NAME

CGI::Untaint - process CGI input parameters

SYNOPSIS

  use CGI::Untaint;

  my $q = new CGI;
  my $handler = CGI::Untaint->new( $q->Vars );
  my $handler2 = CGI::Untaint->new({
                INCLUDE_PATH => 'MyRecipes',
        }, $apr->parms);

  my $name     = $handler->extract(-as_printable => 'name');
  my $homepage = $handler->extract(-as_url => 'homepage');

  my $postcode = $handler->extract(-as_postcode => 'address6');

  # Create your own handler...

  package MyRecipes::CGI::Untaint::legal_age;
  use base 'CGI::Untaint::integer';
  sub is_valid { 
    shift->value > 21;
  }

  package main;
  my $age = $handler->extract(-as_legal_age => 'age');

DESCRIPTION

Dealing with large web based applications with multiple forms is a minefield. It's often hard enough to ensure you validate all your input at all, without having to worry about doing it in a consistent manner. If any of the validation rules change, you often have to alter them in many different places. And, if you want to operate taint-safe, then you're just adding even more headaches.

This module provides a simple, convenient, abstracted and extensible manner for validating and untainting the input from web forms.

You simply create a handler with a hash of your parameters (usually $q->Vars), and then iterate over the fields you wish to extract, performing whatever validations you choose. The resulting variable is guaranteed not only to be valid, but also untainted.

new

  my $handler  = CGI::Untaint->new( $q->Vars );
  my $handler2 = CGI::Untaint->new({
                INCLUDE_PATH => 'MyRecipes',
        }, $apr->parms);

The simplest way to contruct an input handler is to pass a hash of parameters (usually $q->Vars) to new(). Each parameter will then be able to be extracted later by calling an extract() method on it.

However, you may also pass a leading reference to a hash of configuration variables.

Currently the only such variable supported is 'INCLUDE_PATH', which allows you to specify a local path in which to find extraction handlers. See "LOCAL EXTRACTION HANDLERS".

extract

  my $homepage = $handler->extract(-as_url => 'homepage');
  my $state = $handler->extract(-as_us_state => 'address4');
  my $state = $handler->extract(-as_like_us_state => 'address4');

Once you have constructed your Input Handler, you call the 'extract' method on each piece of data with which you are concerned.

The takes an -as_whatever flag to state what type of data you require. This will check that the input value correctly matches the required specification, and return an untainted value. It will then call the is_valid() method, where applicable, to ensure that this doesn't just _look_ like a valid value, but actually is one.

If you want to skip this stage, then you can call -as_like_whatever which will perform the untainting but not the validation.

LOCAL EXTRACTION HANDLERS

As well as as the handlers supplied with this module for extracting data, you may also create your own. In general these should inherit from 'CGI::Untaint::object', and must provide an '_untaint_re' method which returns a compiled regular expression, suitably bracketed such that $1 will return the untainted value required.

e.g. if you often extract single digit variables, you could create

  package Mysite::CGI::Untaint::digit;
  use base 'CGI::Untaint::object';
  sub _untaint_re { qr/^(\d)$/ }
  1;

You should specify the path to 'Mysite' in the INCLUDE_PATH configuration option. (See new() above.)

When extract() is called CGI::Untaint will automatically check to see if you have an is_valid() method also, and if so will run this against the value extracted from the regular expression (available as $self->value). If this returns a true value, then the extracted value will be returned, otherwise we return undef. (is_valid() can also modify the value being returned, by assigning to $self->value)

e.g. in the above example, if you sometimes need to ensure that the digit extracted is prime, you would supply:

  sub is_valid { (1 x shift->value) !~ /^1?$|^(11+?)\1+$/ };

Now, when users call extract(), it will also check that the value is valid(), i.e. prime:

  my $number = $handler->extract(-as_digit => 'value');

A user wishing to skip the validation, but still ensure untainting can call

  my $number = $handler->extract(-as_like_digit => 'value');

Test::CGI::Untaint

If you create your own local handlers, then you may wish to explore Test::CGI::Untaint, available from the CPAN. This makes it very easy to write tests for your handler. (Thanks to Profero Ltd.)

AVAILABLE HANDLERS

This package comes with the following simplistic handlers:

  printable  - a printable string
  integer    - an integer
  hex        - a hexadecimal number (as a string)

To really make this work for you you either need to write, or download from CPAN, other handlers. Currently available handlers from CPAN include:

  CGI::Untaint::creditcard
  CGI::Untaint::date
  CGI::Untaint::email
  CGI::Untaint::isbn
  CGI::Untaint::uk_postcode
  CGI::Untaint::url

If you create any others, please let me know and I'll include them here. (Or, if you have requests for other handlers, let me know and I'll see if I can create them).

BUGS

None known yet.

SEE ALSO

CGI. perlsec. Test::CGI::Untaint.

AUTHOR

Tony Bowden, <kasei@tmtm.com>.

FEEDBACK

I'd love to hear from you if you start using this. I'd particularly like to hear any suggestions as to how to make it even better / easier etc.

COPYRIGHT

Copyright (C) 2001-2003 Tony Bowden. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

cpanm CGI::Untaint

perl -MCPAN -e shell
install CGI::Untaint