Add case for ustar header with gnu longname

[davidMcneil]

Resolves #223

When using 7zip to make an archive on Windows it creates an archive with a ustar header with entries of type GnuLongname. This PR adds support for this case.

I know very little about the tar spec. It would be great if someone could confirm that this is the correct fix. Should support also be added for ustar with GnuLonglink?

Signed-off-by: David McNeil mcneil.david2@gmail.com

[alexcrichton]

Thanks for the PR! Is this perhaps a new feature in 7zip? Would it be possible to file an issue with them indicating that it may be buggy?

[alexcrichton]

Or alternatively, if there's precedent of doing this in other libraries, then we could do that.

[davidMcneil]

Is this perhaps a new feature in 7zip?

I do not believe so. I did some more investigation. This bug also exists for archives created on linux with 7zip version 16.02 from 2016-05-21. Here are the steps to create a failing archive:

> mkdir this_is_a_folder_with_a_name_that_just_keeps_going_on_and_on_and_on_it_is_a_very_very_long_folder_name
> touch this_is_a_folder_with_a_name_that_just_keeps_going_on_and_on_and_on_it_is_a_very_very_long_folder_name/test.txt
> 7z a -ttar 7z_long_path.tar this_is_a_folder_with_a_name_that_just_keeps_going_on_and_on_and_on_it_is_a_very_very_long_folder_name/

tar x -f 7z_long_path.tar works fine so I believe 7zip is creating a valid archive.

Or alternatively, if there's precedent of doing this in other libraries, then we could do that.

I can do some investigation. What projects would you recommend looking at? libarchive?

[davidMcneil]

Is it possible the checks on the header type (1, 2, 3) should be removed (ie do not check for gnu vs ustar) and only use the entry_type in the if statements.

[davidMcneil]

It looks like libsodium treats the two formats identically identically which maybe supports the removal of the gnu vs ustar header checks as commented above.

[alexcrichton]

Ah ok that's good enough for me! In that case want to remove the check for is_gnu above and that should be good to go?

[alexcrichton]

(or actually, update it to is_gnu || is_ustar

[davidMcneil]

I updated the PR to check for both header formats.

[alexcrichton]

Thanks!