src/Composer/Util/GitHub.php
public function isRateLimited(array $headers)
    {
        foreach ($headers as $header) {
            if (preg_match('{^X-RateLimit-Remaining: *0$}i', trim($header))) {
                return true;
            }
        }

        return false;
    }
public function isRateLimited(array $headers)
    {
        foreach ($headers as $header) {
            if (preg_match('{^X-RateLimit-Remaining: *0$}i', trim($header))) {
                return true;
            }
        }

        return false;
    }
Finds whether a request failed due to rate limiting

@param array $headers Headers from Composer\Downloader\TransportException.

@return bool