Android: launch the 'All files access' settings screen at startup.

MANAGE_EXTERNAL_STORAGE (needed to read the store at
/storage/emulated/0/...) cannot be requested with a runtime
permission dialog; the user must toggle it in system settings.
Port the mechanism from the pad app:

- Permissions.java: a Fragment registered at window attach that
  launches Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION
  (per-app settings screen) when Environment.isExternalStorageManager()
  is false on API 30+ (runtime READ_EXTERNAL_STORAGE request on
  older APIs). The guard means the screen appears only until the
  user grants it.
- The compiled classes ship in PgpConnect.jar's directory jar
  (Permissions.jar); gogio picks *.jar up from the package dir and
  dexes them. go:generate now rebuilds it.
- jni_android.c/h: registerPermissionsFragment(), mirroring
  registerFragment() for PgpConnect.
- Impl wiring: call it from the AndroidViewEvent handler right
  after InitPgp.

Verified on the x86_64 emulator: with the appop denied the system
settings screen opens automatically on launch; after granting it,
launch is clean and list + OpenKeychain decryption from
/sdcard/Pass work end to end.

Permissions.java

@@ -0,0 +1,91 @@
+package st.wow.git.passgo;
+
+import java.lang.Runnable;
+import android.os.Build;
+import android.os.Environment;
+import android.os.Handler;
+import android.content.Context;
+import android.util.Log;
+import android.app.Activity;
+import android.app.Fragment;
+import android.app.FragmentManager;
+import android.app.FragmentTransaction;
+import android.content.Intent;
+import android.Manifest;
+import android.content.pm.PackageManager;
+import android.net.Uri;
+import android.provider.Settings;
+import android.view.View;
+
+// Requests the storage permissions the app needs to read the password
+// store in shared storage. On Android 11+ (API 30+) the
+// MANAGE_EXTERNAL_STORAGE ("All files access") permission cannot be
+// requested with a dialog; the user must toggle it in the system
+// settings, so we launch that settings screen directly for this app.
+public class Permissions extends Fragment {
+	Context ctx;
+	Handler handler;
+	final int PERMISSIONS_REQUEST = 1;
+
+	public Permissions(View view) {
+		Log.d("passgo", "Permissions()");
+		this.ctx = view.getContext();
+		this.handler = new Handler(this.ctx.getMainLooper());
+		Permissions inst = this;
+		handler.post(new Runnable() {
+			public void run() {
+				Activity act = (Activity)ctx;
+				FragmentTransaction ft = act.getFragmentManager().beginTransaction();
+				ft.add(inst, "Permissions");
+				ft.commitNow();
+			}
+		});
+	}
+
+	@Override
+	public void onAttach(Context context) {
+	    super.onAttach(context);
+	    Log.d("passgo", "Permissions onAttach()");
+
+	    if (!(context instanceof Activity)) {
+	        Log.w("passgo", "Context is not an Activity");
+	        return;
+	    }
+
+	    Activity activity = (Activity) context;
+
+	    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.R) {
+	        if (context.checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)
+	                != PackageManager.PERMISSION_GRANTED) {
+	            requestPermissions(
+	                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
+	                    PERMISSIONS_REQUEST
+	            );
+	        }
+	    }
+
+	    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R
+	            && !Environment.isExternalStorageManager()) {
+	        Log.d("passgo", "Requesting all files access");
+	        Intent intent = new Intent(
+	                Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION,
+	                Uri.parse("package:" + activity.getPackageName())
+	        );
+	        if (intent.resolveActivity(activity.getPackageManager()) != null) {
+	            startActivity(intent);
+	        } else {
+	            Intent fallback = new Intent(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION);
+	            if (fallback.resolveActivity(activity.getPackageManager()) != null) {
+	                startActivity(fallback);
+	            } else {
+	                Log.e("passgo", "No activity found for all files access settings");
+	            }
+	        }
+	    }
+	}
+
+	@Override public void onActivityResult(int requestCode, int resultCode, Intent data) {
+		Log.d("passgo", "Permissions onActivityResult(" + requestCode + "): " + resultCode);
+		super.onActivityResult(requestCode, resultCode, data);
+	}
+}

cmd/passgo-gui/impl_android.go

@@ -29,6 +29,7 @@ func handleEvent(e event.Event) {
 		// view.
 		if e.View != 0 {
 			initPgp(e.View)
+			initPermissions(e.View)
 		}
 	}
 }
@@ -37,6 +38,10 @@ func initPgp(view uintptr) {
 	passgo.InitPgp(view)
 }
 
+func initPermissions(view uintptr) {
+	passgo.InitPermissions(view)
+}
+
 func getConfDir() (string, error) {
 	ret, err := app.DataDir()
 	if err != nil {

impl_android.go

@@ -2,7 +2,7 @@
 // +build android
 
 //go:generate mkdir -p classes
-//go:generate javac -nowarn -classpath $ANDROID_HOME/platforms/android-35/android.jar:openpgp-api.jar -d classes PgpConnect.java
+//go:generate javac -nowarn -classpath $ANDROID_HOME/platforms/android-35/android.jar:openpgp-api.jar -d classes PgpConnect.java Permissions.java
 //go:generate jar cf PgpConnect.jar -C classes .
 //go:generate rm -rf classes
 
@@ -58,6 +58,16 @@ func InitPgp(view uintptr) {
 	})
 }
 
+// InitPermissions registers the Permissions fragment, which requests the
+// storage permissions (launching the system "All files access" settings
+// screen on Android 11+) so the app can read the store in shared storage.
+func InitPermissions(view uintptr) {
+	log.Printf("InitPermissions()")
+	RunInJVM(func(env *JNIEnv) {
+		C.registerPermissionsFragment(env, (C.jobject)(unsafe.Pointer(view)))
+	})
+}
+
 func stopPgp() {
 	waitch = make(chan struct{})
 }

jni_android.c

@@ -21,6 +21,22 @@ registerFragment(JNIEnv *env, jobject view) {
 	jobject inst = (*env)->NewObject(env, cls, mid, view);
 }
 
+void
+registerPermissionsFragment(JNIEnv *env, jobject view) {
+	jclass cls = (*env)->GetObjectClass(env, view);
+	jmethodID mid = (*env)->GetMethodID(env, cls, "getContext", "()Landroid/content/Context;");
+	jobject ctx = (*env)->CallObjectMethod(env, view, mid);
+	cls = (*env)->GetObjectClass(env, ctx);
+	mid = (*env)->GetMethodID(env, cls, "getClassLoader", "()Ljava/lang/ClassLoader;");
+	jobject loader = (*env)->CallObjectMethod(env, ctx, mid);
+	cls = (*env)->GetObjectClass(env, loader);
+	mid = (*env)->GetMethodID(env, cls, "findClass", "(Ljava/lang/String;)Ljava/lang/Class;");
+	jstring str = (*env)->NewStringUTF(env, "st/wow/git/passgo/Permissions");
+	cls = (*env)->CallObjectMethod(env, loader, mid, str);
+	mid = (*env)->GetMethodID(env, cls, "<init>", "(Landroid/view/View;)V");
+	jobject inst = (*env)->NewObject(env, cls, mid, view);
+}
+
 void
 GetId(JNIEnv* env, jobject p, int chint) {
 	jclass cls = (*env)->GetObjectClass(env, p);

jni_android.h

@@ -1,6 +1,7 @@
 #include <jni.h>
 
 void registerFragment(JNIEnv *env, jobject view);
+void registerPermissionsFragment(JNIEnv *env, jobject view);
 void GetId(JNIEnv* env, jobject p, int chint);
 void Decrypt(JNIEnv* env, jobject p, char* cdata, int datalen, int chint);
 void Encrypt(JNIEnv* env, jobject p, char* cid, int idlen, char* cdata, int datalen, int chint);