How to get the value of custom field checkout address in Carrier Model Magento 2

Question

I followed the tutorial here to make a custom field in address form checkout:

<?php
$customAttributeCode = 'custom_field';
$customField = [
    'component' => 'Magento_Ui/js/form/element/abstract',
    'config' => [
        // customScope is used to group elements within a single form (e.g. they can be validated separately)
        'customScope' => 'shippingAddress.custom_attributes',
        'customEntry' => null,
        'template' => 'ui/form/field',
        'elementTmpl' => 'ui/form/element/input',
        'tooltip' => [
            'description' => 'this is what the field is for',
        ],
    ],
    'dataScope' => 'shippingAddress.custom_attributes' . '.' . $customAttributeCode,
    'label' => 'Custom Attribute',
    'provider' => 'checkoutProvider',
    'sortOrder' => 0,
    'validation' => [
       'required-entry' => true
    ],
    'options' => [],
    'filterBy' => null,
    'customEntry' => null,
    'visible' => true,
];

$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']['children']['shippingAddress']['children']['shipping-address-fieldset']['children'][$customAttributeCode] = $customField;

the above code is showing in in checkout, but when the validation triggered to calculate the shipping method price in Model/Carrier.php that i made following tutorial in here, i'm confused how to get the value from the custom field, here's the Model/Carrier.php :

<?php
namespace Inchoo\Shipping\Model\Carrier;

use Magento\Quote\Model\Quote\Address\RateRequest;
use Magento\Shipping\Model\Rate\Result;

class Example extends \Magento\Shipping\Model\Carrier\AbstractCarrier implements
    \Magento\Shipping\Model\Carrier\CarrierInterface
{
    /**
     * @var string
     */
    protected $_code = 'example';

    /**
     * @param \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
     * @param \Magento\Quote\Model\Quote\Address\RateResult\ErrorFactory $rateErrorFactory
     * @param \Psr\Log\LoggerInterface $logger
     * @param \Magento\Shipping\Model\Rate\ResultFactory $rateResultFactory
     * @param \Magento\Quote\Model\Quote\Address\RateResult\MethodFactory $rateMethodFactory
     * @param array $data
     */
    public function __construct(
        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig,
        \Magento\Quote\Model\Quote\Address\RateResult\ErrorFactory $rateErrorFactory,
        \Psr\Log\LoggerInterface $logger,
        \Magento\Shipping\Model\Rate\ResultFactory $rateResultFactory,
        \Magento\Quote\Model\Quote\Address\RateResult\MethodFactory $rateMethodFactory,
        array $data = []
    ) {
        $this->_rateResultFactory = $rateResultFactory;
        $this->_rateMethodFactory = $rateMethodFactory;
        parent::__construct($scopeConfig, $rateErrorFactory, $logger, $data);
    }

    /**
     * @return array
     */
    public function getAllowedMethods()
    {
        return ['example' => $this->getConfigData('name')];
    }

    /**
     * @param RateRequest $request
     * @return bool|Result
     */
    public function collectRates(RateRequest $request)
    {
        if (!$this->getConfigFlag('active')) {
            return false;
        }

        /** @var \Magento\Shipping\Model\Rate\Result $result */
        $result = $this->_rateResultFactory->create();

        /** @var \Magento\Quote\Model\Quote\Address\RateResult\Method $method */
        $method = $this->_rateMethodFactory->create();

        $method->setCarrier('example');
        $method->setCarrierTitle($this->getConfigData('title'));

        $method->setMethod('example');
        $method->setMethodTitle($this->getConfigData('name'));

        /*you can fetch shipping price from different sources over some APIs, we used price from config.xml - xml node price*/
        $amount = $this->getConfigData('price');

        $method->setPrice($amount);
        $method->setCost($amount);

        $result->append($method);

        return $result;
    }
}

Answer 1

finally found the solution, using php function to get the raw json input, here's the code:

public function collectRates(RateRequest $request)
 {
   $data = json_decode(file_get_contents('php://input'), true);
   $subdistrict = $data['address']['custom_attributes']['subdistrict'];
 }