fix(android): vendor saf_util with a sound pendingResult lifecycle

saf_util 2.0.0 leaves an already-answered MethodChannel.Result behind
in pendingResult: unrelated activity request codes consume (and answer)
the pending picker, and a failed picker launch replies without clearing
the pending state. The next delivery for request 1001 then replies a
second time — IllegalStateException "Reply already submitted" in
MainActivity.onActivityResult, crashing the process.

Vendored at packages/saf_util (BSD-3) with take-and-clear reply
ownership, request codes scoped to the plugin's own pickers, and a
guarded reply on the teardown race.

packages/saf_util/CHANGELOG.md

@@ -0,0 +1,77 @@
+## 2.0.0 (plezy vendored patch)
+
+Vendored from pub.dev saf_util 2.0.0 with a Result-lifecycle fix:
+pending picker replies are take-and-clear (no reply to an already-answered
+Result → no "Reply already submitted" crash), unrelated activity request
+codes no longer consume the pending picker, and failed picker launches
+clear the stale pending state.
+
+## 2.0.0
+
+- Update to Kotlin 2.2.0
+
+## 1.0.0
+
+- No changes. This is just a version bump to mark the stable release.
+
+## 0.12.0
+
+- Add `releasePersistedPermission` to release the persisted permission of a URI.
+
+## 0.11.0
+
+- Allow empty names in `.child`, which returns a [DocumentFile] from the first path param (like `stat`).
+
+## 0.10.0
+
+- Add `stat`. Unlike [documentFileFromUri], `stat` returns null if uri does not exist.
+
+## 0.9.0
+
+- Auto detect path type when `documentFileFromUri.isDir` is null.
+
+## 0.8.0
+
+- Add `hasPersistedPermission`.
+
+## 0.7.0
+
+- Add file descriptor support.
+
+## 0.6.2
+
+- Fix length overflow.
+
+## 0.6.1
+
+- Update docs.
+
+## 0.6.0
+
+- Add `pickFiles` and `pickDirectory` to replace `openFile` and `openDirectory`. The new methods return [DocumentFile] instead of Uri string.
+
+## 0.5.0
+
+- Add `openFile` and `openFiles` to open file picker dialog.
+- Make sure read permission is always set when write permission is on.
+
+## 0.4.0
+
+- Relax minimum Dart and Flutter versions (Fixes #2).
+
+## 0.3.0
+
+- `saveThumbnailToFile` width and height params should be int.
+
+## 0.2.0
+
+- Add `saveThumbnailToFile`, which supports extracting image and video thumbnails from an SAF [DocumentFile].
+
+## 0.1.0
+
+- Add `writePermission` and `persistablePermission` to openDirectory
+- Support renaming on file `DocumentFile`
+
+## 0.0.1
+
+- Initial release.

packages/saf_util/LICENSE

@@ -0,0 +1,29 @@
+BSD 3-Clause License
+
+Copyright (c) 2023, Mgenware (Liu YuanYuan)
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/saf_util/README.md

@@ -0,0 +1,9 @@
+# saf_util
+
+[![pub package](https://img.shields.io/pub/v/saf_util.svg)](https://pub.dev/packages/saf_util)
+
+Util functions for SAF (Storage Access Framework). Note that this package doesn't provide any read / write functions (go to [saf_stream](https://github.com/flutter-cavalry/saf_stream) for that).
+
+## Usage
+
+[Documentation](https://pub.dev/documentation/saf_util/latest/saf_util/)

packages/saf_util/analysis_options.yaml

@@ -0,0 +1,4 @@
+include: package:flutter_lints/flutter.yaml
+
+# Additional information about this file can be found at
+# https://dart.dev/guides/language/analysis-options

packages/saf_util/android/build.gradle.kts

@@ -0,0 +1,77 @@
+group = "com.fluttercavalry.saf_util"
+version = "1.0-SNAPSHOT"
+
+buildscript {
+    val kotlinVersion = "2.2.20"
+    repositories {
+        google()
+        mavenCentral()
+    }
+
+    dependencies {
+        classpath("com.android.tools.build:gradle:8.11.1")
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
+plugins {
+    id("com.android.library")
+    id("kotlin-android")
+}
+
+android {
+    namespace = "com.fluttercavalry.saf_util"
+
+    compileSdk = 36
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17.toString()
+    }
+
+    sourceSets {
+        getByName("main") {
+            java.srcDirs("src/main/kotlin")
+        }
+        getByName("test") {
+            java.srcDirs("src/test/kotlin")
+        }
+    }
+
+    defaultConfig {
+        minSdk = 24
+    }
+
+    testOptions {
+        unitTests {
+            isIncludeAndroidResources = true
+            all {
+                it.useJUnitPlatform()
+
+                it.outputs.upToDateWhen { false }
+
+                it.testLogging {
+                    events("passed", "skipped", "failed", "standardOut", "standardError")
+                    showStandardStreams = true
+                }
+            }
+        }
+    }
+}
+
+dependencies {
+    implementation("androidx.documentfile:documentfile:1.1.0")
+    testImplementation("org.jetbrains.kotlin:kotlin-test")
+    testImplementation("org.mockito:mockito-core:5.0.0")
+}

packages/saf_util/android/settings.gradle

@@ -0,0 +1 @@
+rootProject.name = 'saf_util'

packages/saf_util/android/settings.gradle.kts

@@ -0,0 +1 @@
+rootProject.name = 'saf_util'

packages/saf_util/android/src/main/AndroidManifest.xml

@@ -0,0 +1,3 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+  package="com.fluttercavalry.saf_util">
+</manifest>

packages/saf_util/android/src/main/kotlin/com/fluttercavalry/saf_util/SafUtilPlugin.kt

@@ -0,0 +1,862 @@
+package com.fluttercavalry.saf_util
+
+import android.app.Activity
+import android.content.Context
+import android.content.Intent
+import android.database.Cursor
+import android.graphics.Bitmap
+import android.graphics.Point
+import android.media.MediaMetadataRetriever
+import android.media.MediaMetadataRetriever.OPTION_CLOSEST_SYNC
+import android.net.Uri
+import android.os.Build
+import android.os.ParcelFileDescriptor
+import android.provider.DocumentsContract
+import androidx.documentfile.provider.DocumentFile
+import io.flutter.embedding.engine.plugins.FlutterPlugin
+import io.flutter.embedding.engine.plugins.activity.ActivityAware
+import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding
+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+import io.flutter.plugin.common.MethodChannel.MethodCallHandler
+import io.flutter.plugin.common.MethodChannel.Result
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import java.io.File
+import androidx.core.net.toUri
+
+
+/** SafUtilPlugin */
+class SafUtilPlugin: FlutterPlugin, MethodCallHandler, ActivityAware {
+  /// The MethodChannel that will the communication between Flutter and native Android
+  ///
+  /// This local reference serves to register the plugin with the Flutter Engine and unregister it
+  /// when the Flutter Engine is detached from the Activity
+  private lateinit var channel : MethodChannel
+
+  private lateinit var context: Context
+  private var activity: Activity? = null
+
+  private var pendingResult: Result? = null
+  private var pendingArguments: PendingArguments? = null
+  private val requestCodeOpenDocumentTree = 1001
+  private val requestCodeOpenFiles = 1002
+
+  /// Atomically takes ownership of the pending picker state. Every reply to a
+  /// pending Result must go through this so no already-answered Result is ever
+  /// left behind to be answered again ("Reply already submitted" crashes).
+  private fun takePendingResult(): Result? {
+    val result = pendingResult
+    pendingResult = null
+    pendingArguments = null
+    return result
+  }
+  private val fdMap = mutableMapOf<Int, ParcelFileDescriptor>()
+
+  override fun onAttachedToEngine(flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
+    channel = MethodChannel(flutterPluginBinding.binaryMessenger, "saf_util")
+    channel.setMethodCallHandler(this)
+    context = flutterPluginBinding.applicationContext
+  }
+
+  override fun onDetachedFromActivity() {
+    activity = null
+  }
+
+  override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
+    activity = binding.activity
+  }
+
+  override fun onAttachedToActivity(binding: ActivityPluginBinding) {
+    activity = binding.activity
+    binding.addActivityResultListener { requestCode, resultCode, data ->
+      onActivityResult(requestCode, resultCode, data)
+    }
+  }
+
+  override fun onDetachedFromActivityForConfigChanges() {
+    activity = null
+  }
+
+  override fun onMethodCall(call: MethodCall, result: Result) {
+    when (call.method) {
+      "list" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          var cursor: Cursor? = null
+          try {
+            val uri = call.argument<String>("uri") as String
+
+            val dir = documentFileFromUri(uri, true) ?: throw Exception("Failed to get DocumentFile from $uri")
+            val resolver = context.contentResolver
+            val mUri = dir.uri
+            val childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(
+              mUri,
+              DocumentsContract.getDocumentId(mUri)
+            )
+            val results = mutableListOf<Map<String, Any?>>()
+
+            cursor = resolver.query(
+              childrenUri,
+              arrayOf(
+                DocumentsContract.Document.COLUMN_DOCUMENT_ID,
+                DocumentsContract.Document.COLUMN_DISPLAY_NAME,
+                DocumentsContract.Document.COLUMN_SIZE,
+                DocumentsContract.Document.COLUMN_MIME_TYPE,
+                DocumentsContract.Document.COLUMN_LAST_MODIFIED
+              ),
+              null,
+              null,
+              null
+            )
+
+            while (cursor?.moveToNext() == true) {
+              val documentId = cursor.getString(0)
+              val fileName = cursor.getString(1)
+              val fileSize = cursor.getLong(2)
+              val mimeType = cursor.getString(3)
+              val lastModified = cursor.getLong(4)
+              val documentUri = DocumentsContract.buildDocumentUriUsingTree(mUri, documentId)
+
+              // Determine if the file is a directory based on the MIME type
+              val isDirectory = DocumentsContract.Document.MIME_TYPE_DIR == mimeType
+
+              // Create a dictionary (map) for each file with its details
+              val fileInfo = fileObjMap(
+                documentUri,
+                isDirectory,
+                fileName,
+                fileSize,
+                lastModified,
+              )
+              results.add(fileInfo)
+            }
+
+            launch(Dispatchers.Main) { result.success(results) }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          } finally {
+            try {
+              cursor?.close()
+            } catch (_: Exception) {
+            }
+          }
+        }
+      }
+
+      "documentFileFromUri" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir")
+
+            val df = documentFileFromUri(uri, isDir)
+            if (df == null) {
+              launch(Dispatchers.Main) {
+                result.success(null)
+              }
+              return@launch
+            }
+            launch(Dispatchers.Main) {
+              result.success(documentFileToMap(df))
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "stat" -> {
+        // Unlike `documentFileFromUri` this returns null if `uri` doesn't exist.
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir")
+
+            val df = documentFileFromUri(uri, isDir)
+            if (df == null || !df.exists()) {
+              launch(Dispatchers.Main) {
+                result.success(null)
+              }
+              return@launch
+            }
+            launch(Dispatchers.Main) {
+              result.success(documentFileToMap(df))
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "exists" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir") as Boolean
+
+            val df = documentFileFromUri(uri, isDir)
+            if (df == null) {
+              launch(Dispatchers.Main) {
+                result.success(false)
+              }
+              return@launch
+            }
+            launch(Dispatchers.Main) {
+              result.success(df.exists())
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "delete" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir") as Boolean
+
+            val df = documentFileFromUri(uri, isDir) ?: throw Exception("Failed to get DocumentFile from $uri")
+            launch(Dispatchers.Main) {
+              result.success(df.delete())
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "getFileDescriptor" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+
+            val df = documentFileFromUri(uri, false) ?: throw Exception("Failed to get DocumentFile from $uri")
+            val fd = context.contentResolver.openFileDescriptor(df.uri, "r") ?: throw Exception("Failed to open file descriptor")
+            val fdInt = fd.fd
+            fdMap[fdInt] = fd
+
+            launch(Dispatchers.Main) {
+              result.success(fdInt)
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "closeFileDescriptor" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val fdInt = call.argument<Int>("fd") as Int
+            val fd = fdMap.remove(fdInt)
+            fd?.close()
+
+            launch(Dispatchers.Main) {
+              result.success(null)
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "mkdirp" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String?>("uri") as String
+            val names =
+              call.argument<ArrayList<String>>("names") as ArrayList<String>
+
+            var curDocument = documentFileFromUri(uri, true) ?: throw Exception("Failed to get DocumentFile from $uri")
+            for (curName in names) {
+              val findRes = findDirectChild(curDocument.uri, curName)
+              val nextDocument: DocumentFile?
+              if (findRes == null) {
+                val createRes = curDocument.createDirectory(curName)
+                if (createRes != null && createRes.name != curName) {
+                  // There are cases where the created directory has a different name due to concurrent operations.
+                  // In this case, we need to find the directory with the correct name again.
+                  val findRes2 = findDirectChild(curDocument.uri, curName)
+                  nextDocument = if (findRes2 != null) {
+                    documentFileFromUriObj(findRes2.uri, findRes2.isDir)
+                  } else {
+                    null
+                  }
+                } else {
+                  nextDocument = createRes
+                }
+              } else {
+                nextDocument = documentFileFromUriObj(findRes.uri, findRes.isDir)
+              }
+
+              if (nextDocument == null) {
+                throw Exception("Failed to create directory at $curName")
+              }
+              if (nextDocument.isFile) {
+                throw Exception("File found at $curName while creating directory")
+              }
+              curDocument = nextDocument
+            }
+
+            launch(Dispatchers.Main) {
+              result.success(documentFileToMap(curDocument))
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "child" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val names = call.argument<ArrayList<String>>("names") as ArrayList<String>
+
+            var curDocument = documentFileFromUri(uri, true) ?: throw Exception("Failed to get DocumentFile from $uri")
+            for (curName in names) {
+              val findRes = findDirectChild(curDocument.uri, curName)
+              if (findRes == null) {
+                launch(Dispatchers.Main) {
+                  result.success(null)
+                }
+                return@launch
+              }
+              curDocument = documentFileFromUriObj(findRes.uri, findRes.isDir) ?: throw Exception("Failed to get DocumentFile at $curName")
+            }
+
+            launch(Dispatchers.Main) {
+              result.success(documentFileToMap(curDocument))
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "rename" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir") as Boolean
+            val newName = call.argument<String>("newName") as String
+
+            val df = documentFileFromUri(uri, isDir) ?: throw Exception("Failed to get DocumentFile from $uri")
+            if (isDir) {
+              val success = df.renameTo(newName)
+              if (!success) {
+                throw Exception("Failed to rename to $newName")
+              }
+              launch(Dispatchers.Main) {
+                result.success(documentFileToMap(df))
+              }
+            } else {
+              val newUri = renameFileDocumentFile(df, newName)
+                ?: throw Exception("Failed to rename to $newName")
+              val newDF = documentFileFromUriObj(newUri, false)
+                ?: throw Exception("Failed to get DocumentFile from $newUri")
+              launch(Dispatchers.Main) {
+                result.success(documentFileToMap(newDF))
+              }
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "moveTo" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir") as Boolean
+            val parentUri = call.argument<String>("parentUri") as String
+            val newParentUri = call.argument<String>("newParentUri") as String
+
+            val uriObj = uri.toUri()
+            val parentUriObj = parentUri.toUri()
+            val newParentUriObj = newParentUri.toUri()
+
+            val resUri = DocumentsContract.moveDocument(
+              context.contentResolver,
+              uriObj,
+              parentUriObj,
+              newParentUriObj
+            ) ?: throw Exception("Failed to move document")
+
+            val resultDF = documentFileFromUriObj(resUri, isDir) ?: throw Exception("Failed to get DocumentFile from $resUri")
+            launch(Dispatchers.Main) {
+              result.success(documentFileToMap(resultDF))
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "copyTo" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val isDir = call.argument<Boolean>("isDir") as Boolean
+            val newParentUri = call.argument<String>("newParentUri") as String
+
+            val uriObj = uri.toUri()
+            val newParentUriObj = newParentUri.toUri()
+
+            val resUri = DocumentsContract.copyDocument(
+              context.contentResolver,
+              uriObj,
+              newParentUriObj
+            ) ?: throw Exception("Failed to move document")
+
+            val resultDF = documentFileFromUriObj(resUri, isDir) ?: throw Exception("Failed to get DocumentFile from $resUri")
+
+            launch(Dispatchers.Main) {
+              result.success(documentFileToMap(resultDF))
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "pickDirectory" -> {
+        try {
+          val initialUri = call.argument<String>("initialUri")
+          val writePermission = call.argument<Boolean>("writePermission") ?: false
+          val persistablePermission = call.argument<Boolean>("persistablePermission") ?: false
+
+          if (activity == null) {
+            result.error("NO_ACTIVITY", "Activity is null", null)
+            return
+          }
+          if (pendingResult != null) {
+            result.error("ALREADY_PICKING", "Another picker process is already in progress", null)
+            return
+          }
+
+          // Store the result to return the URI later
+          pendingResult = result
+          pendingArguments = PendingDirArguments(writePermission, persistablePermission)
+          val intent = Intent(Intent.ACTION_OPEN_DOCUMENT_TREE)
+          if (initialUri != null) {
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+              intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, initialUri.toUri())
+            }
+          }
+          if (persistablePermission) {
+            intent.addFlags(
+              Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION
+            )
+          }
+          intent.addFlags(
+            if (writePermission) Intent.FLAG_GRANT_WRITE_URI_PERMISSION or Intent.FLAG_GRANT_READ_URI_PERMISSION
+            else Intent.FLAG_GRANT_READ_URI_PERMISSION
+          )
+
+          activity?.startActivityForResult(intent, requestCodeOpenDocumentTree)
+        } catch (err: Exception) {
+          // Launch failed after pendingResult was set: drop the pending state
+          // so a later activity result can't reply to this Result again.
+          takePendingResult()
+          result.error("PluginError", err.message, null)
+        }
+      }
+
+      "pickFiles" -> {
+        try {
+          val initialUri = call.argument<String>("initialUri")
+          val multiple = call.argument<Boolean>("multiple") ?: false
+          val mimeTypes = call.argument<ArrayList<String>>("mimeTypes") ?: arrayListOf()
+
+          if (activity == null) {
+            result.error("NO_ACTIVITY", "Activity is null", null)
+            return
+          }
+          if (pendingResult != null) {
+            result.error("ALREADY_PICKING", "Another picker process is already in progress", null)
+            return
+          }
+
+          // Store the result to return the URI later
+          pendingResult = result
+          val intent = Intent(Intent.ACTION_OPEN_DOCUMENT)
+          intent.addCategory(Intent.CATEGORY_OPENABLE)
+          if (initialUri != null) {
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+              intent.putExtra(DocumentsContract.EXTRA_INITIAL_URI, initialUri.toUri())
+            }
+          }
+          if (multiple) {
+            intent.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true)
+          }
+
+          if (mimeTypes.isEmpty()) {
+            intent.type = "*/*"
+          } else if (mimeTypes.size == 1) {
+            intent.type = mimeTypes[0]
+          } else {
+            intent.type = "*/*"
+            intent.putExtra(Intent.EXTRA_MIME_TYPES, mimeTypes.toTypedArray())
+          }
+
+          activity?.startActivityForResult(intent, requestCodeOpenFiles)
+        } catch (err: Exception) {
+          // Launch failed after pendingResult was set: drop the pending state
+          // so a later activity result can't reply to this Result again.
+          takePendingResult()
+          result.error("PluginError", err.message, null)
+        }
+      }
+
+      "hasPersistedPermission" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val checkRead = call.argument<Boolean>("checkRead") ?: true
+            val checkWrite = call.argument<Boolean>("checkWrite") ?: false
+
+            val persisted = hasPersistedUriPermission(
+              context,
+              uri.toUri(),
+              checkRead,
+              checkWrite
+            )
+            launch(Dispatchers.Main) {
+              result.success(persisted)
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "releasePersistedPermission" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = call.argument<String>("uri") as String
+            val read = call.argument<Boolean>("read") ?: true
+            val write = call.argument<Boolean>("write") ?: false
+
+            context.contentResolver.releasePersistableUriPermission(
+              uri.toUri(),
+              if (read && write) Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION
+              else if (read) Intent.FLAG_GRANT_READ_URI_PERMISSION
+              else if (write) Intent.FLAG_GRANT_WRITE_URI_PERMISSION
+              else 0
+            )
+            launch(Dispatchers.Main) {
+              result.success(null)
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      "saveThumbnailToFile" -> {
+        CoroutineScope(Dispatchers.IO).launch {
+          try {
+            val uri = (call.argument<String>("uri") as String).toUri()
+            val dest = call.argument<String>("destPath")!!
+            val format = call.argument<String>("format") ?: "jpeg"
+            val isPng = format == "png"
+            val quality = call.argument("quality") ?: if (isPng) 100 else 80
+
+            val width = call.argument<Int>("width")!!
+            val height = call.argument<Int>("height")!!
+
+            val df = DocumentFile.fromSingleUri(context, uri)
+            val mime = df?.type
+            if (mime == null) {
+              launch(Dispatchers.Main) {
+                result.success(false)
+              }
+              return@launch
+            }
+
+            val bitmap: Bitmap?
+            // Use MediaMetadataRetriever for video files.
+            if (mime.startsWith("video/")) {
+              val mmr = MediaMetadataRetriever()
+              mmr.setDataSource(context, uri)
+              bitmap = if (Build.VERSION.SDK_INT >= 27) {
+                mmr.getScaledFrameAtTime(-1, OPTION_CLOSEST_SYNC, width, height)
+              } else {
+                mmr.frameAtTime
+              }
+            } else {
+              // Use DocumentsContract for other files.
+              bitmap = DocumentsContract.getDocumentThumbnail(
+                context.contentResolver,
+                uri,
+                Point(width, height),
+                null
+              )
+            }
+
+            if (bitmap != null) {
+              File(dest).writeBitmap(
+                bitmap,
+                if (isPng) Bitmap.CompressFormat.PNG else Bitmap.CompressFormat.JPEG,
+                quality,
+              )
+              launch(Dispatchers.Main) {
+                result.success(true)
+              }
+            } else {
+              launch(Dispatchers.Main) {
+                result.success(false)
+              }
+            }
+          } catch (err: Exception) {
+            launch(Dispatchers.Main) {
+              result.error("PluginError", err.message, null)
+            }
+          }
+        }
+      }
+
+      else -> result.notImplemented()
+    }
+  }
+
+  // Handle the result of the folder/file pickers. Returns whether the
+  // request code was ours — unrelated request codes must not touch (let
+  // alone answer) the pending picker state.
+  private fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?): Boolean {
+    if (requestCode != requestCodeOpenDocumentTree && requestCode != requestCodeOpenFiles) {
+      return false
+    }
+    // Take ownership before replying: a duplicate delivery finds no pending
+    // state instead of a second reply on an already-answered Result.
+    val args = pendingArguments
+    val result = takePendingResult() ?: return true
+    try {
+      if (requestCode == requestCodeOpenDocumentTree) {
+        // Handle the result of the folder picker.
+        if (resultCode == Activity.RESULT_OK && data != null) {
+          val uri: Uri? = data.data
+          if (uri != null && args is PendingDirArguments) {
+            if (args.persistablePermission) {
+              context.contentResolver.takePersistableUriPermission(
+                uri,
+                if (args.writePermission) Intent.FLAG_GRANT_WRITE_URI_PERMISSION or Intent.FLAG_GRANT_READ_URI_PERMISSION
+                else Intent.FLAG_GRANT_READ_URI_PERMISSION
+              )
+            }
+          }
+          val df = documentFileFromUri(uri.toString(), true)
+          result.success(
+            if (df != null) documentFileToMap(df)
+            else null
+          )
+        } else {
+          result.success(null)
+        }
+      } else {
+        // Handle the result of file picker.
+        if (resultCode == Activity.RESULT_OK && data != null) {
+          val uris: List<Uri> = if (data.clipData != null) {
+            val clipData = data.clipData
+            val uris = mutableListOf<Uri>()
+            for (i in 0 until clipData!!.itemCount) {
+              uris.add(clipData.getItemAt(i).uri)
+            }
+            uris
+          } else {
+            listOf(data.data!!)
+          }
+
+          val documentFileMaps: MutableList<Map<String, Any?>> = mutableListOf()
+          for (uri in uris) {
+            val df = documentFileFromUri(uri.toString(), false)
+            if (df != null) {
+              documentFileMaps.add(documentFileToMap(df))
+            }
+          }
+
+          result.success(documentFileMaps)  // Return the URIs to Flutter
+        } else {
+          result.success(null)
+        }
+      }
+    } catch (err: Exception) {
+      try {
+        result.error("PluginError", err.message, null)
+      } catch (_: IllegalStateException) {
+        // Reply already submitted — never crash the host activity over a
+        // picker teardown race.
+      }
+    }
+    return true
+  }
+
+  override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+    channel.setMethodCallHandler(null)
+  }
+
+  private fun documentFileFromUri(uri: String, isDir: Boolean?): DocumentFile? {
+    val uriObj = uri.toUri()
+    val isDirRes =
+      isDir ?: DocumentsContract.isTreeUri(uriObj)
+    return documentFileFromUriObj(uriObj, isDirRes)
+  }
+
+  private fun documentFileFromUriObj(uriObj: Uri, isDir: Boolean): DocumentFile? {
+    val res = if (isDir) {
+      DocumentFile.fromTreeUri(context, uriObj)
+    } else {
+      DocumentFile.fromSingleUri(context, uriObj)
+    }
+    return res
+  }
+
+  private fun hasPersistedUriPermission(
+    context: Context,
+    uri: Uri,
+    checkRead: Boolean,
+    checkWrite: Boolean
+  ): Boolean {
+    val permissions = context.contentResolver.persistedUriPermissions
+    for (permission in permissions) {
+      if (areSameDocumentLocation(permission.uri, uri)) {
+        val hasRead = !checkRead || permission.isReadPermission
+        val hasWrite = !checkWrite || permission.isWritePermission
+        return hasRead && hasWrite
+      }
+    }
+    return false
+  }
+
+  private fun areSameDocumentLocation(treeUri: Uri, docUri: Uri): Boolean {
+    val treeDocId = DocumentsContract.getTreeDocumentId(treeUri)
+    val docId = DocumentsContract.getDocumentId(docUri)
+    return treeDocId == docId
+  }
+
+  private fun findDirectChild(parentUri: Uri, name: String): UriInfo? {
+    var cursor: Cursor? = null
+    try {
+      val resolver = context.contentResolver
+      val childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(
+        parentUri,
+        DocumentsContract.getDocumentId(parentUri)
+      )
+      cursor = resolver.query(
+        childrenUri,
+        arrayOf(
+          DocumentsContract.Document.COLUMN_DOCUMENT_ID,
+          DocumentsContract.Document.COLUMN_DISPLAY_NAME,
+          DocumentsContract.Document.COLUMN_MIME_TYPE,
+        ),
+        null,
+        null,
+        null
+      )
+
+      while (cursor?.moveToNext() == true) {
+        val documentId = cursor.getString(0)
+        val fileName = cursor.getString(1)
+        val mimeType = cursor.getString(2)
+        val isDirectory = DocumentsContract.Document.MIME_TYPE_DIR == mimeType
+
+        if (fileName == name) {
+          val documentUri = DocumentsContract.buildDocumentUriUsingTree(parentUri, documentId)
+          return UriInfo(documentUri, fileName, isDirectory)
+        }
+      }
+      return null
+    } finally {
+      try {
+        cursor?.close()
+      } catch (_: Exception) {
+      }
+    }
+  }
+
+  private fun renameFileDocumentFile(df: DocumentFile, newName: String): Uri? {
+    // https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:documentfile/documentfile/src/main/java/androidx/documentfile/provider/TreeDocumentFile.java
+    try {
+      val result = DocumentsContract.renameDocument(
+        context.contentResolver, df.uri, newName
+      )
+      return result
+    } catch (err: Exception) {
+      return null
+    }
+  }
+
+  private fun documentFileToMap(file: DocumentFile): Map<String, Any?> {
+    return fileObjMap(
+      file.uri,
+      file.isDirectory,
+      file.name ?: "",
+      file.length(),
+      file.lastModified(),
+    )
+  }
+
+  private fun fileObjMap(
+    uri: Uri,
+    isDir: Boolean,
+    name: String,
+    length: Long,
+    lastMod: Long,
+  ): Map<String, Any?> {
+    return mapOf(
+      "uri" to uri.toString(),
+      "isDir" to isDir,
+      "name" to name,
+      "length" to length,
+      "lastModified" to lastMod,
+    )
+  }
+
+  private fun File.writeBitmap(bitmap: Bitmap, format: Bitmap.CompressFormat, quality: Int) {
+    outputStream().use { out ->
+      bitmap.compress(format, quality, out)
+      out.flush()
+    }
+  }
+}
+
+internal data class UriInfo(val uri: Uri, val name: String, val isDir: Boolean)
+
+internal open class PendingArguments
+
+internal class PendingDirArguments(
+  val writePermission: Boolean,
+  val persistablePermission: Boolean,
+): PendingArguments()

packages/saf_util/android/src/test/kotlin/com/fluttercavalry/saf_util/SafUtilPluginTest.kt

@@ -0,0 +1,27 @@
+package com.fluttercavalry.saf_util
+
+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+import org.mockito.Mockito
+import kotlin.test.Test
+
+/*
+ * This demonstrates a simple unit test of the Kotlin portion of this plugin's implementation.
+ *
+ * Once you have built the plugin's example app, you can run these tests from the command
+ * line by running `./gradlew testDebugUnitTest` in the `example/android/` directory, or
+ * you can run them directly from IDEs that support JUnit such as Android Studio.
+ */
+
+internal class SafUtilPluginTest {
+    @Test
+    fun onMethodCall_getPlatformVersion_returnsExpectedValue() {
+        val plugin = SafUtilPlugin()
+
+        val call = MethodCall("getPlatformVersion", null)
+        val mockResult: MethodChannel.Result = Mockito.mock(MethodChannel.Result::class.java)
+        plugin.onMethodCall(call, mockResult)
+
+        Mockito.verify(mockResult).success("Android " + android.os.Build.VERSION.RELEASE)
+    }
+}

packages/saf_util/lib/saf_util.dart

@@ -0,0 +1,256 @@
+import 'saf_util_platform_interface.dart';
+
+class SafUtil {
+  /// Shows a folder picker dialog and returns the selected folder as [SafDocumentFile].
+  ///
+  /// [initialUri] is the initial URI to show in the dialog.
+  /// [writePermission] is true if the folder should have write permission.
+  /// [persistablePermission] is true if the permission should be persistable.
+  Future<SafDocumentFile?> pickDirectory(
+      {String? initialUri,
+      bool? writePermission,
+      bool? persistablePermission}) {
+    return SafUtilPlatform.instance.pickDirectory(
+        initialUri: initialUri,
+        writePermission: writePermission,
+        persistablePermission: persistablePermission);
+  }
+
+  /// Shows a file picker dialog and returns the selected file [SafDocumentFile].
+  /// This calls [pickFiles] with [multiple] set to false.
+  ///
+  /// [initialUri] is the initial URI to show in the dialog.
+  /// [mimeTypes] is a list of MIME types to filter the files.
+  Future<SafDocumentFile?> pickFile({
+    String? initialUri,
+    List<String>? mimeTypes,
+  }) {
+    return SafUtilPlatform.instance.pickFile(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+    );
+  }
+
+  /// Shows a file picker dialog and returns a list of selected file [SafDocumentFile].
+  ///
+  /// [initialUri] is the initial URI to show in the dialog.
+  /// [mimeTypes] is a list of MIME types to filter the files.
+  /// [multiple] is true if multiple files can be selected.
+  Future<List<SafDocumentFile>?> pickFiles({
+    String? initialUri,
+    List<String>? mimeTypes,
+    multiple = true,
+  }) {
+    return SafUtilPlatform.instance.pickFiles(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+      multiple: multiple,
+    );
+  }
+
+  /// Lists the contents of the specified directory URI.
+  /// Returns a list of [SafDocumentFile] objects.
+  ///
+  /// [uri] is the URI of the directory.
+  Future<List<SafDocumentFile>> list(String uri) {
+    return SafUtilPlatform.instance.list(uri);
+  }
+
+  /// Gets a [SafDocumentFile] object from the specified URI.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [isDir] is true if the URI is a directory. [null] means
+  /// auto-detect.
+  Future<SafDocumentFile?> documentFileFromUri(String uri, bool? isDir) {
+    return SafUtilPlatform.instance.documentFileFromUri(uri, isDir);
+  }
+
+  /// Gets a [SafDocumentFile] object from the specified URI.
+  /// Unlike [documentFileFromUri], this method returns null
+  /// if the URI does not exist.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [isDir] is true if the URI is a directory. [null] means
+  /// auto-detect.
+  Future<SafDocumentFile?> stat(String uri, bool? isDir) {
+    return SafUtilPlatform.instance.stat(uri, isDir);
+  }
+
+  /// Checks if the specified file or directory exists.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [isDir] is true if the URI is a directory.
+  Future<bool> exists(String uri, bool isDir) {
+    return SafUtilPlatform.instance.exists(uri, isDir);
+  }
+
+  /// Deletes the specified file or directory.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [isDir] is true if the URI is a directory.
+  Future<void> delete(String uri, bool isDir) {
+    return SafUtilPlatform.instance.delete(uri, isDir);
+  }
+
+  /// Creates a directory and all its parent directories.
+  /// Returns the created directory as a [SafDocumentFile] object.
+  ///
+  /// [uri] is the URI of the directory to create.
+  /// [names] is a list of directory names to create.
+  Future<SafDocumentFile> mkdirp(String uri, List<String> names) {
+    return SafUtilPlatform.instance.mkdirp(uri, names);
+  }
+
+  /// Gets the child file or directory with the specified name.
+  ///
+  /// [uri] is the URI of the parent directory.
+  /// [names] is a list of directory names to traverse.
+  Future<SafDocumentFile?> child(String uri, List<String> names) {
+    return SafUtilPlatform.instance.child(uri, names);
+  }
+
+  /// Renames the specified file or directory.
+  /// Returns the renamed file or directory as a [SafDocumentFile] object.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [isDir] is true if the URI is a directory.
+  /// [newName] is the new name of the file or directory.
+  Future<SafDocumentFile> rename(String uri, bool isDir, String newName) {
+    return SafUtilPlatform.instance.rename(uri, isDir, newName);
+  }
+
+  /// Moves the specified file or directory to a new parent directory.
+  /// Returns the moved file or directory as a [SafDocumentFile] object.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [parentUri] is the URI of the current parent directory.
+  /// [newParentUri] is the URI of the new parent directory.
+  Future<SafDocumentFile> moveTo(
+      String uri, bool isDir, String parentUri, String newParentUri) {
+    return SafUtilPlatform.instance.moveTo(uri, isDir, parentUri, newParentUri);
+  }
+
+  /// Copies the specified file or directory to a new parent directory.
+  /// Returns the copied file or directory as a [SafDocumentFile] object.
+  ///
+  /// [uri] is the URI of the file or directory.
+  /// [newParentUri] is the URI of the new parent directory.
+  Future<SafDocumentFile> copyTo(String uri, bool isDir, String newParentUri) {
+    return SafUtilPlatform.instance.copyTo(uri, isDir, newParentUri);
+  }
+
+  /// Saves the thumbnail of the specified document [uri] to a local file [destPath].
+  /// Image and video thumbnails are supported.
+  /// Returns true if the thumbnail is saved successfully, or false if no
+  /// thumbnail found in the document.
+  ///
+  /// [uri] is the URI of the document.
+  /// [destPath] is the destination file path to save the thumbnail.
+  /// [width] is the max width of the thumbnail.
+  /// [height] is the max height of the thumbnail.
+  /// [format] is the format of the thumbnail file, default is 'jpeg'.
+  /// Supported formats are 'jpeg' and 'png'.
+  /// [quality] is the quality of the thumbnail file,
+  /// defaults to 80 for 'jpeg' and 100 for 'png'.
+  Future<bool> saveThumbnailToFile({
+    required String uri,
+    required int width,
+    required int height,
+    required String destPath,
+    String? format,
+    int? quality,
+  }) {
+    return SafUtilPlatform.instance.saveThumbnailToFile(
+      uri: uri,
+      width: width,
+      height: height,
+      destPath: destPath,
+      format: format,
+      quality: quality,
+    );
+  }
+
+  /** Deprecated functions. */
+
+  /// Shows a folder picker dialog and returns the selected folder URI.
+  ///
+  /// [initialUri] is the initial URI to show in the dialog.
+  /// [writePermission] is true if the folder should have write permission.
+  /// [persistablePermission] is true if the permission should be persistable.
+  @Deprecated('Use [pickDirectory] instead, which returns a [SafDocumentFile].')
+  Future<String?> openDirectory(
+      {String? initialUri,
+      bool? writePermission,
+      bool? persistablePermission}) {
+    return SafUtilPlatform.instance.openDirectory(
+        initialUri: initialUri,
+        writePermission: writePermission,
+        persistablePermission: persistablePermission);
+  }
+
+  /// Shows a file picker dialog and returns the selected file URI.
+  /// This calls [openFiles] with [multiple] set to false.
+  ///
+  /// [initialUri] is the initial URI to show in the dialog.
+  /// [mimeTypes] is a list of MIME types to filter the files.
+  @Deprecated('Use [pickFile] instead, which returns a [SafDocumentFile].')
+  Future<String?> openFile({
+    String? initialUri,
+    List<String>? mimeTypes,
+  }) {
+    return SafUtilPlatform.instance.openFile(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+    );
+  }
+
+  /// Shows a file picker dialog and returns a list of selected file URIs.
+  ///
+  /// [initialUri] is the initial URI to show in the dialog.
+  /// [mimeTypes] is a list of MIME types to filter the files.
+  @Deprecated('Use [pickFiles] instead, which returns a [SafDocumentFile].')
+  Future<List<String>?> openFiles({
+    String? initialUri,
+    List<String>? mimeTypes,
+    multiple = true,
+  }) {
+    return SafUtilPlatform.instance.openFiles(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+      multiple: multiple,
+    );
+  }
+
+  /// Gets the file descriptor of the specified URI.
+  Future<int> getFileDescriptor(String uri) {
+    return SafUtilPlatform.instance.getFileDescriptor(uri);
+  }
+
+  /// Closes the specified file descriptor.
+  Future<void> closeFileDescriptor(int fd) {
+    return SafUtilPlatform.instance.closeFileDescriptor(fd);
+  }
+
+  /// Checks if the specified URI has persisted permission.
+  /// Use [checkRead] and [checkWrite] to specify the type of permission to check.
+  /// [checkRead] defaults to true.
+  /// [checkWrite] defaults to false.
+  Future<bool> hasPersistedPermission(
+    String uri, {
+    bool checkRead = true,
+    bool checkWrite = false,
+  }) {
+    return SafUtilPlatform.instance.hasPersistedPermission(uri,
+        checkRead: checkRead, checkWrite: checkWrite);
+  }
+
+  /// Releases the persisted permission of the specified URI.
+  /// Use [read] and [write] to specify the type of permission to release.
+  /// [read] defaults to true.
+  /// [write] defaults to false.
+  Future<void> releasePersistedPermission(String uri,
+      {bool read = true, bool write = false}) async {
+    return SafUtilPlatform.instance
+        .releasePersistedPermission(uri, read: read, write: write);
+  }
+}

packages/saf_util/lib/saf_util_method_channel.dart

@@ -0,0 +1,292 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+import 'saf_util_platform_interface.dart';
+
+/// An implementation of [SafUtilPlatform] that uses method channels.
+class MethodChannelSafUtil extends SafUtilPlatform {
+  /// The method channel used to interact with the native platform.
+  @visibleForTesting
+  final methodChannel = const MethodChannel('saf_util');
+
+  @override
+  Future<SafDocumentFile?> pickDirectory(
+      {String? initialUri,
+      bool? writePermission,
+      bool? persistablePermission}) async {
+    final map =
+        await methodChannel.invokeMapMethod<String, dynamic>('pickDirectory', {
+      'initialUri': initialUri,
+      'writePermission': writePermission,
+      'persistablePermission': persistablePermission,
+    });
+    if (map == null) {
+      return null;
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<String?> openDirectory(
+      {String? initialUri,
+      bool? writePermission,
+      bool? persistablePermission}) async {
+    final res = await pickDirectory(
+      initialUri: initialUri,
+      writePermission: writePermission,
+      persistablePermission: persistablePermission,
+    );
+    return res?.uri;
+  }
+
+  @override
+  Future<SafDocumentFile?> pickFile({
+    String? initialUri,
+    List<String>? mimeTypes,
+  }) async {
+    final res = await pickFiles(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+      multiple: false,
+    );
+    return res?.first;
+  }
+
+  @override
+  Future<String?> openFile({
+    String? initialUri,
+    List<String>? mimeTypes,
+  }) async {
+    final res = await pickFile(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+    );
+    return res?.uri;
+  }
+
+  @override
+  Future<List<SafDocumentFile>?> pickFiles({
+    String? initialUri,
+    List<String>? mimeTypes,
+    multiple = true,
+  }) async {
+    final maps = await methodChannel
+        .invokeListMethod<Map<dynamic, dynamic>>('pickFiles', {
+      'initialUri': initialUri,
+      'mimeTypes': mimeTypes,
+      'multiple': multiple,
+    });
+    return maps?.map((map) => SafDocumentFile.fromMap(map)).toList();
+  }
+
+  @override
+  Future<List<String>?> openFiles({
+    String? initialUri,
+    List<String>? mimeTypes,
+    multiple = true,
+  }) async {
+    final res = await pickFiles(
+      initialUri: initialUri,
+      mimeTypes: mimeTypes,
+      multiple: multiple,
+    );
+    return res?.map((file) => file.uri).toList();
+  }
+
+  @override
+  Future<List<SafDocumentFile>> list(String uri) async {
+    final maps = await methodChannel
+        .invokeListMethod<Map<dynamic, dynamic>>('list', {'uri': uri});
+    return (maps ?? []).map((map) => SafDocumentFile.fromMap(map)).toList();
+  }
+
+  @override
+  Future<SafDocumentFile?> documentFileFromUri(String uri, bool? isDir) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'documentFileFromUri',
+      {'uri': uri, 'isDir': isDir},
+    );
+    if (map == null) {
+      return null;
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<SafDocumentFile?> stat(String uri, bool? isDir) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'stat',
+      {'uri': uri, 'isDir': isDir},
+    );
+    if (map == null) {
+      return null;
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<bool> exists(String uri, bool isDir) async {
+    final res = await methodChannel.invokeMethod<bool>(
+      'exists',
+      {'uri': uri, 'isDir': isDir},
+    );
+    if (res == null) {
+      throw Exception('Failed to check if file exists: $uri');
+    }
+    return res;
+  }
+
+  @override
+  Future<void> delete(String uri, bool isDir) async {
+    final res = await methodChannel.invokeMethod<bool>(
+      'delete',
+      {'uri': uri, 'isDir': isDir},
+    );
+    if (res != true) {
+      throw Exception('Failed to delete file: $uri');
+    }
+  }
+
+  @override
+  Future<SafDocumentFile> mkdirp(String uri, List<String> names) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'mkdirp',
+      {'uri': uri, 'names': names},
+    );
+    if (map == null) {
+      throw Exception('Failed to create directory: $uri');
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<SafDocumentFile?> child(String uri, List<String> names) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'child',
+      {'uri': uri, 'names': names},
+    );
+    if (map == null) {
+      return null;
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<SafDocumentFile> rename(String uri, bool isDir, String newName) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'rename',
+      {'uri': uri, 'isDir': isDir, 'newName': newName},
+    );
+    if (map == null) {
+      throw Exception('Failed to rename: $uri');
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<SafDocumentFile> moveTo(
+      String uri, bool isDir, String parentUri, String newParentUri) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'moveTo',
+      {
+        'uri': uri,
+        'isDir': isDir,
+        'parentUri': parentUri,
+        'newParentUri': newParentUri
+      },
+    );
+    if (map == null) {
+      throw Exception('Failed to move: $uri');
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<SafDocumentFile> copyTo(
+      String uri, bool isDir, String newParentUri) async {
+    final map = await methodChannel.invokeMapMethod<String, dynamic>(
+      'copyTo',
+      {'uri': uri, 'isDir': isDir, 'newParentUri': newParentUri},
+    );
+    if (map == null) {
+      throw Exception('Failed to copy: $uri');
+    }
+    return SafDocumentFile.fromMap(map);
+  }
+
+  @override
+  Future<bool> saveThumbnailToFile({
+    required String uri,
+    required int width,
+    required int height,
+    required String destPath,
+    String? format,
+    int? quality,
+  }) async {
+    final res = await methodChannel.invokeMethod<bool>(
+      'saveThumbnailToFile',
+      {
+        'uri': uri.toString(),
+        'width': width,
+        'height': height,
+        'destPath': destPath,
+        'format': format,
+        'quality': quality,
+      },
+    );
+    return res ?? false;
+  }
+
+  @override
+  Future<int> getFileDescriptor(String uri) async {
+    final res = await methodChannel.invokeMethod<int>(
+      'getFileDescriptor',
+      {'uri': uri},
+    );
+    if (res == null) {
+      throw Exception('Failed to get file descriptor: $uri');
+    }
+    return res;
+  }
+
+  @override
+  Future<void> closeFileDescriptor(int fd) {
+    return methodChannel.invokeMethod<void>(
+      'closeFileDescriptor',
+      {'fd': fd},
+    );
+  }
+
+  @override
+  Future<bool> hasPersistedPermission(
+    String uri, {
+    bool checkRead = true,
+    bool checkWrite = false,
+  }) async {
+    final res = await methodChannel.invokeMethod<bool>(
+      'hasPersistedPermission',
+      {
+        'uri': uri,
+        'checkRead': checkRead,
+        'checkWrite': checkWrite,
+      },
+    );
+    if (res == null) {
+      throw Exception('Failed to check persisted permission: $uri');
+    }
+    return res;
+  }
+
+  @override
+  Future<void> releasePersistedPermission(String uri,
+      {bool read = true, bool write = false}) async {
+    await methodChannel.invokeMethod<void>(
+      'releasePersistedPermission',
+      {
+        'uri': uri,
+        'read': read,
+        'write': write,
+      },
+    );
+  }
+}

packages/saf_util/lib/saf_util_platform_interface.dart

@@ -0,0 +1,175 @@
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+import 'saf_util_method_channel.dart';
+
+class SafDocumentFile {
+  final String uri;
+  final String name;
+  final bool isDir;
+  final int length;
+  final int lastModified;
+
+  SafDocumentFile({
+    required this.uri,
+    required this.name,
+    required this.isDir,
+    required this.length,
+    required this.lastModified,
+  });
+
+  static SafDocumentFile fromMap(Map<dynamic, dynamic> map) {
+    return SafDocumentFile(
+      uri: map['uri'],
+      name: map['name'],
+      isDir: map['isDir'] ?? false,
+      length: map['length'] ?? 0,
+      lastModified: map['lastModified'] ?? 0,
+    );
+  }
+
+  @override
+  String toString() {
+    return 'SafDocumentFile{uri: $uri, name: $name, isDir: $isDir, length: $length, lastModified: $lastModified}';
+  }
+}
+
+abstract class SafUtilPlatform extends PlatformInterface {
+  /// Constructs a SafUtilPlatform.
+  SafUtilPlatform() : super(token: _token);
+
+  static final Object _token = Object();
+
+  static SafUtilPlatform _instance = MethodChannelSafUtil();
+
+  /// The default instance of [SafUtilPlatform] to use.
+  ///
+  /// Defaults to [MethodChannelSafUtil].
+  static SafUtilPlatform get instance => _instance;
+
+  /// Platform-specific implementations should set this with their own
+  /// platform-specific class that extends [SafUtilPlatform] when
+  /// they register themselves.
+  static set instance(SafUtilPlatform instance) {
+    PlatformInterface.verifyToken(instance, _token);
+    _instance = instance;
+  }
+
+  Future<SafDocumentFile?> pickDirectory(
+      {String? initialUri,
+      bool? writePermission,
+      bool? persistablePermission}) {
+    throw UnimplementedError('pickDirectory() has not been implemented.');
+  }
+
+  Future<String?> openDirectory(
+      {String? initialUri,
+      bool? writePermission,
+      bool? persistablePermission}) {
+    throw UnimplementedError('openDirectory() has not been implemented.');
+  }
+
+  Future<SafDocumentFile?> pickFile({
+    String? initialUri,
+    List<String>? mimeTypes,
+  }) {
+    throw UnimplementedError('pickFile() has not been implemented.');
+  }
+
+  Future<String?> openFile({
+    String? initialUri,
+    List<String>? mimeTypes,
+  }) {
+    throw UnimplementedError('openFile() has not been implemented.');
+  }
+
+  Future<List<SafDocumentFile>?> pickFiles({
+    String? initialUri,
+    List<String>? mimeTypes,
+    multiple = true,
+  }) {
+    throw UnimplementedError('pickFiles() has not been implemented.');
+  }
+
+  Future<List<String>?> openFiles({
+    String? initialUri,
+    List<String>? mimeTypes,
+    multiple = true,
+  }) {
+    throw UnimplementedError('openFiles() has not been implemented.');
+  }
+
+  Future<List<SafDocumentFile>> list(String uri) {
+    throw UnimplementedError('list() has not been implemented.');
+  }
+
+  Future<SafDocumentFile?> documentFileFromUri(String uri, bool? isDir) {
+    throw UnimplementedError('documentFileFromUri() has not been implemented.');
+  }
+
+  Future<SafDocumentFile?> stat(String uri, bool? isDir) {
+    throw UnimplementedError('stat() has not been implemented.');
+  }
+
+  Future<bool> exists(String uri, bool isDir) {
+    throw UnimplementedError('exists() has not been implemented.');
+  }
+
+  Future<void> delete(String uri, bool isDir) {
+    throw UnimplementedError('delete() has not been implemented.');
+  }
+
+  Future<SafDocumentFile> mkdirp(String uri, List<String> names) {
+    throw UnimplementedError('mkdirp() has not been implemented.');
+  }
+
+  Future<SafDocumentFile?> child(String uri, List<String> names) {
+    throw UnimplementedError('child() has not been implemented.');
+  }
+
+  Future<SafDocumentFile> rename(String uri, bool isDir, String newName) {
+    throw UnimplementedError('rename() has not been implemented.');
+  }
+
+  Future<SafDocumentFile> moveTo(
+      String uri, bool isDir, String parentUri, String newParentUri) {
+    throw UnimplementedError('moveTo() has not been implemented.');
+  }
+
+  Future<SafDocumentFile> copyTo(String uri, bool isDir, String newParentUri) {
+    throw UnimplementedError('copyTo() has not been implemented.');
+  }
+
+  Future<bool> saveThumbnailToFile({
+    required String uri,
+    required int width,
+    required int height,
+    required String destPath,
+    String? format,
+    int? quality,
+  }) {
+    throw UnimplementedError('saveThumbnailToFile() has not been implemented.');
+  }
+
+  Future<int> getFileDescriptor(String uri) {
+    throw UnimplementedError('getFileDescriptor() has not been implemented.');
+  }
+
+  Future<void> closeFileDescriptor(int fd) {
+    throw UnimplementedError('closeFileDescriptor() has not been implemented.');
+  }
+
+  Future<bool> hasPersistedPermission(
+    String uri, {
+    bool checkRead = true,
+    bool checkWrite = false,
+  }) {
+    throw UnimplementedError(
+        'hasPersistedPermission() has not been implemented.');
+  }
+
+  Future<void> releasePersistedPermission(String uri,
+      {bool read = true, bool write = false}) {
+    throw UnimplementedError(
+        'releasePersistedPermission() has not been implemented.');
+  }
+}

packages/saf_util/pubspec.lock

@@ -0,0 +1,213 @@
+# Generated by pub
+# See https://dart.dev/tools/pub/glossary#lockfile
+packages:
+  async:
+    dependency: transitive
+    description:
+      name: async
+      sha256: e2eb0491ba5ddb6177742d2da23904574082139b07c1e33b8503b9f46f3e1a37
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.13.1"
+  boolean_selector:
+    dependency: transitive
+    description:
+      name: boolean_selector
+      sha256: "8aab1771e1243a5063b8b0ff68042d67334e3feab9e95b9490f9a6ebf73b42ea"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  characters:
+    dependency: transitive
+    description:
+      name: characters
+      sha256: faf38497bda5ead2a8c7615f4f7939df04333478bf32e4173fcb06d428b5716b
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.1"
+  clock:
+    dependency: transitive
+    description:
+      name: clock
+      sha256: fddb70d9b5277016c77a80201021d40a2247104d9f4aa7bab7157b7e3f05b84b
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.2"
+  collection:
+    dependency: transitive
+    description:
+      name: collection
+      sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.19.1"
+  fake_async:
+    dependency: transitive
+    description:
+      name: fake_async
+      sha256: "5368f224a74523e8d2e7399ea1638b37aecfca824a3cc4dfdf77bf1fa905ac44"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.3.3"
+  flutter:
+    dependency: "direct main"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
+  flutter_lints:
+    dependency: "direct dev"
+    description:
+      name: flutter_lints
+      sha256: "3105dc8492f6183fb076ccf1f351ac3d60564bff92e20bfc4af9cc1651f4e7e1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.0.0"
+  flutter_test:
+    dependency: "direct dev"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
+  leak_tracker:
+    dependency: transitive
+    description:
+      name: leak_tracker
+      sha256: "33e2e26bdd85a0112ec15400c8cbffea70d0f9c3407491f672a2fad47915e2de"
+      url: "https://pub.dev"
+    source: hosted
+    version: "11.0.2"
+  leak_tracker_flutter_testing:
+    dependency: transitive
+    description:
+      name: leak_tracker_flutter_testing
+      sha256: "1dbc140bb5a23c75ea9c4811222756104fbcd1a27173f0c34ca01e16bea473c1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.10"
+  leak_tracker_testing:
+    dependency: transitive
+    description:
+      name: leak_tracker_testing
+      sha256: "8d5a2d49f4a66b49744b23b018848400d23e54caf9463f4eb20df3eb8acb2eb1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.2"
+  lints:
+    dependency: transitive
+    description:
+      name: lints
+      sha256: "12f842a479589fea194fe5c5a3095abc7be0c1f2ddfa9a0e76aed1dbd26a87df"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.1.0"
+  matcher:
+    dependency: transitive
+    description:
+      name: matcher
+      sha256: dc0b7dc7651697ea4ff3e69ef44b0407ea32c487a39fff6a4004fa585e901861
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.12.19"
+  material_color_utilities:
+    dependency: transitive
+    description:
+      name: material_color_utilities
+      sha256: "9c337007e82b1889149c82ed242ed1cb24a66044e30979c44912381e9be4c48b"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.13.0"
+  meta:
+    dependency: transitive
+    description:
+      name: meta
+      sha256: "1741988757a65eb6b36abe716829688cf01910bbf91c34354ff7ec1c3de2b349"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.18.0"
+  path:
+    dependency: transitive
+    description:
+      name: path
+      sha256: "75cca69d1490965be98c73ceaea117e8a04dd21217b37b292c9ddbec0d955bc5"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.9.1"
+  plugin_platform_interface:
+    dependency: "direct main"
+    description:
+      name: plugin_platform_interface
+      sha256: "4820fbfdb9478b1ebae27888254d445073732dae3d6ea81f0b7e06d5dedc3f02"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.8"
+  sky_engine:
+    dependency: transitive
+    description: flutter
+    source: sdk
+    version: "0.0.0"
+  source_span:
+    dependency: transitive
+    description:
+      name: source_span
+      sha256: "56a02f1f4cd1a2d96303c0144c93bd6d909eea6bee6bf5a0e0b685edbd4c47ab"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.10.2"
+  stack_trace:
+    dependency: transitive
+    description:
+      name: stack_trace
+      sha256: "8b27215b45d22309b5cddda1aa2b19bdfec9df0e765f2de506401c071d38d1b1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.12.1"
+  stream_channel:
+    dependency: transitive
+    description:
+      name: stream_channel
+      sha256: "969e04c80b8bcdf826f8f16579c7b14d780458bd97f56d107d3950fdbeef059d"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.4"
+  string_scanner:
+    dependency: transitive
+    description:
+      name: string_scanner
+      sha256: "921cd31725b72fe181906c6a94d987c78e3b98c2e205b397ea399d4054872b43"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.1"
+  term_glyph:
+    dependency: transitive
+    description:
+      name: term_glyph
+      sha256: "7f554798625ea768a7518313e58f83891c7f5024f88e46e7182a4558850a4b8e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.2"
+  test_api:
+    dependency: transitive
+    description:
+      name: test_api
+      sha256: "949a932224383300f01be9221c39180316445ecb8e7547f70a41a35bf421fb9e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.11"
+  vector_math:
+    dependency: transitive
+    description:
+      name: vector_math
+      sha256: d530bd74fea330e6e364cda7a85019c434070188383e1cd8d9777ee586914c5b
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.2.0"
+  vm_service:
+    dependency: transitive
+    description:
+      name: vm_service
+      sha256: "0016aef94fc66495ac78af5859181e3f3bf2026bd8eecc72b9565601e19ab360"
+      url: "https://pub.dev"
+    source: hosted
+    version: "15.2.0"
+sdks:
+  dart: ">=3.10.0-0 <4.0.0"
+  flutter: ">=3.18.0-18.0.pre.54"

packages/saf_util/pubspec.yaml

@@ -0,0 +1,70 @@
+name: saf_util
+description: "Util functions for SAF (Storage Access Framework)."
+version: 2.0.0
+homepage: https://github.com/flutter-cavalry/saf_util
+
+environment:
+  sdk: ">=2.18.0 <4.0.0"
+  flutter: ">=2.5.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  plugin_platform_interface: ^2.0.2
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^6.0.0
+
+# For information on the generic Dart part of this file, see the
+# following page: https://dart.dev/tools/pub/pubspec
+
+# The following section is specific to Flutter packages.
+flutter:
+  # This section identifies this Flutter project as a plugin project.
+  # The 'pluginClass' specifies the class (in Java, Kotlin, Swift, Objective-C, etc.)
+  # which should be registered in the plugin registry. This is required for
+  # using method channels.
+  # The Android 'package' specifies package in which the registered class is.
+  # This is required for using method channels on Android.
+  # The 'ffiPlugin' specifies that native code should be built and bundled.
+  # This is required for using `dart:ffi`.
+  # All these are used by the tooling to maintain consistency when
+  # adding or updating assets for this project.
+  plugin:
+    platforms:
+      android:
+        package: com.fluttercavalry.saf_util
+        pluginClass: SafUtilPlugin
+
+  # To add assets to your plugin package, add an assets section, like this:
+  # assets:
+  #   - images/a_dot_burr.jpeg
+  #   - images/a_dot_ham.jpeg
+  #
+  # For details regarding assets in packages, see
+  # https://flutter.dev/to/asset-from-package
+  #
+  # An image asset can refer to one or more resolution-specific "variants", see
+  # https://flutter.dev/to/resolution-aware-images
+
+  # To add custom fonts to your plugin package, add a fonts section here,
+  # in this "flutter" section. Each entry in this list should have a
+  # "family" key with the font family name, and a "fonts" key with a
+  # list giving the asset and other descriptors for the font. For
+  # example:
+  # fonts:
+  #   - family: Schyler
+  #     fonts:
+  #       - asset: fonts/Schyler-Regular.ttf
+  #       - asset: fonts/Schyler-Italic.ttf
+  #         style: italic
+  #   - family: Trajan Pro
+  #     fonts:
+  #       - asset: fonts/TrajanPro.ttf
+  #       - asset: fonts/TrajanPro_Bold.ttf
+  #         weight: 700
+  #
+  # For details regarding fonts in packages, see
+  # https://flutter.dev/to/font-from-package