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

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 26, 2018, 17:09 UTC
Message-ID: <xmqq1sctmq3d.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180626122143.GA14052@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

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>> > 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.

FWIW, I fully agree with the assessment; sorry for not saying that together with the devil's advocate comment to save a round-tip.

> 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).

True. I did not offhand recall how protocol whitelist matches the protocol name with config, but transport.c::get_protocol_config() seems to say that the <name> part of "protocol.<name>.allow" is case sensitive, and we match known-safe (and known-unsafe "ext::") protocols with strcmp() not strcasecmp(). We need to figure out the implications of allowing SSH:// not to error out but pretending as if it were ssh:// on those who have protocol.ssh.allow defined.

Show 18 quoted lines

>> > 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.

True.

	$ git clone SSH://example.com/repo.git
	fatal: unable to handle URL that begins with SSH://

would be clear enough, perhaps? At least this line of change is a small first step that would improve the situation without potential to break anybody who has been abusing the case sensitivity loophole.