public function normalizeHeaderKey(string $key)
    {
        $key = strtr(strtolower($key), '_', '-');
        if (strpos($key, 'http-') === 0) {
            $key = substr($key, 5);
        }
        return $key;
    }
public function normalizeHeaderKey(string $key)
    {
        $key = strtr(strtolower($key), '_', '-');
        if (strpos($key, 'http-') === 0) {
            $key = substr($key, 5);
        }
        return $key;
    }
public function normalizeHeaderKey ( string $ key ) { $ key = strtr ( strtolower ( $ key ) , '_' , '-' ) ; if ( strpos ( $ key , 'http-' ) === 0 ) { $ key = substr ( $ key , 5 ) ; } return $ key ; }
Normalize header name

This method transforms header names into a
normalized form. This is how we enable case-insensitive
header names in the other methods in this class.

@param  string $key The case-insensitive header name

@return string Normalized header name
Normalize header name