magento 2 override UPS shipping Carrier getting Error

Question

I want to override _getXmlQuotes() function to set a condition for price based on discount but it's not working anyone has an idea about it?

i have created di.xml to override model/carrier:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
 <preference for="Magento\Ups\Model\Carrier" type="Vendor\Mymodule\Model\Carrier" />    
 </config>

Created Model to override inbuilt model of ups:

  <?php
 /**
 * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
 */
 //declare(strict_types=1);

 namespace Vendor\Module\Model;

use Magento\Quote\Model\Quote\Address\RateResult\Error;
use Magento\Quote\Model\Quote\Address\RateRequest;
use Magento\Shipping\Model\Carrier\AbstractCarrierOnline;
use Magento\Shipping\Model\Carrier\CarrierInterface;
use Magento\Shipping\Model\Rate\Result;
use Magento\Shipping\Model\Simplexml\Element;
use Magento\Ups\Helper\Config;
use Magento\Framework\Xml\Security;
use Magento\Framework\HTTP\AsyncClientInterface;

  /**
  * UPS shipping implementation
  * @SuppressWarnings(PHPMD.ExcessiveClassComplexity)
  * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
  */
 class Carrier extends \Magento\Ups\Model\Carrier
 { 


/**
 * Collect and get rates/errors
 *
 * @param RateRequest $request
 * @return Result|Error|bool
 */
public function collectRates(RateRequest $request)
{ 
    $this->setRequest($request);
    if (!$this->canCollectRates()) {
        return $this->getErrorMessage();
    }

    $this->setRequest($request);
    //To use the correct result in the callback.
    $this->_result = $result = $this->_getQuotes();

    return $this->deferredProxyFactory->create(
        [
            'deferred' => new CallbackDeferred(
                function () use ($request, $result) {
                    $this->_result = $result;
                    $this->_updateFreeMethodQuote($request);
                    return $this->getResult();
                }
            )
        ]
    );
}

/**
 * Do remote request for  and handle errors
 *
 * @return Result|null
 */
protected function _getQuotes()
{ 
    switch ($this->getConfigData('type')) {
        case 'UPS':
            return $this->_getCgiQuotes();
        case 'UPS_XML':
            return $this->_getXmlQuotes();
        default:
            break;
    }

    return null;
}

/**
 * Prepare shipping rate result based on response
 *
 * @param mixed $xmlResponse
 * @return Result
 * @SuppressWarnings(PHPMD.CyclomaticComplexity)
 * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
 * @SuppressWarnings(PHPMD.ElseExpression)
 */
protected function _parseXmlResponse($xmlResponse)
{  
    $costArr = [];
    $priceArr = [];
    if (strlen(trim($xmlResponse)) > 0) {
        $xml = new \Magento\Framework\Simplexml\Config();
        $xml->loadString($xmlResponse);
        $arr = $xml->getXpath("//RatingServiceSelectionResponse/Response/ResponseStatusCode/text()");
        $success = (int)$arr[0];
        if ($success === 1) {
            $arr = $xml->getXpath("//RatingServiceSelectionResponse/RatedShipment");
            $allowedMethods = explode(",", $this->getConfigData('allowed_methods'));

            // Negotiated rates
            $negotiatedArr = $xml->getXpath("//RatingServiceSelectionResponse/RatedShipment/NegotiatedRates");
            $negotiatedActive = $this->getConfigFlag('negotiated_active')
                && $this->getConfigData('shipper_number')
                && !empty($negotiatedArr);

            $allowedCurrencies = $this->_currencyFactory->create()->getConfigAllowCurrencies();
            foreach ($arr as $shipElement) {
                $this->processShippingRateForItem(
                    $shipElement,
                    $allowedMethods,
                    $allowedCurrencies,
                    $costArr,
                    $priceArr,
                    $negotiatedActive,
                    $xml
                );
            }
        } else {
            $arr = $xml->getXpath("//RatingServiceSelectionResponse/Response/Error/ErrorDescription/text()");
            $errorTitle = (string)$arr[0][0];
            $error = $this->_rateErrorFactory->create();
            $error->setCarrier('ups');
            $error->setCarrierTitle($this->getConfigData('title'));
            $error->setErrorMessage($this->getConfigData('specificerrmsg'));
        }
    }

    $result = $this->_rateFactory->create();

    if (empty($priceArr)) {
        $error = $this->_rateErrorFactory->create();
        $error->setCarrier('ups');
        $error->setCarrierTitle($this->getConfigData('title'));
        if ($this->getConfigData('specificerrmsg') !== '') {
            $errorTitle = $this->getConfigData('specificerrmsg');
        }
        if (!isset($errorTitle)) {
            $errorTitle = __('Cannot retrieve shipping rates');
        }
        $error->setErrorMessage($errorTitle);
        $result->append($error);
    } else { 

        foreach ($priceArr as $method => $price) {    
            $rate = $this->_rateMethodFactory->create();
            $rate->setCarrier('ups');
            $rate->setCarrierTitle($this->getConfigData('title'));
            $rate->setMethod($method);
            $methodArr = $this->getShipmentByCode($method);
            $rate->setMethodTitle($methodArr);
            $rate->setCost($costArr[$method]);

            //update price based on shipping discount
            /* $shippingDiscount = 45;   //$this->getConfigData('shipping_discount');         
            $shippingRate = ($shippingDiscount * $price)  / 100;
            $price = $price - $shippingRate; */

            $rate->setPrice($price);      
            $result->append($rate); 
        }
    }

    return $result;
}

Answer 1

A good example on magento doc about overriding a protected fn using preference - https://devdocs.magento.com/guides/v2.3/extension-dev-guide/build/di-xml-file.html

you need just the overriding function not all the things from base copy as you're extending that original class.

namespace ...;

class Success extends \Magento\Checkout\Block\Onepage\Success
{
    ...
    public function __construct(
     ..
    ) {
        parent::__construct(
          ...
        );
    }


    protected function _getXmlQuotes()
    {
       // your code 
    }
}

something like this should work