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Hi, I think I've found the correct solution to the problem 
(though I havn't actually tested it). Looking in tarfile.py...




358:   if self.type == "gz":


359:       self.fileobj.write(struct.pack("<l", self.crc))


360:       self.fileobj.write(struct.pack("<L", self.pos))




...shows that this error only occurs when using .gz extensions. 
Testing shows that this error occurs when self.pos > sys.
maxint*2+2, that is for files larger than 4Gb. This is not good 
since the newest tar and gzip versions can handle files larger 
than that.


   According to the gzip file format spec from www.wotsit.org, 
the last 4 bytes of a gzip file "contains the size of the original 
(uncompressed) input data modulo 2^32". All that has to be 
done is to perform this calculation prior to the call to struct.
pack. Here is my proposed fix:




358:   if self.type == "gz":


359:       self.fileobj.write(struct.pack("<l", self.crc))


360:       self.fileobj.write(struct.pack("<L", self.pos % 2**32)
)




   I also noted that in Jython 2.1 struct.pack('<L', sys.
maxint*2+2) does not raise an OverflowError but wraps around 
and returns '\x00\x00\x00\x00'. This results in the correct size 
calculation for gzip but to silent the overflow is probably not a 
good idea.




...johahn