From: Stefan Sperling <stsp@stsp.name>
Subject: Re: gotwebd: cache repos in struct server
To: Omar Polo <op@omarpolo.com>
Cc: gameoftrees@openbsd.org
Date: Thu, 1 Sep 2022 11:29:34 +0200

On Thu, Sep 01, 2022 at 11:15:55AM +0200, Omar Polo wrote:
> I see two potential problems here:
> 
> > +	if (stat(got_repo_get_path_objects_pack(repo), &sb) == -1) {
> 
> 1. possible TOCTOU?  what if the file is changed between this check
> and its actual use?

This stats the object/pack *directory* to see if anything in it
changed since we last listed this directory. If so, we list it again.

We open individual packs in this directory later, and keep them
open, so there are no TOCTOU issues with our access to those files.

We keep a cached list of existing pack files to avoid a stat on
every such file during object access, which is expensive (there can
be hundreds of pack files in some repositories if people don't keep
their repos tidy).

Packs could be deleted and new packs could appear, but modification
of an existing pack should not happen under normal circumstances.
And once have the pack file handle open and cached, the file
won't disappear until we close the handle.
If a an open pack was modified we would likely run into parsing
errors in got-read-pack and error out.