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# Copyright (c) 2013-2024 by Ron Frederick <ronf@timeheart.net> and others.
#
# This program and the accompanying materials are made available under
# the terms of the Eclipse Public License v2.0 which accompanies this
# distribution and is available at:
#
# http://www.eclipse.org/legal/epl-2.0/
#
# This program may also be made available under the following secondary
# licenses when the conditions for such availability set forth in the
# Eclipse Public License v2.0 are satisfied:
#
# GNU General Public License, Version 2.0, or any later versions of
# that license
#
# SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
#
# Contributors:
# Ron Frederick - initial implementation, API, and documentation
"""SSH compression handlers"""
from typing import Callable, List, Optional
import zlib
_cmp_algs: List[bytes] = []
_default_cmp_algs: List[bytes] = []
_cmp_params = {}
_cmp_compressors = {}
_cmp_decompressors = {}
class Compressor:
"""Base class for data compressor"""
def compress(self, data: bytes) -> Optional[bytes]:
"""Compress data"""
raise NotImplementedError
class Decompressor:
"""Base class for data decompressor"""
def decompress(self, data: bytes) -> Optional[bytes]:
"""Decompress data"""
raise NotImplementedError
_CompressorType = Callable[[], Optional[Compressor]]
_DecompressorType = Callable[[], Optional[Decompressor]]
def _none() -> None:
"""Compressor/decompressor for no compression"""
return None
class _ZLibCompress(Compressor):
"""Wrapper class to force a sync flush and handle exceptions"""
def __init__(self) -> None:
self._comp = zlib.compressobj()
def compress(self, data: bytes) -> Optional[bytes]:
"""Compress data using zlib compression with sync flush"""
try:
return self._comp.compress(data) + \
self._comp.flush(zlib.Z_SYNC_FLUSH)
except zlib.error: # pragma: no cover
return None
class _ZLibDecompress(Decompressor):
"""Wrapper class to handle exceptions"""
def __init__(self) -> None:
self._decomp = zlib.decompressobj()
def decompress(self, data: bytes) -> Optional[bytes]:
"""Decompress data using zlib compression"""
try:
return self._decomp.decompress(data)
except zlib.error: # pragma: no cover
return None
def register_compression_alg(alg: bytes, compressor: _CompressorType,
decompressor: _DecompressorType,
after_auth: bool, default: bool) -> None:
"""Register a compression algorithm"""
_cmp_algs.append(alg)
if default:
_default_cmp_algs.append(alg)
_cmp_params[alg] = after_auth
_cmp_compressors[alg] = compressor
_cmp_decompressors[alg] = decompressor
def get_compression_algs() -> List[bytes]:
"""Return supported compression algorithms"""
return _cmp_algs
def get_default_compression_algs() -> List[bytes]:
"""Return default compression algorithms"""
return _default_cmp_algs
def get_compression_params(alg: bytes) -> bool:
"""Get parameters of a compression algorithm
This function returns whether or not a compression algorithm should
be delayed until after authentication completes.
"""
return _cmp_params[alg]
def get_compressor(alg: bytes) -> Optional[Compressor]:
"""Return an instance of a compressor
This function returns an object that can be used for data compression.
"""
return _cmp_compressors[alg]()
def get_decompressor(alg: bytes) -> Optional[Decompressor]:
"""Return an instance of a decompressor
This function returns an object that can be used for data decompression.
"""
return _cmp_decompressors[alg]()
register_compression_alg(b'none',
_none, _none, False, True)
register_compression_alg(b'zlib@openssh.com',
_ZLibCompress, _ZLibDecompress, True, True)
register_compression_alg(b'zlib',
_ZLibCompress, _ZLibDecompress, False, False)
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