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Based on a suggestion from bruce@hams.com, make a trivial change to

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allow using the 'a' flag as a mode for opening a GzipFile.  gzip
files, surprisingly enough, can be concatenated and then decompressed;
the effect is to concatenate the two chunks of data.

If we support it on writing, it should also be supported on reading.
This *wasn't* trivial, and required rearranging the code in the
reading path, particularly the _read() method.

Raise IOError instead of RuntimeError in two cases, 'Not a gzipped file'
and 'Unknown compression method'
This commit is contained in:
Andrew M. Kuchling 1999-03-25 21:49:14 +00:00
parent 52a0d7d802
commit f4f119c055
1 changed files with 67 additions and 32 deletions
Download patch file Download diff file Expand all files Collapse all files

97
Lib/gzip.py
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@ -40,11 +40,13 @@ class GzipFile:
if mode[0:1] == 'r':
self.mode = READ
self._init_read()
# Set flag indicating start of a new member
self._new_member = 1
self.extrabuf = ""
self.extrasize = 0
self.filename = filename
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
elif mode[0:1] == 'w':
elif mode[0:1] == 'w' or mode[0:1] == 'a':
self.mode = WRITE
self._init_write(filename)
self.compress = zlib.compressobj(compresslevel,
@ -59,8 +61,6 @@ class GzipFile:
if self.mode == WRITE:
self._write_gzip_header()
elif self.mode == READ:
self._read_gzip_header()
def __repr__(self):
s = repr(self.fileobj)
@ -92,16 +92,14 @@ class GzipFile:
def _init_read(self):
self.crc = zlib.crc32("")
self.size = 0
self.extrabuf = ""
self.extrasize = 0
def _read_gzip_header(self):
magic = self.fileobj.read(2)
if magic != '\037\213':
raise RuntimeError, 'Not a gzipped file'
raise IOError, 'Not a gzipped file'
method = ord( self.fileobj.read(1) )
if method != 8:
raise RuntimeError, 'Unknown compression method'
raise IOError, 'Unknown compression method'
flag = ord( self.fileobj.read(1) )
# modtime = self.fileobj.read(4)
# extraflag = self.fileobj.read(1)
@ -170,36 +168,73 @@ class GzipFile:
self.extrasize = len(buf) + self.extrasize
def _read(self, size=1024):
try:
buf = self.fileobj.read(size)
except AttributeError:
raise EOFError, "Reached EOF"
if self.fileobj is None: raise EOFError, "Reached EOF"
if self._new_member:
# If the _new_member flag is set, we have to
#
# First, check if we're at the end of the file;
# if so, it's time to stop; no more members to read.
pos = self.fileobj.tell() # Save current position
self.fileobj.seek(0, 2) # Seek to end of file
if pos == self.fileobj.tell():
self.fileobj = None
return EOFError, "Reached EOF"
else:
self.fileobj.seek( pos ) # Return to original position
self._init_read()
self._read_gzip_header()
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self._new_member = 0
# Read a chunk of data from the file
buf = self.fileobj.read(size)
# If the EOF has been reached, flush the decompression object
# and mark this object as finished.
if buf == "":
uncompress = self.decompress.flush()
if uncompress == "":
self._read_eof()
self.fileobj = None
raise EOFError, 'Reached EOF'
else:
uncompress = self.decompress.decompress(buf)
self.crc = zlib.crc32(uncompress, self.crc)
self.extrabuf = self.extrabuf + uncompress
self.extrasize = self.extrasize + len(uncompress)
self.size = self.size + len(uncompress)
self._read_eof()
self.fileobj = None
self._add_read_data( uncompress )
raise EOFError, 'Reached EOF'
uncompress = self.decompress.decompress(buf)
self._add_read_data( uncompress )
if self.decompress.unused_data != "":
# Ending case: we've come to the end of a member in the file,
# so seek back to the start of the unused data, finish up
# this member, and read a new gzip header.
# (The number of bytes to seek back is the length of the unused
# data, minus 8 because _read_eof() will rewind a further 8 bytes)
self.fileobj.seek( -len(self.decompress.unused_data)+8, 1)
# Check the CRC and file size, and set the flag so we read
# a new member on the next call
self._read_eof()
self._new_member = 1
def _add_read_data(self, data):
self.crc = zlib.crc32(data, self.crc)
self.extrabuf = self.extrabuf + data
self.extrasize = self.extrasize + len(data)
self.size = self.size + len(data)
def _read_eof(self):
# Andrew writes:
## We've read to the end of the file, so we have to rewind in order
## to reread the 8 bytes containing the CRC and the file size. The
## decompressor is smart and knows when to stop, so feeding it
## extra data is harmless.
self.fileobj.seek(-8, 2)
# We've read to the end of the file, so we have to rewind in order
# to reread the 8 bytes containing the CRC and the file size.
# We check the that the computed CRC and size of the
# uncompressed data matches the stored values.
self.fileobj.seek(-8, 1)
crc32 = read32(self.fileobj)
isize = read32(self.fileobj)
if crc32 != self.crc:
self.error = "CRC check failed"
raise ValueError, "CRC check failed"
elif isize != self.size:
self.error = "Incorrect length of data produced"
raise ValueError, "Incorrect length of data produced"
def close(self):
if self.mode == WRITE: