Re: [RFC 1/4 v2] Implement a basic remote helper for svn in C.

From: Florian Achleitner <florian.achleitner.2.6.31@gmail.com>
Date: Jul 27, 2012, 07:23 UTC
Message-ID: <9398008.kKbpiTCtsb@flomedio>
In-Reply-To: <20120726145426.GB3058@burratino>

On Thursday 26 July 2012 09:54:26 Jonathan Nieder wrote:

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> 
> Since the svn remote helper relies on this, it seems worth working on,
> yeah.  As for how to spend your time (and whether to beg someone else
> to work on it instead :)): I'm not sure what's on your plate or where
> you are with respect to the original plan for the summer at the
> moment, so it would be hard for me to give useful advice about how to
> balance things.

Btw, the pipe version did already exist before I started, it was added with the cat-blob command and already used by Dmitry's remote-svn-alpha. I didn't search for design discussions in the past ..

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> 
> What did you think of the suggestion of adding a new bidi-import
> capability and command to the remote helper protocol?  I think this
> would be clean and avoid causing a regression on Windows, but it's
> easily possible I am missing something fundamental.

I don't have much overview over this topic besides the part I'm working on, like other users of fast-import. The bidi-import capability/command would have the advantage, that we don't have to bother with the pipe/fifo at all, if the remote-helper doesn't use it.

When I implemented the two variants I had the idea to pass it to the 'option' command, that fast-import already has. Anyways, specifying cat-blob-fd is not allowed via the 'option' command (see Documentation and 85c62395). It wouldn't make too much sense, because the file descriptor must be set up by the parent.

But for the fifo, it would, probably. The backward channel is only used by the commands 'cat-blob' and 'ls' of fast-import. If a remote helper wants to use them, it would could make fast-import open the pipe by sending an 'option' command with the fifo filename, otherwise it defaults to stdout (like now) and is rather useless. This would take the fifo setup out of transport-helper. The remote-helper would have to create it, if it needs it.

Apropos stdout. That leads to another idea. You already suggested that it would be easiest to only use FDs 0..2. Currently stdout and stderr of fast- import go to the shell. We could connect stdout to the remote-helper and don't need the additional channel at all. (Probably there's a good reason why they haven't done that ..) Maybe this requires many changes to fast-import and breaks existing frontends.

-- Florian