Re: Satisfying IMS from HEAD or IMS would help where browser cach es

Nottingham, Mark (Australia) wrote:
>
> I need to reread your message to really get what you're saying there,
> but FYI Netscape servers do NOT include a LM header when the request is
> a head. This violates the spirit of the HTTP, but not the letter...

Netscape servers (at least the ones I have tested) do return LM headers
when a LM header is returned on a GET request for the same object. No LM
header is returned on SSI parsed objects for either GET or HEAD, but
then is no Content-Length returned either as it is a generated object
and both Last-Modified and Content-Length is unknown at the start of the
generation.

A random HEAD request to a Netscape server:

HTTP/1.0 200 OK
Server: Netscape-Enterprise/2.01
Date: Sat, 31 Oct 1998 15:24:07 GMT
Accept-ranges: bytes
Last-modified: Tue, 22 Sep 1998 12:46:25 GMT
Content-length: 1074
Content-type: image/gif

What RFC 2068 (HTTP/1.1) says about HEAD:

[rfc 2068 section 9.4 HEAD]

   The HEAD method is identical to GET except that the server MUST NOT
   return a message-body in the response. The metainformation contained
   in the HTTP headers in response to a HEAD request SHOULD be identical
   to the information sent in response to a GET request. This method can
   be used for obtaining metainformation about the entity implied by the
   request without transferring the entity-body itself. This method is
   often used for testing hypertext links for validity, accessibility,
   and recent modification.

[rfc 2068 section 1.2 Requirements ]

   MUST
      This word or the adjective "required" means that the item is an
      absolute requirement of the specification.

   SHOULD
      This word or the adjective "recommended" means that there may
      exist valid reasons in particular circumstances to ignore this
      item, but the full implications should be understood and the case
      carefully weighed before choosing a different course.

So yes, it is allowable to send close to any headers in reply to a HEAD
request, but it is strongly discouraged.

---
Henrik Nordstrom
Spare time Squid hacker