Parsing an EWS (Exchange Web Services) WSDL to determine the supported input headers per service operation in PHP

parse_ews_wsdl_supported_operation_input_headers.php

<?php

// The location of the EWS WSDL here (Office365 here for example)
const WSDL_URL = 'https://outlook.office365.com/EWS/Services.wsdl';

const NAMESPACE_WSDL_PREFIX = 'wsdl';
const NAMESPACE_WSDL_URI = 'http://schemas.xmlsoap.org/wsdl/';
const NAMESPACE_SOAP_PREFIX = 'soap';
const NAMESPACE_SOAP_URI = 'http://schemas.xmlsoap.org/wsdl/soap/';

const XML_OPERATION_XPATH = '/wsdl:definitions/wsdl:binding/wsdl:operation';
const XML_OPERATION_INPUT_HEADER_XPATH = 'wsdl:input/soap:header';

const OPERATION_NAME_ATTRIBUTE = 'name';
const HEADER_PART_ATTRIBUTE = 'part';

// Load the remote XML document
$xml = new SimpleXmlElement(WSDL_URL, 0, true);

// Register some element namespaces for stability in XPath queries
$xml->registerXPathNamespace(NAMESPACE_WSDL_PREFIX, NAMESPACE_WSDL_URI);
$xml->registerXPathNamespace(NAMESPACE_SOAP_PREFIX, NAMESPACE_SOAP_URI);

// Build the input header map
$operation_input_header_map = array_reduce(
    $xml->xpath(XML_OPERATION_XPATH), // Query for the WSDL binding operations
    function ($map, SimpleXmlElement $element) {
        if (!isset($element[OPERATION_NAME_ATTRIBUTE])) {
            return $map;
        }

        // Grab the name of each input header for the operation 
        $map[(string) $element[OPERATION_NAME_ATTRIBUTE]] = array_map(
            function (SimpleXmlElement $element) {
                if (!isset($element[HEADER_PART_ATTRIBUTE])) {
                    return null;
                }

                return (string) $element[HEADER_PART_ATTRIBUTE];
            },
            $element->xpath(XML_OPERATION_INPUT_HEADER_XPATH) // Query for the input headers
        );

        return $map;
    },
    []
);

var_dump($operation_input_header_map);