Add different ways of reading the dictionary file.

This change adds basic support for an external dictionary provider.
It adds methods for reading the dictionary itself from an asset in
the dictionary provider package directly, obtaining the file name
through the ContentProvider interface; it also adds a way of getting
the data through an InputStream and copying the file locally.

Incidentally this change also adds the code needed to listen for
updating the dictionary provider package and reloading it in time.

This change also goes hand-in-hand with Iab31db6e, which implements
the small closed part of this.

Issue: 3414944

Change-Id: I5e4fff99a59bb99dbdb002102db6c90e6cb41c8a

1 files changed, 96 insertions, 0 deletions

diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java b/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
new file mode 100644
index 000000000..72512c7e1
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2011 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.android.inputmethod.latin;
+
+import android.content.Context;
+import android.content.res.AssetFileDescriptor;
+import android.util.Log;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.Locale;
+
+/**
+ * Helper class to get the address of a mmap'able dictionary file.
+ */
+class BinaryDictionaryGetter {
+
+    /**
+     * Used for Log actions from this class
+     */
+    private static final String TAG = BinaryDictionaryGetter.class.getSimpleName();
+
+    // Prevents this from being instantiated
+    private BinaryDictionaryGetter() {}
+
+    /**
+     * Returns a file address from a resource, or null if it cannot be opened.
+     */
+    private static AssetFileAddress loadFallbackResource(Context context, int fallbackResId) {
+        final AssetFileDescriptor afd = context.getResources().openRawResourceFd(fallbackResId);
+        if (afd == null) {
+            Log.e(TAG, "Found the resource but cannot read it. Is it compressed? resId="
+                    + fallbackResId);
+            return null;
+        }
+        return AssetFileAddress.makeFromFileNameAndOffset(
+                context.getApplicationInfo().sourceDir, afd.getStartOffset(), afd.getLength());
+    }
+
+    /**
+     * Returns a file address for a given locale, trying relevant methods in order.
+     *
+     * Tries to get a binary dictionary from various sources, in order:
+     * - Uses a private method of getting a private dictionary, as implemented by the
+     *   PrivateBinaryDictionaryGetter class.
+     * If that fails:
+     * - Uses a content provider to get a public dictionary, as per the protocol described
+     *   in BinaryDictionaryFileDumper.
+     * If that fails:
+     * - Gets a file name from the fallback resource passed as an argument.
+     * If that fails:
+     * - Returns null.
+     * @return The address of a valid file, or null.
+     * @throws FileNotFoundException if a dictionary provider returned a file name, but the
+     *                               file cannot be found.
+     * @throws IOException if there was an I/O problem reading or copying a file.
+     */
+    public static AssetFileAddress getDictionaryFile(Locale locale, Context context,
+            int fallbackResId) {
+        // Try first to query a private file signed the same way.
+        final AssetFileAddress privateFile =
+                PrivateBinaryDictionaryGetter.getDictionaryFile(locale, context);
+        if (null != privateFile) {
+            return privateFile;
+        } else {
+            try {
+                // If that was no-go, try to find a publicly exported dictionary.
+                final String fileName = BinaryDictionaryFileDumper.
+                        getDictionaryFileFromContentProvider(locale, context);
+                return AssetFileAddress.makeFromFileName(fileName);
+            } catch (FileNotFoundException e) {
+                Log.e(TAG, "Unable to create dictionary file from provider for locale "
+                        + locale.toString() + ": falling back to internal dictionary");
+                return loadFallbackResource(context, fallbackResId);
+            } catch (IOException e) {
+                Log.e(TAG, "Unable to read source data for locale "
+                        + locale.toString() + ": falling back to internal dictionary");
+                return loadFallbackResource(context, fallbackResId);
+            }
+        }
+    }
+}