Subject: Re: [PATCH] archive: Store checksum correctly

From: Jonathan Nieder <[email-masked]>
Date: Tue, 23 Jul 2019 18:04:45 -0700

(cc: René Scharfe, "git archive" expert)
Matt Turner wrote:

> tar2sqfs (part of https://github.com/topics/tar2sqfs) rejects tarballs
> made with git archive with the message
>
>     invalid tar header checksum!
>
> tar2sqfs recomputes the tarball's checksum to verify it. Its checksum
> implementation agrees with GNU tar, which contains a comment that states
>
>     Fill in the checksum field.  It's formatted differently from the
>     other fields: it has [6] digits, a null, then a space ...
>
> Correcting this allows tar2sqfs to correctly process the tarballs made
> by git archive.
>
> Signed-off-by: Matt Turner <[email-masked]>
> ---
>  archive-tar.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Nice.  Is this something that can be covered in tests as well?  (See
t500* for existing "git archive" tests, and see test_lazy_prereq in case
you'd like the test to use an external tool like tar2sqfs that not all
users may have.)

Thanks,
Jonathan

(patch left unsnipped for reference)

> diff --git a/archive-tar.c b/archive-tar.c
> index 3e53aac1e6..f9a157bfd1 100644
> --- a/archive-tar.c
> +++ b/archive-tar.c
> @@ -215,7 +215,9 @@ static void prepare_header(struct archiver_args *args,
>  	memcpy(header->magic, "ustar", 6);
>  	memcpy(header->version, "00", 2);
>  
> -	xsnprintf(header->chksum, sizeof(header->chksum), "%07o", ustar_header_chksum(header));
> +	xsnprintf(header->chksum, sizeof(header->chksum), "%06o", ustar_header_chksum(header));
> +	header->chksum[6] = '\0';
> +	header->chksum[7] = ' ';
>  }
>  
>  static void write_extended_header(struct archiver_args *args,