml`. Otherwise it will get `PackageSetting{...... com.termux/......} BLOCKED`
+     * errors in `logcat` and `RUN_COMMAND` won't work.
+     * Check [package-visibility](https://developer.android.com/training/basics/intents/package-visibility#package-name),
+     * `QUERY_ALL_PACKAGES` [googleplay policy](https://support.google.com/googleplay/android-developer/answer/10158779
+     * and this [article](https://medium.com/androiddevelopers/working-with-package-visibility-dc252829de2d) for more info.
+     *
+     * {@code
+     * <manifest
+     *     <queries>
+     *         <package android:name="com.termux" />
+     *    </queries>
+     * </manifest>
+     * }
+     *
+     * @param currentPackageContext The context of current package.
+     * @return Returns {@code errmsg} if termux package is not installed or disabled, otherwise {@code null}.
+     */
+    public static String isTermuxAppInstalled(@NonNull final Context currentPackageContext) {
+        String errmsg = null;
+
+        PackageManager packageManager = currentPackageContext.getPackageManager();
+
+        ApplicationInfo applicationInfo;
+        try {
+            applicationInfo = packageManager.getApplicationInfo(TermuxConstants.TERMUX_PACKAGE_NAME, 0);
+        } catch (final PackageManager.NameNotFoundException e) {
+            applicationInfo = null;
+        }
+        boolean termuxAppEnabled = (applicationInfo != null && applicationInfo.enabled);
+
+        // If Termux app is not installed or is disabled
+        if (!termuxAppEnabled)
+            errmsg = currentPackageContext.getString(R.string.error_termux_app_not_installed_or_disabled_warning);
+
+        return errmsg;
+    }
+
+    /**
+     * Check if Termux app is installed and accessible. This can only be used by apps that share
+     * `sharedUserId` with the Termux app.
+     *
+     * This is done by checking if first checking if app is installed and enabled and then if
+     * {@code currentPackageContext} can be used to get the {@link Context} of the app with
+     * {@link TermuxConstants#TERMUX_PACKAGE_NAME} and then if
+     * {@link TermuxConstants#TERMUX_PREFIX_DIR_PATH} exists and has
+     * {@link FileUtils#APP_WORKING_DIRECTORY_PERMISSIONS} permissions. The directory will not
+     * be automatically created and neither the missing permissions automatically set.
+     *
+     * @param currentPackageContext The context of current package.
+     * @return Returns {@code errmsg} if failed to get termux package {@link Context} or
+     *         {@link TermuxConstants#TERMUX_PREFIX_DIR_PATH} is accessible, otherwise {@code null}.
+     */
+    public static String isTermuxAppAccessible(@NonNull final Context currentPackageContext) {
+        String errmsg = isTermuxAppInstalled(currentPackageContext);
+        if (errmsg == null) {
+            Context termuxPackageContext = TermuxUtils.getTermuxPackageContext(currentPackageContext);
+            // If failed to get Termux app package context
+            if (termuxPackageContext == null)
+                errmsg = currentPackageContext.getString(R.string.error_termux_app_package_context_not_accessible);
+
+            if (errmsg == null) {
+                // If TermuxConstants.TERMUX_PREFIX_DIR_PATH is not a directory or does not have required permissions
+                Error error = TermuxFileUtils.isTermuxPrefixDirectoryAccessible(false, false);
+                if (error != null)
+                    errmsg = currentPackageContext.getString(R.string.error_termux_prefix_dir_path_not_accessible,
+                        PackageUtils.getAppNameForPackage(currentPackageContext));
+            }
+        }
+
+        if (errmsg != null)
+            return errmsg + " " + currentPackageContext.getString(R.string.msg_termux_app_required_by_app,
+                PackageUtils.getAppNameForPackage(currentPackageContext));
+        else
+            return null;
+    }
+
+
+
     /**
      * Send the {@link TermuxConstants#BROADCAST_TERMUX_OPENED} broadcast to notify apps that Termux
      * app has been opened.

termux-shared/src/main/res/values/strings.xml

@@ -9,6 +9,7 @@
     <!ENTITY TERMUX_STYLING_APP_NAME "Termux:Styling">
     <!ENTITY TERMUX_TASKER_APP_NAME "Termux:Tasker">
     <!ENTITY TERMUX_WIDGET_APP_NAME "Termux:Widget">
+    <!ENTITY TERMUX_PREFIX_DIR_PATH "/data/data/com.termux/files/usr">
     ]>
 
 <resources>
@@ -71,6 +72,15 @@
         on github or other official termux community forums **will likely be automatically closed/deleted** and may
         even result in **temporary or permanent** ban. Check %1$s/wiki/Hacking for details.</string>
 
+    <string name="msg_termux_app_required_by_app">The &TERMUX_APP_NAME; is required by the %1$s app to run termux commands."</string>
+    <string name="error_termux_app_not_installed_or_disabled_warning">The &TERMUX_APP_NAME; app is not installed or is disabled."</string>
+    <string name="error_termux_app_package_context_not_accessible">The &TERMUX_APP_NAME; app (package context) is not accessible."</string>
+    <string name="error_termux_prefix_dir_path_not_accessible">The &TERMUX_APP_NAME; app $PREFIX directory is not accessible by the %1$s app.
+        This may be because you have not installed or setup &TERMUX_APP_NAME; app or
+        &TERMUX_APP_NAME; app and %1$s app both have different APK signatures because you have managed to install both apps from different sources.
+        It may also be because &TERMUX_APP_NAME; $PREFIX directory \"&TERMUX_PREFIX_DIR_PATH;\" does not exist or does not have read,
+        write and execute permissions."</string>
+
 
 
     <!-- Miscellaneous -->