diff --git a/java/google/registry/tools/LevelDbLogReader.java b/java/google/registry/tools/LevelDbLogReader.java
new file mode 100644
index 000000000..6562acdbc
--- /dev/null
+++ b/java/google/registry/tools/LevelDbLogReader.java
@@ -0,0 +1,173 @@
+// 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.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableList;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.FileSystems;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+/**
+ * Reads records from a set of LevelDB files and builds a gigantic ImmutableList from them.
+ *
+ *
See log_format.md for the
+ * leveldb log format specification.
+ *
+ *
There are several other implementations of this, none of which appeared suitable for our use
+ * case: The original C++ implementation.
+ * com.google.appengine.api.files.RecordWriteChannel - Exactly what we need but deprecated. The
+ * referenced replacement: The App Engine GCS
+ * Client - Does not appear to have any support for working with LevelDB.
+ */
+public final class LevelDbLogReader {
+
+ @VisibleForTesting static final int BLOCK_SIZE = 32 * 1024;
+ @VisibleForTesting static final int HEADER_SIZE = 7;
+
+ private final ByteArrayOutputStream recordContents = new ByteArrayOutputStream();
+ private final ImmutableList.Builder recordListBuilder = new ImmutableList.Builder<>();
+
+ /** Read a complete block, which must be exactly 32 KB. */
+ private void processBlock(byte[] block) {
+ // Read records from the block until there is no longer enough space for a record (i.e. until
+ // we're at HEADER_SIZE - 1 bytes from the end of the block).
+ int i = 0;
+ while (i < BLOCK_SIZE - (HEADER_SIZE - 1)) {
+ RecordHeader recordHeader = readRecordHeader(block, i);
+ if (recordHeader.type == ChunkType.END) {
+ // A type of zero indicates that we've reached the padding zeroes at the end of the block.
+ break;
+ }
+
+ // Copy the contents of the record into recordContents.
+ recordContents.write(block, i + HEADER_SIZE, recordHeader.size);
+
+ // If this is the last (or only) chunk in the record, store the full contents into the List.
+ if (recordHeader.type == ChunkType.FULL || recordHeader.type == ChunkType.LAST) {
+ recordListBuilder.add(recordContents.toByteArray());
+ recordContents.reset();
+ }
+
+ i += recordHeader.size + HEADER_SIZE;
+ }
+ }
+
+ /**
+ * Gets a byte from "block" as an unsigned value.
+ *
+ * Java bytes are signed, which doesn't work very well for our bit-shifting operations.
+ */
+ private int getUnsignedByte(byte[] block, int pos) {
+ return block[pos] & 0xFF;
+ }
+
+ /** Reads the 7 byte record header. */
+ private RecordHeader readRecordHeader(byte[] block, int pos) {
+ // Read checksum (4 bytes, LE).
+ int checksum =
+ getUnsignedByte(block, pos)
+ | (getUnsignedByte(block, pos + 1) << 8)
+ | (getUnsignedByte(block, pos + 2) << 16)
+ | (getUnsignedByte(block, pos + 3) << 24);
+ // Read size (2 bytes, LE).
+ int size = getUnsignedByte(block, pos + 4) | (getUnsignedByte(block, pos + 5) << 8);
+ // Read type (1 byte).
+ int type = getUnsignedByte(block, pos + 6);
+
+ return new RecordHeader(checksum, size, ChunkType.fromCode(type));
+ }
+
+ /** Reads all records in the Reader into the record set. */
+ public void readFrom(InputStream source) throws IOException {
+ byte[] block = new byte[BLOCK_SIZE];
+
+ // read until we have no more.
+ while (true) {
+ int amountRead = source.read(block, 0, BLOCK_SIZE);
+ if (amountRead <= 0) {
+ break;
+ }
+ assert amountRead == BLOCK_SIZE;
+
+ processBlock(block);
+ }
+ }
+
+ /** Reads all records from the file specified by "path" into the record set. */
+ public void readFrom(Path path) throws IOException {
+ readFrom(Files.newInputStream(path));
+ }
+
+ /** Reads all records from the specified file into the record set. */
+ public void readFrom(String filename) throws IOException {
+ readFrom(FileSystems.getDefault().getPath(filename));
+ }
+
+ /**
+ * Gets the list of records constructed so far.
+ *
+ *
Note that this does not invalidate the internal state of the object: we return a copy and
+ * this can be called multiple times.
+ */
+ ImmutableList getRecords() {
+ return recordListBuilder.build();
+ }
+
+ /** Aggregates the fields in a record header. */
+ private static final class RecordHeader {
+ final int checksum;
+ final int size;
+ final ChunkType type;
+
+ public RecordHeader(int checksum, int size, ChunkType type) {
+ this.checksum = checksum;
+ this.size = size;
+ this.type = type;
+ }
+ }
+
+ @VisibleForTesting
+ enum ChunkType {
+ // Warning: these values must map to their array indices. If this relationship is broken,
+ // you'll need to change fromCode() to not simply index into values().
+ END(0),
+ FULL(1),
+ FIRST(2),
+ MIDDLE(3),
+ LAST(4);
+
+ private final int code;
+
+ ChunkType(int code) {
+ this.code = code;
+ }
+
+ int getCode() {
+ return code;
+ }
+
+ /** Construct a record type from the numeric record type code. */
+ static ChunkType fromCode(int code) {
+ return values()[code];
+ }
+ }
+}
diff --git a/javatests/google/registry/tools/LevelDbLogReaderTest.java b/javatests/google/registry/tools/LevelDbLogReaderTest.java
new file mode 100644
index 000000000..606c0a765
--- /dev/null
+++ b/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.
+ *
+ * This currently doesn't write a real checksum since we're not doing anything with that in the
+ * leveldb reader.
+ *
+ *
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 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 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;
+ }
+ }
+}