Apache Commons Compress 1.26.0 · org.apache.commons.compress.compressors.lz77support.AbstractLZ77CompressorInputStream

Encapsulates code common to LZ77 decompressors.

Assumes the stream consists of blocks of literal data and back-references (called copies) in any order. Of course the first block must be a literal block for the scheme to work - unless the prefill method has been used to provide initial data that is never returned by read but only used for back-references.

Subclasses must override the three-arg read method as the no-arg version delegates to it and the default implementation delegates to the no-arg version, leading to infinite mutual recursion and a StackOverflowError otherwise.

The contract for subclasses' read implementation is:

keep track of the current state of the stream. Is it inside a literal block or a back-reference or in-between blocks?
Use readOneByte to access the underlying stream directly.
If a new literal block starts, use startLiteral to tell this class about it and read the literal data using readLiteral until it returns 0. hasMoreDataInBlock will return false before the next call to readLiteral would return 0.
If a new back-reference starts, use startBackReference to tell this class about it and read the literal data using readBackReference until it returns 0. hasMoreDataInBlock will return false before the next call to readBackReference would return 0.
If the end of the stream has been reached, return -1 as this class' methods will never do so themselves.

readOneByte and readLiteral update the counter for bytes read.

Field Summary

Modifier and Type	Field and Description
private int	backReferenceOffset Offset of the current back-reference.
private final byte[]	buf Buffer to write decompressed bytes to for back-references, will be three times windowSize big.
private long	bytesRemaining Number of bytes still to be read from the current literal or back-reference.
private final CountingInputStream	in The underlying stream to read compressed data from
private final byte[]	oneByte
private int	readIndex Index of the next byte to be read.
private int	size Uncompressed size
protected final ByteUtils.ByteSupplier	supplier Supplier that delegates to `readOneByte`.
private final int	windowSize Size of the window - must be bigger than the biggest offset expected.
private int	writeIndex One behind the index of the last byte in the buffer that was written, i.e. the next position to write to

Constructor Summary

Access	Constructor and Description
public	AbstractLZ77CompressorInputStream(final InputStream An InputStream to read compressed data from is, final int Size of the window kept for back-references, must be bigger than the biggest offset expected. windowSize) Creates a new LZ77 input stream.

Method Summary

Modifier and Type	Method and Description
public int	available() Overrides java.io.InputStream.available. Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected.
public void	close() Overrides java.io.InputStream.close. Implements java.io.Closeable.close. Closes this input stream and releases any system resources associated with the stream.
public long	getCompressedCount() Implements org.apache.commons.compress.utils.InputStreamStatistics.getCompressedCount. Gets the amount of raw or compressed bytes read by the stream.
public int	Returns: the uncompressed size getSize() Gets the uncompressed size of the stream
protected final boolean	Returns: true if there is still data remaining inside the current block. hasMoreDataInBlock() Is there still data remaining inside the current block?
public void	prefill(final byte[] the data to fill the window with. data) Adds some initial data to fill the window with.
public int	read() Implements abstract java.io.InputStream.read. Reads the next byte of data from the input stream.
protected final int	Returns: number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass readBackReference(final byte[] buffer to write data to b, final int offset to start writing to off, final int maximum amount of data to read len) Reads data from the current back-reference.
private int	readFromBuffer(final byte[] b, final int off, final int len)
protected final int	Returns: number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass readLiteral(final byte[] buffer to write data to b, final int offset to start writing to off, final int maximum amount of data to read len) Reads data from the current literal block.
protected final int	Returns: the byte read as value between 0 and 255 or -1 if EOF has been reached. readOneByte() Reads a single byte from the real input stream and ensures the data is accounted for.
private void	slideBuffer()
protected final void	startBackReference(final int the offset of the back-reference offset, final long the length of the back-reference length) Used by subclasses to signal the next block contains a back-reference with the given coordinates.
protected final void	startLiteral(final long the length of the block length) Used by subclasses to signal the next block contains the given amount of literal data.
private void	tryToCopy(final int bytesToCopy)
private void	tryToReadLiteral(final int bytesToRead)

Inherited from org.apache.commons.compress.compressors.CompressorInputStream:: count count getBytesRead getCount getUncompressedCount pushedBackBytes

Field Detail

backReferenceOffset	back to summary
private int backReferenceOffset Offset of the current back-reference.

buf	back to summary
private final byte[] buf Buffer to write decompressed bytes to for back-references, will be three times windowSize big. Three times so we can slide the whole buffer a windowSize to the left once we've read twice windowSize and still have enough data inside of it to satisfy back-references.

buf

back to summary

private final byte[] buf

Buffer to write decompressed bytes to for back-references, will be three times windowSize big.

Three times so we can slide the whole buffer a windowSize to the left once we've read twice windowSize and still have enough data inside of it to satisfy back-references.

bytesRemaining	back to summary
private long bytesRemaining Number of bytes still to be read from the current literal or back-reference.

in	back to summary
private final CountingInputStream in The underlying stream to read compressed data from

oneByte	back to summary
private final byte[] oneByte

readIndex	back to summary
private int readIndex Index of the next byte to be read.

size	back to summary
private int size Uncompressed size

supplier	back to summary
protected final ByteUtils.ByteSupplier supplier Supplier that delegates to `readOneByte`.

windowSize	back to summary
private final int windowSize Size of the window - must be bigger than the biggest offset expected.

writeIndex	back to summary
private int writeIndex One behind the index of the last byte in the buffer that was written, i.e. the next position to write to

Constructor Detail

AbstractLZ77CompressorInputStream	back to summary
public AbstractLZ77CompressorInputStream(final InputStream is, final int windowSize) Creates a new LZ77 input stream. Parameters is:InputStream An InputStream to read compressed data from windowSize:int Size of the window kept for back-references, must be bigger than the biggest offset expected. Exceptions IllegalArgumentException: if windowSize is not bigger than 0

AbstractLZ77CompressorInputStream

back to summary

public AbstractLZ77CompressorInputStream(final InputStream is, final int windowSize)

Creates a new LZ77 input stream.

Parameters

is:InputStream: An InputStream to read compressed data from
windowSize:int: Size of the window kept for back-references, must be bigger than the biggest offset expected.

Exceptions

IllegalArgumentException:: if windowSize is not bigger than 0

Method Detail

available back to summary

available	back to summary
public int available() Overrides java.io.InputStream.available. Doc from java.io.InputStream.available. Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected. The read might be on the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. Note that while some implementations of `InputStream` will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream. A subclass's implementation of this method may choose to throw an `IOException` if this input stream has been closed by invoking the `close()` method. Returns:int an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking or `0` when it reaches the end of the input stream. Annotations @Override

public int available()

Overrides java.io.InputStream.available.

Doc from java.io.InputStream.available.

Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected. The read might be on the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

Note that while some implementations of InputStream will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.

A subclass's implementation of this method may choose to throw an IOException if this input stream has been closed by invoking the close() method.

Returns:int

an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking or 0 when it reaches the end of the input stream.

Annotations

@Override

close	back to summary
public void close() throws IOException Overrides java.io.InputStream.close. Implements java.io.Closeable.close. Doc from java.io.InputStream.close. Closes this input stream and releases any system resources associated with the stream. Annotations @Override Exceptions IOException: if an I/O error occurs.

back to summary

public void close() throws IOException

Overrides java.io.InputStream.close.

Implements java.io.Closeable.close.

Doc from java.io.InputStream.close.

Closes this input stream and releases any system resources associated with the stream.

Annotations

@Override

Exceptions

IOException:: if an I/O error occurs.

getCompressedCount	back to summary
public long getCompressedCount() Implements org.apache.commons.compress.utils.InputStreamStatistics.getCompressedCount. Doc from org.apache.commons.compress.utils.InputStreamStatistics.getCompressedCount. Gets the amount of raw or compressed bytes read by the stream. Returns:long the amount of raw or compressed bytes read by the stream. Annotations @Override Since 1.17

getCompressedCount

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public long getCompressedCount()

Implements org.apache.commons.compress.utils.InputStreamStatistics.getCompressedCount.

Doc from org.apache.commons.compress.utils.InputStreamStatistics.getCompressedCount.

Gets the amount of raw or compressed bytes read by the stream.

Returns:long

the amount of raw or compressed bytes read by the stream.

Annotations

@Override

Since

1.17

getSize	back to summary
public int getSize() Gets the uncompressed size of the stream Returns:int the uncompressed size

getSize

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public int getSize()

Gets the uncompressed size of the stream

Returns:int: the uncompressed size

hasMoreDataInBlock	back to summary
protected final boolean hasMoreDataInBlock() Is there still data remaining inside the current block? Returns:boolean true if there is still data remaining inside the current block.

hasMoreDataInBlock

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protected final boolean hasMoreDataInBlock()

Is there still data remaining inside the current block?

Returns:boolean: true if there is still data remaining inside the current block.

prefill	back to summary
public void prefill(final byte[] data) Adds some initial data to fill the window with. This is used if the stream has been cut into blocks and back-references of one block may refer to data of the previous block(s). One such example is the LZ4 frame format using block dependency. Parameters data:byte[] the data to fill the window with. Exceptions IllegalStateException: if the stream has already started to read data

prefill

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public void prefill(final byte[] data)

Adds some initial data to fill the window with.

This is used if the stream has been cut into blocks and back-references of one block may refer to data of the previous block(s). One such example is the LZ4 frame format using block dependency.

Parameters

data:byte[]: the data to fill the window with.

Exceptions

IllegalStateException:: if the stream has already started to read data

read back to summary

read	back to summary
public int read() throws IOException Implements abstract java.io.InputStream.read. Doc from java.io.InputStream.read. Reads the next byte of data from the input stream. The value byte is returned as an `int` in the range `0` to `255`. If no byte is available because the end of the stream has been reached, the value `-1` is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown. Returns:int the next byte of data, or `-1` if the end of the stream is reached. Annotations @Override Exceptions IOException: if an I/O error occurs.

public int read() throws IOException

Implements abstract java.io.InputStream.read.

Doc from java.io.InputStream.read.

Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

Returns:int

the next byte of data, or -1 if the end of the stream is reached.

Annotations

@Override

Exceptions

IOException:: if an I/O error occurs.

readBackReference back to summary

readBackReference	back to summary
protected final int readBackReference(final byte[] b, final int off, final int len) Reads data from the current back-reference. Parameters b:byte[] buffer to write data to off:int offset to start writing to len:int maximum amount of data to read Returns:int number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass Exceptions NullPointerException: if `b` is null IndexOutOfBoundsException: if `off` is negative, `len` is negative, or `len` is greater than `b.length - off`

protected final int readBackReference(final byte[] b, final int off, final int len)

Reads data from the current back-reference.

Parameters

b:byte[]: buffer to write data to
off:int: offset to start writing to
len:int: maximum amount of data to read

Returns:int

number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass

Exceptions

NullPointerException:: if b is null
IndexOutOfBoundsException:: if off is negative, len is negative, or len is greater than b.length - off

readFromBuffer	back to summary
private int readFromBuffer(final byte[] b, final int off, final int len)

readLiteral back to summary

readLiteral	back to summary
protected final int readLiteral(final byte[] b, final int off, final int len) throws IOException Reads data from the current literal block. Parameters b:byte[] buffer to write data to off:int offset to start writing to len:int maximum amount of data to read Returns:int number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass Exceptions IOException: if the underlying stream throws or signals an EOF before the amount of data promised for the block have been read NullPointerException: if `b` is null IndexOutOfBoundsException: if `off` is negative, `len` is negative, or `len` is greater than `b.length - off`

protected final int readLiteral(final byte[] b, final int off, final int len) throws IOException

Reads data from the current literal block.

Parameters

b:byte[]: buffer to write data to
off:int: offset to start writing to
len:int: maximum amount of data to read

Returns:int

number of bytes read, may be 0. Will never return -1 as EOF-detection is the responsibility of the subclass

Exceptions

IOException:: if the underlying stream throws or signals an EOF before the amount of data promised for the block have been read
NullPointerException:: if b is null
IndexOutOfBoundsException:: if off is negative, len is negative, or len is greater than b.length - off

readOneByte	back to summary
protected final int readOneByte() throws IOException Reads a single byte from the real input stream and ensures the data is accounted for. Returns:int the byte read as value between 0 and 255 or -1 if EOF has been reached. Exceptions IOException: if the underlying stream throws

readOneByte

back to summary

protected final int readOneByte() throws IOException

Reads a single byte from the real input stream and ensures the data is accounted for.

Returns:int

the byte read as value between 0 and 255 or -1 if EOF has been reached.

Exceptions

IOException:: if the underlying stream throws

slideBuffer	back to summary
private void slideBuffer()

startBackReference	back to summary
protected final void startBackReference(final int offset, final long length) Used by subclasses to signal the next block contains a back-reference with the given coordinates. Parameters offset:int the offset of the back-reference length:long the length of the back-reference Exceptions IllegalArgumentException: if offset not bigger than 0 or bigger than the number of bytes available for back-references or if length is negative

startBackReference

back to summary

protected final void startBackReference(final int offset, final long length)

Used by subclasses to signal the next block contains a back-reference with the given coordinates.

Parameters

offset:int: the offset of the back-reference
length:long: the length of the back-reference

Exceptions

IllegalArgumentException:: if offset not bigger than 0 or bigger than the number of bytes available for back-references or if length is negative

startLiteral	back to summary
protected final void startLiteral(final long length) Used by subclasses to signal the next block contains the given amount of literal data. Parameters length:long the length of the block Exceptions IllegalArgumentException: if length is negative

startLiteral

back to summary

protected final void startLiteral(final long length)

Used by subclasses to signal the next block contains the given amount of literal data.

Parameters

length:long: the length of the block

Exceptions

IllegalArgumentException:: if length is negative

tryToCopy	back to summary
private void tryToCopy(final int bytesToCopy)

tryToReadLiteral	back to summary
private void tryToReadLiteral(final int bytesToRead) throws IOException

public abstract Class AbstractLZ77CompressorInputStream

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Field Detail

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Method Detail