crunch-core/src/main/java/org/apache/crunch/types/avro/AvroRecordReader.java

/**
 * 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.crunch.types.avro;

import static org.apache.avro.file.DataFileConstants.MAGIC;

import java.io.EOFException;
import java.io.IOException;
import java.util.Arrays;

import org.apache.avro.Schema;
import org.apache.avro.file.DataFileReader;
import org.apache.avro.file.DataFileReader12;
import org.apache.avro.file.FileReader;
import org.apache.avro.file.SeekableInput;
import org.apache.avro.io.DatumReader;
import org.apache.avro.mapred.AvroWrapper;
import org.apache.avro.mapred.FsInput;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;

/** An {@link RecordReader} for Avro data files. */
class AvroRecordReader<T> extends RecordReader<AvroWrapper<T>, NullWritable> {

  private FileReader<T> reader;
  private long start;
  private long end;
  private AvroWrapper<T> key;
  private NullWritable value;
  private Schema schema;

  public AvroRecordReader(Schema schema) {
    this.schema = schema;
  }

  @Override
  public void initialize(InputSplit genericSplit, TaskAttemptContext context) throws IOException, InterruptedException {
    FileSplit split = (FileSplit) genericSplit;
    Configuration conf = context.getConfiguration();
    SeekableInput in = new FsInput(split.getPath(), conf);
    DatumReader<T> datumReader = AvroMode
        .fromConfiguration(context.getConfiguration())
        .getReader(schema);
    this.reader = openAvroDataFileReader(in, datumReader);
    reader.sync(split.getStart()); // sync to start
    this.start = reader.tell();
    this.end = split.getStart() + split.getLength();
  }

  @Override
  public boolean nextKeyValue() throws IOException, InterruptedException {
    if (!reader.hasNext() || reader.pastSync(end)) {
      key = null;
      value = null;
      return false;
    }
    if (key == null) {
      key = new AvroWrapper<T>();
    }
    if (value == null) {
      value = NullWritable.get();
    }
    key.datum(reader.next(key.datum()));
    return true;
  }

  @Override
  public AvroWrapper<T> getCurrentKey() throws IOException, InterruptedException {
    return key;
  }

  @Override
  public NullWritable getCurrentValue() throws IOException, InterruptedException {
    return value;
  }

  @Override
  public float getProgress() throws IOException {
    if (end == start) {
      return 0.0f;
    } else {
      return Math.min(1.0f, (getPos() - start) / (float) (end - start));
    }
  }

  public long getPos() throws IOException {
    return reader.tell();
  }

  @Override
  public void close() throws IOException {
    if (reader != null) {
      reader.close();
      reader = null;
    }
  }

  /**
   * Local patch for AVRO-2944.
   */
  private static <D> FileReader<D> openAvroDataFileReader(SeekableInput in, DatumReader<D> reader) throws IOException {
    if (in.length() < MAGIC.length)
      throw new IOException("Not an Avro data file");

    // read magic header
    byte[] magic = new byte[MAGIC.length];
    in.seek(0);
    int offset = 0;
    int length = magic.length;
    while (length > 0) {
      int bytesRead = in.read(magic, offset, length);
      if (bytesRead < 0)
        throw new EOFException("Unexpected EOF with " + length + " bytes remaining to read");

      length -= bytesRead;
      offset += bytesRead;
    }
    in.seek(0);

    if (Arrays.equals(MAGIC, magic)) // current format
      return new DataFileReader<>(in, reader);
    if (Arrays.equals(new byte[] { (byte) 'O', (byte) 'b', (byte) 'j', (byte) 0 }, magic)) // 1.2 format
      return new DataFileReader12<>(in, reader);

    throw new IOException("Not an Avro data file");
  }
}