ETag

Backup and replace SecureMedia. php with this copy to enable the ETag and Last-Modified headers.

Suttree; Secure Media; Prevent flash games from hotlinking. 2010

This new version of SecureMedia. php handles the creation and sending of ETag and Last-Modified headers, enabling browsers who request multiple copies of the same game to use their own cache, therefore saving the web server a great deal of bandwidth.

Suttree; Secure Media; Prevent flash games from hotlinking. 2010

An update to Florian Metzger's SecureMedia. php class that prevents hotlinking to Flash game and now adds support for ETag and Last-Modified headers, otherwise known as conditional-GET, to help reduce the bandwidth usage by allowing for caching of secured games.

Suttree; code 2009

ETag support is currently supported in WordPress for feeds I added that to the core myself, way-back-when.

W3 Total Cache Plugin 2009

The browser can save a local copy of the page in its cache, along with the ETag.

W3 Total Cache Plugin 2009

Basically, the first time a browser requests a page from a server, the server will generate an ‘ETag’ header with a unique identifier based on the last time the page was modified.

W3 Total Cache Plugin 2009

The next time the browser requests the same page, it can send the ETag back to the server.

W3 Total Cache Plugin 2009

On every request it can then compare the resulting ETag to what's in the database, and if it's the same, use the Last-Modified time stored in the database; if not, update the database to the present date and then use that for the Last-Modified.

Snell-Pym » HTTP caching 2007

But it's not a great solution; as well as expiry-time based cache headers, HTTP also supports validation, whereby a page can emit a Last-Modified and/or ETag header, which both change when the underlying content changes; then clients can check to see if there's a new version available with a request containing an If-Modified-Since header.

Snell-Pym » HTTP caching 2007

If just given a timestamp it would generate an ETag from the timestamp by hashing it; if just given an ETag, it would generate a last-modified timestamp by comparing the ETag to one stored in a database.

Snell-Pym » HTTP caching 2007