I am trying to build a mod_perl handler that will spawn and keep open a Ghostscript session that will produce a page image of from a specified document. The first step is to run Ghostscript and get it to produce a single page image from a specified document. And it's been a challenge.

I am re-using some proprietary Perl code that currently works fine when running from within another script by using IPC::Open3 and using pipes to communicate with Ghostscript. Running the same code under mod_perl causes problems: mod_perl complains that it can't find method FILENO in package Apache::RequestRec, and sure enough with a little googling we find that you can't use IPC::Open3 under mod_perl.

My first choice was to use IPC::Run, which seemed to work fine in my test programs from the command line, but failed when run under mod_perl; right now it seems I'm stuffing data into the input scalar ref, but it's not getting read, and I'm not sure why. (Yes, I do pump every once in a while.) There is a debug switch for this module, but it sends the output to STDOUT, something that's not on in mod_perl.

Off to IRC, good old #perl on freenode, where on Friday Caelum suggested using Expect instead. I made up a test program, it worked a treat, the code's much cleaner, so today I plugged it in, and wound up with a similar error to the one with IPC::Open3: mod_perl hates it when someone tries to close STDIN, which is what Expect is doing.

So today, after a bit of googling I came up with this link which seemed to be what I was looking for .. unfortunately there's no code for me to look at :(

I initialize as follows:

    my ( $in, $out, $timer );
    $logger->debug("Calling start ..");
    $$self{_h} = start ( \@cmd, \$in, \$out,
      $timer = timer ( 5 ) ) or
        $logger->logdie("start returned $?:$!");
    $logger->debug("Back from start ..");

    $$self{_in}    = \$in;
    $$self{_out}   = \$out;
    $$self{_timer} = \$timer;

[download]

I am sending the data like this:

    $$self{_in} .= $thisLine . "\n";
    $$self{_h}->pump_nb;

[download]

Along the way I check out length($$self{_in}), but to my dismay it does not decrease -- there is no action.

So at this point, it seems that IPC::Run will do the trick, if I can only figure out how to unstick the input pipe going to Ghostscript, an thus produce some output, which would be useful. Any suggestions welcome.

Alex / talexb / Toronto

"Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

In reply to Trying to use IPC::Run under mod_perl by talexb

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