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

From: Jonathan Nieder <[email-masked]>
Date: Wed, 1 Aug 2012 12:42:48 -0700

Hi again,

Florian Achleitner wrote:

> When the first line arrives at the remote-helper, it starts importing one line 
> at a time, leaving the remaining lines in the pipe.
> For importing it requires the data from fast-import, which would be mixed with 
> import lines or queued at the end of them.

Oh, good catch.

The way it's supposed to work is that in a bidi-import, the remote
helper reads in the entire list of refs to be imported and only once
the newline indicating that that list is over arrives starts writing
its fast-import stream.  We could make this more obvious by not
spawning fast-import until immediately before writing that newline.

This needs to be clearly documented in the git-remote-helpers(1) page
if the bidi-import command is introduced.

If a remote helper writes commands for fast-import before that newline
comes, that is a bug in the remote helper, plain and simple.  It might
be fun to diagnose this problem:

	static void pipe_drained_or_die(int fd, const char *msg)
	{
		char buf[1];
		int flags = fcntl(fd, F_GETFL);
		if (flags < 0)
			die_errno("cannot get pipe flags");
		if (fcntl(fd, F_SETFL, flags | O_NONBLOCK))
			die_errno("cannot set up non-blocking pipe read");
		if (read(fd, buf, 1) > 0)
			die("%s", msg);
		if (fcntl(fd, F_SETFL, flags))
			die_errno("cannot restore pipe flags");
	}
	...

	for (i = 0; i < nr_heads; i++) {
		write "import %s\n", to_fetch[i]->name;
	}

	if (getenv("GIT_REMOTE_HELPERS_SLOW_SANITY_CHECK"))
		sleep(1);

	pipe_drained_or_die("unexpected output from remote helper before fast-import launch");

	if (get_importer(transport, &fastimport))
		die("couldn't run fast-import");
	write_constant(data->helper->in, "\n");