[WordPress Plugin] Logging HTTP API Request Errors

http-api-error-log.php

<?php
/*
Plugin Name: HTTP API DEBUG LOG
Version: 0.1
*/

add_action('http_api_debug', function ($response, $context, $class, $r, $url) {
//    $response = new WP_Error('http_request_failed', 'debug');

    /** @var WP_Error $response */
    if (is_wp_error($response)) {
        $logfile = WP_CONTENT_DIR . '/http_api_error.log';
        $logformat = '[%s] [%s] [%s] [%s] %s';

        global $wp_filesystem;
        if (!is_object($wp_filesystem)) {
            WP_Filesystem();
        }
        if (!$wp_filesystem->exists($logfile)) {
            $wp_filesystem->touch($logfile);
        }
        $content = $wp_filesystem->get_contents($logfile);
        $wp_filesystem->put_contents(
            $logfile,
            $content = $content . PHP_EOL . sprintf(
                $logformat,
                (new DateTime())->format('Y-m-d H:i:s'),
                $context,
                $class,
                $url,
                $response->get_error_message()
            ),
            FS_CHMOD_FILE
        );
    }
}, 10, 5);