W3C home > Mailing lists > Public > ietf-http-wg-old@w3.org > May to August 1997

Updated proposal for OPTIONS issue

From: Jeffrey Mogul <mogul@pa.dec.com>
Date: Thu, 24 Jul 97 19:10:36 MDT
Message-Id: <9707250210.AA17298@acetes.pa.dec.com>
To: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
[incorporates various changes since the last message, including
 the Non-Compliance header, removal of the GET example, changes
 to Allow and Public, and allows Max-Forwards to be used with
 OPTIONS.]

****** Note: two possible options for item (8) ******

Reference:
	http://www.w3.org/pub/WWW/Protocols/HTTP/Issues/#OPTIONS</a>

Problem statement:
	RFC2068 doesn't really say how to use OPTIONS to discover
	what an implementation supports.

	It's essential to have a simple and reliable mechanism for
	detecting support for extensions as a part of the core HTTP/1.1
	protocol.

Outline of proposed solution:
 
    the URI '*' refers to the server, independent of any specific URI.
   
    The Host: header may be used to specify a named proxy or origin 
    server in a chained environment
   
    The Max-forwards: header may be used to specify a maximum number
    of hops the request may be forwarded in a chained environment
   
    The Compliance: header may be used on requests to ask about
    compliance, and on responses to assert compliance.

    The Non-Compliance header allows proxies to indicate when
    they fail to comply with something that the origin server
    complies with.

    We define a new IANA-registered namespace for compliance
    assertions.

Proposed Solution:

(1) In section 5.1.2, remove this:

   If a proxy receives a request without any path in the Request-URI and
   the method specified is capable of supporting the asterisk form of
   request, then the last proxy on the request chain MUST forward the
   request with "*" as the final Request-URI. For example, the request

          OPTIONS <a href="http://www.ics.uci.edu:8001">http://www.ics.uci.edu:8001</a> HTTP/1.1

   would be forwarded by the proxy as

          OPTIONS * HTTP/1.1
          Host: www.ics.uci.edu:8001

   after connecting to port 8001 of host "www.ics.uci.edu".

(2) In section 9.2 (OPTIONS), replace:

   Unless the server's response is an error, the response MUST NOT
   include entity information other than what can be considered as
   communication options (e.g., Allow is appropriate, but Content-Type
   is not). Responses to this method are not cachable.

with

   An OPTIONS request MAY include Compliance headers (see section 14.ZZZ)
   that indicate the set of options the sender wants information
   about.

   Responses to OPTIONS are not cachable, unless caching is explicitly
   allowed by the originating sender (see section 13.4).

(3) In section 9.2 (OPTIONS), replace:

   If the Request-URI is an asterisk ("*"), the OPTIONS request is
   intended to apply to the server as a whole. A 200 response SHOULD
   include any header fields which indicate optional features
   implemented by the server (e.g., Public), including any extensions
   not defined by this specification, in addition to any applicable
   general or response-header fields. As described in section 5.1.2, an
   "OPTIONS *" request can be applied through a proxy by specifying the
   destination server in the Request-URI without any path information.

with

   If the Request-URI is an asterisk ("*"), the OPTIONS request is
   intended to apply to the server as a whole.  A 200 response SHOULD
   include a Public header field (see section 14.35).  If the request
   includes a Compliance header field, a 200 response SHOULD include a
   Compliance header field, indicating the subset of the requested
   Compliance options supported by the server as a whole.  The response
   SHOULD include any other applicable general or response-header
   fields.

   If an OPTIONS request includes a Host header (see section 14.23),
   this is the intended destination of the OPTIONS method.
   Proxy servers MUST forward such a message until it reaches
   the specified host.  If the specified host has more than
   one `virtual server', the OPTIONS request applies to the
   specified virtual server.
   
       Note: An OPTIONS request may also include a Max-Forwards header,
       as described in section 14.31.  This allows the sender to select
       the Nth proxy on a path, without knowing its hostname.

(4) In section 9.2 (OPTIONS), replace:

   If the Request-URI is not an asterisk, the OPTIONS request applies
   only to the options that are available when communicating with that
   resource.  A 200 response SHOULD include any header fields which
   indicate optional features implemented by the server and applicable
   to that resource (e.g., Allow), including any extensions not defined
   by this specification, in addition to any applicable general or
   response-header fields. If the OPTIONS request passes through a
   proxy, the proxy MUST edit the response to exclude those options
   which apply to a proxy's capabilities and which are known to be
   unavailable through that proxy.

with

   If the Request-URI is not an asterisk, the OPTIONS request applies
   only to the options that are available when communicating with that
   resource.  A 200 response SHOULD include an Allow header field (see
   section 14.7).  If the request includes a Compliance header field, a
   200 response SHOULD include a Compliance header field, indicating
   the subset of the requested Compliance options supported by the
   server as a whole.  If the subset is empty, the response SHOULD
   include a Compliance header with an empty field-value.  The response
   SHOULD include any other applicable general or response-header
   fields.

      Note: if an OPTION request contains a Compliance header, and the
      response does not, the response may have been generated by
      RFC2068-compliant implementation, which would not support
      Compliance.  In this case, it is not possible to infer that the
      sender fails to support all of the options listed in the
      Compliance header of the request.

   If the OPTIONS request passes through a
   proxy, the proxy SHOULD add a Non-Compliance header field (see
   section 14.QQQ) to the response, to list those options that apply to
   a proxy's capabilities and that are known to be unavailable through
   that proxy.

(5) In 14.31 (Max-Forwards), replace:

   Each proxy or gateway recipient of a TRACE request containing a Max-
   Forwards header field SHOULD check and update its value prior to
   forwarding the request.

with

   Each proxy or gateway recipient of a TRACE or OPTIONS request
   containing a Max-Forwards header field SHOULD check and update its
   value prior to forwarding the request.

(6) New section

14.ZZZ Compliance

    The Compliance general header field lists a set of options
    that may or may not be supported by a server.  In a request
    message, this header lists the set of options that a client
    wishes to know about.  In a response message, this header
    lists the set of options that the server complies with.
    
    A compliance header MAY appear on any message, but is
    normally used with the OPTIONS request (see section 9.2).
    
    	Compliance = "Compliance" ":" ("*" | *(compliance-option))

	compliance-option = compliance-namespace "="
				option-item [ option-params ]

	compliance-namespace = token

	option-item = token | quoted-string

	option-params = 1#( ";" option-param)

	option-param = "cond" | "uncond" | token | quoted-string

    A Compliance header field with the field-value of "*" MAY
    be used in a request, to ask about all options complied
    with by the recipient.  This field-value MUST NOT be used
    in a response.

    The compliance-namespace is used to select from one of several
    namespaces for compliance options.  The option-item is used
    to specify one or more options within a namespace.  

    The Internet Assigned Numbers Authority (IANA) acts as a registry
    for compliance-namespace tokens. Initially, the registry contains
    the following tokens:

	"RFC"	Compliance is with an RFC, specified by an RFC number.
		For example, "rfc=1945".

	"HDR"	Compliance is with a named HTTP header.  For example,
		"HDR=Authorization".  There is no IANA registry for
		HTTP header names, but to avoid potential namespace
		confusion, only those HTTP headers listed in an
		IETF standards-track document should be used in
		this namespace.		
		
	"PEP"	Compliance is with a PEP-specified extension, identified
		using a quoted-string containing the PEP extension
		declaration.

    The option-param is used to provide additional parameters.
    Unconditional compliance with a compliance-option is indicated
    using the "uncond" option-param; for example, "rfc=1945;uncond".
    Conditional compliance is indicated using the "cond" option-param;
    for example, "HDR=Authorization;uncond".  Additional option-param
    values might be defined as part of another specification.

    Examples:

	Compliance: rfc=2068;uncond
	Compliance: rfc=1945;uncond, rfc=2068;cond
	Compliance: rfc=2068, hdr=PEP, hdr=SetCookie2
	Compliance: rfc=9999999;uncond;"onlyOn=Tuesdays"


(7) New section:

14.QQQ Non-Compliance

   A proxy server SHOULD add this response-header to a response
   containing a Compliance header if the proxy does not implement one
   or more of the options described in the Compliance header.

        Non-Compliance =  "Non-Compliance" ":" 1#non-compliance-option

        proxy-host = host [ ":" port ]

        non-compliance-option = compliance-option "@" proxy-host

   A non-compliance-option listed in a Non-Compliance response-header
   field indicates that the proxy server named by the proxy-host value
   does not support the listed compliance-option.  The set of
   non-compliance options SHOULD be a subset of the compliance-options
   listed in a Compliance header field of the forwarded message.

      Note: because the proxy-host value is not authenticated,
      this is only for advisory purposes (e.g., for debugging).

   A proxy MUST NOT delete a Non-Compliance header that it has
   received from another server.

(8) [For the moment, two possible alternatives here!]

(8a) In section 14.35 (Public), replace

   This header field applies only to the server directly connected to
   the client (i.e., the nearest neighbor in a chain of connections). If
   the response passes through a proxy, the proxy MUST either remove the
   Public header field or replace it with one applicable to its own
   capabilities.

with

   A proxy MUST NOT modify the Public header field even if it does not
   understand all the methods specified, since the user agent might have
   other means of communicating with the origin server.

(8b) In section 14.7 (Allow) replace:

   A proxy MUST NOT modify the Allow header field even if it does not
   understand all the methods specified, since the user agent MAY have
   other means of communicating with the origin server.

with

   A proxy MUST remove methods from an Allow header field if it
   does not support the use of those methods for the resource
   identified by the Request-URI.

and in section 14.35 (Public), replace this paragraph:

   This header field applies only to the server directly connected to
   the client (i.e., the nearest neighbor in a chain of connections). If
   the response passes through a proxy, the proxy MUST either remove the
   Public header field or replace it with one applicable to its own
   capabilities.

with

   A proxy MUST remove methods from a Public header field if it
   does not support the use of those methods.

(9) Examples (put this in 9.2.1?):

  To list all extensions supported by proxy "proxy4.microscape.com"

    Client sends:
	OPTIONS * HTTP/1.1
	Host: proxy4.microscape.com
	Compliance: *

    proxy4.microscape.com responds:
	HTTP/1.1 200 OK
	Date: Tue, 22 Jul 1997 20:21:51 GMT
	Server: SuperProxy/1.0
	Public: OPTIONS, GET, HEAD, PUT, POST, TRACE
	Compliance: rfc=1543, rfc=2068, hdr=set-proxy
	Compliance: hdr=wonder-bar-http-widget-set
	Compliance: PEP="<a href="http://foobar.pep.org/pepmeister/">http://foobar.pep.org/pepmeister/</a>"
	Content-Length: 0

[Editorial note: check syntax of PEP extensions]
       
  Probing for a feature which is not supported by "proxy4.microscape.com"

    Client sends:
	OPTIONS * HTTP/1.1
	Host: proxy4.microscape.com
	Compliance: PEP="<a href="http://foobar.pep.org/evil-not-implemented">http://foobar.pep.org/evil-not-implemented</a>"

    proxy4.microscape.com responds:
	HTTP/1.1 200 OK
	Date: Tue, 22 Jul 1997 20:21:52 GMT
	Server: SuperProxy/1.0
	Public: OPTIONS, GET, HEAD, PUT, POST, TRACE
	Compliance:
	Content-Length: 0

[End of proposed changes]
Received on Thursday, 24 July 1997 19:21:57 EDT

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