<?php

/**
 * By default, cURL sends the "Expect" header all the time which severely impacts
 * performance. Instead, we'll send it if the body is larger than 1 mb like
 * Guzzle does.
 */
function add_expect_header(array $arguments)
{
    $arguments['headers']['expect'] = '';
    
    if (is_array($arguments['body'])) {
        $bytesize = 0;
        $iterator = new RecursiveIteratorIterator(new RecursiveArrayIterator($arguments['body']));

        foreach ($iterator as $datum) {
            $bytesize += strlen((string) $datum);

            if ($bytesize >= 1048576) {
                $arguments['headers']['expect'] = '100-Continue';
                break;
            }
        }
    } elseif (!empty($arguments['body']) && strlen((string) $arguments['body']) > 1048576) {
        $arguments['headers']['expect'] = '100-Continue';
    }

    return $arguments;
}
add_filter('http_request_args', 'add_expect_header');