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..666227440af90c6a19b3b92c4d9442e52abe07df
--- /dev/null
+++ b/android_webview/java/src/org/chromium/android_webview/AwVariationsSeedFetchService.java
@@ -0,0 +1,157 @@
+// 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.SuppressLint;
+import android.app.job.JobParameters;
+import android.app.job.JobService;
+import android.os.AsyncTask;
+
+import org.chromium.base.ContextUtils;
+import org.chromium.base.Log;
+import org.chromium.base.ThreadUtils;
+import org.chromium.components.variations.firstrun.VariationsSeedFetcher;
+
+import java.io.Closeable;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+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 tesing experiments in the native code. The fetched data is stored in the local
+ * directory which belongs to the Service process.
+ */
+@SuppressLint("NewApi") // 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(final JobParameters params) {
+        new FetchFinchSeedDataTask(params).execute();
+        return true;
+    }
+
+    @Override
+    public boolean onStopJob(JobParameters params) {
+        // When job parameter is not satisfied any more, the job should be rescheduled.
+        return true;
+    }
+
+    private class FetchFinchSeedDataTask extends AsyncTask<Void, Void, Void> {

[Alexei Svitkine (slow), 2017/07/12 15:52:50]

Can this class be static?

[yiyuny, 2017/07/12 18:31:30]

I prefer to make it non-static because function jobFinished needs to be called
after fetching is done and it is a function of JobService, which means in the
task we need to maintain a pointer to the JobService.

[Alexei Svitkine (slow), 2017/07/12 19:01:21]

That makes sense.

+        private JobParameters mJobParams;
+
+        FetchFinchSeedDataTask(JobParameters params) {
+            mJobParams = params;
+        }
+
+        @Override
+        protected Void doInBackground(Void... params) {
+            AwVariationsSeedFetchService.fetchSeed();
+            return null;
+        }
+
+        @Override
+        protected void onPostExecute(Void success) {
+            jobFinished(mJobParams, false);
+        }
+    }
+
+    private static void fetchSeed() {
+        assert !ThreadUtils.runningOnUiThread();
+        // TryLock will drop calls from other threads when one threads are executing the function.
+        // TODO(yiyuny): Add explicitly control to make sure there is only one thread fetching the
+        // seed in a while before the seed is expired.

[Alexei Svitkine (slow), 2017/07/12 15:52:50]

Nit: "before the seed is expired" isn't too meaningful. I think you want to say
"to ensure there's only one threading fetching at a time and that the seed
doesn't get fetched too frequently".

[yiyuny, 2017/07/12 18:31:30]

Done.

+        if (sLock.tryLock()) {
+            try {
+                VariationsSeedFetcher.SeedInfo si = VariationsSeedFetcher.get().downloadContent(

[Alexei Svitkine (slow), 2017/07/12 15:52:50]

Nit: seedInfo

[yiyuny, 2017/07/12 18:31:30]

Done.

+                        VariationsSeedFetcher.VariationsPlatform.ANDROID_WEBVIEW, "");
+                storeVariationsSeed(si);
+            } catch (IOException e) {
+                // Exceptions are handled in the downloadContent function and rethrowing the
+                // exception is to stop the normal logic flow after it, so no error-handling here.
+                // Not explicitly handing SocketTimeoutException and UnknownHostException for they
+                // are both subclasses of IOException.
+            } finally {
+                sLock.unlock();
+            }
+        }
+    }
+
+    /**
+     * Store seed preference independently from Seed Info.

[Alexei Svitkine (slow), 2017/07/12 15:52:49]

This comment reads like a method comment, since it starts with a verb. Can you
describe the class instead and *then* mention how it's used. You say it's stored
independently - stored where? Mention that it's serializable and what it means
for future changes to this class. (i.e. what would someone have to be careful of
when changing the class.)

[yiyuny, 2017/07/12 18:31:30]

Done.

+     */
+    public static class SeedPreference implements Serializable {
+        public String signature;
+        public String country;
+        public String date;
+        public boolean isGzipCompressed;

[Alexei Svitkine (slow), 2017/07/12 15:52:49]

Can these be final - or is that something that's not allowed with Serializable?

[yiyuny, 2017/07/12 18:31:30]

Done.

+
+        public SeedPreference(final VariationsSeedFetcher.SeedInfo si) {

[Alexei Svitkine (slow), 2017/07/12 15:52:49]

Nit: seedInfo. Acronyms are discouraged, especially for such short things. No
need for final qualifier here.

[yiyuny, 2017/07/12 18:31:30]

Done.

+            signature = si.signature;
+            country = si.country;
+            date = si.date;
+            isGzipCompressed = si.isGzipCompressed;
+        }
+    }
+
+    private static File getOrCreateWebViewVariationsDir() {
+        File dir = new File(
+                ContextUtils.getApplicationContext().getFilesDir(), WEBVIEW_VARIATIONS_DIR);

[Alexei Svitkine (slow), 2017/07/12 15:52:50]

Nit: If this is wrapping already, suggest extracting the result of getFilesDir()
to a separate variable above, so it's still 2 lines but a bit nicer.

[yiyuny, 2017/07/12 18:31:30]

Done.

+        if (dir.mkdir() || dir.isDirectory()) {
+            return dir;
+        }
+        return null;
+    }
+
+    private static void storeVariationsSeed(final VariationsSeedFetcher.SeedInfo si) {

[Alexei Svitkine (slow), 2017/07/12 15:52:49]

seedInfo

[yiyuny, 2017/07/12 18:31:30]

Done.

+        FileOutputStream fosSeed = null;
+        ObjectOutputStream oosSeedPref = null;

[Alexei Svitkine (slow), 2017/07/12 15:52:49]

Nit: Move these to right above the try.

[yiyuny, 2017/07/12 18:31:30]

Done.

+        File webViewVariationsDir = getOrCreateWebViewVariationsDir();
+        if (webViewVariationsDir == null) {
+            return;
+        }
+        try {
+            fosSeed = new FileOutputStream(new File(webViewVariationsDir, SEED_DATA_FILENAME));
+            fosSeed.write(si.rawSeed, 0, si.rawSeed.length);
+            // Store separately so that reading large seed data (which is expensive) can be
+            // prevented when checking the last seed fetch time.
+            oosSeedPref = new ObjectOutputStream(
+                    new FileOutputStream(new File(webViewVariationsDir, SEED_PREF_FILENAME)));
+            oosSeedPref.writeObject(new SeedPreference(si));
+        } catch (FileNotFoundException e) {
+            Log.e(TAG,
+                    "FileNotFoundException failed to open file to write seed data or preference.");
+        } catch (IOException e) {
+            Log.e(TAG,
+                    "IOException failed to write variations seed data or preference to the file.");
+        } finally {
+            closeStream(fosSeed, SEED_DATA_FILENAME);
+            closeStream(oosSeedPref, SEED_PREF_FILENAME);
+        }
+    }
+
+    private static void closeStream(Closeable stream, String filename) {
+        if (stream != null) {
+            try {
+                stream.close();
+            } catch (IOException e) {
+                Log.e(TAG, "IOException failed to close " + filename + " file.");
+            }
+        }
+    }
+}