system/HTTP/DownloadResponse.php
public function getContentLength() : int
	{
		if (is_string($this->binary))
		{
			return strlen($this->binary);
		}
		elseif ($this->file instanceof File)
		{
			return $this->file->getSize();
		}

		return 0;
	}
public function getContentLength() : int
	{
		if (is_string($this->binary))
		{
			return strlen($this->binary);
		}
		elseif ($this->file instanceof File)
		{
			return $this->file->getSize();
		}

		return 0;
	}
get content length.

@return integer