Add temporary file storage as discussed in #665

Writable from OpenKeychain, readable worldwide. Should be used to write shared files to it by first creating the file using TemporaryStorageProvider.createFile and then write to the Uri returned.

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/provider/TemporaryStorageProvider.java

@@ -0,0 +1,151 @@
+package org.sufficientlysecure.keychain.provider;
+
+import android.content.ContentProvider;
+import android.content.ContentValues;
+import android.content.Context;
+import android.database.Cursor;
+import android.database.MatrixCursor;
+import android.database.sqlite.SQLiteDatabase;
+import android.database.sqlite.SQLiteOpenHelper;
+import android.net.Uri;
+import android.os.ParcelFileDescriptor;
+import android.provider.OpenableColumns;
+import org.sufficientlysecure.keychain.Constants;
+import org.sufficientlysecure.keychain.util.DatabaseUtil;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+public class TemporaryStorageProvider extends ContentProvider {
+
+    private static final String DB_NAME = "tempstorage.db";
+    private static final String TABLE_FILES = "files";
+    private static final String COLUMN_ID = "id";
+    private static final String COLUMN_NAME = "name";
+    private static final String COLUMN_TIME = "time";
+    private static final Uri BASE_URI = Uri.parse("content://org.sufficientlysecure.keychain.tempstorage/");
+    private static final int DB_VERSION = 1;
+
+    public static Uri createFile(Context context, String targetName) {
+        ContentValues contentValues = new ContentValues();
+        contentValues.put(COLUMN_NAME, targetName);
+        return context.getContentResolver().insert(BASE_URI, contentValues);
+    }
+
+    public static int cleanUp(Context context) {
+        return context.getContentResolver().delete(BASE_URI, COLUMN_TIME + "< ?",
+                new String[]{Long.toString(System.currentTimeMillis() - Constants.TEMPFILE_TTL)});
+    }
+
+    private class TemporaryStorageDatabase extends SQLiteOpenHelper {
+
+        public TemporaryStorageDatabase(Context context) {
+            super(context, DB_NAME, null, DB_VERSION);
+        }
+
+        @Override
+        public void onCreate(SQLiteDatabase db) {
+            db.execSQL("CREATE TABLE IF NOT EXISTS " + TABLE_FILES + " (" +
+                    COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
+                    COLUMN_NAME + " TEXT, " +
+                    COLUMN_TIME + " INTEGER" +
+                    ");");
+        }
+
+        @Override
+        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
+
+        }
+    }
+
+    private TemporaryStorageDatabase db;
+
+    private File getFile(Uri uri) throws FileNotFoundException {
+        try {
+            return getFile(Integer.parseInt(uri.getLastPathSegment()));
+        } catch (NumberFormatException e) {
+            throw new FileNotFoundException();
+        }
+    }
+
+    private File getFile(int id) {
+        return new File(getContext().getCacheDir(), "temp/" + id);
+    }
+
+    @Override
+    public boolean onCreate() {
+        db = new TemporaryStorageDatabase(getContext());
+        return new File(getContext().getCacheDir(), "temp").mkdirs();
+    }
+
+    @Override
+    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
+        File file;
+        try {
+            file = getFile(uri);
+        } catch (FileNotFoundException e) {
+            return null;
+        }
+        Cursor fileName = db.getReadableDatabase().query(TABLE_FILES, new String[]{COLUMN_NAME}, COLUMN_ID + "=?",
+                new String[]{uri.getLastPathSegment()}, null, null, null);
+        if (fileName != null) {
+            if (fileName.moveToNext()) {
+                MatrixCursor cursor =
+                        new MatrixCursor(new String[]{OpenableColumns.DISPLAY_NAME, OpenableColumns.SIZE, "_data"});
+                cursor.newRow().add(fileName.getString(0)).add(file.length()).add(file.getAbsolutePath());
+                fileName.close();
+                return cursor;
+            }
+            fileName.close();
+        }
+        return null;
+    }
+
+    @Override
+    public String getType(Uri uri) {
+        return "*/*";
+    }
+
+    @Override
+    public Uri insert(Uri uri, ContentValues values) {
+        if (!values.containsKey(COLUMN_TIME)) {
+            values.put(COLUMN_TIME, System.currentTimeMillis());
+        }
+        int insert = (int) db.getWritableDatabase().insert(TABLE_FILES, null, values);
+        try {
+            getFile(insert).createNewFile();
+        } catch (IOException e) {
+            return null;
+        }
+        return Uri.withAppendedPath(BASE_URI, Long.toString(insert));
+    }
+
+    @Override
+    public int delete(Uri uri, String selection, String[] selectionArgs) {
+        if (uri.getLastPathSegment() != null) {
+            selection = DatabaseUtil.concatenateWhere(selection, COLUMN_ID + "=?");
+            selectionArgs = DatabaseUtil.appendSelectionArgs(selectionArgs, new String[]{uri.getLastPathSegment()});
+        }
+        Cursor files = db.getReadableDatabase().query(TABLE_FILES, new String[]{COLUMN_ID}, selection,
+                selectionArgs, null, null, null);
+        if (files != null) {
+            while (files.moveToNext()) {
+                getFile(files.getInt(0)).delete();
+            }
+            files.close();
+            return db.getWritableDatabase().delete(TABLE_FILES, selection, selectionArgs);
+        }
+        return 0;
+    }
+
+    @Override
+    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
+        throw new UnsupportedOperationException("Update not supported");
+    }
+
+    @Override
+    public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
+        return openFileHelper(uri, mode);
+    }
+}