Use Storage Access Framework on SDK >= 21 (Lollipop and above)

Summary:
Use Storage Access Framework on Android running SDK >= 21 so writing to
sdcard will work again

|{F6546802}|{F6546803}|{F6546804}|
|API 21+|API 19-|Edit|

Test Plan:
Install patch on Android phone with Build.Version < 19 (Kitkat)

- Without a sdcard: Verify that dolphin displays an "All Files" entry that is empty
- With a sdcard and with "Add camera folder shortcut" turned off: Verify that dolphin displays the configured display name of the sdcard
- With a sdcard and with "Add camera folder shortcut" turned on: Verify that dolphin displays the configured display name of the sdcard and also lists a "Camera pictures" shortcut
- With a sdcard: Verify that when changing the display name or the "Add camera folder shortcut" preference dolphin displays the updated items (after pressing F5)
- With a sdcard: Verify that files can be read and written to/from the sdcard

Install patch on Android phone with Build.Version < 19 (Kitkat)
- Repeat the above tests except for the read/write test: Verify that files can be read from the sdcard

Install patch on Android phone with Build.Version > 21 (Lollipop)

- Without any configured storage locations: Verify dolphin displays an "All Files" entry that is empty
- With configured storage locations: Verify dolphin displays the display names of the configured storage locations and that entering a location displays the correct directory entries
- Make one or several changes to the configured storage locations: Verify dolphin displays the display names of the configured storage locations (after pressing F5) and that entering a location displays the correct directory entries

Reviewers: #kde_connect, albertvaka, sredman

Reviewed By: #kde_connect, albertvaka, sredman

Subscribers: albertvaka, sredman, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D18212

src/org/kde/kdeconnect/Plugins/SftpPlugin/AndroidFileSystemView.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2018 Erik Duisters <e.duisters1@gmail.com>
+ *
+ * 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 2 of
+ * the License or (at your option) version 3 or any later version
+ * accepted by the membership of KDE e.V. (or its successor approved
+ * by the membership of KDE e.V.), which shall act as a proxy
+ * defined in Section 14 of version 3 of the license.
+ *
+ * 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 <http://www.gnu.org/licenses/>.
+ */
+
+package org.kde.kdeconnect.Plugins.SftpPlugin;
+
+import android.content.Context;
+
+import org.apache.sshd.common.file.FileSystemView;
+import org.apache.sshd.common.file.SshFile;
+import org.apache.sshd.common.file.nativefs.NativeFileSystemView;
+import org.apache.sshd.common.file.nativefs.NativeSshFile;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+class AndroidFileSystemView extends NativeFileSystemView {
+    final private String userName;
+    final private Context context;
+    private final Map<String, String> roots;
+    private final RootFile rootFile;
+
+    AndroidFileSystemView(Map<String, String> roots, String currentRoot, final String userName, Context context) {
+        super(userName, roots, currentRoot, File.separatorChar, true);
+        this.roots = roots;
+        this.userName = userName;
+        this.context = context;
+        this.rootFile = new RootFile( createFileList(), userName, true);
+    }
+
+    private List<SshFile> createFileList() {
+        List<SshFile> list = new ArrayList<>();
+        for (Map.Entry<String, String> entry : roots.entrySet()) {
+            String displayName = entry.getKey();
+            String path = entry.getValue();
+
+            list.add(createNativeSshFile(displayName, new File(path), userName));
+        }
+
+        return list;
+    }
+
+    @Override
+    public SshFile getFile(String file) {
+        return getFile("/", file);
+    }
+
+    @Override
+    public SshFile getFile(SshFile baseDir, String file) {
+        return getFile(baseDir.getAbsolutePath(), file);
+    }
+
+    @Override
+    protected SshFile getFile(String dir, String file) {
+        if (!dir.endsWith("/")) {
+            dir = dir + "/";
+        }
+
+        if (!file.startsWith("/")) {
+            file = dir + file;
+        }
+
+        String filename = NativeSshFile.getPhysicalName("/", "/", file, false);
+
+        if (filename.equals("/")) {
+            return rootFile;
+        }
+
+        for (String root : roots.keySet()) {
+            if (filename.indexOf(root) == 1) {
+                String nameWithoutRoot = filename.substring(root.length() + 1);
+                String path = roots.get(root);
+
+                if (nameWithoutRoot.isEmpty()) {
+                    return createNativeSshFile(filename, new File(path), userName);
+                } else {
+                    return createNativeSshFile(filename, new File(path, nameWithoutRoot), userName);
+                }
+            }
+        }
+
+        //It's a file under / but not one covered by any Tree
+        return new RootFile(new ArrayList<>(0), userName, false);
+    }
+
+    // NativeFileSystemView.getFile(), NativeSshFile.getParentFile() and NativeSshFile.listSshFiles() call
+    // createNativeSshFile to create new NativeSshFiles so override that instead of getFile() to always create an AndroidSshFile
+    @Override
+    public AndroidSshFile createNativeSshFile(String name, File file, String username) {
+        return new AndroidSshFile(this, name, file, username, context);
+    }
+
+    @Override
+    public FileSystemView getNormalizedView() {
+        return this;
+    }
+}