sunchao commented on a change in pull request #3250:
URL: https://github.com/apache/hadoop/pull/3250#discussion_r682782504



##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;

Review comment:
       nit: maybe better do `GZIP_HEADER_LEN = GZIP_HEADER.length`.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);
+    trailerBytesWritten += numAvailBytes;
+
+    if (trailerOff == GZIP_TRAILER_LEN) {
+      state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+      currentBufLen = 0;
+      headerOff = trailerOff = 0;
+    }
+
+    return numAvailBytes;
+  }
+
+  @Override
+  public long getBytesRead() {
+    return deflater.getTotalIn();
+  }
+
+  @Override
+  public long getBytesWritten() {
+    return headerBytesWritten + deflater.getTotalOut() + trailerBytesWritten;
+  }
+
+  @Override
+  public void end() {
+    deflater.end();
+  }
+
+  @Override
+  public void finish() {
+    deflater.finish();
+    state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  private void init(Configuration conf) {
+    ZlibCompressor.CompressionLevel level = 
ZlibFactory.getCompressionLevel(conf);
+    ZlibCompressor.CompressionStrategy strategy = 
ZlibFactory.getCompressionStrategy(conf);
+
+    // 'true' (nowrap) => Deflater will handle raw deflate stream only
+    deflater = new Deflater(level.compressionLevel(), true);
+    deflater.setStrategy(strategy.compressionStrategy());
+
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+
+    GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+  }
+
+  @Override
+  public void reinit(Configuration conf) {
+    init(conf);
+    crc.reset();
+    userBufOff = userBufLen = 0;
+    headerBytesWritten = trailerBytesWritten = 0;
+    currentBufLen = 0;
+    headerOff = trailerOff = 0;
+  }
+
+  @Override
+  public void reset() {
+    deflater.reset();
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+    crc.reset();
+    userBufOff = userBufLen = 0;
+    currentBufLen = 0;
+    headerOff = trailerOff = 0;
+  }
+
+  @Override
+  public void setDictionary(byte[] b, int off, int len) {
+    deflater.setDictionary(b, off, len);
+  }
+
+  @Override
+  public void setInput(byte[] b, int off, int len) {
+    if (b == null) {
+      throw new NullPointerException();
+    }
+    if (off < 0 || len < 0 || off > b.length - len) {
+      throw new ArrayIndexOutOfBoundsException();
+    }
+
+    userBuf = b;
+    userBufOff = off;
+    userBufLen = len;
+
+    deflater.reset();
+    crc.reset();
+  }
+
+  private int writeHeader(byte[] b, int off, int len) {
+    if (len <= 0) {
+      return 0;
+    }
+
+    int n = Math.min(len, 10 - headerOff);
+    System.arraycopy(GZIP_HEADER, headerOff, b, off, n);
+    headerOff += n;
+
+    return n;
+  }
+
+  private void fillTrailer() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC) {
+      int streamCrc = (int) crc.getValue();
+      GZIP_TRAILER[0] = (byte) (streamCrc & 0x000000ff);
+      GZIP_TRAILER[1] = (byte) ((streamCrc & 0x0000ff00) >> 8);
+      GZIP_TRAILER[2] = (byte) ((streamCrc & 0x00ff0000) >> 16);
+      GZIP_TRAILER[3] = (byte) ((streamCrc & 0xff000000) >> 24);
+
+      GZIP_TRAILER[4] = (byte) (currentBufLen & 0x000000ff);
+      GZIP_TRAILER[5] = (byte) ((currentBufLen & 0x0000ff00) >> 8);
+      GZIP_TRAILER[6] = (byte) ((currentBufLen & 0x00ff0000) >> 16);
+      GZIP_TRAILER[7] = (byte) ((currentBufLen & 0xff000000) >> 24);
+    }
+  }
+
+  private int writeTrailer(byte[] b, int off, int len) {
+    if (len <= 0) {
+      return 0;
+    }
+
+    int n = Math.min(len, 8 - trailerOff);

Review comment:
       nit: use `GZIP_TRAILER_LEN`?

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {

Review comment:
       nit: maybe move this into `writeHeader` since it's closer to its context.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);
+    trailerBytesWritten += numAvailBytes;
+
+    if (trailerOff == GZIP_TRAILER_LEN) {

Review comment:
       nit: ditto - maybe move this into `writeTrailer` to keep it closer to 
its context.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);
+    trailerBytesWritten += numAvailBytes;
+
+    if (trailerOff == GZIP_TRAILER_LEN) {
+      state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+      currentBufLen = 0;
+      headerOff = trailerOff = 0;
+    }
+
+    return numAvailBytes;
+  }
+
+  @Override
+  public long getBytesRead() {
+    return deflater.getTotalIn();
+  }
+
+  @Override
+  public long getBytesWritten() {
+    return headerBytesWritten + deflater.getTotalOut() + trailerBytesWritten;
+  }
+
+  @Override
+  public void end() {
+    deflater.end();
+  }
+
+  @Override
+  public void finish() {
+    deflater.finish();
+    state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  private void init(Configuration conf) {
+    ZlibCompressor.CompressionLevel level = 
ZlibFactory.getCompressionLevel(conf);
+    ZlibCompressor.CompressionStrategy strategy = 
ZlibFactory.getCompressionStrategy(conf);
+
+    // 'true' (nowrap) => Deflater will handle raw deflate stream only
+    deflater = new Deflater(level.compressionLevel(), true);
+    deflater.setStrategy(strategy.compressionStrategy());
+
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+
+    GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

Review comment:
       not sure if this is necessary, since the array will be overwritten.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);
+    trailerBytesWritten += numAvailBytes;
+
+    if (trailerOff == GZIP_TRAILER_LEN) {
+      state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+      currentBufLen = 0;
+      headerOff = trailerOff = 0;
+    }
+
+    return numAvailBytes;
+  }
+
+  @Override
+  public long getBytesRead() {
+    return deflater.getTotalIn();
+  }
+
+  @Override
+  public long getBytesWritten() {
+    return headerBytesWritten + deflater.getTotalOut() + trailerBytesWritten;
+  }
+
+  @Override
+  public void end() {
+    deflater.end();
+  }
+
+  @Override
+  public void finish() {
+    deflater.finish();
+    state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  private void init(Configuration conf) {
+    ZlibCompressor.CompressionLevel level = 
ZlibFactory.getCompressionLevel(conf);
+    ZlibCompressor.CompressionStrategy strategy = 
ZlibFactory.getCompressionStrategy(conf);
+
+    // 'true' (nowrap) => Deflater will handle raw deflate stream only
+    deflater = new Deflater(level.compressionLevel(), true);
+    deflater.setStrategy(strategy.compressionStrategy());
+
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+
+    GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+  }
+
+  @Override
+  public void reinit(Configuration conf) {
+    init(conf);
+    crc.reset();
+    userBufOff = userBufLen = 0;
+    headerBytesWritten = trailerBytesWritten = 0;
+    currentBufLen = 0;
+    headerOff = trailerOff = 0;
+  }
+
+  @Override
+  public void reset() {
+    deflater.reset();
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+    crc.reset();
+    userBufOff = userBufLen = 0;
+    currentBufLen = 0;
+    headerOff = trailerOff = 0;
+  }
+
+  @Override
+  public void setDictionary(byte[] b, int off, int len) {
+    deflater.setDictionary(b, off, len);
+  }
+
+  @Override
+  public void setInput(byte[] b, int off, int len) {
+    if (b == null) {
+      throw new NullPointerException();
+    }
+    if (off < 0 || len < 0 || off > b.length - len) {
+      throw new ArrayIndexOutOfBoundsException();
+    }
+
+    userBuf = b;
+    userBufOff = off;
+    userBufLen = len;
+
+    deflater.reset();
+    crc.reset();
+  }
+
+  private int writeHeader(byte[] b, int off, int len) {
+    if (len <= 0) {
+      return 0;
+    }
+
+    int n = Math.min(len, 10 - headerOff);

Review comment:
       nit: use `GZIP_HEADER_LEN`?

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);

Review comment:
       I wonder what will happen if we only write part of the trailer and still 
in the `TRAILER_CRC` state. When we return to `compress` next time, we'd check:
   ```java
   if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
     ...
   }
   ```
   first and the condition will be met, then we'll start to write header again?

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+

Review comment:
       nit: extra empty line.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;

Review comment:
       nit: maybe change the variable name to `numBytesWritten` or something 
similar?

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;

Review comment:
       nit: instead of maintaining two variables, maybe we can just use one 
variable `numBytesWritten` and return it from `getBytesWritten()`.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {

Review comment:
       I'm wondering if it's better to do this in `setInput` rather than here. 
Maybe:
   
   ```java
     public void setInput(byte[] b, int off, int len) {
       if (b == null) {
         throw new NullPointerException();
       }
       if (off < 0 || len < 0 || off > b.length - len) {
         throw new ArrayIndexOutOfBoundsException();
       }
   
       deflater.reset();
       crc.reset();
   
       deflater.setInput(b, off, len);
       crc.update(b, off, len);  // CRC-32 is on uncompressed data
       currentBufLen = len;
     }
   ```
   
   with this we can also get rid of `userBuf`, `userBufOff` and `userBufLen`.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {

Review comment:
       Why can't the logic in `compress` like this:
   ```java
       if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
         // now compress it into b[]
         int deflated = deflater.deflate(b, off, len);
   
         numAvailBytes += deflated;
         off += deflated;
         len -= deflated;
     ..
   ```
   if the `deflater` hasn't consumed all the inputs, `deflater.needsInput()` 
will return false and next time it'll call `compress` again here.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);

Review comment:
       what's the value of `headerOff` in this case - is it equal to 
`GZIP_HEADER_LEN`? will it switch to `INFLATE_STREAM` state?
   ```
       // Completes header output.
       if (headerOff == GZIP_HEADER_LEN) {
         state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
       }
   ```

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,270 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = 10;
+  private final int GZIP_TRAILER_LEN = 8;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private byte[] userBuf = null;
+  private int userBufOff = 0;
+  private int userBufLen = 0;
+
+  private int headerBytesWritten = 0;
+  private int trailerBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int numAvailBytes = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      if (userBufLen <= 0) {
+        return numAvailBytes;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      headerBytesWritten += outputHeaderSize;
+
+      // Completes header output.
+      if (headerOff == GZIP_HEADER_LEN) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM;
+      }
+
+      numAvailBytes += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return numAvailBytes;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // hand off user data (or what's left of it) to Deflater--but note that
+      // Deflater may not have consumed all of previous bufferload, in which 
case
+      // userBufLen will be zero
+      if (userBufLen > 0) {
+        deflater.setInput(userBuf, userBufOff, userBufLen);
+
+        crc.update(userBuf, userBufOff, userBufLen);  // CRC-32 is on 
uncompressed data
+
+        currentBufLen = userBufLen;
+        userBufOff += userBufLen;
+        userBufLen = 0;
+      }
+
+
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      numAvailBytes += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return numAvailBytes;
+      }
+    }
+
+    numAvailBytes += writeTrailer(b, off, len);
+    trailerBytesWritten += numAvailBytes;
+
+    if (trailerOff == GZIP_TRAILER_LEN) {
+      state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+      currentBufLen = 0;
+      headerOff = trailerOff = 0;
+    }
+
+    return numAvailBytes;
+  }
+
+  @Override
+  public long getBytesRead() {
+    return deflater.getTotalIn();
+  }
+
+  @Override
+  public long getBytesWritten() {
+    return headerBytesWritten + deflater.getTotalOut() + trailerBytesWritten;
+  }
+
+  @Override
+  public void end() {
+    deflater.end();
+  }
+
+  @Override
+  public void finish() {
+    deflater.finish();
+    state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  private void init(Configuration conf) {
+    ZlibCompressor.CompressionLevel level = 
ZlibFactory.getCompressionLevel(conf);
+    ZlibCompressor.CompressionStrategy strategy = 
ZlibFactory.getCompressionStrategy(conf);
+
+    // 'true' (nowrap) => Deflater will handle raw deflate stream only
+    deflater = new Deflater(level.compressionLevel(), true);
+    deflater.setStrategy(strategy.compressionStrategy());
+
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+
+    GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

Review comment:
       I think it's better to avoid this allocation if not necessary. In this 
case `trailerOff` is always 0 so we can just reuse the array.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,251 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  // The trailer will be overwritten based on crc and output size.
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};

Review comment:
       nit: this could be `private static final`

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/SequenceFile.java
##########
@@ -1180,14 +1180,6 @@ public static Option syncInterval(int value) {
           new Metadata() : metadataOption.getValue();
       this.compress = compressionTypeOption.getValue();
       final CompressionCodec codec = compressionTypeOption.getCodec();
-      if (codec != null &&

Review comment:
       there are a few unused imports in this file.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,251 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  // The trailer will be overwritten based on crc and output size.
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = GZIP_HEADER.length;

Review comment:
       nit: these could be `static`.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,251 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  // The trailer will be overwritten based on crc and output size.
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = GZIP_HEADER.length;
+  private final int GZIP_TRAILER_LEN = GZIP_TRAILER.length;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private int numBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int compressedBytesWritten = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM &&
+            state != BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC) {
+      if (currentBufLen <= 0) {
+        return compressedBytesWritten;
+      }
+
+      int outputHeaderSize = writeHeader(b, off, len);
+      numBytesWritten += outputHeaderSize;
+
+      compressedBytesWritten += outputHeaderSize;
+
+      if (outputHeaderSize == len) {
+        return compressedBytesWritten;
+      }
+
+      off += outputHeaderSize;
+      len -= outputHeaderSize;
+    }
+
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      // now compress it into b[]
+      int deflated = deflater.deflate(b, off, len);
+
+      compressedBytesWritten += deflated;
+      off += deflated;
+      len -= deflated;
+
+      // All current input are processed. Going to output trailer.
+      if (deflater.finished()) {
+        state = BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC;
+        fillTrailer();
+      } else {
+        return compressedBytesWritten;
+      }
+    }
+
+    int outputTrailerSize = writeTrailer(b, off, len);
+    numBytesWritten += outputTrailerSize;
+
+    compressedBytesWritten += outputTrailerSize;
+
+    return compressedBytesWritten;
+  }
+
+  @Override
+  public long getBytesRead() {
+    return deflater.getTotalIn();
+  }
+
+  @Override
+  public long getBytesWritten() {
+    return numBytesWritten + deflater.getTotalOut();
+  }
+
+  @Override
+  public void end() {
+    deflater.end();
+  }
+
+  @Override
+  public void finish() {
+    deflater.finish();
+    state = BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  private void init(Configuration conf) {
+    ZlibCompressor.CompressionLevel level = 
ZlibFactory.getCompressionLevel(conf);
+    ZlibCompressor.CompressionStrategy strategy = 
ZlibFactory.getCompressionStrategy(conf);
+
+    // 'true' (nowrap) => Deflater will handle raw deflate stream only
+    deflater = new Deflater(level.compressionLevel(), true);
+    deflater.setStrategy(strategy.compressionStrategy());
+
+    state = BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC;
+  }
+
+  @Override
+  public void reinit(Configuration conf) {
+    init(conf);
+    crc.reset();
+    numBytesWritten = 0;
+    currentBufLen = 0;
+    headerOff = trailerOff = 0;
+  }
+
+  @Override
+  public void reset() {

Review comment:
       we should reset `numBytesWritten` to 0 here too. BTW I think it might be 
better to name it `numExtraBytesWritten` or something since this only count 
header and trailer.

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,251 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  // The trailer will be overwritten based on crc and output size.
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = GZIP_HEADER.length;
+  private final int GZIP_TRAILER_LEN = GZIP_TRAILER.length;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private int numBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int compressedBytesWritten = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM &&

Review comment:
       nit: maybe just `if (state == 
BuiltInGzipDecompressor.GzipStateLabel.HEADER_BASIC)`?

##########
File path: 
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/zlib/BuiltInGzipCompressor.java
##########
@@ -0,0 +1,251 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.io.compress.zlib;
+
+import java.io.IOException;
+import java.util.zip.Checksum;
+import java.util.zip.Deflater;
+import java.util.zip.GZIPOutputStream;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.io.compress.Compressor;
+import org.apache.hadoop.io.compress.DoNotPool;
+import org.apache.hadoop.util.DataChecksum;
+
+/**
+ * A {@link Compressor} based on the popular gzip compressed file format.
+ * http://www.gzip.org/
+ */
+@DoNotPool
+public class BuiltInGzipCompressor implements Compressor {
+
+  /**
+   * Fixed ten-byte gzip header. See {@link GZIPOutputStream}'s source for
+   * details.
+   */
+  private static final byte[] GZIP_HEADER = new byte[]{
+          0x1f, (byte) 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+  // The trailer will be overwritten based on crc and output size.
+  private byte[] GZIP_TRAILER = new byte[]{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
0x00, 0x00};
+
+  private final int GZIP_HEADER_LEN = GZIP_HEADER.length;
+  private final int GZIP_TRAILER_LEN = GZIP_TRAILER.length;
+
+  private Deflater deflater;
+
+  private int headerOff = 0;
+  private int trailerOff = 0;
+
+  private int numBytesWritten = 0;
+
+  private int currentBufLen = 0;
+
+  private final Checksum crc = DataChecksum.newCrc32();
+
+  private BuiltInGzipDecompressor.GzipStateLabel state;
+
+  public BuiltInGzipCompressor(Configuration conf) { init(conf); }
+
+  @Override
+  public boolean finished() {
+    // Only if the trailer is also written, it is thought as finished.
+    return deflater.finished() && state == 
BuiltInGzipDecompressor.GzipStateLabel.FINISHED;
+  }
+
+  @Override
+  public boolean needsInput() {
+    if (state == BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM) {
+      return deflater.needsInput();
+    }
+
+    return (state != BuiltInGzipDecompressor.GzipStateLabel.FINISHED);
+  }
+
+  @Override
+  public int compress(byte[] b, int off, int len) throws IOException {
+    int compressedBytesWritten = 0;
+
+    // If we are not within uncompressed data yet, output the header.
+    if (state != BuiltInGzipDecompressor.GzipStateLabel.INFLATE_STREAM &&
+            state != BuiltInGzipDecompressor.GzipStateLabel.TRAILER_CRC) {
+      if (currentBufLen <= 0) {

Review comment:
       nit: maybe move this above line 83? it's a bit strange that this is in 
the `if` clause.




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