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

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Jul 30, 2012, 08:29 UTC
Message-ID: <20120730082951.GA7702@burratino>
In-Reply-To: <3225988.4e4jhmQGr7@flomedio>

Florian Achleitner wrote:

> On Saturday 28 July 2012 02:00:31 Jonathan Nieder wrote:

>> a. use --cat-blob-fd, no FIFO

[...]

Show 11 quoted lines

>>    * Make it conditional --- only do it (1) we are not on Windows and
>>      (2) the remote helper requests backflow by advertising the
>>      import-bidi capability.
>>
>>    * Let the remote helper know what's going on by using
>>      "import-bidi" instead of "import" in the command stream to
>>      initiate the import.
>
> Generally I like your prefered solution.
> I think there's one problem:
> The pipe needs to be created before the fork, so that the fd can be inherited.

The relevant pipe already exists at that point: the remote helper's stdin.

In other words, it could work like this (just like the existing demo code, except adding a conditional based on the "capabilities" response):

	0. transport-helper.c invokes the remote helper.  This requires
	   a pipe used to send commands to the remote helper
	   (helper->in) and a pipe used to receive responses from the
	   remote helper (helper->out)

	1. transport-helper.c sends the "capabilities" command to decide
	   what to do.  The remote helper replies that it would like
	   some feedback from fast-import.

	2. transport-helper.c forks and execs git fast-import with input
	   redirected from helper->out and the cat-blob fd redirected
	   to helper->in

	3. transport-helper.c tells the remote helper to start the
	   import

	4. wait for fast-import to exit