router.php

<?php

$action_filename = "action.php";

ob_start();

if($_POST){
    switch($_SERVER['SCRIPT_NAME']) {
        case "/init":
            echo "OK\n";
            break;

        case "/run":
            // load the code, assume function "main"
            require($action_filename);

            // parse incoming data, JSON format, field "value"
            $data = json_decode(file_get_contents("php://input"), true);

            // pass args to function
            $output = main($data['value']);

            // return result
            header("Content-Type: application/json");
            echo json_encode($output);
            break;

        default:
            // do nothing
            
    }

    $output_buffer = ob_get_contents();
    header("Content-Length: " . mb_strlen($output_buffer));
}