src/Request.php
protected function parseHeader(array $headers = [])
    {
        $processedHeaders = array();
        foreach ($headers as $key => $value) {
            if (substr($key, 0, 5) == 'HTTP_') {
                $name = str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($key, 5)))));
                $processedHeaders[$name] = $value;
            } elseif ($key == 'CONTENT_TYPE') {
                $processedHeaders['Content-Type'] = $value;
            } elseif ($key == 'CONTENT_LENGTH') {
                $processedHeaders['Content-Length'] = $value;
            }
        }
        return $processedHeaders;
    }
protected function parseHeader(array $headers = [])
    {
        $processedHeaders = array();
        foreach ($headers as $key => $value) {
            if (substr($key, 0, 5) == 'HTTP_') {
                $name = str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($key, 5)))));
                $processedHeaders[$name] = $value;
            } elseif ($key == 'CONTENT_TYPE') {
                $processedHeaders['Content-Type'] = $value;
            } elseif ($key == 'CONTENT_LENGTH') {
                $processedHeaders['Content-Length'] = $value;
            }
        }
        return $processedHeaders;
    }
Parse headers.

This method should be passed the _SERVER global array. Most http headers
in PHP are prefixed with HTTP_ however, there are two values prefixed
with CONTENT_. All other values in the array will be ignored.

@param string[] $headers
@return string