Subject: Re: [PATCH 3/3] gitweb: remove test when closing file descriptor

From: Jakub Narebski <[email-masked]>
Date: Thu, 16 Dec 2010 14:30:05 -0800 (PST)

Sylvain Rabot <[email-masked]> writes:

> it happens that closing file descriptor fails whereas
> the blob is perfectly readable.
> 
> Signed-off-by: Sylvain Rabot <[email-masked]>
> ---
>  gitweb/gitweb.perl |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
> index 9398475..9a885b1 100755
> --- a/gitweb/gitweb.perl
> +++ b/gitweb/gitweb.perl
> @@ -3450,8 +3450,7 @@ sub run_highlighter {
>  	my ($fd, $highlight, $syntax) = @_;
>  	return $fd unless ($highlight && defined $syntax);
>  
> -	close $fd
> -		or die_error(404, "Reading blob failed");
> +	close $fd;

Actually what I think happens is the following.  "close $fh" cannot
usually fail, unless (`perldoc -f close`):

   If the file handle came from a piped open, "close" will additionally
   return false if one of the other system calls involved fails, or if the
   program exits with non-zero status.  (If the only problem was that the
   program exited non-zero, $! will be set to 0.)  Closing a pipe also waits
   for the process executing on the pipe to complete, in case you want to
   look at the output of the pipe afterwards, and implicitly puts the exit
   status value of that command into $?.

   Prematurely closing the read end of a pipe (i.e. before the process writ-
   ing to it at the other end has closed it) will result in a SIGPIPE being
   delivered to the writer.  If the other end can't handle that, be sure to
   read all the data before closing the pipe.

In this place we close read end of pipe after at most reading a few
bytes (what -T test does), so what might happen is that writer got
SIGPIPE and "failed".  But we are not interested in this, so we can
safely ignore return from 'close'.

I think that some from above explanation should make it to commit
message.

>  	open $fd, quote_command(git_cmd(), "cat-file", "blob", $hash)." | ".
>  	          quote_command($highlight_bin).
>  	          " --xhtml --fragment --syntax $syntax |"

P.S. A better solution would be to redirect opened $fd to highlighter,
instead of closing and reopening a pipe... but I'm not sure how it
could be implemented.

-- 
Jakub Narebski
Poland
ShadeHawk on #git