Implement plugin interface in mobile app

mobile/src/main/scala/com/github/shadowsocks/plugin/PluginManager.scala

@@ -1,8 +1,13 @@
 package com.github.shadowsocks.plugin
 
+import java.io.{File, FileNotFoundException, FileOutputStream, IOException}
+
 import android.content.pm.PackageManager
-import android.content.{BroadcastReceiver, Intent}
+import android.content.{BroadcastReceiver, ContentResolver, Intent}
+import android.net.Uri
 import com.github.shadowsocks.ShadowsocksApplication.app
+import com.github.shadowsocks.utils.CloseUtils.autoClose
+import com.github.shadowsocks.utils.IOUtils
 
 import scala.collection.JavaConverters._
 
@@ -22,4 +27,53 @@ object PluginManager {
     })
     cachedPlugins
   }
+
+  // the following parts are meant to be used by :bg
+  @throws[Throwable]
+  def initPlugin(id: String): String = {
+    if (id.isEmpty) return null
+    var throwable: Throwable = null
+
+    try initNativePlugin(id) match {
+      case null =>
+      case path => return path
+    } catch {
+      case t: Throwable => if (throwable == null) throwable = t
+    }
+
+    // add other plugin types here
+
+    throw if (throwable == null)
+      new FileNotFoundException(app.getString(com.github.shadowsocks.R.string.plugin_unknown, id)) else throwable
+  }
+
+  @throws[IOException]
+  @throws[IndexOutOfBoundsException]
+  @throws[AssertionError]
+  private def initNativePlugin(id: String): String = {
+    val builder = new Uri.Builder()
+      .scheme(ContentResolver.SCHEME_CONTENT)
+      .authority(PluginInterface.getAuthority(id))
+    val cr = app.getContentResolver
+    val cursor = cr.query(builder.build(), Array(PluginInterface.COLUMN_PATH), null, null, null)
+    if (cursor != null) {
+      var initialized = false
+      val pluginDir = new File(app.getFilesDir, "plugin")
+      if (cursor.moveToFirst()) {
+        IOUtils.deleteRecursively(pluginDir)
+        if (!pluginDir.mkdirs()) throw new FileNotFoundException("Unable to create plugin directory")
+        val pluginDirPath = pluginDir.getAbsolutePath + '/'
+        do {
+          val path = cursor.getString(0)
+          val file = new File(pluginDir, path)
+          assert(file.getAbsolutePath.startsWith(pluginDirPath))
+          autoClose(cr.openInputStream(builder.path(path).build()))(in =>
+            autoClose(new FileOutputStream(file))(out => IOUtils.copy(in, out)))
+          if (path == id) initialized = true
+        } while (cursor.moveToNext())
+      }
+      if (!initialized) throw new IndexOutOfBoundsException("Plugin entry binary not found")
+      new File(pluginDir, id).getAbsolutePath
+    } else null
+  }
 }