Validation::Class::Whitepaper - Operate with Impunity

       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.

       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       ago and some of its content may be a bit outdated.

       Al Newkirk <anewkirk@ana.io>

       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.

perl v5.36.0                                       2023-06-11                 Validation::Class::Whitepaper(3pm)

       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)

       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.

       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.

       Validation::Class::Whitepaper - Operate with Impunity

       version 7.900059

       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.

   DynamicParameters
           # 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-TypeParameters
           # 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;

   ComplexConditions
           # 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-VariantParameters
           # 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;

   ParameterDependencies
           # 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;