Chore: Remove temp file

문제: Android 11+ Scoped Storage로 인해 EPERM (Operation not permitted) 에러 발생
- Storage Access Framework로 디렉토리 선택했지만 File API로 쓰기 시도
- 권한 부족으로 파일 업로드(STOR) 실패

해결:
- AndroidManifest.xml에 MANAGE_EXTERNAL_STORAGE 권한 추가
- MainActivity에서 Android 11+ (API 30+) 권한 요청 로직 추가
  * Environment.isExternalStorageManager()로 권한 확인
  * Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION으로 설정 화면 이동
  * 서버 시작 전 권한 체크 추가
- 이 권한으로 외부 저장소 전체에 File API 접근 가능

사용자는 앱 실행 시 "All files access" 권한 활성화 필요

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/caches
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+/.idea/navEditor.xml
+/.idea/assetWizardSettings.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties
+
+.temp

.idea/.gitignore

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+# Default ignored files
+/shelf/
+/workspace.xml

.idea/.name

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+Gyub_s Android FTP Server

.idea/AndroidProjectSystem.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="AndroidProjectSystem">
+    <option name="providerId" value="com.android.tools.idea.GradleProjectSystem" />
+  </component>
+</project>

.idea/compiler.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <bytecodeTargetLevel target="11" />
+  </component>
+</project>

.idea/deploymentTargetSelector.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="deploymentTargetSelector">
+    <selectionStates>
+      <SelectionState runConfigName="app">
+        <option name="selectionMode" value="DROPDOWN" />
+      </SelectionState>
+    </selectionStates>
+  </component>
+</project>

.idea/deviceManager.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="DeviceTable">
+    <option name="columnSorters">
+      <list>
+        <ColumnSorterState>
+          <option name="column" value="Name" />
+          <option name="order" value="ASCENDING" />
+        </ColumnSorterState>
+      </list>
+    </option>
+  </component>
+</project>

.idea/gradle.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
+  <component name="GradleSettings">
+    <option name="linkedExternalProjectsSettings">
+      <GradleProjectSettings>
+        <option name="testRunner" value="CHOOSE_PER_TEST" />
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleJvm" value="jbr-21" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+            <option value="$PROJECT_DIR$/app" />
+          </set>
+        </option>
+      </GradleProjectSettings>
+    </option>
+  </component>
+</project>

.idea/markdown.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MarkdownSettings">
+    <option name="previewPanelProviderInfo">
+      <ProviderInfo name="Compose (experimental)" className="com.intellij.markdown.compose.preview.ComposePanelProvider" />
+    </option>
+  </component>
+</project>

.idea/misc.xml

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+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="true" project-jdk-name="Android Studio default JDK" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/build/classes" />
+  </component>
+  <component name="ProjectType">
+    <option name="id" value="Android" />
+  </component>
+</project>

.idea/runConfigurations.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RunConfigurationProducerService">
+    <option name="ignoredProducers">
+      <set>
+        <option value="com.intellij.execution.junit.AbstractAllInDirectoryConfigurationProducer" />
+        <option value="com.intellij.execution.junit.AllInPackageConfigurationProducer" />
+        <option value="com.intellij.execution.junit.PatternConfigurationProducer" />
+        <option value="com.intellij.execution.junit.TestInClassConfigurationProducer" />
+        <option value="com.intellij.execution.junit.UniqueIdConfigurationProducer" />
+        <option value="com.intellij.execution.junit.testDiscovery.JUnitTestDiscoveryConfigurationProducer" />
+        <option value="org.jetbrains.kotlin.idea.junit.KotlinJUnitRunConfigurationProducer" />
+        <option value="org.jetbrains.kotlin.idea.junit.KotlinPatternConfigurationProducer" />
+      </set>
+    </option>
+  </component>
+</project>

.idea/vcs.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

app/.gitignore

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+/build

app/build.gradle

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+plugins {
+    id 'com.android.application'
+}
+
+android {
+    compileSdk 34
+
+    defaultConfig {
+        applicationId "be.gyu.android.server.ftp"
+        minSdk 21
+        targetSdk 34
+        versionCode 1
+        versionName "1.0"
+
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+    }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+}
+
+dependencies {
+
+    implementation 'androidx.appcompat:appcompat:1.3.0'
+    implementation 'com.google.android.material:material:1.4.0'
+    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
+    testImplementation 'junit:junit:4.13.2'
+    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
+    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
+}

app/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

app/src/androidTest/java/be/gyu/android/server/ftp/ExampleInstrumentedTest.java

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+package be.gyu.android.server.ftp;
+
+import android.content.Context;
+
+import androidx.test.platform.app.InstrumentationRegistry;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.*;
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
+ */
+@RunWith(AndroidJUnit4.class)
+public class ExampleInstrumentedTest {
+    @Test
+    public void useAppContext() {
+        // Context of the app under test.
+        Context appContext = InstrumentationRegistry.getInstrumentation().getTargetContext();
+        assertEquals("be.gyu.android.server.ftp", appContext.getPackageName());
+    }
+}

app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="be.gyu.android.server.ftp">
+
+    <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"
+        android:maxSdkVersion="32" />
+    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
+        android:maxSdkVersion="32" />
+    <uses-permission android:name="android.permission.READ_MEDIA_IMAGES" />
+    <uses-permission android:name="android.permission.READ_MEDIA_VIDEO" />
+    <uses-permission android:name="android.permission.READ_MEDIA_AUDIO" />
+    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
+
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.Gyub_sAndroidFTPServer">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+
+        <service
+            android:name=".FTPService"
+            android:enabled="true"
+            android:exported="false"
+            android:foregroundServiceType="dataSync" />
+    </application>
+
+</manifest>

app/src/main/java/be/gyu/android/server/ftp/FTPConfig.java

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+package be.gyu.android.server.ftp;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.net.Uri;
+
+public class FTPConfig {
+    private static final String PREF_NAME = "FTPServerConfig";
+    private static final String KEY_PORT = "ftp_port";
+    private static final String KEY_ROOT_DIR_URI = "root_directory_uri";
+    private static final String KEY_ROOT_DIR_PATH = "root_directory_path";
+
+    private static final int DEFAULT_PORT = 2121;
+
+    private final SharedPreferences preferences;
+
+    public FTPConfig(Context context) {
+        this.preferences = context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE);
+    }
+
+    public int getPort() {
+        return preferences.getInt(KEY_PORT, DEFAULT_PORT);
+    }
+
+    public void setPort(int port) {
+        preferences.edit().putInt(KEY_PORT, port).apply();
+    }
+
+    public String getRootDirectoryUri() {
+        return preferences.getString(KEY_ROOT_DIR_URI, null);
+    }
+
+    public void setRootDirectoryUri(String uriString) {
+        preferences.edit().putString(KEY_ROOT_DIR_URI, uriString).apply();
+    }
+
+    public String getRootDirectoryPath() {
+        return preferences.getString(KEY_ROOT_DIR_PATH, null);
+    }
+
+    public void setRootDirectoryPath(String path) {
+        preferences.edit().putString(KEY_ROOT_DIR_PATH, path).apply();
+    }
+
+    public boolean hasRootDirectory() {
+        return getRootDirectoryPath() != null && !getRootDirectoryPath().isEmpty();
+    }
+
+    public void clearRootDirectory() {
+        preferences.edit()
+                .remove(KEY_ROOT_DIR_URI)
+                .remove(KEY_ROOT_DIR_PATH)
+                .apply();
+    }
+
+    public void saveSettings(int port, String rootDirUri, String rootDirPath) {
+        preferences.edit()
+                .putInt(KEY_PORT, port)
+                .putString(KEY_ROOT_DIR_URI, rootDirUri)
+                .putString(KEY_ROOT_DIR_PATH, rootDirPath)
+                .apply();
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/FTPDataConnection.java

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+package be.gyu.android.server.ftp;
+
+import android.util.Log;
+
+import java.io.BufferedInputStream;
+import java.io.BufferedOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+public class FTPDataConnection {
+    private static final String TAG = "FTPDataConnection";
+    private static final int DATA_CONNECTION_TIMEOUT = 30000; // 30 seconds
+
+    private ServerSocket passiveSocket;
+    private Socket dataSocket;
+    private int passivePort;
+
+    public boolean openPassiveMode(InetAddress bindAddress) {
+        try {
+            // Use port 0 to get a random available port
+            passiveSocket = new ServerSocket(0, 1, bindAddress);
+            passiveSocket.setSoTimeout(DATA_CONNECTION_TIMEOUT);
+            passivePort = passiveSocket.getLocalPort();
+
+            Log.i(TAG, "Passive mode enabled on port: " + passivePort);
+            return true;
+        } catch (IOException e) {
+            Log.e(TAG, "Error opening passive mode: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean acceptConnection() {
+        if (passiveSocket == null) {
+            Log.e(TAG, "Passive socket not initialized");
+            return false;
+        }
+
+        try {
+            Log.d(TAG, "Waiting for data connection...");
+            dataSocket = passiveSocket.accept();
+            Log.i(TAG, "Data connection established from: " + dataSocket.getInetAddress());
+            return true;
+        } catch (IOException e) {
+            Log.e(TAG, "Error accepting data connection: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean sendData(byte[] data) {
+        if (dataSocket == null || dataSocket.isClosed()) {
+            Log.e(TAG, "Data socket not available");
+            return false;
+        }
+
+        try {
+            OutputStream out = new BufferedOutputStream(dataSocket.getOutputStream());
+            out.write(data);
+            out.flush();
+            Log.d(TAG, "Sent " + data.length + " bytes");
+            return true;
+        } catch (IOException e) {
+            Log.e(TAG, "Error sending data: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean sendData(String text) {
+        return sendData(text.getBytes());
+    }
+
+    public byte[] receiveData(int maxSize) {
+        if (dataSocket == null || dataSocket.isClosed()) {
+            Log.e(TAG, "Data socket not available");
+            return null;
+        }
+
+        try {
+            InputStream in = new BufferedInputStream(dataSocket.getInputStream());
+            byte[] buffer = new byte[maxSize];
+            int bytesRead = in.read(buffer);
+
+            if (bytesRead > 0) {
+                byte[] data = new byte[bytesRead];
+                System.arraycopy(buffer, 0, data, 0, bytesRead);
+                Log.d(TAG, "Received " + bytesRead + " bytes");
+                return data;
+            } else {
+                Log.w(TAG, "No data received");
+                return null;
+            }
+        } catch (IOException e) {
+            Log.e(TAG, "Error receiving data: " + e.getMessage());
+            return null;
+        }
+    }
+
+    public boolean transferStream(InputStream inputStream) {
+        if (dataSocket == null || dataSocket.isClosed()) {
+            Log.e(TAG, "Data socket not available");
+            return false;
+        }
+
+        try {
+            OutputStream out = new BufferedOutputStream(dataSocket.getOutputStream());
+            byte[] buffer = new byte[8192];
+            int bytesRead;
+            long totalBytes = 0;
+
+            while ((bytesRead = inputStream.read(buffer)) != -1) {
+                out.write(buffer, 0, bytesRead);
+                totalBytes += bytesRead;
+            }
+
+            out.flush();
+            Log.i(TAG, "Transferred " + totalBytes + " bytes via stream");
+            return true;
+        } catch (IOException e) {
+            Log.e(TAG, "Error transferring stream: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean receiveStream(OutputStream outputStream) {
+        if (dataSocket == null || dataSocket.isClosed()) {
+            Log.e(TAG, "Data socket not available");
+            return false;
+        }
+
+        try {
+            InputStream in = new BufferedInputStream(dataSocket.getInputStream());
+            byte[] buffer = new byte[8192];
+            int bytesRead;
+            long totalBytes = 0;
+
+            while ((bytesRead = in.read(buffer)) != -1) {
+                outputStream.write(buffer, 0, bytesRead);
+                totalBytes += bytesRead;
+            }
+
+            outputStream.flush();
+            Log.i(TAG, "Received " + totalBytes + " bytes via stream");
+            return true;
+        } catch (IOException e) {
+            Log.e(TAG, "Error receiving stream: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public void close() {
+        try {
+            if (dataSocket != null && !dataSocket.isClosed()) {
+                dataSocket.close();
+                Log.d(TAG, "Data socket closed");
+            }
+        } catch (IOException e) {
+            Log.e(TAG, "Error closing data socket: " + e.getMessage());
+        }
+
+        try {
+            if (passiveSocket != null && !passiveSocket.isClosed()) {
+                passiveSocket.close();
+                Log.d(TAG, "Passive socket closed");
+            }
+        } catch (IOException e) {
+            Log.e(TAG, "Error closing passive socket: " + e.getMessage());
+        }
+
+        dataSocket = null;
+        passiveSocket = null;
+    }
+
+    public int getPassivePort() {
+        return passivePort;
+    }
+
+    public boolean isDataConnectionOpen() {
+        return dataSocket != null && !dataSocket.isClosed();
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/FTPFileSystem.java

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+package be.gyu.android.server.ftp;
+
+import android.os.Environment;
+import android.util.Log;
+
+import java.io.File;
+import java.text.SimpleDateFormat;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.List;
+import java.util.Locale;
+
+public class FTPFileSystem {
+    private static final String TAG = "FTPFileSystem";
+
+    private final File rootDirectory;
+    private File currentDirectory;
+
+    public FTPFileSystem() {
+        this(null);
+    }
+
+    public FTPFileSystem(String rootDirectoryPath) {
+        if (rootDirectoryPath != null && !rootDirectoryPath.isEmpty()) {
+            // Use user-specified directory
+            File userDir = new File(rootDirectoryPath);
+            if (userDir.exists() && userDir.isDirectory()) {
+                this.rootDirectory = userDir;
+                Log.i(TAG, "Using user-specified root: " + rootDirectory.getAbsolutePath());
+            } else {
+                Log.w(TAG, "User-specified directory does not exist: " + rootDirectoryPath);
+                this.rootDirectory = getDefaultRootDirectory();
+            }
+        } else {
+            // Use default directory
+            this.rootDirectory = getDefaultRootDirectory();
+        }
+
+        this.currentDirectory = rootDirectory;
+        Log.d(TAG, "File system initialized. Root: " + rootDirectory.getAbsolutePath());
+    }
+
+    private File getDefaultRootDirectory() {
+        File externalStorage = Environment.getExternalStorageDirectory();
+        File ftpServerDir = new File(externalStorage, "FTPServer");
+
+        // Create root directory if it doesn't exist
+        if (!ftpServerDir.exists()) {
+            if (ftpServerDir.mkdirs()) {
+                Log.i(TAG, "Root directory created: " + ftpServerDir.getAbsolutePath());
+                return ftpServerDir;
+            } else {
+                Log.w(TAG, "Failed to create root directory, using external storage root");
+                return externalStorage;
+            }
+        } else {
+            return ftpServerDir;
+        }
+    }
+
+    public String getCurrentPath() {
+        String relativePath = getRelativePath(currentDirectory);
+        return relativePath.isEmpty() ? "/" : "/" + relativePath;
+    }
+
+    public boolean changeDirectory(String path) {
+        File newDir;
+
+        if (path.startsWith("/")) {
+            // Absolute path
+            newDir = new File(rootDirectory, path.substring(1));
+        } else {
+            // Relative path
+            newDir = new File(currentDirectory, path);
+        }
+
+        try {
+            String canonicalPath = newDir.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            // Security check: prevent escaping root directory
+            if (!canonicalPath.startsWith(rootPath)) {
+                Log.w(TAG, "Attempted to escape root directory: " + canonicalPath);
+                return false;
+            }
+
+            if (newDir.exists() && newDir.isDirectory()) {
+                currentDirectory = newDir;
+                Log.d(TAG, "Changed directory to: " + currentDirectory.getAbsolutePath());
+                return true;
+            } else {
+                Log.w(TAG, "Directory does not exist: " + newDir.getAbsolutePath());
+                return false;
+            }
+        } catch (Exception e) {
+            Log.e(TAG, "Error changing directory: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean changeToParentDirectory() {
+        File parent = currentDirectory.getParentFile();
+
+        if (parent == null) {
+            return false;
+        }
+
+        try {
+            String parentPath = parent.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            // Cannot go above root directory
+            if (!parentPath.startsWith(rootPath)) {
+                return false;
+            }
+
+            currentDirectory = parent;
+            Log.d(TAG, "Changed to parent directory: " + currentDirectory.getAbsolutePath());
+            return true;
+        } catch (Exception e) {
+            Log.e(TAG, "Error changing to parent directory: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public List<File> listFiles() {
+        File[] files = currentDirectory.listFiles();
+        List<File> fileList = new ArrayList<>();
+
+        if (files != null) {
+            for (File file : files) {
+                fileList.add(file);
+            }
+        }
+
+        return fileList;
+    }
+
+    public String formatFileList(boolean detailed) {
+        List<File> files = listFiles();
+        StringBuilder sb = new StringBuilder();
+
+        if (detailed) {
+            // LIST format: Unix-style detailed listing
+            SimpleDateFormat dateFormat = new SimpleDateFormat("MMM dd HH:mm", Locale.US);
+
+            for (File file : files) {
+                sb.append(formatDetailedFile(file, dateFormat)).append("\r\n");
+            }
+        } else {
+            // NLST format: names only
+            for (File file : files) {
+                sb.append(file.getName()).append("\r\n");
+            }
+        }
+
+        return sb.toString();
+    }
+
+    private String formatDetailedFile(File file, SimpleDateFormat dateFormat) {
+        // Format: drwxrwxrwx 1 owner group size date name
+        String permissions = file.isDirectory() ? "drwxr-xr-x" : "-rw-r--r--";
+        String owner = "ftp";
+        String group = "ftp";
+        long size = file.length();
+        String date = dateFormat.format(new Date(file.lastModified()));
+        String name = file.getName();
+
+        return String.format("%s %4d %-8s %-8s %10d %s %s",
+                permissions, 1, owner, group, size, date, name);
+    }
+
+    public boolean makeDirectory(String dirName) {
+        File newDir = new File(currentDirectory, dirName);
+
+        try {
+            String canonicalPath = newDir.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            if (!canonicalPath.startsWith(rootPath)) {
+                return false;
+            }
+
+            if (newDir.mkdir()) {
+                Log.i(TAG, "Directory created: " + newDir.getAbsolutePath());
+                return true;
+            } else {
+                Log.w(TAG, "Failed to create directory: " + newDir.getAbsolutePath());
+                return false;
+            }
+        } catch (Exception e) {
+            Log.e(TAG, "Error creating directory: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean removeDirectory(String dirName) {
+        File dir = new File(currentDirectory, dirName);
+
+        try {
+            String canonicalPath = dir.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            if (!canonicalPath.startsWith(rootPath)) {
+                return false;
+            }
+
+            if (dir.exists() && dir.isDirectory() && dir.delete()) {
+                Log.i(TAG, "Directory removed: " + dir.getAbsolutePath());
+                return true;
+            } else {
+                Log.w(TAG, "Failed to remove directory: " + dir.getAbsolutePath());
+                return false;
+            }
+        } catch (Exception e) {
+            Log.e(TAG, "Error removing directory: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public boolean deleteFile(String fileName) {
+        File file = new File(currentDirectory, fileName);
+
+        try {
+            String canonicalPath = file.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            if (!canonicalPath.startsWith(rootPath)) {
+                return false;
+            }
+
+            if (file.exists() && file.isFile() && file.delete()) {
+                Log.i(TAG, "File deleted: " + file.getAbsolutePath());
+                return true;
+            } else {
+                Log.w(TAG, "Failed to delete file: " + file.getAbsolutePath());
+                return false;
+            }
+        } catch (Exception e) {
+            Log.e(TAG, "Error deleting file: " + e.getMessage());
+            return false;
+        }
+    }
+
+    public File getFile(String fileName) {
+        File file = new File(currentDirectory, fileName);
+
+        try {
+            String canonicalPath = file.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            if (!canonicalPath.startsWith(rootPath)) {
+                return null;
+            }
+
+            return file.exists() ? file : null;
+        } catch (Exception e) {
+            Log.e(TAG, "Error getting file: " + e.getMessage());
+            return null;
+        }
+    }
+
+    public long getFileSize(String fileName) {
+        File file = getFile(fileName);
+        return (file != null && file.isFile()) ? file.length() : -1;
+    }
+
+    private String getRelativePath(File file) {
+        try {
+            String filePath = file.getCanonicalPath();
+            String rootPath = rootDirectory.getCanonicalPath();
+
+            if (filePath.equals(rootPath)) {
+                return "";
+            } else if (filePath.startsWith(rootPath + File.separator)) {
+                return filePath.substring(rootPath.length() + 1).replace(File.separator, "/");
+            } else {
+                return "";
+            }
+        } catch (Exception e) {
+            Log.e(TAG, "Error getting relative path: " + e.getMessage());
+            return "";
+        }
+    }
+
+    public File getRootDirectory() {
+        return rootDirectory;
+    }
+
+    public File getCurrentDirectory() {
+        return currentDirectory;
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/FTPResponse.java

@@ -0,0 +1,68 @@
+package be.gyu.android.server.ftp;
+
+public class FTPResponse {
+    // 1xx - Positive Preliminary reply
+    public static final int RESTART_MARKER = 110;
+    public static final int SERVICE_READY_IN_N_MINUTES = 120;
+    public static final int DATA_CONNECTION_ALREADY_OPEN = 125;
+    public static final int FILE_STATUS_OK = 150;
+
+    // 2xx - Positive Completion reply
+    public static final int COMMAND_OK = 200;
+    public static final int COMMAND_NOT_IMPLEMENTED = 202;
+    public static final int SYSTEM_STATUS = 211;
+    public static final int DIRECTORY_STATUS = 212;
+    public static final int FILE_STATUS = 213;
+    public static final int HELP_MESSAGE = 214;
+    public static final int SYSTEM_TYPE = 215;
+    public static final int SERVICE_READY = 220;
+    public static final int SERVICE_CLOSING = 221;
+    public static final int DATA_CONNECTION_OPEN = 225;
+    public static final int CLOSING_DATA_CONNECTION = 226;
+    public static final int ENTERING_PASSIVE_MODE = 227;
+    public static final int USER_LOGGED_IN = 230;
+    public static final int REQUESTED_FILE_ACTION_OK = 250;
+    public static final int PATHNAME_CREATED = 257;
+
+    // 3xx - Positive Intermediate reply
+    public static final int USERNAME_OK_NEED_PASSWORD = 331;
+    public static final int NEED_ACCOUNT = 332;
+    public static final int FILE_ACTION_PENDING = 350;
+
+    // 4xx - Transient Negative Completion reply
+    public static final int SERVICE_NOT_AVAILABLE = 421;
+    public static final int CANNOT_OPEN_DATA_CONNECTION = 425;
+    public static final int CONNECTION_CLOSED = 426;
+    public static final int FILE_ACTION_NOT_TAKEN = 450;
+    public static final int ACTION_ABORTED = 451;
+    public static final int INSUFFICIENT_STORAGE = 452;
+
+    // 5xx - Permanent Negative Completion reply
+    public static final int SYNTAX_ERROR = 500;
+    public static final int SYNTAX_ERROR_PARAMETERS = 501;
+    public static final int COMMAND_NOT_IMPLEMENTED_502 = 502;
+    public static final int BAD_SEQUENCE = 503;
+    public static final int COMMAND_NOT_IMPLEMENTED_FOR_PARAMETER = 504;
+    public static final int NOT_LOGGED_IN = 530;
+    public static final int NEED_ACCOUNT_FOR_STORING = 532;
+    public static final int FILE_UNAVAILABLE = 550;
+    public static final int PAGE_TYPE_UNKNOWN = 551;
+    public static final int EXCEEDED_STORAGE = 552;
+    public static final int FILE_NAME_NOT_ALLOWED = 553;
+
+    public static String format(int code, String message) {
+        return code + " " + message + "\r\n";
+    }
+
+    public static String formatMultiline(int code, String[] messages) {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < messages.length; i++) {
+            if (i < messages.length - 1) {
+                sb.append(code).append("-").append(messages[i]).append("\r\n");
+            } else {
+                sb.append(code).append(" ").append(messages[i]).append("\r\n");
+            }
+        }
+        return sb.toString();
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/FTPServer.java

@@ -0,0 +1,115 @@
+package be.gyu.android.server.ftp;
+
+import android.util.Log;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class FTPServer {
+    private static final String TAG = "FTPServer";
+    private static final int DEFAULT_PORT = 2121;
+    private static final int MAX_CONNECTIONS = 10;
+
+    private ServerSocket serverSocket;
+    private ExecutorService executorService;
+    private Thread acceptThread;
+    private boolean isRunning = false;
+    private int port;
+    private String rootDirectory;
+
+    public FTPServer() {
+        this(DEFAULT_PORT, null);
+    }
+
+    public FTPServer(int port) {
+        this(port, null);
+    }
+
+    public FTPServer(int port, String rootDirectory) {
+        this.port = port;
+        this.rootDirectory = rootDirectory;
+        this.executorService = Executors.newFixedThreadPool(MAX_CONNECTIONS);
+    }
+
+    public void start() {
+        if (isRunning) {
+            Log.w(TAG, "Server is already running");
+            return;
+        }
+
+        acceptThread = new Thread(() -> {
+            try {
+                serverSocket = new ServerSocket(port);
+                isRunning = true;
+                Log.i(TAG, "FTP Server started on port " + port);
+
+                while (isRunning && !Thread.currentThread().isInterrupted()) {
+                    try {
+                        Socket clientSocket = serverSocket.accept();
+                        Log.i(TAG, "New client connection from: " + clientSocket.getInetAddress());
+
+                        FTPSession session = new FTPSession(clientSocket, rootDirectory);
+                        executorService.execute(session);
+
+                    } catch (IOException e) {
+                        if (isRunning) {
+                            Log.e(TAG, "Error accepting connection: " + e.getMessage());
+                        }
+                    }
+                }
+            } catch (IOException e) {
+                Log.e(TAG, "Server socket error: " + e.getMessage());
+            } finally {
+                Log.i(TAG, "Server accept thread stopped");
+            }
+        });
+
+        acceptThread.start();
+    }
+
+    public void stop() {
+        if (!isRunning) {
+            Log.w(TAG, "Server is not running");
+            return;
+        }
+
+        Log.i(TAG, "Stopping FTP Server...");
+        isRunning = false;
+
+        try {
+            if (serverSocket != null && !serverSocket.isClosed()) {
+                serverSocket.close();
+            }
+        } catch (IOException e) {
+            Log.e(TAG, "Error closing server socket: " + e.getMessage());
+        }
+
+        if (acceptThread != null) {
+            acceptThread.interrupt();
+        }
+
+        executorService.shutdown();
+        try {
+            if (!executorService.awaitTermination(5, TimeUnit.SECONDS)) {
+                executorService.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            executorService.shutdownNow();
+            Thread.currentThread().interrupt();
+        }
+
+        Log.i(TAG, "FTP Server stopped");
+    }
+
+    public boolean isRunning() {
+        return isRunning;
+    }
+
+    public int getPort() {
+        return port;
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/FTPService.java

@@ -0,0 +1,122 @@
+package be.gyu.android.server.ftp;
+
+import android.app.Notification;
+import android.app.NotificationChannel;
+import android.app.NotificationManager;
+import android.app.PendingIntent;
+import android.app.Service;
+import android.content.Intent;
+import android.os.Build;
+import android.os.IBinder;
+import android.util.Log;
+
+import androidx.core.app.NotificationCompat;
+
+public class FTPService extends Service {
+    private static final String TAG = "FTPService";
+    private static final String CHANNEL_ID = "FTPServerChannel";
+    private static final int NOTIFICATION_ID = 1;
+
+    public static final String ACTION_START = "be.gyu.android.server.ftp.ACTION_START";
+    public static final String ACTION_STOP = "be.gyu.android.server.ftp.ACTION_STOP";
+
+    private FTPServer ftpServer;
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        Log.d(TAG, "Service created");
+        createNotificationChannel();
+    }
+
+    @Override
+    public int onStartCommand(Intent intent, int flags, int startId) {
+        if (intent != null) {
+            String action = intent.getAction();
+
+            if (ACTION_START.equals(action)) {
+                int port = intent.getIntExtra("port", 2121);
+                String rootDir = intent.getStringExtra("rootDir");
+                startFTPServer(port, rootDir);
+            } else if (ACTION_STOP.equals(action)) {
+                stopFTPServer();
+            }
+        }
+
+        return START_STICKY;
+    }
+
+    private void startFTPServer(int port, String rootDir) {
+        if (ftpServer != null && ftpServer.isRunning()) {
+            Log.w(TAG, "FTP Server is already running");
+            return;
+        }
+
+        ftpServer = new FTPServer(port, rootDir);
+        ftpServer.start();
+
+        Notification notification = createNotification("FTP Server is running on port " + ftpServer.getPort());
+        startForeground(NOTIFICATION_ID, notification);
+
+        Log.i(TAG, "FTP Server started on port " + port + " with root: " + rootDir);
+    }
+
+    private void stopFTPServer() {
+        if (ftpServer != null) {
+            ftpServer.stop();
+            ftpServer = null;
+        }
+
+        stopForeground(true);
+        stopSelf();
+
+        Log.i(TAG, "FTP Server stopped");
+    }
+
+    @Override
+    public void onDestroy() {
+        super.onDestroy();
+        if (ftpServer != null) {
+            ftpServer.stop();
+        }
+        Log.d(TAG, "Service destroyed");
+    }
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        return null;
+    }
+
+    private void createNotificationChannel() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            NotificationChannel channel = new NotificationChannel(
+                    CHANNEL_ID,
+                    "FTP Server Service",
+                    NotificationManager.IMPORTANCE_LOW
+            );
+            channel.setDescription("FTP Server running notification");
+
+            NotificationManager manager = getSystemService(NotificationManager.class);
+            if (manager != null) {
+                manager.createNotificationChannel(channel);
+            }
+        }
+    }
+
+    private Notification createNotification(String contentText) {
+        Intent notificationIntent = new Intent(this, MainActivity.class);
+        PendingIntent pendingIntent = PendingIntent.getActivity(
+                this,
+                0,
+                notificationIntent,
+                PendingIntent.FLAG_IMMUTABLE
+        );
+
+        return new NotificationCompat.Builder(this, CHANNEL_ID)
+                .setContentTitle("FTP Server")
+                .setContentText(contentText)
+                .setSmallIcon(android.R.drawable.stat_sys_upload)
+                .setContentIntent(pendingIntent)
+                .build();
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/FTPSession.java

@@ -0,0 +1,506 @@
+package be.gyu.android.server.ftp;
+
+import android.util.Log;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.net.Socket;
+
+public class FTPSession implements Runnable {
+    private static final String TAG = "FTPSession";
+
+    private final Socket controlSocket;
+    private BufferedReader reader;
+    private BufferedWriter writer;
+
+    private String username;
+    private boolean isAuthenticated = false;
+    private boolean isRunning = true;
+    private FTPFileSystem fileSystem;
+    private FTPDataConnection dataConnection;
+    private String transferType = "A"; // A = ASCII, I = Binary
+
+    public FTPSession(Socket socket) {
+        this(socket, null);
+    }
+
+    public FTPSession(Socket socket, String rootDirectory) {
+        this.controlSocket = socket;
+        this.fileSystem = new FTPFileSystem(rootDirectory);
+        this.dataConnection = null;
+    }
+
+    @Override
+    public void run() {
+        try {
+            reader = new BufferedReader(new InputStreamReader(controlSocket.getInputStream()));
+            writer = new BufferedWriter(new OutputStreamWriter(controlSocket.getOutputStream()));
+
+            Log.d(TAG, "Client connected: " + controlSocket.getInetAddress());
+            sendResponse(FTPResponse.SERVICE_READY, "FTP Server ready");
+
+            String line;
+            while (isRunning && (line = reader.readLine()) != null) {
+                line = line.trim();
+                Log.d(TAG, "Command received: " + line);
+
+                if (line.isEmpty()) {
+                    continue;
+                }
+
+                handleCommand(line);
+            }
+        } catch (IOException e) {
+            Log.e(TAG, "Session error: " + e.getMessage());
+        } finally {
+            closeSession();
+        }
+    }
+
+    private void handleCommand(String commandLine) throws IOException {
+        String[] parts = commandLine.split("\\s+", 2);
+        String command = parts[0].toUpperCase();
+        String argument = parts.length > 1 ? parts[1] : "";
+
+        switch (command) {
+            case "USER":
+                handleUser(argument);
+                break;
+            case "PASS":
+                handlePass(argument);
+                break;
+            case "QUIT":
+                handleQuit();
+                break;
+            case "SYST":
+                handleSyst();
+                break;
+            case "PWD":
+                handlePwd();
+                break;
+            case "CWD":
+                handleCwd(argument);
+                break;
+            case "CDUP":
+                handleCdup();
+                break;
+            case "LIST":
+                handleList(argument);
+                break;
+            case "NLST":
+                handleNlst(argument);
+                break;
+            case "MKD":
+                handleMkd(argument);
+                break;
+            case "RMD":
+                handleRmd(argument);
+                break;
+            case "DELE":
+                handleDele(argument);
+                break;
+            case "SIZE":
+                handleSize(argument);
+                break;
+            case "TYPE":
+                handleType(argument);
+                break;
+            case "PASV":
+                handlePasv();
+                break;
+            case "RETR":
+                handleRetr(argument);
+                break;
+            case "STOR":
+                handleStor(argument);
+                break;
+            case "NOOP":
+                handleNoop();
+                break;
+            default:
+                sendResponse(FTPResponse.COMMAND_NOT_IMPLEMENTED_502, "Command not implemented");
+                break;
+        }
+    }
+
+    private void handleUser(String username) throws IOException {
+        this.username = username;
+        sendResponse(FTPResponse.USERNAME_OK_NEED_PASSWORD, "Username OK, password required");
+    }
+
+    private void handlePass(String password) throws IOException {
+        if (username == null || username.isEmpty()) {
+            sendResponse(FTPResponse.BAD_SEQUENCE, "Login with USER first");
+            return;
+        }
+
+        // Simple authentication - accept any password for now
+        // In production, implement proper authentication
+        isAuthenticated = true;
+        sendResponse(FTPResponse.USER_LOGGED_IN, "User logged in");
+    }
+
+    private void handleQuit() throws IOException {
+        sendResponse(FTPResponse.SERVICE_CLOSING, "Goodbye");
+        isRunning = false;
+    }
+
+    private void handleSyst() throws IOException {
+        sendResponse(FTPResponse.SYSTEM_TYPE, "UNIX Type: L8");
+    }
+
+    private void handlePwd() throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+        String path = fileSystem.getCurrentPath();
+        sendResponse(FTPResponse.PATHNAME_CREATED, "\"" + path + "\" is current directory");
+    }
+
+    private void handleCwd(String path) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (path.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No directory specified");
+            return;
+        }
+
+        if (fileSystem.changeDirectory(path)) {
+            sendResponse(FTPResponse.REQUESTED_FILE_ACTION_OK, "Directory changed to " + fileSystem.getCurrentPath());
+        } else {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "Failed to change directory");
+        }
+    }
+
+    private void handleCdup() throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (fileSystem.changeToParentDirectory()) {
+            sendResponse(FTPResponse.REQUESTED_FILE_ACTION_OK, "Directory changed to " + fileSystem.getCurrentPath());
+        } else {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "Already at root directory");
+        }
+    }
+
+    private void handleList(String path) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (dataConnection == null) {
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Use PASV first");
+            return;
+        }
+
+        String fileList = fileSystem.formatFileList(true);
+
+        sendResponse(FTPResponse.FILE_STATUS_OK, "Opening data connection for directory list");
+
+        if (dataConnection.acceptConnection()) {
+            if (dataConnection.sendData(fileList)) {
+                dataConnection.close();
+                sendResponse(FTPResponse.CLOSING_DATA_CONNECTION, "Directory send OK");
+            } else {
+                dataConnection.close();
+                sendResponse(FTPResponse.CONNECTION_CLOSED, "Transfer failed");
+            }
+        } else {
+            dataConnection.close();
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Cannot open data connection");
+        }
+
+        dataConnection = null;
+    }
+
+    private void handleNlst(String path) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (dataConnection == null) {
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Use PASV first");
+            return;
+        }
+
+        String fileList = fileSystem.formatFileList(false);
+
+        sendResponse(FTPResponse.FILE_STATUS_OK, "Opening data connection for name list");
+
+        if (dataConnection.acceptConnection()) {
+            if (dataConnection.sendData(fileList)) {
+                dataConnection.close();
+                sendResponse(FTPResponse.CLOSING_DATA_CONNECTION, "Transfer complete");
+            } else {
+                dataConnection.close();
+                sendResponse(FTPResponse.CONNECTION_CLOSED, "Transfer failed");
+            }
+        } else {
+            dataConnection.close();
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Cannot open data connection");
+        }
+
+        dataConnection = null;
+    }
+
+    private void handleMkd(String dirName) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (dirName.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No directory name specified");
+            return;
+        }
+
+        if (fileSystem.makeDirectory(dirName)) {
+            String newPath = fileSystem.getCurrentPath() + "/" + dirName;
+            sendResponse(FTPResponse.PATHNAME_CREATED, "\"" + newPath + "\" directory created");
+        } else {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "Failed to create directory");
+        }
+    }
+
+    private void handleRmd(String dirName) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (dirName.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No directory name specified");
+            return;
+        }
+
+        if (fileSystem.removeDirectory(dirName)) {
+            sendResponse(FTPResponse.REQUESTED_FILE_ACTION_OK, "Directory removed");
+        } else {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "Failed to remove directory");
+        }
+    }
+
+    private void handleDele(String fileName) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (fileName.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No file name specified");
+            return;
+        }
+
+        if (fileSystem.deleteFile(fileName)) {
+            sendResponse(FTPResponse.REQUESTED_FILE_ACTION_OK, "File deleted");
+        } else {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "Failed to delete file");
+        }
+    }
+
+    private void handleSize(String fileName) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (fileName.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No file name specified");
+            return;
+        }
+
+        long size = fileSystem.getFileSize(fileName);
+        if (size >= 0) {
+            sendResponse(FTPResponse.FILE_STATUS, String.valueOf(size));
+        } else {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "File not found");
+        }
+    }
+
+    private void handleType(String typeCode) throws IOException {
+        if (typeCode.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No type specified");
+            return;
+        }
+
+        String type = typeCode.toUpperCase();
+        if (type.equals("A") || type.equals("I")) {
+            transferType = type;
+            String typeName = type.equals("A") ? "ASCII" : "Binary";
+            sendResponse(FTPResponse.COMMAND_OK, "Type set to " + typeName);
+        } else {
+            sendResponse(FTPResponse.COMMAND_NOT_IMPLEMENTED_FOR_PARAMETER, "Type not supported");
+        }
+    }
+
+    private void handlePasv() throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        // Close previous data connection if exists
+        if (dataConnection != null) {
+            dataConnection.close();
+        }
+
+        dataConnection = new FTPDataConnection();
+
+        // Get server address from control socket
+        String serverAddress = controlSocket.getLocalAddress().getHostAddress();
+
+        if (dataConnection.openPassiveMode(controlSocket.getLocalAddress())) {
+            int port = dataConnection.getPassivePort();
+
+            // Format: h1,h2,h3,h4,p1,p2
+            // where IP is h1.h2.h3.h4 and port is p1*256+p2
+            String[] addressParts = serverAddress.split("\\.");
+            int p1 = port / 256;
+            int p2 = port % 256;
+
+            String pasvResponse = String.format("Entering Passive Mode (%s,%s,%s,%s,%d,%d)",
+                    addressParts[0], addressParts[1], addressParts[2], addressParts[3], p1, p2);
+
+            sendResponse(FTPResponse.ENTERING_PASSIVE_MODE, pasvResponse);
+            Log.i(TAG, "Passive mode: " + serverAddress + ":" + port);
+        } else {
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Cannot open passive mode");
+        }
+    }
+
+    private void handleRetr(String fileName) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (fileName.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No file name specified");
+            return;
+        }
+
+        if (dataConnection == null) {
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Use PASV first");
+            return;
+        }
+
+        java.io.File file = fileSystem.getFile(fileName);
+        if (file == null || !file.exists() || !file.isFile()) {
+            sendResponse(FTPResponse.FILE_UNAVAILABLE, "File not found");
+            dataConnection.close();
+            dataConnection = null;
+            return;
+        }
+
+        sendResponse(FTPResponse.FILE_STATUS_OK, "Opening data connection for " + fileName + " (" + file.length() + " bytes)");
+
+        if (dataConnection.acceptConnection()) {
+            try {
+                java.io.FileInputStream fis = new java.io.FileInputStream(file);
+                if (dataConnection.transferStream(fis)) {
+                    fis.close();
+                    dataConnection.close();
+                    sendResponse(FTPResponse.CLOSING_DATA_CONNECTION, "Transfer complete");
+                    Log.i(TAG, "File sent: " + fileName + " (" + file.length() + " bytes)");
+                } else {
+                    fis.close();
+                    dataConnection.close();
+                    sendResponse(FTPResponse.CONNECTION_CLOSED, "Transfer failed");
+                }
+            } catch (Exception e) {
+                Log.e(TAG, "Error sending file: " + e.getMessage());
+                dataConnection.close();
+                sendResponse(FTPResponse.CONNECTION_CLOSED, "Transfer error: " + e.getMessage());
+            }
+        } else {
+            dataConnection.close();
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Cannot open data connection");
+        }
+
+        dataConnection = null;
+    }
+
+    private void handleStor(String fileName) throws IOException {
+        if (!isAuthenticated) {
+            sendResponse(FTPResponse.NOT_LOGGED_IN, "Please login first");
+            return;
+        }
+
+        if (fileName.isEmpty()) {
+            sendResponse(FTPResponse.SYNTAX_ERROR_PARAMETERS, "No file name specified");
+            return;
+        }
+
+        if (dataConnection == null) {
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Use PASV first");
+            return;
+        }
+
+        java.io.File file = new java.io.File(fileSystem.getCurrentDirectory(), fileName);
+
+        sendResponse(FTPResponse.FILE_STATUS_OK, "Opening data connection for " + fileName);
+
+        if (dataConnection.acceptConnection()) {
+            try {
+                java.io.FileOutputStream fos = new java.io.FileOutputStream(file);
+                if (dataConnection.receiveStream(fos)) {
+                    fos.close();
+                    dataConnection.close();
+                    sendResponse(FTPResponse.CLOSING_DATA_CONNECTION, "Transfer complete");
+                    Log.i(TAG, "File received: " + fileName + " (" + file.length() + " bytes)");
+                } else {
+                    fos.close();
+                    dataConnection.close();
+                    sendResponse(FTPResponse.CONNECTION_CLOSED, "Transfer failed");
+                }
+            } catch (Exception e) {
+                Log.e(TAG, "Error receiving file: " + e.getMessage());
+                dataConnection.close();
+                sendResponse(FTPResponse.CONNECTION_CLOSED, "Transfer error: " + e.getMessage());
+            }
+        } else {
+            dataConnection.close();
+            sendResponse(FTPResponse.CANNOT_OPEN_DATA_CONNECTION, "Cannot open data connection");
+        }
+
+        dataConnection = null;
+    }
+
+    private void handleNoop() throws IOException {
+        sendResponse(FTPResponse.COMMAND_OK, "OK");
+    }
+
+    private void sendResponse(int code, String message) throws IOException {
+        String response = FTPResponse.format(code, message);
+        writer.write(response);
+        writer.flush();
+        Log.d(TAG, "Response sent: " + response.trim());
+    }
+
+    private void closeSession() {
+        try {
+            if (dataConnection != null) {
+                dataConnection.close();
+            }
+            if (reader != null) reader.close();
+            if (writer != null) writer.close();
+            if (controlSocket != null && !controlSocket.isClosed()) {
+                controlSocket.close();
+            }
+            Log.d(TAG, "Session closed");
+        } catch (IOException e) {
+            Log.e(TAG, "Error closing session: " + e.getMessage());
+        }
+    }
+}

app/src/main/java/be/gyu/android/server/ftp/MainActivity.java

@@ -0,0 +1,241 @@
+package be.gyu.android.server.ftp;
+
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts;
+import androidx.appcompat.app.AppCompatActivity;
+import androidx.core.app.ActivityCompat;
+import androidx.core.content.ContextCompat;
+import androidx.documentfile.provider.DocumentFile;
+
+import android.Manifest;
+import android.content.Intent;
+import android.content.pm.PackageManager;
+import android.net.Uri;
+import android.os.Build;
+import android.os.Bundle;
+import android.os.Environment;
+import android.provider.Settings;
+import android.widget.Button;
+import android.widget.EditText;
+import android.widget.TextView;
+import android.widget.Toast;
+
+public class MainActivity extends AppCompatActivity {
+
+    private static final int PERMISSION_REQUEST_CODE = 100;
+
+    private TextView statusTextView;
+    private TextView portTextView;
+    private Button startButton;
+    private Button stopButton;
+
+    private EditText portEditText;
+    private TextView rootDirPathTextView;
+    private Button selectDirButton;
+    private Button saveSettingsButton;
+
+    private FTPConfig config;
+    private ActivityResultLauncher<Uri> directoryPickerLauncher;
+    private boolean isServerRunning = false;
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_main);
+
+        config = new FTPConfig(this);
+
+        setupDirectoryPicker();
+        initViews();
+        loadSettings();
+        setupListeners();
+        requestPermissions();
+    }
+
+    private void setupDirectoryPicker() {
+        directoryPickerLauncher = registerForActivityResult(
+                new ActivityResultContracts.OpenDocumentTree(),
+                uri -> {
+                    if (uri != null) {
+                        getContentResolver().takePersistableUriPermission(
+                                uri,
+                                Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION
+                        );
+
+                        DocumentFile pickedDir = DocumentFile.fromTreeUri(this, uri);
+                        if (pickedDir != null && pickedDir.isDirectory()) {
+                            String path = uri.getPath();
+                            if (path != null) {
+                                path = path.replace("/tree/primary:", "/storage/emulated/0/");
+                                path = path.replace("/tree/", "/");
+                            }
+                            rootDirPathTextView.setText(path != null ? path : uri.toString());
+                            config.setRootDirectoryUri(uri.toString());
+                            config.setRootDirectoryPath(path);
+                            Toast.makeText(this, "Directory selected", Toast.LENGTH_SHORT).show();
+                        }
+                    }
+                }
+        );
+    }
+
+    private void initViews() {
+        statusTextView = findViewById(R.id.statusTextView);
+        portTextView = findViewById(R.id.portTextView);
+        startButton = findViewById(R.id.startButton);
+        stopButton = findViewById(R.id.stopButton);
+
+        portEditText = findViewById(R.id.portEditText);
+        rootDirPathTextView = findViewById(R.id.rootDirPathTextView);
+        selectDirButton = findViewById(R.id.selectDirButton);
+        saveSettingsButton = findViewById(R.id.saveSettingsButton);
+    }
+
+    private void loadSettings() {
+        int port = config.getPort();
+        String rootPath = config.getRootDirectoryPath();
+
+        portEditText.setText(String.valueOf(port));
+        portTextView.setText("Port: " + port);
+
+        if (rootPath != null && !rootPath.isEmpty()) {
+            rootDirPathTextView.setText(rootPath);
+        } else {
+            rootDirPathTextView.setText("Not selected");
+        }
+    }
+
+    private void setupListeners() {
+        startButton.setOnClickListener(v -> startFTPServer());
+        stopButton.setOnClickListener(v -> stopFTPServer());
+        selectDirButton.setOnClickListener(v -> selectDirectory());
+        saveSettingsButton.setOnClickListener(v -> saveSettings());
+    }
+
+    private void selectDirectory() {
+        directoryPickerLauncher.launch(null);
+    }
+
+    private void saveSettings() {
+        String portStr = portEditText.getText().toString().trim();
+        if (portStr.isEmpty()) {
+            Toast.makeText(this, "Please enter a port number", Toast.LENGTH_SHORT).show();
+            return;
+        }
+
+        int port;
+        try {
+            port = Integer.parseInt(portStr);
+            if (port < 1024 || port > 65535) {
+                Toast.makeText(this, "Port must be between 1024 and 65535", Toast.LENGTH_SHORT).show();
+                return;
+            }
+        } catch (NumberFormatException e) {
+            Toast.makeText(this, "Invalid port number", Toast.LENGTH_SHORT).show();
+            return;
+        }
+
+        if (!config.hasRootDirectory()) {
+            Toast.makeText(this, "Please select a root directory", Toast.LENGTH_SHORT).show();
+            return;
+        }
+
+        config.setPort(port);
+        portTextView.setText("Port: " + port);
+
+        Toast.makeText(this, "Settings saved", Toast.LENGTH_SHORT).show();
+    }
+
+    private void requestPermissions() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+            // Android 11+ - Need MANAGE_EXTERNAL_STORAGE
+            if (!Environment.isExternalStorageManager()) {
+                try {
+                    Intent intent = new Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION);
+                    intent.setData(Uri.parse("package:" + getPackageName()));
+                    startActivity(intent);
+                    Toast.makeText(this, "Please grant 'All files access' permission", Toast.LENGTH_LONG).show();
+                } catch (Exception e) {
+                    Intent intent = new Intent(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION);
+                    startActivity(intent);
+                }
+            }
+        } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+            // Android 6.0 - 10
+            if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
+                    != PackageManager.PERMISSION_GRANTED) {
+                ActivityCompat.requestPermissions(this,
+                        new String[]{
+                                Manifest.permission.READ_EXTERNAL_STORAGE,
+                                Manifest.permission.WRITE_EXTERNAL_STORAGE
+                        },
+                        PERMISSION_REQUEST_CODE);
+            }
+        }
+    }
+
+    private void startFTPServer() {
+        // Check permission first
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+            if (!Environment.isExternalStorageManager()) {
+                Toast.makeText(this, "Please grant 'All files access' permission first", Toast.LENGTH_LONG).show();
+                requestPermissions();
+                return;
+            }
+        }
+
+        if (!config.hasRootDirectory()) {
+            Toast.makeText(this, "Please select a root directory first", Toast.LENGTH_LONG).show();
+            return;
+        }
+
+        Intent serviceIntent = new Intent(this, FTPService.class);
+        serviceIntent.setAction(FTPService.ACTION_START);
+        serviceIntent.putExtra("port", config.getPort());
+        serviceIntent.putExtra("rootDir", config.getRootDirectoryPath());
+
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            startForegroundService(serviceIntent);
+        } else {
+            startService(serviceIntent);
+        }
+
+        isServerRunning = true;
+        updateUI();
+        Toast.makeText(this, "FTP Server Started on port " + config.getPort(), Toast.LENGTH_SHORT).show();
+    }
+
+    private void stopFTPServer() {
+        Intent serviceIntent = new Intent(this, FTPService.class);
+        serviceIntent.setAction(FTPService.ACTION_STOP);
+        startService(serviceIntent);
+
+        isServerRunning = false;
+        updateUI();
+        Toast.makeText(this, "FTP Server Stopped", Toast.LENGTH_SHORT).show();
+    }
+
+    private void updateUI() {
+        if (isServerRunning) {
+            statusTextView.setText("Server Status: Running");
+            startButton.setEnabled(false);
+            stopButton.setEnabled(true);
+        } else {
+            statusTextView.setText("Server Status: Stopped");
+            startButton.setEnabled(true);
+            stopButton.setEnabled(false);
+        }
+    }
+
+    @Override
+    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
+        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
+        if (requestCode == PERMISSION_REQUEST_CODE) {
+            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+                Toast.makeText(this, "Permissions granted", Toast.LENGTH_SHORT).show();
+            } else {
+                Toast.makeText(this, "Permissions denied. App may not work correctly.", Toast.LENGTH_LONG).show();
+            }
+        }
+    }
+}

app/src/main/res/drawable-v24/ic_launcher_foreground.xml

@@ -0,0 +1,30 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:aapt="http://schemas.android.com/aapt"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <path android:pathData="M31,63.928c0,0 6.4,-11 12.1,-13.1c7.2,-2.6 26,-1.4 26,-1.4l38.1,38.1L107,108.928l-32,-1L31,63.928z">
+        <aapt:attr name="android:fillColor">
+            <gradient
+                android:endX="85.84757"
+                android:endY="92.4963"
+                android:startX="42.9492"
+                android:startY="49.59793"
+                android:type="linear">
+                <item
+                    android:color="#44000000"
+                    android:offset="0.0" />
+                <item
+                    android:color="#00000000"
+                    android:offset="1.0" />
+            </gradient>
+        </aapt:attr>
+    </path>
+    <path
+        android:fillColor="#FFFFFF"
+        android:fillType="nonZero"
+        android:pathData="M65.3,45.828l3.8,-6.6c0.2,-0.4 0.1,-0.9 -0.3,-1.1c-0.4,-0.2 -0.9,-0.1 -1.1,0.3l-3.9,6.7c-6.3,-2.8 -13.4,-2.8 -19.7,0l-3.9,-6.7c-0.2,-0.4 -0.7,-0.5 -1.1,-0.3C38.8,38.328 38.7,38.828 38.9,39.228l3.8,6.6C36.2,49.428 31.7,56.028 31,63.928h46C76.3,56.028 71.8,49.428 65.3,45.828zM43.4,57.328c-0.8,0 -1.5,-0.5 -1.8,-1.2c-0.3,-0.7 -0.1,-1.5 0.4,-2.1c0.5,-0.5 1.4,-0.7 2.1,-0.4c0.7,0.3 1.2,1 1.2,1.8C45.3,56.528 44.5,57.328 43.4,57.328L43.4,57.328zM64.6,57.328c-0.8,0 -1.5,-0.5 -1.8,-1.2s-0.1,-1.5 0.4,-2.1c0.5,-0.5 1.4,-0.7 2.1,-0.4c0.7,0.3 1.2,1 1.2,1.8C66.5,56.528 65.6,57.328 64.6,57.328L64.6,57.328z"
+        android:strokeWidth="1"
+        android:strokeColor="#00000000" />
+</vector>

app/src/main/res/drawable/ic_launcher_background.xml

@@ -0,0 +1,170 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <path
+        android:fillColor="#3DDC84"
+        android:pathData="M0,0h108v108h-108z" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M9,0L9,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,0L19,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M29,0L29,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M39,0L39,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M49,0L49,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M59,0L59,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M69,0L69,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M79,0L79,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M89,0L89,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M99,0L99,108"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,9L108,9"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,19L108,19"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,29L108,29"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,39L108,39"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,49L108,49"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,59L108,59"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,69L108,69"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,79L108,79"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,89L108,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M0,99L108,99"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,29L89,29"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,39L89,39"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,49L89,49"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,59L89,59"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,69L89,69"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M19,79L89,79"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M29,19L29,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M39,19L39,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M49,19L49,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M59,19L59,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M69,19L69,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+    <path
+        android:fillColor="#00000000"
+        android:pathData="M79,19L79,89"
+        android:strokeWidth="0.8"
+        android:strokeColor="#33FFFFFF" />
+</vector>

app/src/main/res/layout/activity_main.xml

@@ -0,0 +1,159 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    tools:context=".MainActivity">
+
+<androidx.constraintlayout.widget.ConstraintLayout
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:padding="16dp">
+
+    <TextView
+        android:id="@+id/titleTextView"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Android FTP Server"
+        android:textSize="24sp"
+        android:textStyle="bold"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        android:layout_marginTop="32dp" />
+
+    <TextView
+        android:id="@+id/statusTextView"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Server Status: Stopped"
+        android:textSize="16sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/titleTextView"
+        android:layout_marginTop="24dp" />
+
+    <TextView
+        android:id="@+id/portTextView"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Port: 2121"
+        android:textSize="14sp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/statusTextView"
+        android:layout_marginTop="8dp" />
+
+    <Button
+        android:id="@+id/startButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Start Server"
+        android:minWidth="150dp"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/portTextView"
+        android:layout_marginTop="32dp" />
+
+    <Button
+        android:id="@+id/stopButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Stop Server"
+        android:minWidth="150dp"
+        android:enabled="false"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/startButton"
+        android:layout_marginTop="16dp" />
+
+    <View
+        android:id="@+id/divider"
+        android:layout_width="match_parent"
+        android:layout_height="1dp"
+        android:background="#CCCCCC"
+        android:layout_marginTop="32dp"
+        app:layout_constraintTop_toBottomOf="@id/stopButton"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintEnd_toEndOf="parent" />
+
+    <TextView
+        android:id="@+id/settingsTitle"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Settings"
+        android:textSize="20sp"
+        android:textStyle="bold"
+        android:layout_marginTop="24dp"
+        app:layout_constraintTop_toBottomOf="@id/divider"
+        app:layout_constraintStart_toStartOf="parent" />
+
+    <TextView
+        android:id="@+id/portLabel"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Port:"
+        android:textSize="16sp"
+        android:layout_marginTop="24dp"
+        app:layout_constraintTop_toBottomOf="@id/settingsTitle"
+        app:layout_constraintStart_toStartOf="parent" />
+
+    <EditText
+        android:id="@+id/portEditText"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:inputType="number"
+        android:hint="2121"
+        android:layout_marginStart="16dp"
+        app:layout_constraintBaseline_toBaselineOf="@id/portLabel"
+        app:layout_constraintStart_toEndOf="@id/portLabel"
+        app:layout_constraintEnd_toEndOf="parent" />
+
+    <TextView
+        android:id="@+id/rootDirLabel"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Root Directory:"
+        android:textSize="16sp"
+        android:layout_marginTop="16dp"
+        app:layout_constraintTop_toBottomOf="@id/portLabel"
+        app:layout_constraintStart_toStartOf="parent" />
+
+    <TextView
+        android:id="@+id/rootDirPathTextView"
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:text="Not selected"
+        android:textSize="14sp"
+        android:layout_marginTop="8dp"
+        android:padding="8dp"
+        android:background="@android:color/darker_gray"
+        android:ellipsize="start"
+        android:singleLine="true"
+        app:layout_constraintTop_toBottomOf="@id/rootDirLabel"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintEnd_toEndOf="parent" />
+
+    <Button
+        android:id="@+id/selectDirButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Select Directory"
+        android:layout_marginTop="8dp"
+        app:layout_constraintTop_toBottomOf="@id/rootDirPathTextView"
+        app:layout_constraintStart_toStartOf="parent" />
+
+    <Button
+        android:id="@+id/saveSettingsButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Save Settings"
+        android:minWidth="150dp"
+        android:layout_marginTop="24dp"
+        app:layout_constraintTop_toBottomOf="@id/selectDirButton"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintEnd_toEndOf="parent" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>
+</ScrollView>

app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@drawable/ic_launcher_background" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+</adaptive-icon>

app/src/main/res/mipmap-anydpi-v26/ic_launcher_round.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@drawable/ic_launcher_background" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+</adaptive-icon>

app/src/main/res/values-night/themes.xml

@@ -0,0 +1,16 @@
+<resources xmlns:tools="http://schemas.android.com/tools">
+    <!-- Base application theme. -->
+    <style name="Theme.Gyub_sAndroidFTPServer" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
+        <!-- Primary brand color. -->
+        <item name="colorPrimary">@color/purple_200</item>
+        <item name="colorPrimaryVariant">@color/purple_700</item>
+        <item name="colorOnPrimary">@color/black</item>
+        <!-- Secondary brand color. -->
+        <item name="colorSecondary">@color/teal_200</item>
+        <item name="colorSecondaryVariant">@color/teal_200</item>
+        <item name="colorOnSecondary">@color/black</item>
+        <!-- Status bar color. -->
+        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
+        <!-- Customize your theme here. -->
+    </style>
+</resources>

app/src/main/res/values/colors.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="purple_200">#FFBB86FC</color>
+    <color name="purple_500">#FF6200EE</color>
+    <color name="purple_700">#FF3700B3</color>
+    <color name="teal_200">#FF03DAC5</color>
+    <color name="teal_700">#FF018786</color>
+    <color name="black">#FF000000</color>
+    <color name="white">#FFFFFFFF</color>
+</resources>

app/src/main/res/values/strings.xml

@@ -0,0 +1,3 @@
+<resources>
+    <string name="app_name">Gyub_s Android FTP Server</string>
+</resources>

app/src/main/res/values/themes.xml

@@ -0,0 +1,16 @@
+<resources xmlns:tools="http://schemas.android.com/tools">
+    <!-- Base application theme. -->
+    <style name="Theme.Gyub_sAndroidFTPServer" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
+        <!-- Primary brand color. -->
+        <item name="colorPrimary">@color/purple_500</item>
+        <item name="colorPrimaryVariant">@color/purple_700</item>
+        <item name="colorOnPrimary">@color/white</item>
+        <!-- Secondary brand color. -->
+        <item name="colorSecondary">@color/teal_200</item>
+        <item name="colorSecondaryVariant">@color/teal_700</item>
+        <item name="colorOnSecondary">@color/black</item>
+        <!-- Status bar color. -->
+        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
+        <!-- Customize your theme here. -->
+    </style>
+</resources>

app/src/test/java/be/gyu/android/server/ftp/ExampleUnitTest.java

@@ -0,0 +1,17 @@
+package be.gyu.android.server.ftp;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * Example local unit test, which will execute on the development machine (host).
+ *
+ * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
+ */
+public class ExampleUnitTest {
+    @Test
+    public void addition_isCorrect() {
+        assertEquals(4, 2 + 2);
+    }
+}

build.gradle

@@ -0,0 +1,9 @@
+// Top-level build file where you can add configuration options common to all sub-projects/modules.
+plugins {
+    id 'com.android.application' version '7.1.3' apply false
+    id 'com.android.library' version '7.1.3' apply false
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}

gradle.properties

@@ -0,0 +1,21 @@
+# Project-wide Gradle settings.
+# IDE (e.g. Android Studio) users:
+# Gradle settings configured through the IDE *will override*
+# any settings specified in this file.
+# For more details on how to configure your build environment visit
+# http://www.gradle.org/docs/current/userguide/build_environment.html
+# Specifies the JVM arguments used for the daemon process.
+# The setting is particularly useful for tweaking memory settings.
+org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+# When configured, Gradle will run in incubating parallel mode.
+# This option should only be used with decoupled projects. More details, visit
+# http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
+# org.gradle.parallel=true
+# AndroidX package structure to make it clearer which packages are bundled with the
+# Android operating system, and which are packaged with your app"s APK
+# https://developer.android.com/topic/libraries/support-library/androidx-rn
+android.useAndroidX=true
+# Enables namespacing of each library's R class so that its R class includes only the
+# resources declared in the library itself and none from the library's dependencies,
+# thereby reducing the size of the R class for that library
+android.nonTransitiveRClass=true

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Thu Jan 01 02:08:51 KST 2026
+distributionBase=GRADLE_USER_HOME
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.2-bin.zip
+distributionPath=wrapper/dists
+zipStorePath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME

gradlew

@@ -0,0 +1,185 @@
+#!/usr/bin/env sh
+
+#
+# Copyright 2015 the original author or authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if [ "$cygwin" = "true" -o "$msys" = "true" ] ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=`expr $i + 1`
+    done
+    case $i in
+        0) set -- ;;
+        1) set -- "$args0" ;;
+        2) set -- "$args0" "$args1" ;;
+        3) set -- "$args0" "$args1" "$args2" ;;
+        4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=`save "$@"`
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle

@@ -0,0 +1,16 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        google()
+        mavenCentral()
+    }
+}
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+rootProject.name = "Gyub_s Android FTP Server"
+include ':app'