Create an entity record accumulator

RecordAccumulator builds a set of datastore Entity records from a set of
leveldb logfiles in a directory tree (which is how we receive them for
database backup/restore testing).

This CL also refactors some of the logfile test code out of
LevelDbLogReaderTest so that we can reuse it for building test logs.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167313553

java/google/registry/tools/RecordAccumulator.java

@@ -0,0 +1,59 @@
+// 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 com.google.appengine.api.datastore.EntityTranslator;
+import com.google.common.collect.ImmutableSet;
+import com.google.storage.onestore.v3.OnestoreEntity.EntityProto;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+
+/** Utility class that accumulates Entity records from level db files. */
+class RecordAccumulator {
+  private final LevelDbLogReader reader = new LevelDbLogReader();
+
+  /** Recursively reads all records in the directory. */
+  public final RecordAccumulator readDirectory(File dir) {
+    for (File child : dir.listFiles()) {
+      if (child.isDirectory()) {
+        readDirectory(child);
+      } else if (child.isFile()) {
+        try {
+          reader.readFrom(new FileInputStream(child));
+        } catch (IOException e) {
+          throw new RuntimeException("IOException reading from file: " + child, e);
+        }
+      }
+    }
+
+    return this;
+  }
+
+  /** Creates an entity set from the current set of raw records. */
+  ImmutableSet<ComparableEntity> getComparableEntitySet() {
+    ImmutableSet.Builder<ComparableEntity> builder = new ImmutableSet.Builder<>();
+    for (byte[] rawRecord : reader.getRecords()) {
+      // Parse the entity proto and create an Entity object from it.
+      EntityProto proto = new EntityProto();
+      proto.parseFrom(rawRecord);
+      ComparableEntity entity = new ComparableEntity(EntityTranslator.createFromPb(proto));
+
+      builder.add(entity);
+    }
+
+    return builder.build();
+  }
+}