Allow making AssetFileDescriptors from SQLite blobs.
This change adds a new class SQLiteContentHelper, which contains
a static method for creating an AssetFileDescriptor from
an SQLite query that returns a blob.
Internally, this uses a file descriptor for a MemoryFile.
The implementation is temporary. Ideally, the data should be copied
directly from SQLite to the MemoryFile ashmem region, using
sqlite3_blob_read().
This is part of the implementation of http://b/issue?id=1871731
diff --git a/core/java/android/database/sqlite/SQLiteContentHelper.java b/core/java/android/database/sqlite/SQLiteContentHelper.java
new file mode 100644
index 0000000..2800d86
--- /dev/null
+++ b/core/java/android/database/sqlite/SQLiteContentHelper.java
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * 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
+ *
+ * http://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.
+ */
+
+package android.database.sqlite;
+
+import android.content.res.AssetFileDescriptor;
+import android.database.Cursor;
+import android.os.MemoryFile;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+/**
+ * Some helper functions for using SQLite database to implement content providers.
+ *
+ * @hide
+ */
+public class SQLiteContentHelper {
+
+ /**
+ * Runs an SQLite query and returns an AssetFileDescriptor for the
+ * blob in column 0 of the first row. If the first column does
+ * not contain a blob, an unspecified exception is thrown.
+ *
+ * @param db Handle to a readable database.
+ * @param sql SQL query, possibly with query arguments.
+ * @param selectionArgs Query argument values, or {@code null} for no argument.
+ * @return If no exception is thrown, a non-null AssetFileDescriptor is returned.
+ * @throws FileNotFoundException If the query returns no results or the
+ * value of column 0 is NULL, or if there is an error creating the
+ * asset file descriptor.
+ */
+ public static AssetFileDescriptor getBlobColumnAsAssetFile(SQLiteDatabase db, String sql,
+ String[] selectionArgs) throws FileNotFoundException {
+ try {
+ MemoryFile file = simpleQueryForBlobMemoryFile(db, sql, selectionArgs);
+ if (file == null) {
+ throw new FileNotFoundException("No results.");
+ }
+ return AssetFileDescriptor.fromMemoryFile(file);
+ } catch (IOException ex) {
+ throw new FileNotFoundException(ex.toString());
+ }
+ }
+
+ /**
+ * Runs an SQLite query and returns a MemoryFile for the
+ * blob in column 0 of the first row. If the first column does
+ * not contain a blob, an unspecified exception is thrown.
+ *
+ * @return A memory file, or {@code null} if the query returns no results
+ * or the value column 0 is NULL.
+ * @throws IOException If there is an error creating the memory file.
+ */
+ // TODO: make this native and use the SQLite blob API to reduce copying
+ private static MemoryFile simpleQueryForBlobMemoryFile(SQLiteDatabase db, String sql,
+ String[] selectionArgs) throws IOException {
+ Cursor cursor = db.rawQuery(sql, selectionArgs);
+ if (cursor == null) {
+ return null;
+ }
+ try {
+ if (!cursor.moveToFirst()) {
+ return null;
+ }
+ byte[] bytes = cursor.getBlob(0);
+ if (bytes == null) {
+ return null;
+ }
+ MemoryFile file = new MemoryFile(null, bytes.length);
+ file.writeBytes(bytes, 0, 0, bytes.length);
+ file.deactivate();
+ return file;
+ } finally {
+ cursor.close();
+ }
+ }
+
+}
