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/*
* Copyright (c) 2010-2011 Michael Laudati, N1 Concepts LLC.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. The names of the authors may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL N1
* CONCEPTS LLC OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.vngx.jsch.algorithm;
/**
* Interface for defining an algorithm which supports compressing and
* decompressing byte data for an SSH session.
*
* If compression has been negotiated, the 'payload' field (and only it) will
* be compressed using the negotiated algorithm. The 'packet_length' field and
* 'mac' will be computed from the compressed payload. Encryption will be done
* after compression.
*
* Compression MAY be stateful, depending on the method. Compression MUST be
* independent for each direction, and implementations MUST allow independent
* choosing of the algorithm for each direction. In practice however, it is
* RECOMMENDED that the compression method be the same in both directions.
*
* The following compression methods are currently defined:
*
* none REQUIRED no compression
* zlib OPTIONAL ZLIB (LZ77) compression
*
*
* Note: Implementations may not be thread-safe and should
* be externally synchronized.
*
* Note: Instances should be created using the
* {@code AlgorithmManager} factory.
*
* RFC4253 - The
* Secure Shell (SSH) Transport Layer Protocol: 6.2. Compression
*
* @see org.vngx.jsch.algorithm.AlgorithmManager
*
* @author Michael Laudati
*/
public interface Compression extends Algorithm {
/** Algorithm name {@value} for using 'none' {@code Compression}. */
String COMPRESSION_NONE = "none";
/** Algorithm name {@value} for using 'zlib' {@code Compression.} */
String COMPRESSION_ZLIB = "zlib";
/** Algorithm name {@value} for using '[email protected]' {@code Compression}. */
String COMPRESSION_ZLIB_OPENSSH = "[email protected]";
/** Constant for initializing decompression mode. */
int DECOMPRESS_MODE = 0;
/** Constant for initializing compression mode. */
int COMPRESS_MODE = 1;
/**
* Initializes the compression stream with the specified mode and level.
*
* @param mode (compress or decompress)
* @param level of compression
*/
void init(int mode, int level);
/**
* Compresses the specified buffer data from offset through length.
*
* @param buffer to compress
* @param offset position in buffer
* @param length of buffer to compress
* @return compressed output length in bytes
*/
int compress(byte[] buffer, int offset, int length);
/**
* Decompresses the specified buffer data from offset through length.
*
* @param buffer to decompress
* @param offset position in buffer
* @param length in buffer (updated to hold decompressed length)
* @return decompressed data
*/
byte[] uncompress(byte[] buffer, int offset, int[] length);
}