510 Not Extended

RFC2774 is an experimental RFC, that introduces a mechanism to allow developers to extend the HTTP protocol with vendor-specific features in a safe namespaced way.

Around this time many new protocols and systems started to get built on top of HTTP, and the authors might have felt there was a need to do this in a namespaced way.

This is not unlike XML namespaces, where it’s possible for one standards organization to define a new format (for example ATOM), and other corporations wanting to add new properties, avoiding the possibility of collision if a second vendor also introduced a property with the same name.

As far as I know this extension to HTTP can be considered dead.

The 510 Not Extended statuscode could be used when a server requires that a client uses an ‘extended HTTP request’, but didn’t. When a server emits this response, it should also tell the client how to extend the request, but the specification doesn’t specify a format for this.

Because this error is a ‘client error’, it should probably have had a 4xx code, not a 5xx one.

I would not recommend for anyone to use this.

Should I use this?

No. RFC2774 is a very obscure extension to HTTP, and as far as I know has never really been picked up. If you feel you have a need for this, I believe there is likely to be a different way to extend HTTP. Perhaps via content negotiation, or just different kinds of messaging from client to server.


HTTP series

This article is part of an ongoing series about the HTTP protocol.

If you want to follow along as I write them, you can Subscribe to my Atom feed or Mailing list.

Informational 1xx

Successful 2xx

Redirection 3xx

Client Error 4xx

Server Error 5xx

Web mentions