Re: [PATCH] import-tars: ignore the global PAX header

From: "brian m. carlson" <sandals@crustytoothpaste.net>
To: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Johannes Schindelin <johannes.schindelin@gmx.de>
Subject: Re: [PATCH] import-tars: ignore the global PAX header
Date: Mon, 23 Mar 2020 23:25:20 +0000	[thread overview]
Message-ID: <20200323232520.GE6499@camp.crustytoothpaste.net> (raw)
In-Reply-To: <pull.577.git.1584968924555.gitgitgadget@gmail.com>

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On 2020-03-23 at 13:08:44, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <johannes.schindelin@gmx.de>
> 
> Git's own `git archive` inserts that header, but it often gets into the
> way of `import-tars.perl` e.g. when a prefix was specified (for example
> via `--prefix=my-project-1.0.0/`, or when downloading a `.tar.gz` from
> GitHub releases): this prefix _should_ be stripped.
> 
> Let's just skip it.
> 
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>     Ignore the global PAX header in import-tars.perl
>     
>     This problem came up in Pacman-related work, where PKGBUILD definitions
>     would reference the tarballs downloaded from GitHub, and patches would
>     be applied on top. To work on those patches efficiently (e.g. when an
>     upgrade to a new version of the project no longer lets those patches
>     apply), I need to be able to import those tarballs into playground
>     worktrees and work on them. I like to use 
>     contrib/fast-import/import-tars.perl for that purpose, but it really
>     needs to strip the prefix, otherwise it is too tedious to work with it.
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-577%2Fdscho%2Fimport-tars-skip-pax-header-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-577/dscho/import-tars-skip-pax-header-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/577
> 
>  contrib/fast-import/import-tars.perl | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/contrib/fast-import/import-tars.perl b/contrib/fast-import/import-tars.perl
> index e800d9f5c9c..d50ce26d5d9 100755
> --- a/contrib/fast-import/import-tars.perl
> +++ b/contrib/fast-import/import-tars.perl
> @@ -139,6 +139,8 @@
>  			print FI "\n";
>  		}
>  
> +		next if ($typeflag eq 'g'); # ignore global header
> +

In general, it isn't safe to do this.  A pax global header contains
attributes that may live in a normal extended header at a lower
priority.  So it is valid, for example, to write an mtime field in the
global header that applies to the entire archive and overrides the
ustar header block (and is overridden by a normal extended header).

I think we need a different solution for this case.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204

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