RESTful API methods; HEAD & OPTIONS

Question

I'm writing a RESTful API module for an application in PHP, and I'm a bit mixed on the verbs HEAD and OPTIONS.

• OPTIONS  Used to retrieve the available HTTP verbs for a given resource?
• HEAD Used to determine whether a given resource is available?

If someone could clarify* these verbs, that would be much appreciated.

_{* The clarification was with respect to RESTful API architectures re-purposing HTTP verbs. I've since come to the realization that both HEAD and OPTIONS should not be re-purposed, and instead behave predictably as any HTTP application should. Oh, how we grow in 2 years.}

Answer 1

OPTIONS method returns info about API (methods/content type)

HEAD method returns info about resource (version/length/type)

Server response

OPTIONS

HTTP/1.1 200 OK
Allow: GET,HEAD,POST,OPTIONS,TRACE
Content-Type: text/html; charset=UTF-8
Date: Wed, 08 May 2013 10:24:43 GMT
Content-Length: 0

HEAD

HTTP/1.1 200 OK
Accept-Ranges: bytes
Content-Type: text/html; charset=UTF-8
Date: Wed, 08 May 2013 10:12:29 GMT
ETag: "780602-4f6-4db31b2978ec0"
Last-Modified: Thu, 25 Apr 2013 16:13:23 GMT
Content-Length: 1270

• OPTIONS Identifying which HTTP methods a resource supports, e.g. can we DELETE it or update it via a PUT?
• HEAD Checking whether a resource has changed. This is useful when maintaining a cached version of a resource
• HEAD Retrieving metadata about the resource, e.g. its media type or its size, before making a possibly costly retrieval
• HEAD, OPTIONS Testing whether a resource exists and is accessible. For example, validating user-submitted links in an application

Here is nice and concise article about how HEAD and OPTIONS fit into RESTful architecture.