unzipping old zip archive

SvA · Post by **SvA** » 03 Mar 2007, 15:20

I tried to unpack some very old zip archives. Salamander's Zip plugin did better on it than any other unzipper i tried (pkzip 2.50, 7-zip 4.42, InfoZip's unzip 5.50, XP's built-in zip support). The archives do not contain any errors, just files compressed with methods no longer in use.

Salamander's Zip plugin still it fails on any files compressed with the Reduced method.

If you could support this, that was great, if not, no problem (it is obsolete anyway).

However, the error message displayed by the plugin confused me. It read: Error in compressed data.

This suggests to me the archive was corrupted. I would expect to see an error message stating: Unsupported compression method

If it helps, I can send you an archive (~200k) and the accompanying DOS unpacker pkunzip.exe V. 0.92 (~18k)

Post by **Jan Rysavy** » 05 Mar 2007, 14:01

Hello, please send me this ZIP archive.

Post by **Lukas Cerman** » 05 Mar 2007, 14:54

SvA,

the unreduce method is supported by our ZIP plugin, maybe the file is corrupted or in some unexpected format.

Please, could you send me it? Including the packer/unpacker software which can handle such archive?

Sincerely
Lukas Cerman

therube · Post by **therube** » 05 Mar 2007, 17:17

SvA is likely running into this situation:

Why does UnZip say "'shrink' method not supported"?

http://www.info-zip.org/FAQ.html#unshrink

Or perhaps not.
Looks like SS supports both the older Shrink & Implode (zip) compression methods.

Perhaps it was a 'reduce' algorithm?

Post by **Lukas Cerman** » 05 Mar 2007, 20:16

therube wrote:SvA is likely running into this situation:
Why does UnZip say "'shrink' method not supported"?

http://www.info-zip.org/FAQ.html#unshrink
Or perhaps not.
Looks like SS supports both the older Shrink & Implode (zip) compression methods.

Perhaps it was a 'reduce' algorithm?

All of the following compression methods are supported:

0 - The file is stored (no compression)
1 - The file is Shrunk
2 - The file is Reduced with compression factor 1
3 - The file is Reduced with compression factor 2
4 - The file is Reduced with compression factor 3
5 - The file is Reduced with compression factor 4
6 - The file is Imploded
7 - Reserved for Tokenizing compression algorithm
8 - The file is Deflated
9 - Enhanced Deflating using Deflate64(tm)

With regards
Lukas Cerman

Post by **Petr Solin** » 23 Mar 2007, 14:46

I have fixed this problem. It was bug in caching of bits read from compressed stream.