Ovid has asked for the wisdom of the Perl Monks concerning the following question:

I am rewriting a debugging module to be object-oriented. This module makes extensive use of CGI.pm's HTML tag generation capability. As a result, it instantiates a new CGI object when my object's new() constructor is called. Unfortunately, if the calling CGI program uses the POST method to receive data, my routine's instantiation of a new CGI object will cause the data in STDIN to be read. As a result, if they create my object before a new CGI object, they lose all of their POST data!

To get around this, I try to read $ENV{'CONTENT_LENGTH'} amount of data from STDIN if the POST method is used. If read any data, I kill the program telling the user that they need to instantiate a new CGI object before they instantiate a debugging object. Here's the code: 

sub new {
    my $class  = $_[0];
    my $buffer;

    if ( $ENV{'REQUEST_METHOD'} eq 'POST' ) {
        read (STDIN, $buffer, $ENV{'CONTENT_LENGTH'});
    }

    my $cgi = CGI->new();

    if ( length $buffer ) {
        print $cgi->header( "text/plain" ) .
              "Data was read from STDIN while using the POST method.\n
+" .
              "You must instantiate a new CGI::DebugVars object AFTER\
+n" .
              "instantiating a CGI object.";
        exit;
    }
    my $objref = { _active   => 1,
                   _border   => 1,
                   _continue => 0,
                   _cgi      => $cgi,
                   _pretty_not_installed => 0 };
    bless $objref, $class;
    return $objref;
}

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My problem is that it seems like a very ugly hack. I'm really not testing to see if a CGI object already exists, I'm inferring its existence from the presense of data available in STDIN. Is there a clean way to determine if the user has already instantiated a CGI object (short of searching through the packages for one)?

I'm also wondering if it's possible that other data may be available through STDIN in a CGI script? Since my routine reads that data, it will cause a problem for the end-user's code.

Cheers,
Ovid

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Replies are listed 'Best First'.
RE: CGI object already instantiated?
by Dominus (Parson) on Nov 13, 2000 at 00:36 UTC
    You're doing way too much work. The CGI::new method will only read the POST data by default. If you specify another source of data, it won't read the POST data at all.

    Try this: 

        my $cgi = CGI->new({});

    [download]

    This tells CGI to make a new query object using the data from the anonymous hash you passed. Since there isn't any data, you get a new, empty query.

    See the documentation for the CGI::new method for more complete information.

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      It's also amazing how I could use the wrong browser and fail to log in.

      The new "Mark Dominus Approved" ;) method: 

      sub new {
    my $class  = $_[0];
    my $cgi = CGI->new({});
    my $objref = { _active   => 1,
                   _border   => 1,
                   _continue => 0,
                   _cgi      => $cgi,
                   _pretty_not_installed => 0 };
    bless $objref, $class;
    return $objref;
}

      [download]
      Much simpler, much easier, no headaches. Thanks!

      Cheers,
      Ovid

      Join the Perlmonks Setiathome Group or just go the the link and check out our stats.

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      Gah! It's amazing how simple that was. Thanks!

      Cheers, Ovid

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(tye)Re: CGI object already instantiated?
by tye (Sage) on Nov 13, 2000 at 00:32 UTC

    Two ideas. First, $INC{"CGI.pm"} won't be set until someone has done something like require CGI. So this might give you a false positive if someone has done require CGI and not use CGI but that seem pretty unlikely.

    Second, you could check if %CGI::EXPORT is empty. It appears to me that just about any flavor of use CGI will put values into %CGI::EXPORT.

    Between the two, I'd use the first one since it doesn't depend on how CGI.pm is implemented and I can't think of any reason to only require CGI.

            - tye (but my friends call me "Tye")
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