system/HTTP/Response.php
public function sendHeaders()
	{
		// Have the headers already been sent?
		if ($this->pretend || headers_sent())
		{
			return $this;
		}

		// Per spec, MUST be sent with each request, if possible.
		// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
		if (! isset($this->headers['Date']))
		{
			$this->setDate(\DateTime::createFromFormat('U', time()));
		}

		// HTTP Status
		header(sprintf('HTTP/%s %s %s', $this->protocolVersion, $this->statusCode, $this->reason), true, $this->statusCode);

		// Send all of our headers
		foreach ($this->getHeaders() as $name => $values)
		{
			header($name . ': ' . $this->getHeaderLine($name), false, $this->statusCode);
		}

		return $this;
	}
public function sendHeaders()
	{
		// Have the headers already been sent?
		if ($this->pretend || headers_sent())
		{
			return $this;
		}

		// Per spec, MUST be sent with each request, if possible.
		// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
		if (! isset($this->headers['Date']))
		{
			$this->setDate(\DateTime::createFromFormat('U', time()));
		}

		// HTTP Status
		header(sprintf('HTTP/%s %s %s', $this->protocolVersion, $this->statusCode, $this->reason), true, $this->statusCode);

		// Send all of our headers
		foreach ($this->getHeaders() as $name => $values)
		{
			header($name . ': ' . $this->getHeaderLine($name), false, $this->statusCode);
		}

		return $this;
	}
Sends the headers of this HTTP request to the browser.

@return Response