android: expand SAF FileOps implementation

This expands the SAF FileOps to implement the refactored FileOps

Updates tailscale/corp#29211

Signed-off-by: kari-ts <kari@tailscale.com>

android/src/main/java/com/tailscale/ipn/ui/util/OutputStreamAdapter.kt

@@ -24,3 +24,4 @@ class OutputStreamAdapter(private val outputStream: OutputStream) : libtailscale
     outputStream.close()
   }
 }
+

android/src/main/java/com/tailscale/ipn/ui/view/UserSwitcherView.kt

@@ -3,6 +3,8 @@
 
 package com.tailscale.ipn.ui.view
 
+import android.content.Intent
+import android.net.Uri
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
@@ -12,6 +14,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.MoreVert
+import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.DropdownMenu
 import androidx.compose.material3.DropdownMenuItem
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -20,12 +23,15 @@ import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
@@ -138,6 +144,7 @@ fun UserSwitcherView(nav: UserSwitcherNav, viewModel: UserSwitcherViewModel = vi
                           }
                         })
                   }
+
                 }
               }
             }

android/src/main/java/com/tailscale/ipn/util/ShareFileHelper.kt

@@ -5,9 +5,14 @@ package com.tailscale.ipn.util
 
 import android.content.Context
 import android.net.Uri
+import android.os.ParcelFileDescriptor
+import android.provider.DocumentsContract
 import androidx.documentfile.provider.DocumentFile
+import com.tailscale.ipn.ui.util.InputStreamAdapter
 import com.tailscale.ipn.ui.util.OutputStreamAdapter
 import libtailscale.Libtailscale
+import org.json.JSONObject
+import java.io.FileOutputStream
 import java.io.IOException
 import java.io.OutputStream
 import java.util.UUID
@@ -29,59 +34,69 @@ object ShareFileHelper : libtailscale.ShareFileHelper {
   // A simple data class that holds a SAF OutputStream along with its URI.
   data class SafStream(val uri: String, val stream: OutputStream)
 
-  // Cache for streams; keyed by file name and savedUri.
-  private val streamCache = ConcurrentHashMap<String, SafStream>()
-
-  // A helper function that creates (or reuses) a SafStream for a given file.
-  private fun createStreamCached(fileName: String): SafStream {
-    val key = "$fileName|$savedUri"
-    return streamCache.getOrPut(key) {
-      val context: Context =
-          appContext
-              ?: run {
-                TSLog.e("ShareFileHelper", "appContext is null, cannot create file: $fileName")
-                return SafStream("", OutputStream.nullOutputStream())
-              }
-      val directoryUriString =
-          savedUri
-              ?: run {
-                TSLog.e("ShareFileHelper", "savedUri is null, cannot create file: $fileName")
-                return SafStream("", OutputStream.nullOutputStream())
-              }
-      val dirUri = Uri.parse(directoryUriString)
-      val pickedDir: DocumentFile =
-          DocumentFile.fromTreeUri(context, dirUri)
-              ?: run {
-                TSLog.e("ShareFileHelper", "Could not access directory for URI: $dirUri")
-                return SafStream("", OutputStream.nullOutputStream())
-              }
-      val newFile: DocumentFile =
-          pickedDir.createFile("application/octet-stream", fileName)
-              ?: run {
-                TSLog.e("ShareFileHelper", "Failed to create file: $fileName in directory: $dirUri")
-                return SafStream("", OutputStream.nullOutputStream())
-              }
-      // Attempt to open an OutputStream for writing.
-      val os: OutputStream? = context.contentResolver.openOutputStream(newFile.uri)
-      if (os == null) {
-        TSLog.e("ShareFileHelper", "openOutputStream returned null for URI: ${newFile.uri}")
-        SafStream(newFile.uri.toString(), OutputStream.nullOutputStream())
-      } else {
-        TSLog.d("ShareFileHelper", "Opened OutputStream for file: $fileName")
-        SafStream(newFile.uri.toString(), os)
-      }
-    }
+  // A helper function that opens or creates a SafStream for a given file.
+  private fun openSafFileOutputStream(fileName: String): Pair<String, OutputStream?> {
+    val context = appContext ?: return "" to null
+    val dirUri = savedUri ?: return "" to null
+    val dir = DocumentFile.fromTreeUri(context, Uri.parse(dirUri)) ?: return "" to null
+
+    val file =
+        dir.findFile(fileName)
+            ?: dir.createFile("application/octet-stream", fileName)
+            ?: return "" to null
+
+    val os = context.contentResolver.openOutputStream(file.uri, "rw")
+    return file.uri.toString() to os
   }
 
-  // This method returns a SafStream containing the SAF URI and its corresponding OutputStream.
+  private fun openWriterFD(fileName: String, offset: Long): Pair<String, SeekableOutputStream?> {
+
+    val ctx = appContext ?: return "" to null
+    val dirUri = savedUri ?: return "" to null
+    val dir = DocumentFile.fromTreeUri(ctx, Uri.parse(dirUri)) ?: return "" to null
+
+    // Reuse existing doc if it exists
+    val file =
+        dir.findFile(fileName)
+            ?: dir.createFile("application/octet-stream", fileName)
+            ?: return "" to null
+
+    // Always get a ParcelFileDescriptor so we can sync
+    val pfd = ctx.contentResolver.openFileDescriptor(file.uri, "rw") ?: return "" to null
+    val fos = FileOutputStream(pfd.fileDescriptor)
+
+    if (offset != 0L) fos.channel.position(offset) else fos.channel.truncate(0)
+
+    return file.uri.toString() to SeekableOutputStream(fos, pfd)
+  }
+
+  private val currentUri = ConcurrentHashMap<String, String>()
+
   override fun openFileWriter(fileName: String): libtailscale.OutputStream {
-    val stream = createStreamCached(fileName)
-    return OutputStreamAdapter(stream.stream)
+    val (uri, stream) = openWriterFD(fileName, 0)
+    currentUri[fileName] = uri // 🠚 cache the exact doc we opened
+    return OutputStreamAdapter(stream ?: OutputStream.nullOutputStream())
+  }
+
+  override fun openFileWriterAt(fileName: String, offset: Long): libtailscale.OutputStream {
+    val (uri, stream) = openWriterFD(fileName, offset)
+    currentUri[fileName] = uri
+    return OutputStreamAdapter(stream ?: OutputStream.nullOutputStream())
   }
 
   override fun openFileURI(fileName: String): String {
-    val safFile = createStreamCached(fileName)
-    return safFile.uri
+    currentUri[fileName]?.let {
+      return it
+    }
+    val ctx = appContext ?: return ""
+    val dirStr = savedUri ?: return ""
+    val dir = DocumentFile.fromTreeUri(ctx, Uri.parse(dirStr)) ?: return ""
+
+    val file = dir.findFile(fileName) ?: return ""
+    val uri = file.uri.toString()
+
+    currentUri[fileName] = uri
+    return uri
   }
 
   override fun renamePartialFile(
@@ -89,40 +104,98 @@ object ShareFileHelper : libtailscale.ShareFileHelper {
       targetDirUri: String,
       targetName: String
   ): String {
+    val ctx = appContext ?: throw IOException("not initialized")
+    val srcUri = Uri.parse(partialUri)
+    val dir =
+        DocumentFile.fromTreeUri(ctx, Uri.parse(targetDirUri))
+            ?: throw IOException("cannot open dir $targetDirUri")
+
+    var finalName = targetName
+    dir.findFile(finalName)?.let { existing ->
+      if (lengthOfUri(ctx, existing.uri) == 0L) {
+        existing.delete() // remove stale 0‑byte file
+      } else {
+        finalName = generateNewFilename(finalName)
+      }
+    }
+
     try {
-      val context = appContext ?: throw IllegalStateException("appContext is null")
-      val partialUriObj = Uri.parse(partialUri)
-      val targetDirUriObj = Uri.parse(targetDirUri)
-      val targetDir =
-          DocumentFile.fromTreeUri(context, targetDirUriObj)
-              ?: throw IllegalStateException(
-                  "Unable to get target directory from URI: $targetDirUri")
-      var finalTargetName = targetName
-
-      var destFile = targetDir.findFile(finalTargetName)
-      if (destFile != null) {
-        finalTargetName = generateNewFilename(finalTargetName)
+      DocumentsContract.renameDocument(ctx.contentResolver, srcUri, finalName)?.also { newUri ->
+        runCatching { ctx.contentResolver.delete(srcUri, null, null) }
+        cleanupPartials(dir, targetName)
+        return newUri.toString()
+      }
+    } catch (_: Exception) {
+      // rename not supported; fall through to copy‑delete
+    }
+
+    // fallback - copy contents then delete source
+    val dest =
+        dir.createFile("application/octet-stream", finalName)
+            ?: throw IOException("createFile failed for $finalName")
+
+    ctx.contentResolver.openInputStream(srcUri).use { inp ->
+      ctx.contentResolver.openOutputStream(dest.uri, "w").use { out ->
+        if (inp == null || out == null) {
+          dest.delete()
+          throw IOException("Unable to open output stream for URI: ${dest.uri}")
+        }
+        inp.copyTo(out)
+      }
+    }
+    // delete the original .partial
+    ctx.contentResolver.delete(srcUri, null, null)
+    cleanupPartials(dir, targetName)
+    return dest.uri.toString()
+  }
+
+  private fun lengthOfUri(ctx: Context, uri: Uri): Long =
+      ctx.contentResolver.openAssetFileDescriptor(uri, "r").use { it?.length ?: -1 }
+
+  // delete any stray “.partial” files for this base name
+  private fun cleanupPartials(dir: DocumentFile, base: String) {
+    for (child in dir.listFiles()) {
+      val n = child.name ?: continue
+      if (n.endsWith(".partial") && n.contains(base, ignoreCase = false)) {
+        child.delete()
       }
+    }
+  }
+
+  @Throws(IOException::class)
+  override fun deleteFile(uriString: String) {
+    val ctx = appContext ?: throw IOException("DeleteFile: not initialized")
+
+    val uri = Uri.parse(uriString)
+    val doc =
+        DocumentFile.fromSingleUri(ctx, uri)
+            ?: throw IOException("DeleteFile: cannot resolve URI $uriString")
 
-      destFile =
-          targetDir.createFile("application/octet-stream", finalTargetName)
-              ?: throw IOException("Failed to create new file with name: $finalTargetName")
-
-      context.contentResolver.openInputStream(partialUriObj)?.use { input ->
-        context.contentResolver.openOutputStream(destFile.uri)?.use { output ->
-          input.copyTo(output)
-        } ?: throw IOException("Unable to open output stream for URI: ${destFile.uri}")
-      } ?: throw IOException("Unable to open input stream for URI: $partialUri")
-
-      DocumentFile.fromSingleUri(context, partialUriObj)?.delete()
-      return destFile.uri.toString()
-    } catch (e: Exception) {
-      throw IOException(
-          "Failed to rename partial file from URI $partialUri to final file in $targetDirUri with name $targetName: ${e.message}",
-          e)
+    if (!doc.delete()) {
+      throw IOException("DeleteFile: delete() returned false for $uriString")
     }
   }
 
+  override fun treeURI(): String = savedUri ?: throw IllegalStateException("not initialized")
+
+  override fun getFileInfo(fileName: String): String {
+    val context = appContext ?: return ""
+    val dirUri = savedUri ?: return ""
+    val dir = DocumentFile.fromTreeUri(context, Uri.parse(dirUri)) ?: return ""
+
+    val file = dir.findFile(fileName) ?: return ""
+
+    val name = file.name ?: return ""
+    val size = file.length()
+    val modTime = file.lastModified() // milliseconds since epoch
+
+    return """{"name":${jsonEscape(name)},"size":$size,"modTime":$modTime}"""
+  }
+
+  private fun jsonEscape(s: String): String {
+    return JSONObject.quote(s)
+  }
+
   fun generateNewFilename(filename: String): String {
     val dotIndex = filename.lastIndexOf('.')
     val baseName = if (dotIndex != -1) filename.substring(0, dotIndex) else filename
@@ -131,4 +204,83 @@ object ShareFileHelper : libtailscale.ShareFileHelper {
     val uuid = UUID.randomUUID()
     return "$baseName-$uuid$extension"
   }
+
+  fun listPartialFiles(suffix: String): Array<String> {
+    val context = appContext ?: return emptyArray()
+    val rootUri = savedUri ?: return emptyArray()
+    val dir = DocumentFile.fromTreeUri(context, Uri.parse(rootUri)) ?: return emptyArray()
+
+    return dir.listFiles()
+        .filter { it.name?.endsWith(suffix) == true }
+        .mapNotNull { it.name }
+        .toTypedArray()
+  }
+
+  override fun listPartialFilesJSON(suffix: String): String {
+    return listPartialFiles(suffix)
+        .joinToString(prefix = "[\"", separator = "\",\"", postfix = "\"]")
+  }
+
+  override fun openPartialFileReader(name: String): libtailscale.InputStream? {
+    val context = appContext ?: return null
+    val rootUri = savedUri ?: return null
+    val dir = DocumentFile.fromTreeUri(context, Uri.parse(rootUri)) ?: return null
+
+    // We know `name` includes the suffix (e.g. ".<id>.partial"), but the actual
+    // file in SAF might include extra bits, so let's just match by that suffix.
+    // You could also match exactly `endsWith(name)` if the filenames line up
+    val suffix = name.substringAfterLast('.', ".$name") // or hard-code ".partial"
+
+    val file =
+        dir.listFiles().firstOrNull {
+          val fname = it.name ?: return@firstOrNull false
+          // call the String overload explicitly:
+          fname.endsWith(suffix, /*ignoreCase=*/ false)
+        }
+            ?: run {
+              TSLog.d("ShareFileHelper", "no file ending with $suffix in SAF directory")
+              return null
+            }
+
+    TSLog.d("ShareFileHelper", "found SAF file ${file.name}, opening")
+    val inStream =
+        context.contentResolver.openInputStream(file.uri)
+            ?: run {
+              TSLog.d("ShareFileHelper", "openInputStream returned null for ${file.uri}")
+              return null
+            }
+    return InputStreamAdapter(inStream)
+  }
+}
+
+private class SeekableOutputStream(
+    private val fos: FileOutputStream,
+    private val pfd: ParcelFileDescriptor
+) : OutputStream() {
+
+  private var closed = false
+
+  override fun write(b: Int) = fos.write(b)
+
+  override fun write(b: ByteArray) = fos.write(b)
+
+  override fun write(b: ByteArray, off: Int, len: Int) {
+    fos.write(b, off, len)
+  }
+
+  override fun close() {
+    if (!closed) {
+      closed = true
+      try {
+        fos.flush()
+        fos.fd.sync() // blocks until data + metadata are durable
+        val size = fos.channel.size()
+      } finally {
+        fos.close()
+        pfd.close()
+      }
+    }
+  }
+
+  override fun flush() = fos.flush()
 }

libtailscale/fileops.go

@@ -3,36 +3,100 @@
 package libtailscale
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
+	"os"
+	"time"
+
+	"tailscale.com/feature/taildrop"
 )
 
-// AndroidFileOps implements the ShareFileHelper interface using the Android helper.
+// AndroidFileOps implements the FileOps interface using the Android ShareFileHelper.
 type AndroidFileOps struct {
 	helper ShareFileHelper
 }
 
+var _ taildrop.FileOps = (*AndroidFileOps)(nil)
+
 func NewAndroidFileOps(helper ShareFileHelper) *AndroidFileOps {
 	return &AndroidFileOps{helper: helper}
 }
 
-func (ops *AndroidFileOps) OpenFileURI(filename string) string {
-	return ops.helper.OpenFileURI(filename)
+func (ops *AndroidFileOps) OpenWriter(name string, offset int64, perm os.FileMode) (io.WriteCloser, string, error) {
+	var wc OutputStream
+	if offset == 0 {
+		wc = ops.helper.OpenFileWriter(name)
+	} else {
+		wc = ops.helper.OpenFileWriterAt(name, offset)
+	}
+	if wc == nil {
+		return nil, "", fmt.Errorf("OpenFileWriter returned nil for %q", name)
+	}
+	uri := ops.helper.OpenFileURI(name)
+	return wc, uri, nil
 }
 
-func (ops *AndroidFileOps) OpenFileWriter(filename string) (io.WriteCloser, string, error) {
-	uri := ops.helper.OpenFileURI(filename)
-	outputStream := ops.helper.OpenFileWriter(filename)
-	if outputStream == nil {
-		return nil, uri, fmt.Errorf("failed to open SAF output stream for %s", filename)
-	}
-	return outputStream, uri, nil
+func (ops *AndroidFileOps) Remove(baseName string) error {
+	uri := ops.helper.OpenFileURI(baseName)
+	return ops.helper.DeleteFile(uri)
 }
 
-func (ops *AndroidFileOps) RenamePartialFile(partialUri, targetDirUri, targetName string) (string, error) {
-	newURI := ops.helper.RenamePartialFile(partialUri, targetDirUri, targetName)
+func (ops *AndroidFileOps) Rename(oldPath, newName string) (string, error) {
+	tree := ops.helper.TreeURI()
+	newURI := ops.helper.RenamePartialFile(oldPath, tree, newName)
 	if newURI == "" {
 		return "", fmt.Errorf("failed to rename partial file via SAF")
 	}
 	return newURI, nil
 }
+
+func (ops *AndroidFileOps) ListFiles() ([]string, error) {
+	namesJSON := ops.helper.ListPartialFilesJSON("")
+	var names []string
+	if err := json.Unmarshal([]byte(namesJSON), &names); err != nil {
+		return nil, err
+	}
+	return names, nil
+}
+
+func (ops *AndroidFileOps) OpenReader(name string) (io.ReadCloser, error) {
+	in := ops.helper.OpenPartialFileReader(name)
+	if in == nil {
+		return nil, fmt.Errorf("OpenPartialFileReader returned nil for %q", name)
+	}
+	return adaptInputStream(in), nil
+}
+
+func (ops *AndroidFileOps) Stat(name string) (os.FileInfo, error) {
+	infoJSON := ops.helper.GetFileInfo(name)
+	if infoJSON == "" {
+		return nil, os.ErrNotExist
+	}
+	var info struct {
+		Name    string `json:"name"`
+		Size    int64  `json:"size"`
+		ModTime int64  `json:"modTime"` // Unix millis
+	}
+	if err := json.Unmarshal([]byte(infoJSON), &info); err != nil {
+		return nil, err
+	}
+	return &androidFileInfo{
+		name:    info.Name,
+		size:    info.Size,
+		modTime: time.UnixMilli(info.ModTime),
+	}, nil
+}
+
+type androidFileInfo struct {
+	name    string
+	size    int64
+	modTime time.Time
+}
+
+func (fi *androidFileInfo) Name() string       { return fi.name }
+func (fi *androidFileInfo) Size() int64        { return fi.size }
+func (fi *androidFileInfo) Mode() os.FileMode  { return 0o600 }
+func (fi *androidFileInfo) ModTime() time.Time { return fi.modTime }
+func (fi *androidFileInfo) IsDir() bool        { return false }
+func (fi *androidFileInfo) Sys() interface{}   { return nil }

libtailscale/interfaces.go

@@ -175,14 +175,45 @@ type OutputStream interface {
 
 // ShareFileHelper corresponds to the Kotlin ShareFileHelper class
 type ShareFileHelper interface {
+	// OpenFileWriter creates or truncates a file named fileName
+	// and returns an OutputStream for writing to it from the beginning.
+	// Returns nil if the file cannot be opened.
 	OpenFileWriter(fileName string) OutputStream
 
-	// OpenFileURI opens the file and returns its SAF URI.
-	OpenFileURI(filename string) string
+	// OpenFileWriterAt opens fileName for writing at a given offset.
+	// Returns nil if the file cannot be opened.
+	OpenFileWriterAt(fileName string, offset int64) OutputStream
 
-	// RenamePartialFile takes SAF URIs and a target file name,
-	// and returns the new SAF URI and an error.
-	RenamePartialFile(partialUri string, targetDirUri string, targetName string) string
+	// OpenFileURI returns the SAF URI string for the file named fileName,
+	// or an empty string if the file cannot be resolved.
+	OpenFileURI(fileName string) string
+
+	// RenamePartialFile renames the file at oldPath (a SAF URI)
+	// into the directory identified by newPath (a tree URI),
+	// giving it the new targetName. Returns the SAF URI of the renamed file,
+	// or an empty string if the operation failed.
+	RenamePartialFile(oldPath string, newPath string, targetName string) string
+
+	// ListPartialFilesJSON returns a JSON-encoded list of partial filenames
+	// (e.g., ["foo.partial", "bar.partial"]) that match the given suffix.
+	ListPartialFilesJSON(suffix string) string
+
+	// OpenPartialFileReader opens the file with the given name (typically a .partial file)
+	// and returns an InputStream for reading its contents.
+	// Returns nil if the file cannot be opened.
+	OpenPartialFileReader(name string) InputStream
+
+	// DeleteFile deletes the file identified by the given SAF URI string.
+	// Returns an error if the file could not be deleted.
+	DeleteFile(uriString string) error
+
+	// TreeURI returns the SAF tree URI representing the root directory for Taildrop files.
+	// This is typically the URI granted by the user via the Android directory picker.
+	TreeURI() string
+
+	// GetFileInfo returns a JSON-encoded string with file metadata for fileName.
+	// Returns an empty string if the file does not exist or cannot be accessed.
+	GetFileInfo(fileName string) string
 }
 
 // The below are global callbacks that allow the Java application to notify Go

libtailscale/localapi.go

@@ -230,27 +230,6 @@ func (r *Response) Flush() {
 	})
 }
 
-func adaptInputStream(in InputStream) io.ReadCloser {
-	if in == nil {
-		return nil
-	}
-	r, w := io.Pipe()
-	go func() {
-		defer w.Close()
-		for {
-			b, err := in.Read()
-			if err != nil {
-				log.Printf("error reading from inputstream: %s", err)
-			}
-			if b == nil {
-				return
-			}
-			w.Write(b)
-		}
-	}()
-	return r
-}
-
 // Below taken from Go stdlib
 var quoteEscaper = strings.NewReplacer("\\", "\\\\", `"`, "\\\"")
 

libtailscale/streamutil.go

@@ -0,0 +1,32 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package libtailscale
+
+import (
+	"io"
+	"log"
+)
+
+// adaptInputStream wraps a libtailscale.InputStream into an io.ReadCloser.
+// It launches a goroutine to stream reads into a pipe.
+func adaptInputStream(in InputStream) io.ReadCloser {
+	if in == nil {
+		return nil
+	}
+	r, w := io.Pipe()
+	go func() {
+		defer w.Close()
+		for {
+			b, err := in.Read()
+			if err != nil {
+				log.Printf("error reading from inputstream: %s", err)
+			}
+			if b == nil {
+				return
+			}
+			w.Write(b)
+		}
+	}()
+	return r
+}