Re: [PATCH v2] fetch-pack: optionally save packs to disk

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 12, 2015, 15:07 UTC
Message-ID: <xmqqmw05dkxz.fsf@gitster.dls.corp.google.com>
In-Reply-To: <557A7ABA.2000404@kdbg.org>

Johannes Sixt <j6t@kdbg.org> writes:

> What is the problem with the current fetch-pack implementation? Does
> it remove a bogus packfile after download? Does it abort during
> download when it detects a broken packfile? Does --keep not do what
> you need?

Doesn't the incoming data still go through the fattening process, though? You will not be able to inspect the byte-for-byte identical stream that came out of the server end whose packfile generation logic is suspect.

For the purpose of debugging your own new server implementation, it might be a better approach to capture the pack as it comes out at the server end, instead of doing it at the fetch-pack end as it comes in. But the approach to add this "dump" at the fetch-pack side is that it gives us a tool to diagnose problems that come from broken server (re)implementations by other people we cannot debug, i.e. "you are spewing this corrupt pack against this request; here is a dump we took to help you go fix your server".

> Instead of your approach (which forks off tee to dump a copy of the
> packfile), would it not be simpler to add an option --debug-pack
> (probably not the best name) that skips the cleanup step when a broken
> packfile is detected and prints the name of the downloaded packfile?

As long as we need to debug a thin pack that comes from the other end, that approach is not sufficient, I am afraid.

I anticipated that you'd have problem with its use of "tee". It probably can do this internally with async interface, perhaps, instead?