Re: Request for detailed documentation of git pack protocol

From: Shawn O. Pearce <spearce@spearce.org>
Date: Jun 4, 2009, 18:41 UTC
Message-ID: <20090604184109.GR3355@spearce.org>
In-Reply-To: <200906041045.11328.jnareb@gmail.com>

Jakub Narebski <jnareb@gmail.com> wrote:

Show 20 quoted lines

> Dnia ?roda 3. czerwca 2009 23:53, Tony Finch napisa?:
> > On Wed, 3 Jun 2009, Jakub Narebski wrote:
> > >
> > > Actually git accepts both lowercase and uppercase in HEXDIG (at least
> > > for pkt-length), but it prefers lowercase.
> > 
> > You should ensure that all hex digit strings follow the same rule.
> > Are SHA-1 object names case insensitive too?
> > 
> > Case insensitivity has a history of being awkward. SMTP has always had
> > case-insensitive commands, though the RFCs have always written them in
> > upper case and implementations have pretty much all emitted them in upper
> > case. See http://tools.ietf.org/html/rfc5321#section-2.4 especially the
> > caveat about broken case-sensitive implementations.
> 
> There should be no problem with pkt-length being case insensitive, as
> standard conversion routines (strtol, sprintf) accept 0-9a-fA-F for 
> base 16 / hexadecimal conversion.  The requirement here is that client
> and server SHOULD use lowercase, but MUST accept mixed case (do case
> insensitive parsing of hex4).

ACK.  This is what C Git does today.  JGit sends lower case, but
is wrong by only accepting lowercase.  I will patch it today to
accept mixed case.

> I think SHA-1 is lowercased, so mixed case should work there. Well, at
> least "git show 6096D7" (note the uppercase 'D' in shortened SHA-1 name)
> works as expected.

ACK.  Mixed case SHA-1 MUST be accepted, but lower case SHOULD
be output.

> But I do not know what are, or what should be protocol requirements.
> Should SHA-1 use lowercase, or be case insensitive?

SHA-1 SHOULD be lowercase (a-f), MUST accept a-f or A-F.

> Should commands such as "have", "want", "done" use lower case or
> be case insensitive?

These MUST be lowercase.

> Should status indicators "ACK" and "NAK" be upper case,

These MUST be uppercase. Though "ACK %s continue" MUST be mixed case, as I just wrote it.

> Should capabilities be case sensitive, and should they be
> compared case sensitive or not?

No, they are case sensitive.

Why? All of the above is the current C code implementation. We have to follow what the code does today, and it does case sensitive compares almost everywhere... except in the SHA-1 parsing.

-- 
Shawn.