Neos Eel evaluator as XML-RPC service (just a crazy demo, don't use this in production!)

EelRpcMiddleware.php

<?php
declare(strict_types=1);
namespace Some\Package;

use GuzzleHttp\Psr7\Response;
use Neos\Eel\Context;
use Neos\Eel\EelEvaluatorInterface;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\MiddlewareInterface;
use Psr\Http\Server\RequestHandlerInterface;


final class EelRpcMiddleware implements MiddlewareInterface
{

    private EelEvaluatorInterface $eelEvaluator;

    public function __construct(EelEvaluatorInterface $eelEvaluator)
    {
        $this->eelEvaluator = $eelEvaluator;
    }

    public function process(ServerRequestInterface $request, RequestHandlerInterface $next): ResponseInterface
    {
        // FIXME better way to detect XML RPC calls?
        if ($request->getHeaderLine('Content-Type') !== 'text/xml') {
            return $next->handle($request);
        }
        $server = xmlrpc_server_create();
        xmlrpc_server_register_method($server, 'eel', function(string $methodName, array $params) {
            try {
                return $this->eelEvaluator->evaluate($params[0], new Context($params[1] ?? []));
            } catch (\Throwable $exception) {
                return ['faultCode' => 1, 'faultString' => $exception->getMessage()];
            }
        });
        $response = xmlrpc_server_call_method($server, $request->getBody()->getContents(), null);
        xmlrpc_server_destroy($server);

        return new Response(200, ['Content-Type' => 'Content-Type: text/xml'], $response);
    }
}

Settings.yaml

Neos:
  Flow:
    http:
      middlewares:
        'EelRpc':
          middleware: 'Some\Package\EelRpcMiddleware'
          position: 'before routing'

DISCLAIMER: Don't use this example without modifications. Exposing the (whole) power of Eel to the client is unsafe!

Example request payload:

<methodCall>
    <methodName>eel</methodName>
    <params>
        <param>
            <value>
                <string>'your name is: ' + name</string>
            </value>
        </param>
        <param>
            <value>
                <struct>
                    <member>
                        <name>name</name>
                        <value>
                            <string>John</string>
                        </value>
                    </member>
                </struct>
            </value>
        </param>
    </params>
</methodCall>