src/Http/Response/BinaryFileResponse.php
public function setAutoEtag()
	{
		$this->setEtag(md5(serialize(fileinfo($this->file->getPathname()))));
		return $this;
	}
public function setAutoEtag()
	{
		$this->setEtag(md5(serialize(fileinfo($this->file->getPathname()))));
		return $this;
	}
Automatically sets the ETag header according to the checksum of the file.