RE: git clone silently aborts if stdout gets a broken pipe

> -----Original Message-----
> From: git-owner@vger.kernel.org [mailto:git-owner@vger.kernel.org] On
> Behalf Of Jeff King
> Sent: den 19 september 2013 10:36
> To: Peter Kjellerstedt
> Cc: Junio C Hamano; Nguyen Thai Ngoc Duy; git@vger.kernel.org
> Subject: Re: git clone silently aborts if stdout gets a broken pipe
> 
> On Thu, Sep 19, 2013 at 09:54:38AM +0200, Peter Kjellerstedt wrote:
> 
> > > I think your perl script is somewhat questionable, as it is making
> > > assumptions about the output of git-clone, and you would do better
> to
> > > accept arbitrary-sized output
> >
> > Well, the whole idea of using Git::command_oneline() is that we
> > are only interested in the first line of output, similar to using
> > "| head -1". If we had wanted all of the output we would have used
> > Git::command() instead. Since the Git Perl module is released as a
> > part of Git, I would expect it to work as documented regardless of
> > which Git command is used with Git::command_oneline().
> 
> I think command_oneline is exactly like "| head -1" in this case. Doing
> "git clone | head -1" would also fail, and should not be used. In
> general, you do not want to put a limiting pipe on a command with side
> effects beyond output. The design of unix pipes and SIGPIPE is such that
> you can do "generate_output | head", and "generate_output" will get
> SIGPIPE and die after realizing that its writer no longer cares about
> the output. But if your command is doing something besides output, that
> assumption doesn't hold.

> Arguably, "git clone" should be taking the initiative to ignore SIGPIPE
> itself.  Its primary function is not output, but doing the clone. If
> output fails, we would want to continue the clone, not die.
> 
> By the way, did you actually want to capture the stdout of git-clone, or
> were you just trying to suppress it? Because the eventual patch I posted
> sends it to stderr, under the assumption that what used to go to stdout
> should not be captured and parsed (because it is localized and subject
> to change).

> > However, what surprised me most was that git clone failed silently
> > when it got a broken pipe.
> 
> It's not "git clone" that is doing this, I think, but rather the design
> of command_oneline. If I do:
> 
>   (sleep 1; git clone ...; echo >&2 exit=$?) | false
> 
> then I see:
> 
>   exit=141
> 
> That is, clone dies from SIGPIPE trying to write "Cloning into...". But
> command_oneline is specifically designed to ignore SIGPIPE death,
> because you would want something like:
> 
>   command_oneline("git", "rev-list", "$A..$B");
> 
> to give you the first line, and then you do not care if the rest of the
> rev-list dies due to SIGPIPE (it is a good thing, because by closing the
> pipe you are telling it that its output is not needed). It may be that
> the documentation for command_oneline can be improved to mention this
> subtlety.

> -Peff
> --
> To unsubscribe from this list: send the line "unsubscribe git" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html