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In another thread, Phil Carmody recently talked about the theoretical maximum compression ratio of zlib and about recompressing gzip data. This reminded me of a question I've had for a while. The short version is: is it possible to have a compressed archive file that contains itself and some other data as well?
For example, is there any foo.tar.gz that I could extract and get a copy of the same foo.tar.gz plus some other file(s)?
I have thought about this a little, and I'm pretty confident that it is possible in a theoretical sense. What I'd like to know is whether it's possible with any commonly-used existing archive format (.tar.gz, .tar.bz2, .tar.Z, .zip, .sit, etc.) or any other archive format not specifically designed to make it happen. :-)
I would not care if the filename changes or if it takes several rounds of extraction to get the original file back. (I believe allowing several rounds of extraction makes the whole thing equivalent to asking whether there is any foo.tar.gz that, when recursively extracted, produces an infinite amount of data.)
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