Re: Add Git-aware CGI for Git-aware smart HTTP transport

From: Shawn O. Pearce <spearce@spearce.org>
Date: Aug 13, 2008, 14:53 UTC
Message-ID: <20080813145341.GA3782@spearce.org>
In-Reply-To: <48A262B9.8020608@zytor.com>

[...added git ML back to thread...]

"H. Peter Anvin" <hpa@zytor.com> wrote:

Show 9 quoted lines

> Shawn O. Pearce wrote:
>> The plan I've proposed requires wedging the CGI in between the HTTP
>> server and the repository files.  Which means older dumb clients
>> get data by forking off the CGI, rather than letting the HTTP server
>> stream the file itself.
>
> Yeah, that's quite a bit unfortunate, because it means some potentially  
> very expensive buffering in Apache.  That's one reason to do some kind  
> of redirection.

Hmm. So what if the "smart" protocol used a redirect to the CGI and the dumb protocol didn't use any redirects at all? I say this because I think the dumb protocol won't handle redirects well. It will do them, but it would incur a redirect on every request it makes.

So if we have the "smart" protocol perform detection by trying:

	C: HEAD /path/to/repository.git/git-http-backend HTTP/1.0

	S: HTTP/1.0 302 Found
	S: Location: /git-http/path/to/repository.git

Under Apache this server configuration can be easily handled by a mod_rewrite regex:

	RewriteRule ^(/pub/scm/.*)/git-http-backend$ /git/$1 [R,L]
	ScriptAlias /git/ /path/to/git-http-backend/

Individual users could also install the git-http-backend CGI right into their repository, in which case the CGI if invoked with no PATH_INFO can do a redirect back to itself to indicate where GIT_DIR is:

	C: HEAD /path/to/repository.git/git-http-backend HTTP/1.0

	S: HTTP/1.0 302 Found
	S: Location: /path/to/repository.git/git-http-backend/.

Individual operations can be selected by appending on the operation name, so <Location ~ > style rules can be used to apply access controls, such as:

	# Disallow push to any smart repository via ScriptAlias
	#
	<Location ~ ^/git/.*/receive-pack$>
		Order Deny,Allow
		Deny from all
	</Location>

	# Disallow push to any smart repository with CGI in tree.
	#
	<Location ~ .*/git-http-backend/./receive-pack$>
		Order Deny,Allow
		Deny from all
	</Location>

Setting this up on a server which doesn't have the power of mod_regex available would be tricky, as you need to link the CGI into every single repository you are serving. I don't know (or use) many other HTTP servers beyond Apache so I'm not sure if they can do this.

-- 
Shawn.