Restrict email addresses on Gravity forms register sign up.

sl_email_domain_validator.php

<?php

/*
 *
 *  Include a list of valid domains for Gravity Form Email fields.
 *
 * @version   1.4
 * @author    Matt Neal <[email protected]>
 * @license   GPL-2.0+
*/
class sl_Email_Domain_Validator {
  
    private $_args;
  
    function __construct($args) {
  
    	$this->_args = wp_parse_args( $args, [
    	    'form_id' => false,
    	    'field_id' => false,
    	    'domains' => false,
    	    'validation_message' => __( 'Sorry, <strong>%s</strong> email accounts are not eligible for this form.' ),
    	    'mode' => 'ban' // also accepts "limit"
		] );
  
        // convert field ID to an array for consistency, it can be passed as an array or a single ID
        if($this->_args['field_id'] && !is_array($this->_args['field_id']))
        	$this->_args['field_id'] = array($this->_args['field_id']);

        	$form_filter = $this->_args['form_id'] ? "_{$this->_args['form_id']}" : '';

        add_filter("gform_validation{$form_filter}", array($this, 'validate'));
  
    }
  
    function validate($validation_result) {
  
        $form = $validation_result['form'];
  
        foreach($form['fields'] as &$field) {
  
            // if this is not an email field, skip
            if(RGFormsModel::get_input_type($field) != 'email')
                continue;
  
            // if field ID was passed and current field is not in that array, skip
            if($this->_args['field_id'] && !in_array($field['id'], $this->_args['field_id']))
                continue;
  
            $page_number = GFFormDisplay::get_source_page( $form['id'] );
            if( $page_number > 0 && $field->pageNumber != $page_number ) {
                continue;
            }
  
            if( GFFormsModel::is_field_hidden( $form, $field, array() ) ) {
                continue;
            }
  
            $domain = $this->get_email_domain($field);
  
            // if domain is valid OR if the email field is empty, skip
            if($this->is_domain_valid($domain) || empty($domain))
                continue;
  
            $validation_result['is_valid'] = false;
            $field['failed_validation'] = true;
            $field['validation_message'] = sprintf($this->_args['validation_message'], $domain);
  
        }
  
        $validation_result['form'] = $form;
        return $validation_result;
    }
  
    function get_email_domain( $field ) {
        $email = explode( '@', rgpost( "input_{$field['id']}" ) );
        return trim( rgar( $email, 1 ) );
    }
  
    function is_domain_valid( $domain ) {
  
        $mode   = $this->_args['mode'];
        $domain = strtolower( $domain );
  
        foreach( $this->_args['domains'] as $_domain ) {
  
            $_domain = strtolower( $_domain );
            $full_match   = $domain == $_domain;
            $suffix_match = strpos( $_domain, '.' ) === 0 && $this->str_ends_with( $domain, $_domain );
            $has_match    = $full_match || $suffix_match;
  
            if( $mode == 'ban' && $has_match ) {
                return false;
            } else if( $mode == 'limit' && $has_match ) {
                return true;
            }
  
        }
  
        return $mode == 'limit' ? false : true;
    }
  
    function str_ends_with( $string, $text ) {
  
        $length      = strlen( $string );
        $text_length = strlen( $text );
  
        if( $text_length > $length ) {
            return false;
        }
  
        return substr_compare( $string, $text, $length - $text_length, $text_length ) === 0;
    }
  
}
  
/*
 * Valid email addresses and options for validation.
*/ 
class lsEmailDomainControl extends sl_Email_Domain_Validator { }

new sl_Email_Domain_Validator( [
    'form_id' => 1,
    'field_id' => 2,
    'domains' => ['nitschke.com.au', 'stafflink.com.au'],
    'validation_message' => __( 'Sorry! <strong>%s</strong> email accounts are not eligible for this form. Please use a valid email address.' ),
    'mode' => 'limit'
] );