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import struct
import sys
import zlib
crc32_type = "L" if sys.version_info.major >= 3 else "l"
class GzipDecompressor(object):
"""An interface to gzip which is similar to bz2.BZ2Decompressor and
lzma.LZMADecompressor."""
def __init__(self):
self.sawheader = False
self.inbuffer = b""
self.decompressor = None
self.crc = 0
self.size = 0
def decompress(self, data):
"""
@raises ValueError: if no gzip magic is found
@raises zlib.error: from zlib invocations
"""
while True:
if self.decompressor:
data = self.decompressor.decompress(data)
self.crc = zlib.crc32(data, self.crc)
self.size += len(data)
unused_data = self.decompressor.unused_data
if not unused_data:
return data
self.decompressor = None
return data + self.decompress(unused_data)
self.inbuffer += data
skip = 10
if len(self.inbuffer) < skip:
return b""
if not self.inbuffer.startswith(b"\037\213\010"):
raise ValueError("gzip magic not found")
flag = ord(self.inbuffer[3:4])
if flag & 4:
if len(self.inbuffer) < skip + 2:
return b""
length, = struct.unpack("<H", self.inbuffer[skip:skip+2])
skip += 2 + length
for field in (8, 16):
if flag & field:
length = self.inbuffer.find(b"\0", skip)
if length < 0:
return b""
skip = length + 1
if flag & 2:
skip += 2
if len(self.inbuffer) < skip:
return b""
data = self.inbuffer[skip:]
self.inbuffer = b""
self.sawheader = True
self.decompressor = zlib.decompressobj(-zlib.MAX_WBITS)
@property
def unused_data(self):
if self.decompressor:
return self.decompressor.unused_data
elif not self.sawheader:
return self.inbuffer
else:
expect = struct.pack("<" + crc32_type + "L", self.crc, self.size)
if self.inbuffer.startswith(expect) and \
self.inbuffer[len(expect):].replace(b"\0", b"") == b"":
return b""
return self.inbuffer
def flush(self):
"""
@raises zlib.error: from zlib invocations
"""
if not self.decompressor:
return b""
return self.decompressor.flush()
def copy(self):
new = GzipDecompressor()
new.inbuffer = self.inbuffer
if self.decompressor:
new.decompressor = self.decompressor.copy()
new.sawheader = self.sawheader
new.crc = self.crc
new.size = self.size
return new
class DecompressedStream(object):
"""Turn a readable file-like into a decompressed file-like. It supports
read(optional length), tell, seek(forward only) and close."""
blocksize = 65536
def __init__(self, fileobj, decompressor):
"""
@param fileobj: a file-like object providing read(size)
@param decompressor: a bz2.BZ2Decompressor or lzma.LZMADecompressor
like object providing methods decompress and flush and an
attribute unused_data
"""
self.fileobj = fileobj
self.decompressor = decompressor
self.buff = b""
self.pos = 0
self.closed = False
def read(self, length=None):
assert not self.closed
data = True
while True:
if length is not None and len(self.buff) >= length:
ret = self.buff[:length]
self.buff = self.buff[length:]
break
elif not data: # read EOF in last iteration
ret = self.buff
self.buff = b""
break
data = self.fileobj.read(self.blocksize)
if data:
self.buff += self.decompressor.decompress(data)
else:
self.buff += self.decompressor.flush()
self.pos += len(ret)
return ret
def tell(self):
assert not self.closed
return self.pos
def seek(self, pos):
"""Forward seeks by absolute position only."""
assert not self.closed
if pos < self.pos:
raise ValueError("negative seek not allowed on decompressed stream")
while True:
left = pos - self.pos
# Reading self.buff entirely avoids string concatenation.
size = len(self.buff) or self.blocksize
if left > size:
self.read(size)
else:
self.read(left)
return
def close(self):
if not self.closed:
self.fileobj.close()
self.fileobj = None
self.decompressor = None
self.buff = b""
self.closed = True
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