CompressionInputStream.java

/**
 * Copyright 2013 Netflix, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.netflix.aegisthus.io.sstable.compression;

import org.xerial.snappy.SnappyOutputStream;

import javax.annotation.Nonnull;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

import static java.lang.Math.min;

/**
 * This class implements an input stream for reading Snappy compressed data of
 * the format produced by {@link SnappyOutputStream}.
 */
public class CompressionInputStream extends InputStream {
    private final byte[] buffer;
    private final CompressionMetadata cm;
    private final InputStream in;
    private final byte[] input;
    private boolean closed;
    private int position;
    private int valid;

    /**
     * Creates a Snappy input stream to read data from the specified underlying
     * input stream.
     *
     * @param in
     *            the underlying input stream
     */
    public CompressionInputStream(InputStream in, CompressionMetadata cm) {
        this.cm = cm;
        this.in = in;
        //chunkLength*2 because there are some cases where the data is larger than specified
        input = new byte[cm.chunkLength() * 2];
        buffer = new byte[cm.chunkLength() * 2];
    }

    @Override
    public int available() throws IOException {
        if (closed) {
            return 0;
        }
        if (valid > position) {
            return valid - position;
        }
        if (cm.currentLength() <= 0) {
            return 0;
        }
        readInput(cm.currentLength());
        cm.incrementChunk();
        return valid;
    }

    @Override
    public void close() throws IOException {
        try {
            in.close();
        } finally {
            if (!closed) {
                closed = true;
            }
        }
    }

    private boolean finishedReading() throws IOException {
        return available() <= 0;
    }

    @Override
    public int read() throws IOException {
        if (closed) {
            return -1;
        }
        if (finishedReading()) {
            return -1;
        }
        return buffer[position++] & 0xFF;
    }

    @Override
    public int read(@Nonnull byte[] output, int offset, int length) throws IOException {
        if (closed) {
            throw new IOException("Stream is closed");
        }

        if (length == 0) {
            return 0;
        }
        if (finishedReading()) {
            return -1;
        }

        int size = min(length, available());
        System.arraycopy(buffer, position, output, offset, size);
        position += size;
        return size;
    }

    private void readInput(int length) throws IOException {
        int offset = 0;
        while (offset < length) {
            int size = in.read(input, offset, length - offset);
            if (size == -1) {
                throw new EOFException("encountered EOF while reading block data");
            }
            offset += size;
        }
        // ignore checksum for now
        readChecksum(4);

        valid = cm.compressor().uncompress(input, 0, length, buffer, 0);
        position = 0;
    }
    
    private void readChecksum(int length) throws IOException {
        byte[] checksum = new byte[length];
        int offset = 0;
        while (offset < length) {

            int size = in.read(checksum, offset, length - offset);
            if (size == -1) {
                throw new EOFException("encountered EOF while reading checksum.");
            }
            offset += size;
        }
    }

}