email.module

<?php
/**
 * @file
 * Module file for the email module, which creates an email address field.
 */

/**
 * Implements hook_field_info().
 */
function email_field_info() {
  return array(
    'email' => array(
      'label' => 'Email',
      'description' => t('This field stores and renders email addresses.'),
      'default_widget' => 'email_textfield',
      'default_formatter' => 'email_default',
    ),
  );
}

/**
 * Implements hook_field_validate().
 *
 * Possible error codes:
 * - 'email_invalid': The email address is not valid
 */
function email_field_validate($entity_type, $entity, $field, $instance, $langcode, $items, &$errors) {
  foreach ($items as $delta => $item) {
    if ($item['email'] != '' && !valid_email_address(trim($item['email']))) {
      $message = t('"%mail" is not a valid email address', array('%mail' => $item['email']));
      $errors[$field['field_name']][$langcode][$delta][] = array(
        'error' => 'email_invalid',
        'message' => $message,
      );
    }
  }
}

/**
 * Implements hook_field_widget_error().
 */
function email_field_widget_error($element, $error, $form, &$form_state) {
  form_error($element, $error['message']);
}

/**
 * Implements hook_field_is_empty().
 */
function email_field_is_empty($item, $field) {
  return empty($item['email']);
}

/**
 * Implements hook_field_formatter_info().
 *
 */
function email_field_formatter_info() {
  $formats = array(
    'email_default' => array(
      'label' => t('Default email link'),
      'description' => t('Display the email address as a mailto link.'),
      'field types' => array('email'),
    ),
    'email_plain' => array(
      'label' => t('Email plain text'),
      'description' => t('Display the email address as plain text.'),
      'field types' => array('email'),
    ),
  );
  return $formats;
}

/**
 * Implements hook_field_formatter_view().
 */
function email_field_formatter_view($object_type, $object, $field, $instance, $langcode, $items, $display) {
  $element = array();
  switch ($display['type']) {
    case 'email_default':
      foreach ($items as $delta => $item) {
        $output = l($item['email'], 'mailto:' . $item['email']);
        $element[$delta] = array('#markup' => $output);
      }
      break;

    case 'email_plain':
      foreach ($items as $delta => $item) {
        $element[$delta] = array('#markup' => check_plain($item['email']));
      }
      break;

  }
  return $element;
}


/**
 * Implements hook_field_widget_info().
 */
function email_field_widget_info() {
  return array(
    'email_textfield' => array(
      'label' => t('Text field'),
      'field types' => array('email'),
      'settings' => array(
        'size' => 60,
      ),
    ),
  );
}

/**
 * Implements hook_field_widget_settings_form().
 */
function email_field_widget_settings_form($field, $instance) {
  $widget = $instance['widget'];
  $settings = $widget['settings'];

  $form['size'] = array(
    '#type' => 'number',
    '#title' => t('Size of textfield'),
    '#default_value' => $settings['size'],
    '#required' => TRUE,
    '#min' => 1,
  );

  return $form;
}

/**
 * Implements hook_field_widget_form().
 */
function email_field_widget_form(&$form, &$form_state, $field, $instance, $langcode, $items, $delta, $base) {
  $element = $base;
  $element['email'] = $base + array(
    '#type' => 'email',
    '#default_value' => isset($items[$delta]['email']) ? $items[$delta]['email'] : NULL,
    '#size' => $instance['widget']['settings']['size'],
  );
  return $element;
}