Re: zeroseek and qmail

On Tue, Aug 27, 2002 at 02:28:26PM -0400, Russell Nelson allegedly wrote:
> Mark Delany writes:
>  > Strictly speaking, it doesn't follow that the fd that qmail-local
>  > gives to the delivery command has to likewise be seeakable, but in
>  > practice that's the expectation the author has as we see in things
>  > like condredirect.
> 
> Unless it's in the documentation, we must treat it as a detail of the
> implementation.  Just because Dan feels free to use that detail in his 
> set of programs, that doesn't mean that we should feel equally free.

I was going to say that a new delivery instruction, say, '>' could
signify a seekable pipeline, but it's such a trivial thing to do in
.qmail space that you wouldn't bother, eg:

| make-seekable-pipe my-command my-params


Where:

cat <<EOD >make-seekable-pipe
#! /bin/sh

set -e

# The risk to using /tmp out-weighs the auto-cleanup bennies so we do
# it ourselves by minimizing the window in which the filename exists
# in the home dir. Any failure after the rm means that the file is not
# left around.

tmp=seekable.$$
exec 3<&0 4<&1 >$tmp <$tmp
rm $tmp

cat <&3                 # Create the seekable file

# Recover stdout, close holding fds and start the real command. Note
# that stdin is already opened to the tmp file.

exec ${1+"$@"} 1<&4 3>&- 4>&-
EOD


Regards.