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

1 files changed, 92 insertions, 0 deletions

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();
+        }
+    }
+
+}