/*
* 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.commons.compress.compressors.snappy;
import java.io.IOException;
import java.io.InputStream;
import org.apache.commons.compress.compressors.lz77support.AbstractLZ77CompressorInputStream;
import org.apache.commons.compress.utils.ByteUtils;
/**
* CompressorInputStream for the raw Snappy format.
*
* <p>This implementation uses an internal buffer in order to handle
* the back-references that are at the heart of the LZ77 algorithm.
* The size of the buffer must be at least as big as the biggest
* offset used in the compressed stream. The current version of the
* Snappy algorithm as defined by Google works on 32k blocks and
* doesn't contain offsets bigger than 32k which is the default block
* size used by this class.</p>
*
* @see <a href="https://github.com/google/snappy/blob/master/format_description.txt">Snappy compressed format description</a>
* @since 1.7
*/
public class SnappyCompressorInputStream extends AbstractLZ77CompressorInputStream {
/** Mask used to determine the type of "tag" is being processed */
private static final int TAG_MASK = 0x03;
/** Default block size */
public static final int DEFAULT_BLOCK_SIZE = 32768;
/** The size of the uncompressed data */
private final int size;
/** Number of uncompressed bytes still to be read. */
private int uncompressedBytesRemaining;
/** Current state of the stream */
private State state = State.NO_BLOCK;
private boolean endReached = false;
/**
* Constructor using the default buffer size of 32k.
*
* @param is
* An InputStream to read compressed data from
*
* @throws IOException if reading fails
*/
public SnappyCompressorInputStream(final InputStream is) throws IOException {
this(is, DEFAULT_BLOCK_SIZE);
}
/**
* Constructor using a configurable buffer size.
*
* @param is
* An InputStream to read compressed data from
* @param blockSize
* The block size used in compression
*
* @throws IOException if reading fails
*/
public SnappyCompressorInputStream(final InputStream is, final int blockSize)
throws IOException {
super(is, blockSize);
uncompressedBytesRemaining = size = (int) readSize();
}
/**
* {@inheritDoc}
*/
@Override
public int read(final byte[] b, final int off, final int len) throws IOException {
if (endReached) {
return -1;
}
switch (state) {
case NO_BLOCK:
fill();
return read(b, off, len);
case IN_LITERAL:
int litLen = readLiteral(b, off, len);
if (!hasMoreDataInBlock()) {
state = State.NO_BLOCK;
}
return litLen;
case IN_BACK_REFERENCE:
int backReferenceLen = readBackReference(b, off, len);
if (!hasMoreDataInBlock()) {
state = State.NO_BLOCK;
}
return backReferenceLen;
default:
throw new IOException("Unknown stream state " + state);
}
}
/**
* Try to fill the buffer with the next block of data.
*/
private void fill() throws IOException {
if (uncompressedBytesRemaining == 0) {
endReached = true;
return;
}
int b = readOneByte();
if (b == -1) {
throw new IOException("Premature end of stream reading block start");
}
int length = 0;
int offset = 0;
switch (b & TAG_MASK) {
case 0x00:
length = readLiteralLength(b);
uncompressedBytesRemaining -= length;
startLiteral(length);
state = State.IN_LITERAL;
break;
case 0x01:
/*
* These elements can encode lengths between [4..11] bytes and
* offsets between [0..2047] bytes. (len-4) occupies three bits
* and is stored in bits [2..4] of the tag byte. The offset
* occupies 11 bits, of which the upper three are stored in the
* upper three bits ([5..7]) of the tag byte, and the lower
* eight are stored in a byte following the tag byte.
*/
length = 4 + ((b >> 2) & 0x07);
uncompressedBytesRemaining -= length;
offset = (b & 0xE0) << 3;
b = readOneByte();
if (b == -1) {
throw new IOException("Premature end of stream reading back-reference length");
}
offset |= b;
startBackReference(offset, length);
state = State.IN_BACK_REFERENCE;
break;
case 0x02:
/*
* These elements can encode lengths between [1..64] and offsets
* from [0..65535]. (len-1) occupies six bits and is stored in
* the upper six bits ([2..7]) of the tag byte. The offset is
* stored as a little-endian 16-bit integer in the two bytes
* following the tag byte.
*/
length = (b >> 2) + 1;
uncompressedBytesRemaining -= length;
offset = (int) ByteUtils.fromLittleEndian(supplier, 2);
startBackReference(offset, length);
state = State.IN_BACK_REFERENCE;
break;
case 0x03:
/*
* These are like the copies with 2-byte offsets (see previous
* subsection), except that the offset is stored as a 32-bit
* integer instead of a 16-bit integer (and thus will occupy
* four bytes).
*/
length = (b >> 2) + 1;
uncompressedBytesRemaining -= length;
offset = (int) ByteUtils.fromLittleEndian(supplier, 4) & 0x7fffffff;
startBackReference(offset, length);
state = State.IN_BACK_REFERENCE;
break;
default:
// impossible as TAG_MASK is two bits and all four possible cases have been covered
break;
}
}
/*
* For literals up to and including 60 bytes in length, the
* upper six bits of the tag byte contain (len-1). The literal
* follows immediately thereafter in the bytestream. - For
* longer literals, the (len-1) value is stored after the tag
* byte, little-endian. The upper six bits of the tag byte
* describe how many bytes are used for the length; 60, 61, 62
* or 63 for 1-4 bytes, respectively. The literal itself follows
* after the length.
*/
private int readLiteralLength(final int b) throws IOException {
int length;
switch (b >> 2) {
case 60:
length = readOneByte();
if (length == -1) {
throw new IOException("Premature end of stream reading literal length");
}
break;
case 61:
length = (int) ByteUtils.fromLittleEndian(supplier, 2);
break;
case 62:
length = (int) ByteUtils.fromLittleEndian(supplier, 3);
break;
case 63:
length = (int) ByteUtils.fromLittleEndian(supplier, 4);
break;
default:
length = b >> 2;
break;
}
return length + 1;
}
/**
* The stream starts with the uncompressed length (up to a maximum of 2^32 -
* 1), stored as a little-endian varint. Varints consist of a series of
* bytes, where the lower 7 bits are data and the upper bit is set iff there
* are more bytes to be read. In other words, an uncompressed length of 64
* would be stored as 0x40, and an uncompressed length of 2097150 (0x1FFFFE)
* would be stored as 0xFE 0xFF 0x7F.
*
* @return The size of the uncompressed data
*
* @throws IOException
* Could not read a byte
*/
private long readSize() throws IOException {
int index = 0;
long sz = 0;
int b = 0;
do {
b = readOneByte();
if (b == -1) {
throw new IOException("Premature end of stream reading size");
}
sz |= (b & 0x7f) << (index++ * 7);
} while (0 != (b & 0x80));
return sz;
}
/**
* Get the uncompressed size of the stream
*
* @return the uncompressed size
*/
@Override
public int getSize() {
return size;
}
private enum State {
NO_BLOCK, IN_LITERAL, IN_BACK_REFERENCE
}
}