Re: How to call another program

From: Joe Smith (Joe.Smith_at_inwap.com)
Date: 05/04/04 

Date: Tue, 04 May 2004 08:50:00 GMT

Alan J. Flavell wrote:

> On Mon, 3 May 2004, Joe Smith wrote:
>
>
>>You could have part-1.pl output HTML that runs two CGIs in parallel.
>>
>> <frameset rows="100%,*">
>> <frame src="/cgi-bin/part-2.pl">
>> <frame src="http://www.domain.com/cgi-bin/copyprog.pl">
>> </frameset>
>> <noframes>
>> <body><img src="/cgi-bin/part-2.pl" width=1 height=1">
>> <img src="http://www.domain.com/cgi-bin/copyprog.pl" width=1 height=1>
>> </body>
>> </noframes>
>
>
> Was that wise? While it seems to have got the questioner off our
> backs, I'd have to say that if it were to be presented as a solution
> in a WWW group (which is where I suspect it would be more on-topic,
> since there's almost no specifically Perl-language relevance here), it
> would likely have been shot down in flames.

I did give it some thought, and decided that the expedient solution
would be worth it, if only to reduce flamage and allow other threads
of discussion to prosper.

> There's just too many imponderables being left to the client side
> (who'd be perfectly entitled to disable frames and/or images if they
> felt like it) for this to rate as a robust piece of web engineering,
> I'm afraid.

No frames: taken care of. Both no frames and no images: only the OP
would know if that would be a concern for his expected audience.
As for robustness, I expect the OP will eventually realize that he
had 95% of the solution with the script that use LWP twice.

I would have done it this way:

1) Output the HTTP and HTML headers immediately, to give the user
    feedback. This would include sending <BR>, <HR>, <P></P>, or other
    HTML tag that forces a line break, so that the browser will
    render the partial page. (No <table> at this stage.)

2) Execute an LWP request inside the CGI, with a suitable timeout
    being set. When the results come back, output more HTML, with
    another line break.

3) Do post-processing. This could be fork()+exec(), system("... &"),
    or just let the browser sit and wait for processing to complete.
    [I've seen one CGI output <HR width="10%">(pause)<HR width="20%">,
    etc as a pseudo progress bar.]

        -Joe

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