ConfigurationAccessService: prevent service from being stopped when app loses focus

This makes the ConfigurationAccessService (formerly ConfigurationFtpService) start in foreground
through the use of a persistent notification so that it isn't stopped by the system after the app
loses the focus on the user's screen, which happens when the user switches to an FTP client
application on the same device.

1 files changed, 174 insertions, 0 deletions

diff --git a/app/src/main/java/org/pacien/tincapp/service/ConfigurationAccessService.kt b/app/src/main/java/org/pacien/tincapp/service/ConfigurationAccessService.kt
new file mode 100644
index 0000000..b083a83
--- /dev/null
+++ b/app/src/main/java/org/pacien/tincapp/service/ConfigurationAccessService.kt
@@ -0,0 +1,174 @@
+/*
+ * Tinc App, an Android binding and user interface for the tinc mesh VPN daemon
+ * Copyright (C) 2017-2020 Pacien TRAN-GIRARD
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.pacien.tincapp.service
+
+import android.app.PendingIntent
+import android.app.Service
+import android.content.Intent
+import android.os.IBinder
+import androidx.databinding.ObservableBoolean
+import ch.qos.logback.classic.Level
+import ch.qos.logback.classic.Logger
+import org.apache.ftpserver.FtpServer
+import org.apache.ftpserver.FtpServerFactory
+import org.apache.ftpserver.ftplet.*
+import org.apache.ftpserver.listener.ListenerFactory
+import org.apache.ftpserver.usermanager.UsernamePasswordAuthentication
+import org.apache.ftpserver.usermanager.impl.WritePermission
+import org.pacien.tincapp.R
+import org.pacien.tincapp.activities.configure.ConfigureActivity
+import org.pacien.tincapp.context.App
+import org.pacien.tincapp.context.AppNotificationManager
+import org.pacien.tincapp.extensions.Java.defaultMessage
+import org.slf4j.LoggerFactory
+import java.io.IOException
+
+/**
+ * FTP server service allowing a remote and local user to access and modify configuration files in
+ * the application's context.
+ *
+ * @author pacien
+ */
+class ConfigurationAccessService : Service() {
+  companion object {
+    // Apache Mina FtpServer's INFO log level is actually VERBOSE.
+    // The object holds static references to those loggers so that they stay around.
+    @Suppress("unused")
+    private val MINA_FTP_LOGGER_OVERRIDER = MinaLoggerOverrider(Level.WARN)
+
+    const val FTP_PORT = 65521 // tinc port `concat` FTP port
+    const val FTP_USERNAME = "tincapp"
+    val FTP_HOME_DIR = App.getContext().applicationInfo.dataDir!!
+    val FTP_PASSWORD = generateRandomString(8)
+
+    val runningState = ObservableBoolean(false)
+
+    private fun generateRandomString(length: Int): String {
+      val alphabet = ('a'..'z') + ('A'..'Z') + ('0'..'9')
+      return List(length) { alphabet.random() }.joinToString("")
+    }
+  }
+
+  private val log by lazy { LoggerFactory.getLogger(this.javaClass)!! }
+  private val notificationManager by lazy { App.notificationManager }
+  private var sftpServer: FtpServer? = null
+
+  override fun onBind(intent: Intent): IBinder? = null // non-bindable service
+
+  override fun onDestroy() {
+    sftpServer?.stop()
+    sftpServer = null
+    runningState.set(false)
+    log.info("Stopped FTP server")
+    super.onDestroy()
+  }
+
+  override fun onStartCommand(intent: Intent, flags: Int, startId: Int): Int {
+    val ftpUser = StaticFtpUser(FTP_USERNAME, FTP_PASSWORD, FTP_HOME_DIR, listOf(WritePermission()))
+    sftpServer = setupSingleUserServer(ftpUser).also {
+      try {
+        it.start()
+        runningState.set(true)
+        log.info("Started FTP server on port {}", FTP_PORT)
+        pinInForeground()
+      } catch (e: IOException) {
+        log.error("Could not start FTP server", e)
+        App.alert(R.string.notification_error_title_unable_to_start_ftp_server, e.defaultMessage())
+      }
+    }
+
+    return START_NOT_STICKY
+  }
+
+  /**
+   * Pins the service in the foreground so that it doesn't get stopped by the system when the
+   * application's activities are put in the background, which is the case when the user sets the
+   * focus on an FTP client app for example.
+   */
+  private fun pinInForeground() {
+    startForeground(
+      AppNotificationManager.CONFIG_ACCESS_NOTIFICATION_ID,
+      notificationManager.newConfigurationAccessNotificationBuilder()
+        .setSmallIcon(R.drawable.ic_baseline_folder_open_primary_24dp)
+        .setContentTitle(resources.getString(R.string.notification_config_access_server_running_title))
+        .setContentText(resources.getString(R.string.notification_config_access_server_running_message))
+        .setContentIntent(Intent(this, ConfigureActivity::class.java).let {
+          PendingIntent.getActivity(this, 0, it, 0)
+        })
+        .build()
+    )
+  }
+
+  private fun setupSingleUserServer(ftpUser: User): FtpServer {
+    return FtpServerFactory()
+      .apply { addListener("default", ListenerFactory().apply { port = FTP_PORT }.createListener()) }
+      .apply { userManager = StaticFtpUserManager(listOf(ftpUser)) }
+      .createServer()
+  }
+
+  private class StaticFtpUserManager(users: List<User>) : UserManager {
+    private val userMap: Map<String, User> = users.map { it.name to it }.toMap()
+    override fun getUserByName(username: String?): User? = userMap[username]
+    override fun getAllUserNames(): Array<String> = userMap.keys.toTypedArray()
+    override fun doesExist(username: String?): Boolean = username in userMap
+    override fun delete(username: String?) = throw UnsupportedOperationException()
+    override fun save(user: User?) = throw UnsupportedOperationException()
+    override fun getAdminName(): String = throw UnsupportedOperationException()
+    override fun isAdmin(username: String?): Boolean = throw UnsupportedOperationException()
+    override fun authenticate(authentication: Authentication?): User = when (authentication) {
+      is UsernamePasswordAuthentication -> getUserByName(authentication.username).let {
+        if (it != null && authentication.password == it.password) it
+        else throw AuthenticationFailedException()
+      }
+      else -> throw IllegalArgumentException()
+    }
+  }
+
+  private data class StaticFtpUser(
+    private val name: String,
+    private val password: String,
+    private val homeDirectory: String,
+    private val authorities: List<Authority>
+  ) : User {
+    override fun getName(): String = name
+    override fun getPassword(): String = password
+    override fun getAuthorities(): List<Authority> = authorities
+    override fun getAuthorities(clazz: Class<out Authority>): List<Authority> = authorities.filter(clazz::isInstance)
+    override fun getMaxIdleTime(): Int = 0 // unlimited
+    override fun getEnabled(): Boolean = true
+    override fun getHomeDirectory(): String = homeDirectory
+    override fun authorize(request: AuthorizationRequest?): AuthorizationRequest? =
+      authorities.filter { it.canAuthorize(request) }.fold(request) { req, auth -> auth.authorize(req) }
+  }
+
+  /**
+   * This registers package loggers filtering the output of the Mina FtpServer.
+   * The object holds static references to those loggers so that they stay around.
+   */
+  private class MinaLoggerOverrider(logLevel: Level) {
+    @Suppress("unused")
+    private val ftpServerLogger = forceLogLevel("org.apache.ftpserver", logLevel)
+
+    @Suppress("unused")
+    private val minaLogger = forceLogLevel("org.apache.mina", logLevel)
+
+    private fun forceLogLevel(pkgName: String, logLevel: Level) =
+      (LoggerFactory.getLogger(pkgName) as Logger).apply { level = logLevel }
+  }
+}