Re: [BUG] url schemes should be case-insensitive

[Jeff King <peff@peff.net>]

On Mon, Jun 25, 2018 at 11:19:51AM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > We seem to match url schemes case-sensitively:
> >
> >   $ git clone SSH://example.com/repo.git
> >   Cloning into 'repo'...
> >   fatal: Unable to find remote helper for 'SSH'
> >
> > whereas rfc3986 is clear that the scheme portion is case-insensitive.
> > We probably ought to match at least our internal ones with strcasecmp.
> 
> That may break if somebody at DevToolGroup@$BIGCOMPANY got cute and
> named their custom remote helper SSH:// that builds on top of the
> normal ssh:// protocol with something extra and gave it to their
> developers (and they named the http counterpart that has the same
> extra HTTP://, of course).

True, though I am on the fence whether that is a property worth
maintaining. AFAIK it was not planned and is just a "this is how it
happened to work" case that is (IMHO) doing the wrong thing.

c.f. https://xkcd.com/1172/

Is this a hypothetical, or do you know of a $BIGCOMPANY that uses this?
The only similar case I know of is contrib/persistent-https, where we
realized the better way to do it is:

  [url "my-custom-ssh://"]
  insteadOf = ssh://

> If we probe for git-remote-SSH first and
> then fall back to git-remote-ssh, then we won't break these people,
> though.  I agree that it may be a good bite-sized #leftoverbit
> material.

This is probably a little tricky to implement, since there is no
git-remote-ssh, and we handle it internally in a totally separate
code path. So "probe for git-remote-SSH" is probably not "try to run
it", but really "search the PATH for something plausible". That may be
good enough.

It may also interact in a funny way with our allowed-protocol code, if
"SSH" gets a pass as "ssh" under the default config, but actually runs
the otherwise-disallowed git-remote-SSH (though one would _hope_ if you
have such a git-remote-SSH that it behaves just like an ssh remote).

> > We could probably also give an advise() message in the above output,
> > suggesting that the problem is likely one of:
> >
> >   1. They misspelled the scheme.
> >
> >   2. They need to install the appropriate helper.
> >
> > This may be a good topic for somebody looking for low-hanging fruit to
> > get involved in development (I'd maybe call it a #leftoverbits, but
> > since I didn't start on it, I'm not sure if it counts as "left over" ;)).
> [..]
> It may probably be a good idea to do an advice, but I'd think
> "Untable to find remote helper for 'SSH'" may be clear enough.  If
> anything, perhaps saying "remote helper for 'SSH' protocol" would
> make it even clear?  I dunno.

I think it doesn't help much if the user does not know what a remote
helper is, or why Git is looking for one. Though at least it gives a
term to start searching for, I guess. The original motivation for my
mail was the real-world report at:

  https://github.com/git/git-scm.com/issues/1219

-Peff