# PODNAME: Validation::Class::Whitepaper
# ABSTRACT: Operate with Impunity

# VERSION

__END__

=pod

=head1 NAME

Validation::Class::Whitepaper - Operate with Impunity

=head1 VERSION

version 7.900057

=head1 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.

=head1 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)

=head1 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.

=head1 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.

=head2 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;

=head2 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;

=head2 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;

=head2 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;

=head2 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;

=head2 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;

=head1 GETTING STARTED

If you are looking for a simple way to get started with L<Validation::Class>,
please review L<Validation::Class::Simple>. The instructions contained there
are also relevant for configuring any class derived from L<Validation::Class>.

=head1 ADDITIONAL INSIGHT

The following L<screencast|http://youtu.be/YCPViiB5jv0> and/or
L<slideshow|http://www.slideshare.net/slideshow/embed_code/9632123> explains
what L<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.

=head1 AUTHOR

Al Newkirk <anewkirk@ana.io>

=head1 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.

=cut