Hi all,
Thanks for all the input. Here a simple implementation that I've come
up
with; I'm not sure it's bullet-proof. This scenario is so common—using
open-input-output-port on a Unix filter—that I would argue that the
rw-port
design is broken; there really should be a way to close the input and
output independently. I checked back on the mailing list to the genesis
of
this feature, and there didn't seem to be a lot of discussion of the
design. Something that's analogous to open-process, which returns
multiple
values, or a hypothetical (call-with-port-input-output ARGS (lambda (in
out) ...)) would seem to be better. I'm going to try out these ideas
when I
get a bit of spare time.
(define (generate-digest str)
(call-with-values
(lambda () (open-process OPEN_BOTH "shasum" "-a" "256"))
(lambda (read-port write-port pid)
(write str write-port)
(close-port write-port)
(let ((line (read-line read-port)))
(close-port read-port)
(car (string-split line #\space))))))
Regards,
Edwin
On Mon, Jan 22, 2018 at 6:00 AM, Chris Vine <address@hidden>
wrote:
> On 01/21/2018 12:31 PM, Edwin Watkeys wrote:
>
> > Hi all,
> >
> > I'm trying to write a procedure that processes some input through a
> > unix utility. Open-input-output-pipe returns a bidirectional pipe
> > that I can both read and write to. However, there is no way that I
> > can figure out to tell the external process that input is complete,
> > as there is no way to determine the output port of the rw-port and
> > therefore no way to close it. Closing an rw-port closes both the
> > read and write ports.
> >
> > Open-input-output-port therefore seems useful for line-based
> > external processes but not for ones that function on the entirety
> > of user input e.g. wc and sort.
> >
> > Is my analysis of the situation roughly accurate?
> >
> > Regards,
> > Edwin
If you want fine-grained control, you might want to look at some of
the
procedures in guile-lib's (os process) module, and in particular the
'run-with-pipe' procedure, or using its 'run-concurrently+' procedure
with guile's 'pipe' (the parent can block on its read pipe once it has
completed writing to the child until the child process closes the
other
end of the pipe upon finishing, causing the parent to get an
eof-object
provided it has itself previously closed the write end of its read
pipe).
Otherwise if you want to stick to guile proper, you may have to do it
by
hand. As 'pipe' gives you an input and output port for each pipe
which
can be independently closed, you could use two of these with the
'dup2', 'fork' and 'execl' procedures. It's tedious though.
Chris