Add AssetProvider to common dirctory

This is a basic ContentProvider which will serve any files located
in an application's assets directory.

Change-Id: I7b7fa13bc58d48178bef7c94e16dba6348864eca
(cherry picked from commit 72dfa39262bc1261d3dd413f137e4147fd14b939)

1 files changed, 140 insertions, 0 deletions

diff --git a/common/src/java/com/example/android/common/assetprovider/AssetProvider.java b/common/src/java/com/example/android/common/assetprovider/AssetProvider.java
new file mode 100644
index 00000000..f6c0f613
--- /dev/null
+++ b/common/src/java/com/example/android/common/assetprovider/AssetProvider.java
@@ -0,0 +1,140 @@
+/*
+* Copyright (C) 2013 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 com.example.android.common.assetprovider;
+
+import android.content.ContentProvider;
+import android.content.ContentValues;
+import android.content.Context;
+import android.content.res.AssetFileDescriptor;
+import android.content.res.AssetManager;
+import android.database.Cursor;
+import android.net.Uri;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import static java.net.URLConnection.guessContentTypeFromName;
+
+/**
+ * Generic content provider, which makes any files available in this app's "assets" directory
+ * available publicly.
+ *
+ * <p>To use, add the following to your AndroidManifest.xml:
+ *
+ * <code><pre>
+ * <provider
+ *   android:name=".AssetProvider"
+ *   android:authorities="[YOUR CONTENT PROVIDER DOMAIN HERE]"
+ *   android:exported="true"/>
+ * </pre></code>
+ */
+public class AssetProvider extends ContentProvider {
+    AssetManager mAssets;
+
+    @Override
+    public boolean onCreate() {
+        Context ctx = getContext();
+        if (ctx == null) {
+            // Context not available. Give up.
+            return false;
+        }
+        mAssets = ctx.getAssets();
+        return true;
+    }
+
+    @Override
+    public String getType(Uri uri){
+        // Returns the MIME type for the selected URI, in conformance with the ContentProvider
+        // interface. Looks up the file indicated by /res/assets/{uri.path}, and returns the MIME
+        // type for that file as guessed by the URLConnection class.
+
+        // Setup
+        String path = uri.getPath();
+
+        // Check if file exists
+        if (!fileExists(path)) {
+            return null;
+        }
+
+        // Determine MIME-type based on filename
+        return guessContentTypeFromName(uri.toString());
+    }
+
+
+    @Override
+    public AssetFileDescriptor openAssetFile (Uri uri, String mode)
+            throws FileNotFoundException, SecurityException {
+        // ContentProvider interface for opening a file descriptor by URI. This content provider
+        // maps all URIs to the contents of the APK's assets folder, so a file handle to
+        // /res/assets/{uri.path} will be returned.
+
+        // Security check. This content provider only supports read-only access. (Also, the contents
+        // of an APKs assets folder are immutable, so read-write access doesn't make sense here.)
+        if (!"r".equals(mode)) {
+            throw new SecurityException("Only read-only access is supported, mode must be [r]");
+        }
+
+        // Open asset from within APK and return file descriptor
+        String path = uri.getPath();
+        try {
+            return mAssets.openFd(path);
+        } catch (IOException e) {
+            throw new FileNotFoundException();
+        }
+    }
+
+    /**
+     * Check if file exists inside APK assets.
+     *
+     * @param path Fully qualified path to file.
+     * @return true if exists, false otherwise.
+     */
+    private boolean fileExists(String path) {
+        try {
+            // Check to see if file can be opened. If so, file exists.
+            mAssets.openFd(path).close();
+            return true;
+        } catch (IOException e) {
+            // Unable to open file descriptor for specified path; file doesn't exist.
+            return false;
+        }
+    }
+
+    // Required/unused ContentProvider methods below.
+    @Override
+    public Cursor query(Uri uri, String[] projection, String selection,
+                        String[] selectionArgs, String sortOrder) {
+        // Note: It might be worth implementing support for querying
+        //       android.provider.OpenableColumns here in the future.
+        throw new RuntimeException("Operation not supported");
+    }
+
+    @Override
+    public Uri insert(Uri uri, ContentValues contentValues) {
+        throw new RuntimeException("Operation not supported");
+    }
+
+    @Override
+    public int delete(Uri uri, String selection, String[] selectionArgs) {
+        throw new RuntimeException("Operation not supported");
+    }
+
+    @Override
+    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
+        throw new RuntimeException("Operation not supported");
+    }
+}