src/MessageHelper.php
protected function ifNoneMatch(Request $request, Response $response, string $etag): Response
    {
        $ifNoneMatch = $request->getHeaderLine('If-None-Match');
        if ($ifNoneMatch && $etag === $ifNoneMatch) {
            return $response->withStatus(304, "Not Modified");
        }
        return $response;
    }
protected function ifNoneMatch(Request $request, Response $response, string $etag): Response
    {
        $ifNoneMatch = $request->getHeaderLine('If-None-Match');
        if ($ifNoneMatch && $etag === $ifNoneMatch) {
            return $response->withStatus(304, "Not Modified");
        }
        return $response;
    }
protected function ifNoneMatch ( Request $ request , Response $ response , string $ etag ) : Response { $ ifNoneMatch = $ request -> getHeaderLine ( 'If-None-Match' ) ; if ( $ ifNoneMatch && $ etag === $ ifNoneMatch ) { return $ response -> withStatus ( 304 , "Not Modified" ) ; } return $ response ; }
Checks the `If-None-Match` header, maybe sending 304 Not Modified.

@param \Psr\Http\Message\ServerRequestInterface $request  The HTTP request
@param \Psr\Http\Message\ResponseInterface $response  The HTTP response
@param string $etag  The ETag for comparison
@return \Psr\Http\Message\ResponseInterface  The same or new response
Checks the If - None - Match header maybe sending 304 Not Modified .