feat(send): share folders as multi-file collections

Add folder pickers on Android, iOS, and desktop. Desktop and iOS walk
directory paths in Rust; Android expands SAF trees to per-file FDs
with relative collection paths because directory FDs are unsupported.

shared/src/androidMain/kotlin/com/vnidrop/app/core/FilePicker.android.kt

@@ -20,7 +20,7 @@ actual fun rememberShareFilePicker(
 	onError: (String) -> Unit,
 ): ShareFilePicker {
 	val context = LocalContext.current
-	val launcher = rememberLauncherForActivityResult(ActivityResultContracts.OpenMultipleDocuments()) { uris ->
+	val filesLauncher = rememberLauncherForActivityResult(ActivityResultContracts.OpenMultipleDocuments()) { uris ->
 		if (uris.isEmpty()) return@rememberLauncherForActivityResult
 		runCatching {
 			uris.map { uri -> context.pickedShareFile(uri) }
@@ -29,10 +29,41 @@ actual fun rememberShareFilePicker(
 			onFailure = { onError(it.message ?: "Could not open the selected files") },
 		)
 	}
-	return remember(launcher) {
+	val folderLauncher = rememberLauncherForActivityResult(ActivityResultContracts.OpenDocumentTree()) { uri ->
+		if (uri == null) return@rememberLauncherForActivityResult
+		runCatching {
+			// Read permission only — we expand the tree into file FDs at share time.
+			context.contentResolver.takePersistableUriPermission(
+				uri,
+				Intent.FLAG_GRANT_READ_URI_PERMISSION,
+			)
+			val displayName = uri.lastPathSegment
+				?.substringAfterLast(':')
+				?.substringAfterLast('/')
+				?.ifBlank { null }
+				?: "Folder"
+			listOf(
+				PickedShareFile(
+					value = uri.toString(),
+					displayName = displayName,
+					sizeBytes = null,
+					thumbnailBytes = null,
+					isDirectory = true,
+				),
+			)
+		}.fold(
+			onSuccess = onFilesPicked,
+			onFailure = { onError(it.message ?: "Could not open the selected folder") },
+		)
+	}
+	return remember(filesLauncher, folderLauncher) {
 		object : ShareFilePicker {
 			override fun pickFiles() {
-				launcher.launch(arrayOf("*/*"))
+				filesLauncher.launch(arrayOf("*/*"))
+			}
+
+			override fun pickFolder() {
+				folderLauncher.launch(null)
 			}
 		}
 	}

shared/src/androidMain/kotlin/com/vnidrop/app/core/FileSystemService.android.kt

@@ -71,12 +71,18 @@ private class AndroidFileSystemService(
 		accessPolicy: ShareAccessPolicy,
 	): Result<Share> = runCatching {
 		require(files.isNotEmpty()) { "Select at least one file to share" }
-		val descriptors = files.map { file ->
+		// Android cannot pass a directory as a single FD. Expand SAF trees into
+		// individual document files with relative collection paths, then open FDs.
+		val expanded = files.flatMap { file ->
+			if (file.isDirectory) context.expandShareDirectory(file) else listOf(file)
+		}
+		require(expanded.isNotEmpty()) { "No files found in the selected folder" }
+		val descriptors = expanded.map { file ->
 			context.contentResolver.openFileDescriptor(Uri.parse(file.value), "r")
 				?: error("Could not open selected file descriptor for ${file.displayName}")
 		}
 		try {
-			val sources = files.zip(descriptors) { file, descriptor ->
+			val sources = expanded.zip(descriptors) { file, descriptor ->
 				uniffi.vnidrop.ShareSource(
 					kind = uniffi.vnidrop.SourceKind.FILE_DESCRIPTOR,
 					value = descriptor.fd.toString(),
@@ -140,6 +146,63 @@ private class AndroidFileSystemService(
 	}
 }
 
+/**
+ * Expand a SAF document tree into individual file documents.
+ *
+ * Rust cannot accept a directory FD. Collection paths preserve the folder
+ * root name so receivers see `Folder/nested/file.txt`.
+ */
+private fun Context.expandShareDirectory(folder: PickedShareFile): List<PickedShareFile> {
+	val treeUri = Uri.parse(folder.value)
+	val rootId = DocumentsContract.getTreeDocumentId(treeUri)
+	val out = mutableListOf<PickedShareFile>()
+	fun walk(documentId: String, relativePath: String) {
+		val childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(treeUri, documentId)
+		contentResolver.query(
+			childrenUri,
+			arrayOf(
+				DocumentsContract.Document.COLUMN_DOCUMENT_ID,
+				DocumentsContract.Document.COLUMN_DISPLAY_NAME,
+				DocumentsContract.Document.COLUMN_MIME_TYPE,
+				DocumentsContract.Document.COLUMN_SIZE,
+			),
+			null,
+			null,
+			null,
+		)?.use { cursor ->
+			val idIndex = cursor.getColumnIndex(DocumentsContract.Document.COLUMN_DOCUMENT_ID)
+			val nameIndex = cursor.getColumnIndex(DocumentsContract.Document.COLUMN_DISPLAY_NAME)
+			val mimeIndex = cursor.getColumnIndex(DocumentsContract.Document.COLUMN_MIME_TYPE)
+			val sizeIndex = cursor.getColumnIndex(DocumentsContract.Document.COLUMN_SIZE)
+			while (cursor.moveToNext()) {
+				val id = cursor.getString(idIndex) ?: continue
+				val name = cursor.getString(nameIndex) ?: continue
+				val mime = cursor.getString(mimeIndex)
+				val childRelative = if (relativePath.isEmpty()) name else "$relativePath/$name"
+				if (mime == DocumentsContract.Document.MIME_TYPE_DIR) {
+					walk(id, childRelative)
+				} else {
+					val documentUri = DocumentsContract.buildDocumentUriUsingTree(treeUri, id)
+					val size = if (sizeIndex >= 0 && !cursor.isNull(sizeIndex)) {
+						cursor.getLong(sizeIndex).takeIf { it >= 0L }?.toULong()
+					} else {
+						null
+					}
+					out += PickedShareFile(
+						value = documentUri.toString(),
+						displayName = childRelative,
+						sizeBytes = size,
+						isDirectory = false,
+					)
+				}
+			}
+		}
+	}
+	// Prefix paths with the folder display name so nested structure is preserved.
+	walk(rootId, folder.displayName)
+	return out
+}
+
 /**
  * Writes into the shared system Downloads collection via MediaStore.
  *

shared/src/commonMain/composeResources/values/strings.xml

@@ -10,8 +10,9 @@
     <string name="send_transfers_title">Your transfers</string>
     <string name="send_new_transfer_title">New transfer</string>
     <string name="send_choose_file_title">Choose what to share</string>
-    <string name="send_choose_file_body">Select one or more files from this device. You can review them before creating the transfer.</string>
+    <string name="send_choose_file_body">Select files or a folder from this device. You can review the selection before creating the transfer.</string>
     <string name="send_selected_files_count">%1$d files selected</string>
+    <string name="send_folder_label">Folder</string>
     <string name="button_remove_file">Remove file</string>
     <string name="button_choose_files">Choose files</string>
     <string name="button_change_files">Change files</string>

shared/src/commonMain/kotlin/com/vnidrop/app/core/FilePicker.kt

@@ -7,11 +7,20 @@ data class PickedShareFile(
 	val displayName: String,
 	val sizeBytes: ULong? = null,
 	val thumbnailBytes: ByteArray? = null,
+	/**
+	 * When true, [value] is a directory (filesystem path, iOS security-scoped
+	 * folder URL, or Android document tree URI). Platform share code expands or
+	 * walks it; Rust cannot treat an Android FD as a directory.
+	 */
+	val isDirectory: Boolean = false,
 )
 
 interface ShareFilePicker {
 	/** Opens a platform picker that may return one or more files. */
 	fun pickFiles()
+
+	/** Opens a platform folder picker for sharing a directory as one transfer. */
+	fun pickFolder()
 }
 
 interface ReceiveFolderPicker {

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/SendRoute.kt

@@ -24,6 +24,7 @@ fun SendRoute(
 		viewModel.effectFlow.collect { effect ->
 			when (effect) {
 				SendEffect.OpenFilePicker -> picker.pickFiles()
+				SendEffect.OpenFolderPicker -> picker.pickFolder()
 				is SendEffect.CopyTicket -> clipboard.setText(AnnotatedString(effect.ticket))
 			}
 		}
@@ -37,6 +38,7 @@ fun SendRoute(
 		onOpenComposer = viewModel::openComposer,
 		onDismissComposer = viewModel::dismissComposer,
 		onSelectFile = viewModel::selectFile,
+		onSelectFolder = viewModel::selectFolder,
 		onClearFile = viewModel::clearSelectedSource,
 		onRemoveFile = viewModel::removeSelectedFile,
 		onTransferNameChanged = viewModel::setTransferName,

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/SendScreen.kt

@@ -24,6 +24,7 @@ fun SendScreen(
 	onOpenComposer: () -> Unit,
 	onDismissComposer: () -> Unit,
 	onSelectFile: () -> Unit,
+	onSelectFolder: () -> Unit = {},
 	onClearFile: () -> Unit,
 	onRemoveFile: (String) -> Unit = {},
 	onTransferNameChanged: (String) -> Unit,
@@ -83,6 +84,7 @@ fun SendScreen(
 				state = state,
 				windowClass = windowClass,
 				onSelectFile = onSelectFile,
+				onSelectFolder = onSelectFolder,
 				onClearFile = onClearFile,
 				onRemoveFile = onRemoveFile,
 				onTransferNameChanged = onTransferNameChanged,

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/SendViewModel.kt

@@ -54,6 +54,7 @@ enum class TransferDetailPanel { Activity, Receivers, Share }
 
 sealed interface SendEffect {
 	data object OpenFilePicker : SendEffect
+	data object OpenFolderPicker : SendEffect
 	data class CopyTicket(val ticket: String) : SendEffect
 }
 
@@ -135,6 +136,7 @@ class SendViewModel(
 	}
 
 	fun selectFile() = sendEffect(SendEffect.OpenFilePicker)
+	fun selectFolder() = sendEffect(SendEffect.OpenFolderPicker)
 
 	fun onFilesPicked(files: List<PickedShareFile>) {
 		if (files.isEmpty()) return
@@ -271,9 +273,11 @@ class SendViewModel(
 		}
 	}
 
-	private fun defaultTransferName(files: List<PickedShareFile>): String = when (files.size) {
-		0 -> ""
-		1 -> files.first().displayName
+	private fun defaultTransferName(files: List<PickedShareFile>): String = when {
+		files.isEmpty() -> ""
+		files.size == 1 && files.first().isDirectory -> files.first().displayName
+		files.size == 1 -> files.first().displayName
+		files.all { it.isDirectory } -> "${files.size} folders"
 		else -> "${files.size} files"
 	}
 

shared/src/commonMain/kotlin/com/vnidrop/app/feature/send/TransferComposer.kt

@@ -42,6 +42,7 @@ import org.jetbrains.compose.resources.stringResource
 import vnidrop.shared.generated.resources.Res
 import vnidrop.shared.generated.resources.button_change_files
 import vnidrop.shared.generated.resources.button_choose_files
+import vnidrop.shared.generated.resources.button_choose_folder
 import vnidrop.shared.generated.resources.button_clear
 import vnidrop.shared.generated.resources.button_remove_file
 import vnidrop.shared.generated.resources.button_share_file
@@ -56,6 +57,7 @@ import vnidrop.shared.generated.resources.send_access_title
 import vnidrop.shared.generated.resources.send_choose_file_body
 import vnidrop.shared.generated.resources.send_choose_file_title
 import vnidrop.shared.generated.resources.send_file_size_unknown
+import vnidrop.shared.generated.resources.send_folder_label
 import vnidrop.shared.generated.resources.send_review_title
 import vnidrop.shared.generated.resources.send_selected_files_count
 
@@ -65,6 +67,7 @@ internal fun TransferComposer(
 	state: SendState,
 	windowClass: WindowClass,
 	onSelectFile: () -> Unit,
+	onSelectFolder: () -> Unit,
 	onClearFile: () -> Unit,
 	onRemoveFile: (String) -> Unit,
 	onTransferNameChanged: (String) -> Unit,
@@ -77,12 +80,13 @@ internal fun TransferComposer(
 		verticalArrangement = Arrangement.spacedBy(16.dp),
 	) {
 		if (state.selectedFiles.isEmpty()) {
-			ChooseFileStep(onSelectFile)
+			ChooseFileStep(onSelectFile, onSelectFolder)
 		} else {
 			ReviewFileStep(
 				state = state,
 				windowClass = windowClass,
 				onSelectFile = onSelectFile,
+				onSelectFolder = onSelectFolder,
 				onClearFile = onClearFile,
 				onRemoveFile = onRemoveFile,
 				onTransferNameChanged = onTransferNameChanged,
@@ -96,7 +100,7 @@ internal fun TransferComposer(
 }
 
 @Composable
-private fun ChooseFileStep(onSelectFile: () -> Unit) {
+private fun ChooseFileStep(onSelectFile: () -> Unit, onSelectFolder: () -> Unit) {
 	Text(stringResource(Res.string.send_choose_file_title), style = MaterialTheme.typography.titleLarge, fontWeight = FontWeight.SemiBold)
 	Text(
 		stringResource(Res.string.send_choose_file_body),
@@ -111,6 +115,7 @@ private fun ChooseFileStep(onSelectFile: () -> Unit) {
 		) {
 			Icon(SendIcons.File, contentDescription = null, tint = LocalVniDropColors.current.brandLink, modifier = Modifier.size(32.dp))
 			PrimaryButton(stringResource(Res.string.button_choose_files), onClick = onSelectFile)
+			QuietButton(stringResource(Res.string.button_choose_folder), onClick = onSelectFolder)
 		}
 	}
 }
@@ -120,6 +125,7 @@ private fun ReviewFileStep(
 	state: SendState,
 	windowClass: WindowClass,
 	onSelectFile: () -> Unit,
+	onSelectFolder: () -> Unit,
 	onClearFile: () -> Unit,
 	onRemoveFile: (String) -> Unit,
 	onTransferNameChanged: (String) -> Unit,
@@ -164,11 +170,13 @@ private fun ReviewFileStep(
 		Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
 			ShareButton(state, coreInitialized, onCreateShare, Modifier.fillMaxWidth())
 			QuietButton(stringResource(Res.string.button_change_files), onClick = onSelectFile, modifier = Modifier.fillMaxWidth(), enabled = !state.isSharing)
+			QuietButton(stringResource(Res.string.button_choose_folder), onClick = onSelectFolder, modifier = Modifier.fillMaxWidth(), enabled = !state.isSharing)
 		}
 	} else {
 		Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
 			ShareButton(state, coreInitialized, onCreateShare)
 			QuietButton(stringResource(Res.string.button_change_files), onClick = onSelectFile, enabled = !state.isSharing)
+			QuietButton(stringResource(Res.string.button_choose_folder), onClick = onSelectFolder, enabled = !state.isSharing)
 			QuietButton(stringResource(Res.string.button_clear), onClick = onClearFile, enabled = !state.isSharing)
 		}
 	}
@@ -199,7 +207,11 @@ private fun SelectedFileCard(
 			Column(Modifier.weight(1f), verticalArrangement = Arrangement.spacedBy(3.dp)) {
 				Text(file.displayName, fontWeight = FontWeight.SemiBold, maxLines = 1, overflow = TextOverflow.Ellipsis)
 				Text(
-					file.sizeBytes?.let(::formatBytes) ?: stringResource(Res.string.send_file_size_unknown),
+					when {
+						file.isDirectory -> stringResource(Res.string.send_folder_label)
+						file.sizeBytes != null -> formatBytes(file.sizeBytes)
+						else -> stringResource(Res.string.send_file_size_unknown)
+					},
 					color = LocalVniDropColors.current.foregroundLighter,
 					style = MaterialTheme.typography.bodySmall,
 				)

shared/src/commonTest/kotlin/com/vnidrop/app/feature/ViewModelsTest.kt

@@ -246,6 +246,24 @@ class ViewModelsTest {
 		assertTrue(viewModel.state.value.selectedFiles.isEmpty())
 	}
 
+	@Test
+	fun sendViewModelNamesFolderSelectionAfterFolderDisplayName() = runTest {
+		Dispatchers.setMain(StandardTestDispatcher(testScheduler))
+		val viewModel = SendViewModel(FakeCoreGateway(), FakeFileSystemService(folder), preferences(), FakeFilePreviewRepository(), UiMessageController())
+		advanceUntilIdle()
+		viewModel.onFilesPicked(
+			listOf(
+				com.vnidrop.app.core.PickedShareFile(
+					value = "/tmp/photos",
+					displayName = "photos",
+					isDirectory = true,
+				),
+			),
+		)
+		assertEquals("photos", viewModel.state.value.transferName)
+		assertTrue(viewModel.state.value.selectedFiles.single().isDirectory)
+	}
+
 	@Test
 	fun sendDeletionRemovesCoreTransferAndOwnedPreview() = runTest {
 		Dispatchers.setMain(StandardTestDispatcher(testScheduler))

shared/src/iosMain/kotlin/com/vnidrop/app/core/FilePicker.ios.kt

@@ -46,6 +46,32 @@ actual fun rememberShareFilePicker(
 			picker.modalPresentationStyle = UIModalPresentationFormSheet
 			presenter.presentViewController(picker, animated = true, completion = null)
 		}
+
+		@OptIn(ExperimentalForeignApi::class)
+		override fun pickFolder() {
+			val presenter = UIApplication.sharedApplication.keyWindow?.rootViewController
+			if (presenter == null) {
+				onError("Could not find an iOS view controller for the folder picker")
+				return
+			}
+			val picker = UIDocumentPickerViewController(forOpeningContentTypes = listOf(UTTypeFolder), asCopy = false)
+			val delegate = DocumentPickerDelegate(
+				onFilesPicked = { folders ->
+					val folder = folders.firstOrNull() ?: return@DocumentPickerDelegate
+					onFilesPicked(
+						listOf(
+							folder.copy(isDirectory = true),
+						),
+					)
+				},
+				onError = onError,
+				forceDirectory = true,
+			)
+			retainedPickerDelegate = delegate
+			picker.delegate = delegate
+			picker.modalPresentationStyle = UIModalPresentationFormSheet
+			presenter.presentViewController(picker, animated = true, completion = null)
+		}
 	}
 }
 
@@ -88,6 +114,7 @@ actual fun rememberReceiveFolderPicker(
 private class DocumentPickerDelegate(
 	private val onFilesPicked: (List<PickedShareFile>) -> Unit,
 	private val onError: (String) -> Unit,
+	private val forceDirectory: Boolean = false,
 ) : NSObject(), UIDocumentPickerDelegateProtocol {
 	override fun documentPicker(controller: UIDocumentPickerViewController, didPickDocumentsAtURLs: List<*>) {
 		val files = didPickDocumentsAtURLs.mapNotNull { raw ->
@@ -95,8 +122,12 @@ private class DocumentPickerDelegate(
 			val displayName = url.lastPathComponent ?: "transfer"
 			val didStartAccess = url.startAccessingSecurityScopedResource()
 			val sizeBytes = try {
+				if (forceDirectory) {
+					null
+				} else {
 					val attributes = url.path?.let { NSFileManager.defaultManager.attributesOfItemAtPath(it, null) }
 					(attributes?.get(NSFileSize) as? NSNumber)?.unsignedLongLongValue
+				}
 			} finally {
 				if (didStartAccess) url.stopAccessingSecurityScopedResource()
 			}
@@ -105,6 +136,7 @@ private class DocumentPickerDelegate(
 				displayName,
 				sizeBytes,
 				nativeFileIcon(url),
+				isDirectory = forceDirectory,
 			)
 		}
 		if (files.isEmpty()) {

shared/src/iosMain/kotlin/com/vnidrop/app/core/FileSystemService.ios.kt

@@ -56,7 +56,7 @@ private class IosFileSystemService : FileSystemService {
 				kind = uniffi.vnidrop.SourceKind.IOS_SECURITY_SCOPED_URL,
 				value = file.value,
 				displayName = file.displayName,
-				isDirectory = false,
+				isDirectory = file.isDirectory,
 			)
 		}
 		return repository.shareSources(sources, transferName, senderName, accessPolicy)

shared/src/jvmMain/kotlin/com/vnidrop/app/core/FilePicker.jvm.kt

@@ -25,6 +25,23 @@ actual fun rememberShareFilePicker(
 				if (selected.isNotEmpty()) onFilesPicked(selected)
 			}
 		}
+
+		override fun pickFolder() {
+			openPicker(onError) {
+				val selected = pickDirectory(title = "Select folder to share") ?: return@openPicker
+				onFilesPicked(
+					listOf(
+						PickedShareFile(
+							value = selected.absolutePath,
+							displayName = selected.name.ifBlank { selected.absolutePath },
+							sizeBytes = null,
+							thumbnailBytes = selected.systemIconPng(),
+							isDirectory = true,
+						),
+					),
+				)
+			}
+		}
 	}
 }
 
@@ -36,7 +53,7 @@ actual fun rememberReceiveFolderPicker(
 	object : ReceiveFolderPicker {
 		override fun pickFolder() {
 			openPicker(onError) {
-				val selected = pickDirectory() ?: return@openPicker
+				val selected = pickDirectory(title = "Select receive folder") ?: return@openPicker
 				onFolderPicked(
 					ReceiveFolder(
 						kind = ReceiveFolderKind.FileSystemPath,
@@ -111,10 +128,10 @@ private fun File.systemIconPng(): ByteArray? = runCatching {
 	}
 }.getOrNull()
 
-private fun pickDirectory(): File? =
+private fun pickDirectory(title: String): File? =
 	if (isMacOs()) {
 		val dialog = withMacDirectoryDialog {
-			nativeFileDialog("Select receive folder").apply { isVisible = true }
+			nativeFileDialog(title).apply { isVisible = true }
 		}
 		try {
 			val directory = dialog.directory ?: return null
@@ -126,7 +143,7 @@ private fun pickDirectory(): File? =
 		}
 	} else {
 		val chooser = JFileChooser().apply {
-			dialogTitle = "Select receive folder"
+			dialogTitle = title
 			fileSelectionMode = JFileChooser.DIRECTORIES_ONLY
 			isAcceptAllFileFilterUsed = false
 		}

shared/src/jvmMain/kotlin/com/vnidrop/app/core/FileSystemService.jvm.kt

@@ -41,7 +41,7 @@ private class JvmFileSystemService : FileSystemService {
 				kind = uniffi.vnidrop.SourceKind.PATH,
 				value = file.value,
 				displayName = file.displayName,
-				isDirectory = false,
+				isDirectory = file.isDirectory || File(file.value).isDirectory,
 			)
 		}
 		return repository.shareSources(sources, transferName, senderName, accessPolicy)