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# Copyright (C) 2006-2011 Canonical Ltd
# Written by Robert Collins <robert.collins@canonical.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
"""Legacy breezy specific gzip tunings."""
from __future__ import absolute_import
import struct
import zlib
__all__ = ["chunks_to_gzip"]
def U32(i):
"""Return i as an unsigned integer, assuming it fits in 32 bits.
If it's >= 2GB when viewed as a 32-bit unsigned int, return a long.
"""
if i < 0:
i += 1 << 32
return i
def LOWU32(i):
"""Return the low-order 32 bits of an int, as a non-negative int."""
return i & 0xFFFFFFFF
def chunks_to_gzip(chunks, factory=zlib.compressobj,
level=zlib.Z_DEFAULT_COMPRESSION, method=zlib.DEFLATED,
width=-zlib.MAX_WBITS, mem=zlib.DEF_MEM_LEVEL,
crc32=zlib.crc32):
"""Create a gzip file containing chunks and return its content.
:param chunks: An iterable of strings. Each string can have arbitrary
layout.
"""
result = [
b'\037\213' # self.fileobj.write('\037\213') # magic header
b'\010' # self.fileobj.write('\010') # compression method
# fname = self.filename[:-3]
# flags = 0
# if fname:
# flags = FNAME
b'\x00' # self.fileobj.write(chr(flags))
b'\0\0\0\0' # write32u(self.fileobj, long(time.time()))
b'\002' # self.fileobj.write('\002')
b'\377' # self.fileobj.write('\377')
# if fname:
b'' # self.fileobj.write(fname + '\000')
]
# using a compressobj avoids a small header and trailer that the compress()
# utility function adds.
compress = factory(level, method, width, mem, 0)
crc = 0
total_len = 0
for chunk in chunks:
crc = crc32(chunk, crc)
total_len += len(chunk)
zbytes = compress.compress(chunk)
if zbytes:
result.append(zbytes)
result.append(compress.flush())
# size may exceed 2GB, or even 4GB
result.append(struct.pack("<LL", LOWU32(crc), LOWU32(total_len)))
return result
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