Provided by: libvalidation-class-perl_7.900054-1_all 
NAME
Validation::Class::Whitepaper - Operate with Impunity
VERSION
version 7.900054
INTRODUCTION
This whitepaper will serves as a guide to help readers understand the common data
validation issues as well as the the rationale and various usage scenarios for
Validation::Class.
Data validation is an important aspect of every application yet it is often overlooked or
neglected. Data validation should be thought of as your data input firewall, a layer that
exist between the user of your application and the application's business objects.
DATA VALIDATION PROBLEMS
The most common application security weakness is the failure to properly validate input
from the client or environment. Data validation is important because it provides security,
it allows you to ensure user supplied data is formatted properly, is within length
boundaries, contains permitted characters and adheres to business rules.
To understand the problem domain we need to first ask ourselves:
* what is data validation? and ... is that what I've been doing?
* what are the common data validation requirements?
* what are the common use-cases where validation becomes tricky?
Data validation is the process of auditing a piece of data to ensure it fits a specific
criteria. Standard data validation requirements are:
* existence checking
* range checking
* type checking
* list-lookup checking
* dependency checking
* pattern checking
* custom validation checking (business logic)
Typically when designing an application we tend to name input parameters in an arbitrarily
fashion and validate the same data at various stages during a program's execution
(duplicating logic and validation routines) in various places in the application stack.
This approach is inefficient and prone to bugs, inconsistencies and security problems.
Data can be submitted to an application in various formats and it is not always ideal, and
the option to pre-format the data is not always ideal or even possible. A few common use-
cases were validation is required and often fails (in a big big way) are as follows:
* handling arbitrarily and/or dynamically-named parameters
* handling input for batch-processing
* handling multi-type parameters (array or scalar depending on context)
* handling complex conditional validation logic
* handling multi-variant parameter names (aliases)
* handling parameter dependencies
* handling errors (reporting messages, localization, etc)
A DATA VALIDATION SOLUTION
A better approach to data validation is to first consider each parameter hitting your
application as a transmission fitting a very specific criteria and construct a data
validation layer that operates with that in mind (e.g. exactly like a network firewall).
Your data validation rules should act as filters which will accept or reject and format
the transmission for use within your application.
A proper validation framework should allow you to model data and construct validation
objects with a focus on structuring rules, reusing common declarations, defining input
filters and validating data. Its main purpose should be to properly handle data input
errors. It's ulterior motive should be to ensure consistency and promote reuse of data
validation rules.
WHY VALIDATION::CLASS
Validation::Class was built around the concept of compartmentalization and re-use. That
premise gave birth to the idea of persistent data validation rules which exist in a class
configuration which is associated with a class which acts as a validation domain for
related validation rules.
Validation classes derived from Validation::Class are typically configured using the
Validation::Class sugar functions (or keywords). Validation classes are typically defined
using the following keywords:
* field - a data validation rule that matches an input parameter
* mixin - a configuration template which can be merged with a field
* directive - a field/mixin rule corresponding to a directive class name
* filter - a custom filtering routine which transforms a field value
* method - a self-validating sub-routine w/ associated validation profile
A data validation framework exists to handle failures, it is its main function and
purpose, in-fact, the difference between a validation framework and a type-constraint
system is how it responds to errors.
There are generally two types of errors that occur in an application, user-errors which
are expected and should be handled and reported so that a user can correct the problem,
and system-errors which are unexpected and should cause the application to terminate
and/or handling the exception. Exception handling is the process of responding to the
occurrence, during computation, of exceptions (anomalous or exceptional situations).
User errors and system errors are poplar opposites. It is not always desired and/or
appropriate to crash from a failure to validate user input. The following examples should
clearly display how Validation::Class addresses key pain-points and handles common use-
cases were validation is usually quite arduous.
Dynamic Parameters
# handling arbitrary and/or dynamically-named parameters
package DynamicParameters;
use Validation::Class;
field email => {
required => 1,
pattern => qr/\@localhost$/
};
field login => {
required => 1,
min_length => 5,
alias => ['user']
};
field password => {
required => 1,
min_length => 5,
min_digits => 1,
alias => ['pass']
};
package main;
my $params = {
user => 'admin', # arbitrary
pass => 's3cret', # arbitrary
email_1 => 'admin@localhost', # dynamic created
email_2 => 'root@localhost', # dynamic created
email_3 => 'sa@localhost', # dynamic created
};
my $dp = DynamicParameters->new(params => $params);
$dp->proto->clone_field('email', $_)
for $dp->params->grep(qr/^email/)->keys
;
print $dp->validate ? "OK" : "NOT OK";
1;
Batch-Processing
# handling input for batch-processing
package BatchProcessing;
use Validation::Class;
mixin scrub => {
required => 1,
filters => ['trim', 'strip']
};
field header => {
mixin => 'scrub',
options => ['name', 'email', 'contact', 'dob', 'country'],
multiples => 1 # handle param as a scalar or arrayref
};
field name => {
mixin => 'scrub',
filters => ['titlecase'],
min_length => 2
};
field email => {
mixin => 'scrub',
min_length => 3
};
field contact => {
mixin => 'scrub',
length => 10
};
field dob => {
mixin => 'scrub',
length => 8,
pattern => '##/##/##'
};
field country => {
mixin => 'scrub'
};
package main;
my $params = {
pasted_data => q{
name email contact dob country
john john@zuzu.com 9849688899 12/05/98 UK
jim kathy kjim@zuz.com 8788888888 05/07/99 India
Federar fed@zuzu.com 4484848989 11/21/80 USA
Micheal micheal@zuzu.com 6665551212 06/10/87 USA
Kwang Kit kwang@zuzu.com 7775551212 07/09/91 India
Martin jmartin@zuzu.com 2159995959 02/06/85 India
Roheeth roheeth@zuzu.com 9596012020 01/10/89 USA
}
};
# ... there are many ways this could be parsed and validated
# ... but this is simple
my $bpi = my @pasted_lines = map { s/^\s+//; $_ } split /\n/, $params->{pasted_data};
my @headers = split /\t/, shift @pasted_lines;
my $bp = BatchProcessing->new(params => { header => [@headers] });
# validate headers first
if ($bp->validate) {
$bp->params->clear;
$bpi--;
# validate each line, halt on first bad line
while (my $line = shift @pasted_lines) {
my @data = split /\t/, $line;
for (my $i=0; $i<@data; $i++) {
$bp->params->add($headers[$i], $data[$i]);
}
last unless $bp->validate;
$bp->params->clear;
$bpi--;
}
}
print ! $bpi ? "OK" : "NOT OK";
1;
Multi-Type Parameters
# handling multi-type parameters (array or scalar depending on context)
package MultiType;
use Validation::Class;
field letter_type => {
required => 1,
options => [ 'A' .. 'Z' ],
multiples => 1 # turn on multi-type processing
};
package main;
my $mt = MultiType->new;
my $ok = 0;
$mt->params->add(letter_type => 'A');
$ok++ if $mt->validate;
$mt->params->clear->add(letter_type => ['A', 'B', 'C']);
$ok++ if $mt->validate;
print $ok == 2 ? "OK" : "NOT OK";
1;
Complex Conditions
# handling complex conditional validation logic
package ComplexCondition;
use Validation::Class;
mixin scrub => {
required => 1,
filters => ['trim', 'strip']
};
mixin flag => {
length => 1,
options => [0, 1]
};
field first_name => {
mixin => 'scrub',
filters => ['titlecase']
};
field last_name => {
mixin => 'scrub',
filters => ['titlecase']
};
field role => {
mixin => 'scrub',
filters => ['titlecase'],
options => ['Client', 'Employee', 'Administrator'],
default => 'Client'
};
field address => {
mixin => 'scrub',
required => 0,
depends_on => ['city', 'state', 'zip']
};
field city => {
mixin => 'scrub',
required => 0,
depends_on => 'address'
};
field state => {
mixin => 'scrub',
required => 0,
length => '2',
pattern => 'XX',
depends_on => 'address'
};
field zip => {
mixin => 'scrub',
required => 0,
length => '5',
pattern => '#####',
depends_on => 'address'
};
field has_mail => {
mixin => 'flag'
};
profile 'registration' => sub {
my ($self) = @_;
# address info not required unless role is client or has_mail is true
return unless $self->validate('has_mail');
$self->queue(qw/first_name last_name/);
if ($self->param('has_mail') || $self->param('role') eq 'Client') {
# depends_on directive kinda makes city, state and zip required too
$self->queue(qw/+address/);
}
my $ok = $self->validate;
$self->clear_queue;
return $ok;
};
package main;
my $ok = 0;
my $mt;
$mt = ComplexCondition->new(
first_name => 'Rachel',
last_name => 'Green'
);
# defaults to client, missing address info
$ok++ if ! $mt->validate_profile('registration');
$mt = ComplexCondition->new(
first_name => 'monica',
last_name => 'geller',
role => 'employee'
);
# filters (pre-process) role and titlecase, as employee no address needed
$ok++ if $mt->validate_profile('registration');
$mt = ComplexCondition->new(
first_name => 'phoebe',
last_name => 'buffay',
address => '123 street road',
city => 'nomans land',
state => 'zz',
zip => '54321'
);
$ok++ if $mt->validate_profile('registration');
print $ok == 3 ? "OK" : "NOT OK";
1;
Multi-Variant Parameters
# handling multi-variant parameter names (aliases)
package MultiName;
use Validation::Class;
field login => {
required => 1,
min_length => 5, # must be 5 or more chars
min_alpha => 1, # must have at-least 1 alpha char
min_digits => 1, # must have at-least 1 digit char
min_symbols => 1, # must have at-least 1 non-alphanumeric char
alias => [
'signin',
'username',
'email',
'email_address'
]
};
package main;
my $ok = 0;
# fail
$ok++ if ! MultiName->new(login => 'miso')->validate;
# nice
$ok++ if MultiName->new(login => 'm!s0_soup')->validate;
# no signin field exists, however, the alias directive pre-processing DWIM
$ok++ if MultiName->new(signin => 'm!s0_soup')->validate;
# process aliases
$ok++ if MultiName->new(params => {signin => 'm!s0_soup'})->validate;
$ok++ if MultiName->new(params => {username => 'm!s0_soup'})->validate;
$ok++ if MultiName->new(params => {email => 'm!s0_soup'})->validate;
$ok++ if MultiName->new(params => {email_address => 'm!s0_soup'})->validate;
print $ok == 7 ? "OK" : "NOT OK";
1;
Parameter Dependencies
# handling parameter dependencies
package ParamDependencies;
use Validation::Class;
mixin scrub => {
required => 1,
filters => ['trim', 'strip']
};
mixin flag => {
length => 1,
options => [0, 1]
};
field billing_address => {
mixin => 'scrub',
required => 1,
depends_on => ['billing_city', 'billing_state', 'billing_zip']
};
field billing_city => {
mixin => 'scrub',
required => 0,
depends_on => 'billing_address'
};
field billing_state => {
mixin => 'scrub',
required => 0,
length => '2',
pattern => 'XX',
depends_on => 'billing_address'
};
field billing_zip => {
mixin => 'scrub',
required => 0,
length => '5',
pattern => '#####',
depends_on => 'billing_address'
};
field shipping_address => {
mixin_field => 'billing_address',
depends_on => ['shipping_city', 'shipping_state', 'shipping_zip']
};
field shipping_city => {
mixin_field => 'billing_city',
depends_on => 'shipping_address'
};
field shipping_state => {
mixin_field => 'billing_state',
depends_on => 'shipping_address'
};
field shipping_zip => {
mixin_field => 'billing_zip',
depends_on => 'shipping_address'
};
field same_billing_shipping => {
mixin => 'flag'
};
profile 'addresses' => sub {
my ($self) = @_;
return unless $self->validate('same_billing_shipping');
# billing and shipping address always required
$self->validate(qw/+billing_address +shipping_address/);
# address must match if option is selected
if ($self->param('same_billing_shipping')) {
foreach my $param ($self->params->grep(qr/^shipping_/)->keys) {
my ($suffix) = $param =~ /^shipping_(.*)/;
my $billing = $self->param("billing_$suffix");
my $shipping = $self->param("shipping_$suffix");
# shipping_* must match billing_*
unless ($billing eq $shipping) {
$self->errors->add(
"Billing and shipping addresses do not match"
);
last;
}
}
}
return $self->error_count ? 0 : 1;
};
package main;
my $ok = 0;
my $pd;
$pd = ParamDependencies->new(
billing_address => '10 liberty boulevard',
billing_city => 'malvern',
billing_state => 'pa',
billing_zip => '19355'
);
# missing shipping address info
$ok++ if ! $pd->validate_profile('addresses');
$pd = ParamDependencies->new(
billing_address => '10 liberty boulevard',
billing_city => 'malvern',
billing_state => 'pa',
billing_zip => '19355',
shipping_address => '301 cherry street',
shipping_city => 'pottstown',
shipping_state => 'pa',
shipping_zip => '19464'
);
$ok++ if $pd->validate_profile('addresses');
$pd = ParamDependencies->new(
billing_address => '10 liberty boulevard',
billing_city => 'malvern',
billing_state => 'pa',
billing_zip => '19355',
same_billing_shipping => 1,
shipping_address => '301 cherry street',
shipping_city => 'pottstown',
shipping_state => 'pa',
shipping_zip => '19464'
);
# billing and shipping don't match
$ok++ if ! $pd->validate_profile('addresses');
$pd = ParamDependencies->new(
billing_address => '10 liberty boulevard',
billing_city => 'malvern',
billing_state => 'pa',
billing_zip => '19355',
same_billing_shipping => 1,
shipping_address => '10 liberty boulevard',
shipping_city => 'malvern',
shipping_state => 'pa',
shipping_zip => '19355'
);
$ok++ if $pd->validate_profile('addresses');
print $ok == 4 ? "OK" : "NOT OK";
1;
GETTING STARTED
If you are looking for a simple way to get started with Validation::Class, please review
Validation::Class::Simple. The instructions contained there are also relevant for
configuring any class derived from Validation::Class.
ADDITIONAL INSIGHT
The following screencast <http://youtu.be/YCPViiB5jv0> and/or slideshow
<http://www.slideshare.net/slideshow/embed_code/9632123> explains what Validation::Class
is, why it was created, and what it has to offer. Please note that this screencast and
slideshow was created many moons ago and some of its content may be a bit outdated.
AUTHOR
Al Newkirk <anewkirk@ana.io>
COPYRIGHT AND LICENSE
This software is copyright (c) 2011 by Al Newkirk.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.