74 lines
2.7 KiB
Python
74 lines
2.7 KiB
Python
# Copyright (c) 2010-2011 OpenStack, LLC.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import zlib
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import struct
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class CompressingFileReader(object):
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'''
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Wraps a file object and provides a read method that returns gzip'd data.
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One warning: if read is called with a small value, the data returned may
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be bigger than the value. In this case, the "compressed" data will be
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bigger than the original data. To solve this, use a bigger read buffer.
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An example use case:
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Given an uncompressed file on disk, provide a way to read compressed data
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without buffering the entire file data in memory. Using this class, an
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uncompressed log file could be uploaded as compressed data with chunked
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transfer encoding.
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gzip header and footer code taken from the python stdlib gzip module
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:param file_obj: File object to read from
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:param compresslevel: compression level
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'''
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def __init__(self, file_obj, compresslevel=9):
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self._f = file_obj
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self._compressor = zlib.compressobj(compresslevel,
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zlib.DEFLATED,
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-zlib.MAX_WBITS,
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zlib.DEF_MEM_LEVEL,
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0)
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self.done = False
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self.first = True
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self.crc32 = 0
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self.total_size = 0
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def read(self, *a, **kw):
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if self.done:
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return ''
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x = self._f.read(*a, **kw)
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if x:
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self.crc32 = zlib.crc32(x, self.crc32) & 0xffffffffL
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self.total_size += len(x)
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compressed = self._compressor.compress(x)
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if not compressed:
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compressed = self._compressor.flush(zlib.Z_SYNC_FLUSH)
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else:
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compressed = self._compressor.flush(zlib.Z_FINISH)
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crc32 = struct.pack("<L", self.crc32 & 0xffffffffL)
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size = struct.pack("<L", self.total_size & 0xffffffffL)
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footer = crc32 + size
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compressed += footer
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self.done = True
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if self.first:
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self.first = False
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header = '\037\213\010\000\000\000\000\000\002\377'
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compressed = header + compressed
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return compressed
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