feat(android): expose content URI file descriptor

app/android/app/src/main/kotlin/org/localsend/localsend_app/MainActivity.kt

@@ -2,6 +2,7 @@ package org.localsend.localsend_app
 
 import android.annotation.SuppressLint
 import android.app.Activity
+import android.content.ContentResolver
 import android.content.Context
 import android.content.Intent
 import android.database.Cursor
@@ -58,6 +59,8 @@ class MainActivity : FlutterActivity() {
 
                 "createDirectory" -> handleCreateDirectory(call, result)
 
+                "getFileDescriptor" -> handleGetFileDescriptor(call, result)
+
                 "openContentUri" -> {
                     openUri(context, call.argument<String>("uri")!!)
                     result.success(null)
@@ -82,6 +85,38 @@ class MainActivity : FlutterActivity() {
             Settings.Global.ANIMATOR_DURATION_SCALE, 1.0f) != 0.0f;
     }
 
+    private fun handleGetFileDescriptor(call: MethodCall, result: MethodChannel.Result) {
+        val uriString = call.argument<String>("uri")
+        if (uriString == null) {
+            result.error("INVALID_ARGUMENT", "Missing content URI", null)
+            return
+        }
+
+        val uri = Uri.parse(uriString)
+        if (uri.scheme != ContentResolver.SCHEME_CONTENT) {
+            result.error("INVALID_ARGUMENT", "Expected a content:// URI", null)
+            return
+        }
+
+        try {
+            val parcelFileDescriptor = contentResolver.openFileDescriptor(uri, "r")
+            if (parcelFileDescriptor == null) {
+                result.error("OPEN_FAILED", "The content provider did not return a file descriptor", null)
+                return
+            }
+
+            // Ownership of the detached descriptor is transferred to the caller. It must be
+            // closed by Rust (or whichever native consumer receives it) after use.
+            parcelFileDescriptor.use {
+                result.success(it.detachFd())
+            }
+        } catch (e: SecurityException) {
+            result.error("PERMISSION_DENIED", e.message ?: "Permission denied for content URI", null)
+        } catch (e: Exception) {
+            result.error("OPEN_FAILED", e.message ?: "Failed to open content URI", null)
+        }
+    }
+
     private fun openDirectoryPicker(onlyPath: Boolean) {
         val intent = Intent(Intent.ACTION_OPEN_DOCUMENT_TREE)
         intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION)

app/lib/util/native/channel/android_channel.dart

@@ -44,6 +44,20 @@ Future<bool> getSystemAnimationsStatusAndroid() async {
   return await _methodChannel.invokeMethod('isAnimationsEnabled') ?? true;
 }
 
+/// Opens [uri] for reading and returns an owned Linux file descriptor.
+///
+/// The descriptor stays open after this call and must be closed by the native
+/// consumer it is passed to.
+Future<int> getFileDescriptorAndroid({required String uri}) async {
+  final fileDescriptor = await _methodChannel.invokeMethod<int>('getFileDescriptor', {
+    'uri': uri,
+  });
+  if (fileDescriptor == null) {
+    throw StateError('Android returned no file descriptor for $uri');
+  }
+  return fileDescriptor;
+}
+
 Future<void> createDirectory({
   required String documentUri,
   required String directoryName,