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OPTIONS Spec

From: Josh Cohen <josh@netscape.com>
Date: Mon, 21 Jul 1997 23:03:12 -0700 (PDT)
To: josh@netscape.com
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <ML-3.3.869551392.7543.josh@birdcage>
Here is the draft changes for the specification of the OPTIONS
method.

As stated in the attachment, there is some overlap with PEP.
Overall, PEP is much more flexible and efficient.
OPTIONS is simpler at the possible expense of efficiency.
 
However, OPTIONS is simple and easy to implement, and thus
more likely to be accepted in the HTTP/1.1 spec.  I think
that since many things which were once supposed to be
part of the HTTP/1.1 spec are now on their own track,
Its essential to have a simple mechanism of detecting
support for those extensions as a part of the core
HTTP/1.1 protocol.


-----------------------------------------------------------------------------
Josh Cohen				      Netscape Communications Corp.
Netscape Fire Department	           	     #include<disclaimer.h>
Server Engineering
josh@netscape.com                          http://people.netscape.com/josh/
-----------------------------------------------------------------------------

Options Method specification:

Overall Changes:
 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 actual OPTIONS message is contained in the request/response
 body.

Editing changes:
In section 5.1.2:
-   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 http://www.ics.uci.edu:8001 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".

+   Proxy Servers should use the Host: or max-forwards: header
+   to determine whether or not to forward the reqeust as 
+   specified in section 9.2

In section 9.2:

   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.

+   general or response-header fields.

+   OPTIONS messages may be passed through a proxy by using
+   either the host: header to indicate the intended destination
+   of the OPTIONS message.  The max-forwards: header may also
+   be used to indicate that the destination is the Nth hop,
+   as specified by the max-forwards: header.

+   Origin servers supporting 'virtual interfaces' or 
+   'virtual servers' may use the Host: header or the max-forwards:
+   header to determine the intended destination as well.

New definitions:

9.2.1 OPTIONS Messages

9.2.1.1 The REQUEST:

 The body of the OPTIONS request will containt the specific
 information requested.

 The body will be of mime type TBD (text/ietf-http-options)

9.2.1.2 The REPLY:

 The server will respond with 200 if it supports the OPTIONS
 method.

 The OPTIONS reply will contain a content of mime type
 TBD ( text/ietf-http-options )

9.2.2.1 Body definition:

9.2.2.2 REQUEST:

 The body will be a text formatted content, where:

	body = 1(header-token) #(request)

	header-token = "OPTIONS" options-version new-line

	options-version = "1.0"

	request = command-token (feature-token | "*" ) new-line

	new-line = CRLF

	command-parameters = token
		(defined per command )


9.2.2.3 REPLY:
	body = 1(header-token) #(response)

	header-token = "OPTIONS" options-version new-line

	options-version = "1.0"

	response = command-token feature-token response-parameters new-line

	new-line = CRLF

	feature-token = token

	response-parameters = token
		(defined per command )

9.2.3 OPTIONS commands

9.2.3.1 COMPLIANCE

 command-token =  "COMPLIANCE"
	REQUEST
	command-parameters = feature-token | "*"

	REPLY
	feature-token = opaque string representing a feature/extenstion
	response-parameters = token representing feature/extension
		specific parameters

9.2.4 Usage:

 The first line contains:
 OPTIONS <options spec version>

 Followed by a series of answers, as defined according to the 
 command issued:

 COMPLIANCE:
  The COMPLIANCE response is a list of COMPLIANCE indications,
  one per line:
  COMPLIANCE <feature-name> <parameters>

  where feature-name was the argument to the COMPLIANCE request.
  parameters is an optional opaque string indicating parameters
    for that feature.

9.2.5 Examples

9.2.5.1 To list all extensions supported by proxy "proxy4.mcom.com"

 OPTIONS * HTTP/1.1
 Host: proxy4.mcom.com
 Content-type: text/ietf-http-options
 Content-length: 44 (or whatever)

 OPTIONS 1.0
 COMPLIANCE * 

 HTTP/1.1 200 OK
 Server: SuperServer/1.0
 Content-type: text/ietf-http-options
 Content-length: 44 ( feh )

 OPTIONS 1.0
 COMPLIANCE http://foobar.pep.org/pepmeister/
 COMPLIANCE set-proxy
 COMPLIANCE wonder-bar-http-widget-set
 COMPLIANCE rfc1543

9.2.5.2 Probing for a feature which is NOT supported:

 OPTIONS * HTTP/1.1
 Host: proxy4.mcom.com
 Content-type: text/ietf-http-options
 Content-length: 44 (or whatever)

 OPTIONS 1.0
 COMPLIANCE http://foobar.pep.org/evil-not-implemented

 HTTP/1.1 200 OK
 Server: SuperServer/1.0
 Content-type: text/ietf-http-options
 Content-length: 44 ( feh )

 OPTIONS 1.0


9.2.5.3 Probing a 1.0 server/proxy ( response will vary )

 OPTIONS * HTTP/1.1
 Content-Type: text/ietf-http-options
 Content-length: 40
  
 HTTP/1.0 400 Malformed URL
 Proxy-agent: Netscape-Proxy/2.52
 Date: Wed, 16 Jul 1997 02:35:54 GMT
 Content-type: text/html
 Content-length: 157
 
 <HTML><HEAD><TITLE>Malformed URL</TITLE></HEAD>
 <BODY><H1>Malformed URL</H1>
 Your browser sent a request that this proxy could not understand.
 </BODY></HTML>Connection closed by foreign host.

9.2.6 Applicability

  The OPTIONS method is intended to provide a mechanism by which
 a downstream client or proxy may query an upstream proxy or
 origin server about what HTTP/1.1 extensions it supports.

  While this has some overlap with the PEP[ref] specification,
 it only provides functionality for the lower spectrum of PEP.
 It is simple to implement and should be a MUST for implementations.
 Along with the simplicity comes a cost. OPTIONS request need a
 network round trip, while PEP does not.  Therefore, should
 PEP become a standard, or be rolled into this specification,
 implementations are encouraged to use PEP where applicable
 to gain extra flexibility and performance, however, they MUST
 support OPTIONS as well.
Received on Monday, 21 July 1997 23:08:05 EDT

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