flight/net/Response.php
public function header($name, $value = null) {
        if (is_array($name)) {
            foreach ($name as $k => $v) {
                $this->headers[$k] = $v;
            }
        }
        else {
            $this->headers[$name] = $value;
        }

        return $this;
    }
public function header($name, $value = null) {
        if (is_array($name)) {
            foreach ($name as $k => $v) {
                $this->headers[$k] = $v;
            }
        }
        else {
            $this->headers[$name] = $value;
        }

        return $this;
    }
Adds a header to the response.

@param string|array $name Header name or array of names and values
@param string $value Header value
@return object Self reference