Look here:
http://en.wikipedia.org/wiki/HTTP_ETag
the german one is better:
http://de.wikipedia.org/wiki/HTTP_ETag
and
http://solariz.de/2044/etag_webseite...chleunigen.htm
Depending on the Webserver you have a strong Etag or not.
Strong ETags using checksums.
Weak ETags you can detect on "W/" before the Etag-Code.
last link uses php code for MD5-Etaging
Delphi-Quellcode:
uses
MSXML2_TLB;
var
req : IXMLHTTPRequest;
str_link: string;
begin
req := CoXMLHTTP40.Create;
str_link:='http://linktofile';
req.Open('HEAD', str_link, False, EmptyParam, EmptyParam);
req.send(EmptyParam);
// check for req.status=200 -> if true no error
MessageDlg(req.getAllResponseHeaders(), mtWarning, [mbOK], 0);
MessageDlg(req.getResponseHeader('Etag'), mtWarning, [mbOK], 0);
req:=nil;
end;
the headers may look like:
Code:
Date Mon, 19 Apr 2010 15:45:57 GMT
Server Apache
Pragma public
Expires Mon, 19 Apr 2010 16:34:07 GMT
Last-Modified Mon, 19 Apr 2010 15:34:07 GMT
Cache-Control max-age=2890, public, must-revalidate, proxy-revalidate Vary Accept-Encoding,Cookie,User-Agent
Etag 7e828ab2622e112d6a6bd3b7083a560b
Content-Encoding gzip
Content-Type text/
html; charset=UTF-8