Implement compare_db_backups "main"

Implement toplevel class that reads in two database backups and displays
diffs.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=168592124

javatests/google/registry/tools/LevelDbFileBuilderTest.java

@@ -0,0 +1,98 @@
+// Copyright 2017 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.tools;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.appengine.api.datastore.Entity;
+import com.google.appengine.api.datastore.EntityTranslator;
+import com.google.common.collect.ImmutableList;
+import com.google.storage.onestore.v3.OnestoreEntity.EntityProto;
+import google.registry.testing.AppEngineRule;
+import google.registry.tools.LevelDbFileBuilder.Property;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class LevelDbFileBuilderTest {
+
+  public static final int BASE_ID = 1001;
+
+  @Rule public final TemporaryFolder tempFs = new TemporaryFolder();
+  @Rule public final AppEngineRule appEngine = AppEngineRule.builder().withDatastore().build();
+
+  @Test
+  public void testSingleRecordWrites() throws FileNotFoundException, IOException {
+    File subdir = tempFs.newFolder("folder");
+    File logFile = new File(subdir, "testfile");
+    LevelDbFileBuilder builder = new LevelDbFileBuilder(logFile);
+    ComparableEntity entity =
+        builder.addEntityProto(
+            BASE_ID, Property.create("first", 100L), Property.create("second", 200L));
+    builder.build();
+
+    LevelDbLogReader reader = new LevelDbLogReader();
+    reader.readFrom(new FileInputStream(logFile));
+
+    ImmutableList<byte[]> records = reader.getRecords();
+    assertThat(records).hasSize(1);
+
+    // Reconstitute an entity, make sure that what we've got is the same as what we started with.
+    EntityProto proto = new EntityProto();
+    proto.parseFrom(records.get(0));
+    Entity materializedEntity = EntityTranslator.createFromPb(proto);
+    assertThat(new ComparableEntity(materializedEntity)).isEqualTo(entity);
+  }
+
+  @Test
+  public void testMultipleRecordWrites() throws FileNotFoundException, IOException {
+    File subdir = tempFs.newFolder("folder");
+    File logFile = new File(subdir, "testfile");
+    LevelDbFileBuilder builder = new LevelDbFileBuilder(logFile);
+
+    // Generate enough records to cross a block boundary.  These records end up being around 80
+    // bytes, so 1000 works.
+    ImmutableList.Builder<ComparableEntity> originalEntitiesBuilder = new ImmutableList.Builder<>();
+    for (int i = 0; i < 1000; ++i) {
+      ComparableEntity entity =
+          builder.addEntityProto(
+              BASE_ID + i, Property.create("first", 100L), Property.create("second", 200L));
+      originalEntitiesBuilder.add(entity);
+    }
+    builder.build();
+    ImmutableList<ComparableEntity> originalEntities = originalEntitiesBuilder.build();
+
+    LevelDbLogReader reader = new LevelDbLogReader();
+    reader.readFrom(new FileInputStream(logFile));
+
+    ImmutableList<byte[]> records = reader.getRecords();
+    assertThat(records).hasSize(1000);
+    int index = 0;
+    for (byte[] record : records) {
+      EntityProto proto = new EntityProto();
+      proto.parseFrom(record);
+      Entity materializedEntity = EntityTranslator.createFromPb(proto);
+      assertThat(new ComparableEntity(materializedEntity)).isEqualTo(originalEntities.get(index));
+      ++index;
+    }
+  }
+}