| /* |
| * 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; |
| |
| import java.io.IOException; |
| import java.io.InputStream; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| |
| /** |
| * This interface is meant to be implemented by those compression codecs |
| * which are capable to compress / de-compress a stream starting at any |
| * arbitrary position. |
| * |
| * Especially the process of de-compressing a stream starting at some arbitrary |
| * position is challenging. Most of the codecs are only able to successfully |
| * de-compress a stream, if they start from the very beginning till the end. |
| * One of the reasons is the stored state at the beginning of the stream which |
| * is crucial for de-compression. |
| * |
| * Yet there are few codecs which do not save the whole state at the beginning |
| * of the stream and hence can be used to de-compress stream starting at any |
| * arbitrary points. This interface is meant to be used by such codecs. Such |
| * codecs are highly valuable, especially in the context of Hadoop, because |
| * an input compressed file can be split and hence can be worked on by multiple |
| * machines in parallel. |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Evolving |
| public interface SplittableCompressionCodec extends CompressionCodec { |
| |
| /** |
| * During decompression, data can be read off from the decompressor in two |
| * modes, namely continuous and blocked. Few codecs (e.g. BZip2) are capable |
| * of compressing data in blocks and then decompressing the blocks. In |
| * Blocked reading mode codecs inform 'end of block' events to its caller. |
| * While in continuous mode, the caller of codecs is unaware about the blocks |
| * and uncompressed data is spilled out like a continuous stream. |
| */ |
| public enum READ_MODE {CONTINUOUS, BYBLOCK}; |
| |
| /** |
| * Create a stream as dictated by the readMode. This method is used when |
| * the codecs wants the ability to work with the underlying stream positions. |
| * |
| * @param seekableIn The seekable input stream (seeks in compressed data) |
| * @param start The start offset into the compressed stream. May be changed |
| * by the underlying codec. |
| * @param end The end offset into the compressed stream. May be changed by |
| * the underlying codec. |
| * @param readMode Controls whether stream position is reported continuously |
| * from the compressed stream only only at block boundaries. |
| * @return a stream to read uncompressed bytes from |
| */ |
| SplitCompressionInputStream createInputStream(InputStream seekableIn, |
| Decompressor decompressor, long start, long end, READ_MODE readMode) |
| throws IOException; |
| |
| } |