Create a LevelDBLogReader class for java

This is a first step towards porting our database backup comparison tool
(which was written in Crack and subsequently in Python) to Java so that we can
run it in a reasonable amount of time.  Ideally, this functionality should be
available in Java, however the only instance of it that I can find is
currently deprecated without a replacement.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=165433766

javatests/google/registry/tools/LevelDbLogReaderTest.java

@@ -0,0 +1,164 @@
+// 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 static google.registry.tools.LevelDbLogReader.ChunkType;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.primitives.Bytes;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** LevelDbLogReader tests. */
+@RunWith(JUnit4.class)
+public final class LevelDbLogReaderTest {
+
+  private static final int MAX_RECORD = LevelDbLogReader.BLOCK_SIZE - LevelDbLogReader.HEADER_SIZE;
+
+  // Size of the test record.  Any value < 256 will do.
+  private static final int TEST_RECORD_SIZE = 231;
+
+  // The maximum offset at which a test record can be inserted, measured in bytes from the beginning
+  // of the block.
+  private static final int MAX_TEST_RECORD_OFFSET =
+      LevelDbLogReader.BLOCK_SIZE - (LevelDbLogReader.HEADER_SIZE + TEST_RECORD_SIZE);
+
+  /**
+   * Adds a record of bytes of 'val' of the given size to bytes.
+   *
+   * <p>This currently doesn't write a real checksum since we're not doing anything with that in the
+   * leveldb reader.
+   *
+   * <p>Returns the new offset for the next block.
+   */
+  private static int addRecord(
+      byte[] bytes, int pos, ChunkType type, int size, int val) {
+
+    // Write a bogus checksum.
+    for (int i = 0; i < 4; ++i) {
+      bytes[pos++] = -1;
+    }
+
+    // Write size and type.
+    bytes[pos++] = (byte) size;
+    bytes[pos++] = (byte) (size >> 8);
+    bytes[pos++] = (byte) type.getCode();
+
+    // Write "size" bytes of data.
+    for (int i = 0; i < size; ++i) {
+      bytes[pos + i] = (byte) val;
+
+      // Swap the least significant bytes in val so we can have more than 256 different same-sized
+      // records.
+      val = (val >> 8) | ((val & 0xff) << 8);
+    }
+
+    return pos + size;
+  }
+
+  private TestBlock makeBlockOfRepeatingBytes(int startVal) {
+    byte[] block = new byte[LevelDbLogReader.BLOCK_SIZE];
+    int pos = 0;
+    int recordCount = 0;
+    while (pos < MAX_TEST_RECORD_OFFSET) {
+      pos =
+          addRecord(
+              block,
+              pos,
+              ChunkType.FULL,
+              TEST_RECORD_SIZE,
+              0xffff & (pos + startVal));
+      ++recordCount;
+    }
+    return new TestBlock(block, recordCount);
+  }
+
+  @Test
+  public void testSimpleBlock() throws IOException {
+    TestBlock block = makeBlockOfRepeatingBytes(0);
+    LevelDbLogReader reader = new LevelDbLogReader();
+    reader.readFrom(new ByteArrayInputStream(block.data));
+    ImmutableList<byte[]> records = reader.getRecords();
+    assertThat(records).hasSize(block.recordCount);
+  }
+
+  @Test
+  public void testLargeRecord() throws IOException {
+    byte[] block = new byte[LevelDbLogReader.BLOCK_SIZE];
+    addRecord(block, 0, ChunkType.FIRST, MAX_RECORD, (byte) 1);
+    LevelDbLogReader reader = new LevelDbLogReader();
+    reader.readFrom(new ByteArrayInputStream(block));
+    assertThat(reader.getRecords()).isEmpty();
+
+    addRecord(block, 0, ChunkType.MIDDLE, MAX_RECORD, (byte) 2);
+    reader.readFrom(new ByteArrayInputStream(block));
+    assertThat(reader.getRecords()).isEmpty();
+
+    addRecord(block, 0, ChunkType.LAST, MAX_RECORD, (byte) 3);
+    reader.readFrom(new ByteArrayInputStream(block));
+
+    List<byte[]> records = reader.getRecords();
+    assertThat(records).hasSize(1);
+    byte[] record = records.get(0);
+
+    for (int i = 0; i < MAX_RECORD; ++i) {
+      assertThat(record[i]).isEqualTo((i % 2 == 1) ? 0 : 1);
+    }
+    for (int i = MAX_RECORD; i < MAX_RECORD * 2; ++i) {
+      // Note that we have to invert the byte check here because MAX_RECORD is not divisible by two.
+      assertThat(record[i]).isEqualTo((i % 2 == 0) ? 0 : 2);
+    }
+    for (int i = MAX_RECORD * 2; i < MAX_RECORD * 3; ++i) {
+      assertThat(record[i]).isEqualTo((i % 2 == 1) ? 0 : 3);
+    }
+  }
+
+  @Test
+  public void readFromMultiBlockStream() throws IOException {
+    TestBlock block0 = makeBlockOfRepeatingBytes(0);
+    TestBlock block1 = makeBlockOfRepeatingBytes(138);
+    ByteArrayInputStream source = new ByteArrayInputStream(Bytes.concat(block0.data, block1.data));
+
+    LevelDbLogReader reader = new LevelDbLogReader();
+    reader.readFrom(source);
+    assertThat(reader.getRecords()).hasSize(block0.recordCount + block1.recordCount);
+  }
+
+  @Test
+  public void testChunkTypesToCode() {
+    // Verify that we're translating chunk types to code values correctly.z
+    assertThat(ChunkType.fromCode(ChunkType.END.getCode())).isEqualTo(ChunkType.END);
+    assertThat(ChunkType.fromCode(ChunkType.FULL.getCode())).isEqualTo(ChunkType.FULL);
+    assertThat(ChunkType.fromCode(ChunkType.FIRST.getCode())).isEqualTo(ChunkType.FIRST);
+    assertThat(ChunkType.fromCode(ChunkType.MIDDLE.getCode())).isEqualTo(ChunkType.MIDDLE);
+    assertThat(ChunkType.fromCode(ChunkType.LAST.getCode())).isEqualTo(ChunkType.LAST);
+  }
+
+  /** Aggregates the bytes of a test block with the record count. */
+  private static final class TestBlock {
+    final byte[] data;
+    final int recordCount;
+
+    TestBlock(byte[] data, int recordCount) {
+      this.data = data;
+      this.recordCount = recordCount;
+    }
+  }
+}