Re: git-archive loses path info when opened with Winzip?

From: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Date: Mar 31, 2008, 19:47 UTC
Message-ID: <47F13FCE.1010502@lsrfire.ath.cx>
In-Reply-To: <47F0D215.1060700@dawes.za.net>

Rogan Dawes schrieb:

Show 13 quoted lines

> Hi folks,
> 
> I have noticed something strange with "git-archive"-created tarballs. It
> seems that Winzip has trouble parsing the paths for certain files
> correctly.
> 
> The symptom is that Winzip shows some files as having been created at
> the "top level" of the zip, without any path at all, while the rest of
> the files are within their correct directory structure.
> 
> I have attached a screenshot of a gitweb-created snapshot opened in
> Winzip 9.0 SR1 (build 6224), but it apparently happens in other (more
> recent) versions of Winzip as well.

Oh, well.

Each file in a tar archive has at least a 512-byte header. This header contains a name field, 100 bytes long. When it became clear that it would be nice to support file names longer than 100 characters, another 155 bytes in the header was designated as a prefix field (see tar.h).

The full file name is constructed by concatenating the prefix, a path separator (/) and the name field -- if a prefix exists. That's how POSIX defines it, anyway. Apparently WinZip ignores the prefix field.

7-Zip honours the prefix field, by the way. But it doesn't understand POSIX extended headers; I suspect that WinZip doesn't, too.

That probably makes the easiest way to fix this problem at git's end a non-starter. Git-archive tries to:

   1. fit the path in the name field (up to 100 bytes),
   2. in the prefix and name fields (up to 255 bytes),
   3. or if even that isn't enough it stores it in an extended header.

Now we could simply make git-archive forget the second option -- but since support for POSIX extended headers is even more scarce, this probably won't help.

The second option is to stop encoding long paths using the POSIX method and start doing it e.g. the GNU way -- or some other tar dialect that is supported more widely than the official one. NOTE: I haven't checked if WinZip understands the GNU extensions; it's possible that this problem can't be solved on git's side at all!

In any case, there are better options:

  - Don't use long file names (just kidding :).
  - Use a tar extractor that understands the prefix field, e.g. 7-Zip.
  - Use zip (but beware of its 65535 bytes name length limit! ;).
  - File a bug report with WinZip.

René