PERL Beginners - Howto check a parameter size in CGI.pm

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Howto check a parameter size in CGI.pm

Wijaya Edward

2006-05-22, 3:59 am

Hi,

Is there a way to determine the size of a parameter of a textarea or filefield in CGI.pm?
For example, given this form.

__BEGIN__
use CGI qw/:standard/;

# snip
textarea(
-name => 'some_name',
-rows => 10,
-columns => 50,
-wrap => 'physical'
);

#or

filefield(-name=>'upload_file', -size=>60)
__END__

We would like to know the size of:

param('some_name'); # of text area

and

param('upload_file') # of file field

I've tried with:
uploadInfo($file)->{'Content-Length'};

But it doesn't print anything.

Regards,
Edward

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JupiterHost.Net

2006-05-22, 7:00 pm

Wijaya Edward wrote:
> Hi,
>
> Is there a way to determine the size of a parameter of a textarea or filefield in CGI.pm?
> For example, given this form.
>
> __BEGIN__
> use CGI qw/:standard/;
>
> # snip
> textarea(
> -name => 'some_name',
> -rows => 10,
> -columns => 50,
> -wrap => 'physical'
> );
>
> #or
>
> filefield(-name=>'upload_file', -size=>60)
> __END__
>
>
> We would like to know the size of:
>
> param('some_name'); # of text area

You can't use the HTML tag's size attribute because:

a) its nbot passed in the reauest
b) even if it was it can easily be spoofed:
- say "state" has size="2" simply enter a url where
state=ajhsdbajhbcjkhasdbvkjhabdcjkhadbvj
habdfh

and its obvious that knowing it was 2 woudl be pointless and possibly
dangerous eif you were relying on it.

- same proinciple if it was passed, what woudl keep them from
spoofing it "state_size=99" obviously checking that would be pointless
at best, dangerous at worst

The best bet is to check it in your script:
if( length( param('state') ) != 2) {
die 'State must be 2 characters long!';
}

> and
>
> param('upload_file') # of file field
>

>
> I've tried with:
> uploadInfo($file)->{'Content-Length'};
>
> But it doesn't print anything.

Becaus ethere is no contetn-length header for it :)

You can read the uploaded file in in chunks and either do the length
afterwards or, my fav, throw an error when it reaches a given size
(which also stops processing it so hopefully it will do its little part
to cut down on attempts to DOS your server :)

Charles K. Clarkson

2006-05-22, 7:00 pm

Wijaya Edward wrote:

: Is there a way to determine the size of a parameter of a
: textarea or filefield in CGI.pm?

You can determine the length (using the length() function)
of a field, but not the size of the control on the form. That
information is not sent via the Common Gateway Interface. The
CGI specification is available here.

http://hoohoo.ncsa.uiuc.edu/cgi/

#!/usr/bin/perl

use strict;
use warnings;

use CGI qw/param/;

# Simulate form input.
param( foo => "Text from\na textarea control\n" );

print length param( 'foo' );

__END__

You could hide information about form field sizes
in hidden fields in the form. Here's is a meta field
hidden in a form which also has a textarea by the name
textarea_1 with 5 rows and 40 columns.

<input type="hidden" name="textarea_1_meta" value="5,40">

#!/usr/bin/perl

use strict;
use warnings;

use CGI qw/param/;

# Simulate form input.
param( textarea_1 => "Text from\na textarea control.\n" );
param( textarea_1_meta => '5,40' );

print form_field_stats( textarea_1 => 'textarea' );

sub form_field_stats {
my( $field, $type ) = @_;

return unless $type eq 'textarea';

my( $rows, $columns ) = split ',', param( $field . '_meta' );

return sprintf
qq|The textarea "$field" is %s characters long.\n| .
qq|\tIt is %s rows by %s columns wide.\n|,
length param( $field ),
$rows,
$columns;
}

__END__

HTH,

Charles K. Clarkson
--
Mobile Homes Specialist
Free Market Advocate
Web Programmer

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