Add AwVariationsSeedFetchService and refactory VariationsSeedFetcher

android_webview/java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java

Index: android_webview/java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java b/android_webview/java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java
new file mode 100644
index 0000000000000000000000000000000000000000..27bdaad23a4ac3b79617592a1e0ad5e4cb095063
--- /dev/null
+++ b/android_webview/java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java
@@ -0,0 +1,237 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.android_webview;
+
+import android.annotation.TargetApi;
+import android.app.job.JobParameters;
+import android.app.job.JobService;
+import android.os.AsyncTask;
+import android.os.Build;
+
+import org.chromium.base.ContextUtils;
+import org.chromium.base.Log;
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.VisibleForTesting;
+import org.chromium.base.annotations.SuppressFBWarnings;
+import org.chromium.components.variations.firstrun.VariationsSeedFetcher;
+import org.chromium.components.variations.firstrun.VariationsSeedFetcher.SeedInfo;
+
+import java.io.Closeable;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * AwVariationsSeedFetchService is a Job Service to fetch test seed data which is used by Finch
+ * to enable AB testing experiments in the native code. The fetched data is stored in the local
+ * directory which belongs to the Service process. This is a prototype of the Variations Seed Fetch
+ * Service which is one part of the work of adding Finch to Android WebView.
+ */
+@TargetApi(Build.VERSION_CODES.LOLLIPOP) // JobService requires API level 21.
+public class AwVariationsSeedFetchService extends JobService {
+    private static final String TAG = "AwVartnsSeedFetchSvc";
+
+    public static final String WEBVIEW_VARIATIONS_DIR = "WebView_Variations/";
+    public static final String SEED_DATA_FILENAME = "variations_seed_data";
+    public static final String SEED_PREF_FILENAME = "variations_seed_pref";
+
+    // Synchronization lock to prevent simultaneous local seed file writing.
+    private static final Lock sLock = new ReentrantLock();
+
+    @Override
+    public boolean onStartJob(JobParameters params) {
+        // Ensure we can use ContextUtils later on.
+        ContextUtils.initApplicationContext(this.getApplicationContext());
+        new FetchFinchSeedDataTask(params).execute();
+        return true;
+    }
+
+    @Override
+    public boolean onStopJob(JobParameters params) {
+        // This method is called by the JobScheduler to stop a job before it has finished.
+        // Return true here to reschedule the job.
+        return true;
+    }
+
+    private class FetchFinchSeedDataTask extends AsyncTask<Void, Void, Void> {
+        private JobParameters mJobParams;
+
+        FetchFinchSeedDataTask(JobParameters params) {
+            mJobParams = params;
+        }
+
+        @Override
+        protected Void doInBackground(Void... params) {
+            fetchVariationsSeed();
+            return null;
+        }
+
+        @Override
+        protected void onPostExecute(Void success) {
+            jobFinished(mJobParams, false /* false -> don't reschedule */);
+        }
+    }
+
+    private static void fetchVariationsSeed() {
+        assert !ThreadUtils.runningOnUiThread();
+        // TryLock will drop calls from other threads when there is a thread executing the function.
+        // TODO(yiyuny): Add explicitly control to ensure there's only one threading fetching at a
+        // time and that the seed doesn't get fetched too frequently.
+        if (sLock.tryLock()) {
+            try {
+                SeedInfo seedInfo = VariationsSeedFetcher.get().downloadContent(
+                        VariationsSeedFetcher.VariationsPlatform.ANDROID_WEBVIEW, "");
+                storeVariationsSeed(seedInfo);
+            } catch (IOException e) {
+                // Exceptions are handled and logged in the downloadContent method, so we don't
+                // need any exception handling here. The only reason we need a catch-statement here
+                // is because those exceptions are re-thrown from downloadContent to skip the
+                // normal logic flow within that method.
+            } finally {
+                sLock.unlock();
+            }
+        }
+    }
+
+    /**
+     * SeedPreference is used to serialize/deserialize related fields of seed data when reading or
+     * writing them to the internal storage.
+     */
+    public static class SeedPreference implements Serializable {
+        /**
+         * Let the program deserialize the data when the fields are changed.
+         */
+        private static final long serialVersionUID = 0L;
+
+        public final String signature;
+        public final String country;
+        public final String date;
+        public final boolean isGzipCompressed;
+
+        public SeedPreference(SeedInfo seedInfo) {
+            signature = seedInfo.signature;
+            country = seedInfo.country;
+            date = seedInfo.date;
+            isGzipCompressed = seedInfo.isGzipCompressed;
+        }
+    }
+
+    private static File getOrCreateWebViewVariationsDir() throws IOException {
+        File webViewFileDir = ContextUtils.getApplicationContext().getFilesDir();
+        File dir = new File(webViewFileDir, WEBVIEW_VARIATIONS_DIR);
+        if (dir.mkdir() || dir.isDirectory()) {
+            return dir;
+        }
+        throw new IOException("Failed to get or create the WebView variations directory.");
+    }
+
+    /**
+     * Store the variations seed data and its related header fields into two separate files in the
+     * directory of Android WebView.
+     * @param seedInfo The seed data and its related header fields fetched from the finch server.
+     */
+    @VisibleForTesting
+    public static void storeVariationsSeed(SeedInfo seedInfo) {
+        FileOutputStream fosSeedData = null;
+        ObjectOutputStream oosSeedPref = null;
+        try {
+            File webViewVariationsDir = getOrCreateWebViewVariationsDir();
+            File seedDataFile = File.createTempFile(SEED_DATA_FILENAME, null, webViewVariationsDir);
+            fosSeedData = new FileOutputStream(seedDataFile);
+            fosSeedData.write(seedInfo.seedData, 0, seedInfo.seedData.length);
+            renameTempFile(seedDataFile, new File(webViewVariationsDir, SEED_DATA_FILENAME));
+            // Store separately so that reading large seed data (which is expensive) can be
+            // prevented when checking the last seed fetch time.
+            File seedPrefFile = File.createTempFile(SEED_PREF_FILENAME, null, webViewVariationsDir);
+            oosSeedPref = new ObjectOutputStream(new FileOutputStream(seedPrefFile));
+            oosSeedPref.writeObject(new SeedPreference(seedInfo));
+            renameTempFile(seedPrefFile, new File(webViewVariationsDir, SEED_PREF_FILENAME));
+        } catch (IOException e) {
+            Log.e(TAG, "Failed to write variations seed data or preference to a file." + e);
+        } finally {
+            closeStream(fosSeedData);
+            closeStream(oosSeedPref);
+        }
+    }
+
+    /**
+     * Get the variations seed data from the file in the internal storage.
+     * @return The byte array which contains the seed data.
+     * @throws IOException if fail to get or create the WebView Variations directory.
+     */
+    @VisibleForTesting
+    public static byte[] getVariationsSeedData() throws IOException {
+        FileInputStream fisSeedData = null;
+        try {
+            File webViewVariationsDir = getOrCreateWebViewVariationsDir();
+            fisSeedData = new FileInputStream(new File(webViewVariationsDir, SEED_DATA_FILENAME));
+            return VariationsSeedFetcher.convertInputStreamToByteArray(fisSeedData);
+        } finally {
+            if (fisSeedData != null) {
+                fisSeedData.close();
+            }
+        }
+    }
+
+    /**
+     * Get the variations seed preference from the file in the internal storage.
+     * @return The seed preference which holds related header fields of the seed.
+     * @throws IOException if fail to get or create the WebView Variations directory.
+     * @throws ClassNotFoundException if fail to load the class of the serialized object.
+     */
+    @VisibleForTesting
+    public static SeedPreference getVariationsSeedPreference()
+            throws IOException, ClassNotFoundException {
+        ObjectInputStream oisSeedPref = null;
+        try {
+            File webViewVariationsDir = getOrCreateWebViewVariationsDir();
+            oisSeedPref = new ObjectInputStream(
+                    new FileInputStream(new File(webViewVariationsDir, SEED_PREF_FILENAME)));
+            return (SeedPreference) oisSeedPref.readObject();
+        } finally {
+            if (oisSeedPref != null) {
+                oisSeedPref.close();
+            }
+        }
+    }
+
+    /**
+     * Clear the test data.
+     * @throws IOException if fail to get or create the WebView Variations directory.
+     */
+    @SuppressFBWarnings("RV_RETURN_VALUE_IGNORED_BAD_PRACTICE") // ignoring File.delete() return
+    @VisibleForTesting
+    public static void clearDataForTesting() throws IOException {
+        File webViewVariationsDir = getOrCreateWebViewVariationsDir();
+        File seedDataFile = new File(webViewVariationsDir, SEED_DATA_FILENAME);
+        File seedPrefFile = new File(webViewVariationsDir, SEED_PREF_FILENAME);
+        seedDataFile.delete();
+        seedPrefFile.delete();
+        webViewVariationsDir.delete();
+    }
+
+    @SuppressFBWarnings("RV_RETURN_VALUE_IGNORED_BAD_PRACTICE")
+    // ignoring File.delete() and File.renameTo() return
+    private static void renameTempFile(File tempFile, File newFile) {
+        newFile.delete();
+        tempFile.renameTo(newFile);
+    }
+
+    private static void closeStream(Closeable stream) {
+        if (stream != null) {
+            try {
+                stream.close();
+            } catch (IOException e) {
+                Log.e(TAG, "Failed to close stream. " + e);
+            }
+        }
+    }
+}