org.apache.hadoop.io.compress.BlockCompressorStream.java Source code

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Here is the source code for org.apache.hadoop.io.compress.BlockCompressorStream.java

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/*
 * 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.OutputStream;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

/**
 * A {@link org.apache.hadoop.io.compress.CompressorStream} which works
 * with 'block-based' based compression algorithms, as opposed to 
 * 'stream-based' compression algorithms.
 *
 * It should be noted that this wrapper does not guarantee that blocks will
 * be sized for the compressor. If the
 * {@link org.apache.hadoop.io.compress.Compressor} requires buffering to
 * effect meaningful compression, it is responsible for it.
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public class BlockCompressorStream extends CompressorStream {

    // The 'maximum' size of input data to be compressed, to account
    // for the overhead of the compression algorithm.
    private final int MAX_INPUT_SIZE;

    /**
     * Create a {@link BlockCompressorStream}.
     * 
     * @param out stream
     * @param compressor compressor to be used
     * @param bufferSize size of buffer
     * @param compressionOverhead maximum 'overhead' of the compression 
     *                            algorithm with given bufferSize
     */
    public BlockCompressorStream(OutputStream out, Compressor compressor, int bufferSize, int compressionOverhead) {
        super(out, compressor, bufferSize);
        MAX_INPUT_SIZE = bufferSize - compressionOverhead;
    }

    /**
     * Create a {@link BlockCompressorStream} with given output-stream and 
     * compressor.
     * Use default of 512 as bufferSize and compressionOverhead of 
     * (1% of bufferSize + 12 bytes) =  18 bytes (zlib algorithm).
     * 
     * @param out stream
     * @param compressor compressor to be used
     */
    public BlockCompressorStream(OutputStream out, Compressor compressor) {
        this(out, compressor, 512, 18);
    }

    /**
     * Write the data provided to the compression codec, compressing no more
     * than the buffer size less the compression overhead as specified during
     * construction for each block.
     *
     * Each block contains the uncompressed length for the block, followed by
     * one or more length-prefixed blocks of compressed data.
     */
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        // Sanity checks
        if (compressor.finished()) {
            throw new IOException("write beyond end of stream");
        }
        if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) || ((off + len) > b.length)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }

        long limlen = compressor.getBytesRead();
        if (len + limlen > MAX_INPUT_SIZE && limlen > 0) {
            // Adding this segment would exceed the maximum size.
            // Flush data if we have it.
            finish();
            compressor.reset();
        }

        if (len > MAX_INPUT_SIZE) {
            // The data we're given exceeds the maximum size. Any data
            // we had have been flushed, so we write out this chunk in segments
            // not exceeding the maximum size until it is exhausted.
            rawWriteInt(len);
            do {
                int bufLen = Math.min(len, MAX_INPUT_SIZE);

                compressor.setInput(b, off, bufLen);
                compressor.finish();
                while (!compressor.finished()) {
                    compress();
                }
                compressor.reset();
                off += bufLen;
                len -= bufLen;
            } while (len > 0);
            return;
        }

        // Give data to the compressor
        compressor.setInput(b, off, len);
        if (!compressor.needsInput()) {
            // compressor buffer size might be smaller than the maximum
            // size, so we permit it to flush if required.
            rawWriteInt((int) compressor.getBytesRead());
            do {
                compress();
            } while (!compressor.needsInput());
        }
    }

    @Override
    public void finish() throws IOException {
        if (!compressor.finished()) {
            rawWriteInt((int) compressor.getBytesRead());
            compressor.finish();
            while (!compressor.finished()) {
                compress();
            }
        }
    }

    @Override
    protected void compress() throws IOException {
        int len = compressor.compress(buffer, 0, buffer.length);
        if (len > 0) {
            // Write out the compressed chunk
            rawWriteInt(len);
            out.write(buffer, 0, len);
        }
    }

    private void rawWriteInt(int v) throws IOException {
        out.write((v >>> 24) & 0xFF);
        out.write((v >>> 16) & 0xFF);
        out.write((v >>> 8) & 0xFF);
        out.write((v >>> 0) & 0xFF);
    }

}