Implement compare_db_backups "main"

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

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

javatests/google/registry/tools/LevelDbFileBuilder.java

@@ -0,0 +1,83 @@
+// 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 google.registry.tools.LevelDbLogReader.BLOCK_SIZE;
+import static google.registry.tools.LevelDbLogReader.HEADER_SIZE;
+
+import com.google.appengine.api.datastore.Entity;
+import com.google.appengine.api.datastore.EntityTranslator;
+import com.google.auto.value.AutoValue;
+import com.google.storage.onestore.v3.OnestoreEntity.EntityProto;
+import google.registry.tools.LevelDbLogReader.ChunkType;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+/** Utility class for building a leveldb logfile. */
+final class LevelDbFileBuilder {
+  private static final String TEST_ENTITY_KIND = "TestEntity";
+
+  private final FileOutputStream out;
+  private byte[] currentBlock = new byte[BLOCK_SIZE];
+
+  // Write position in the current block.
+  private int currentPos = 0;
+
+  LevelDbFileBuilder(File file) throws FileNotFoundException {
+    out = new FileOutputStream(file);
+  }
+
+  /**
+   * Adds a record containing a new entity protobuf to the file.
+   *
+   * <p>Returns the ComparableEntity object rather than "this" so that we can check for the presence
+   * of the entity in the result set.
+   */
+  ComparableEntity addEntityProto(int id, Property... properties) throws IOException {
+    Entity entity = new Entity(TEST_ENTITY_KIND, id);
+    for (Property prop : properties) {
+      entity.setProperty(prop.name(), prop.value());
+    }
+    EntityProto proto = EntityTranslator.convertToPb(entity);
+    byte[] protoBytes = proto.toByteArray();
+    if (protoBytes.length > BLOCK_SIZE - (currentPos + HEADER_SIZE)) {
+      out.write(currentBlock);
+      currentBlock = new byte[BLOCK_SIZE];
+      currentPos = 0;
+    }
+
+    currentPos = LevelDbUtil.addRecord(currentBlock, currentPos, ChunkType.FULL, protoBytes);
+    return new ComparableEntity(entity);
+  }
+
+  /** Writes all remaining data and closes the block. */
+  void build() throws IOException {
+    out.write(currentBlock);
+    out.close();
+  }
+
+  @AutoValue
+  abstract static class Property {
+    static Property create(String name, Object value) {
+      return new AutoValue_LevelDbFileBuilder_Property(name, value);
+    }
+
+    abstract String name();
+
+    abstract Object value();
+  }
+}