Re: RFC: Missing blob hook might be invoked infinitely recursively

Hi,

Jonathan Tan wrote:

Suppose you have missing blob AB12 and CD34 that you now need, so
fetch-blob is invoked. It sends the literals AB12 and CD34 to a new
server endpoint and obtains a packfile, which it then pipes through "git
index-pack". The issue is that "git index-pack" wants to try to access
AB12 and CD34 in the local repo in order to do a SHA-1 collision check,
and therefore fetch-blob is invoked once again, creating infinite
recursion.

[...]

2. Add support for an environment variable to Git that suppresses access
to the missing blob manifest, in effect, suppressing invocation of the
hook. This allows anyone (the person configuring Git or the hook writer)
to suppress this access, although they might need in-depth knowledge to
know whether the hook is meant to be run with such access suppressed or
required.

Small tweak: what if Git itself sets that environment variable when
invoking the hook?  A fetch-blob hook author can then explicitly unset
the environment variable to request recursion if they need it.

I should credit Shawn Pearce for saying this a little more clearly
offline a moment ago.

Thanks,
Jonathan