One document matched: draft-hallam-http-proxy-note-00.txt

   INTERNET DRAFT                           Phillip M. Hallam-Baker, W3C
   Expires in six months                          email: <hallam@w3.org>
                                                      21st February 1996
   

                        Notification for Proxy Caches 

                     <draft-hallam-http-proxy-note-00.txt>

Status of this Memo

   This document is an Internet draft. Internet drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas
   and its working groups. Note that other groups may also distribute
   working information as Internet drafts. 

   Internet Drafts are draft documents valid for a maximum of six
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   Distribution of this document is unlimited. Please send comments to
   the HTTP working group (HTTP-WG) of the Internet Engineering Task
   Force (IETF) at < http://www.ics.uci.edu/pub/ietf/http/. This note
   is also avaliable as a World Wide Web Consortium Working Draft
   WD-proxy-960221, archived at 
   http://www.w3.org/pub/WWW/TR/WD-proxy-960221.html 

Abstract 

   A mechanism to enable better functioning of proxies is proposed.
   This mechanism allows proxies to inform a remote server about
   transactions performed using the cache and for servers to inform
   proxies when data becomes stale. 

Introduction 

   Proxies [Luotonen94] and in particular caching proxies have become a
   useful and necessary tool for many Web users. Proxy caches help
   reduce network load by allowing pages to be served from a local
   cache.. 

   Current proxy behavior is undesirable in a number of ways. There is
   no mechanism whereby a proxy can be informed of changes to the
   source data. Such a facility would permit greater use of server side
   proxies for load balancing purposes. 

Phillip M. Hallam-Baker                                                 Page 1



Notification for Proxy Caches                                                 

   Another problem with the current protocol is that a server has no
   knowledge of hits served from a proxy's cache. This is a significant
   concern for commercial sites whose revenues depend upon traffic
   measurements. 

Implementation 

   These proposals create two new headers, Proxy-Features and
   Proxy-Instruction. In addition and extra method, NOTIFY and an
   additional Cache-Control directive are specified. 

Proxy-Features 

   The proxy features header is used by a proxy sending data to a
   server. It specifies the features supported by the specified proxy. 

   
   	Proxy-Feature	= "Proxy-Features" ":" _proxy-name_ 1*(; proxy-option)
   
   	proxy-name	= dns-name
   	proxy-option	= "notify" | "loging" | log 
   
   	log		= "log" "=" uri 1*(; log-option)
   	log-option	= "expires" "=" 1*digit
   			| "peak" = 1*hexdigit
   
   

   The proxy-name field specifies the proxy offering the features. 

   The notify directive indicates that the proxy can accept
   notification messages. The log directive indicates that the server
   is will on request store logs of transactions performed by the proxy
   on behalf of the particular server. The logging directive indicates
   that the proxy is already engaged in a logging transaction. The log
   and logging directives are mutually exclusive. 

   The log option has a required URI parameter. This should be an
   absolute URI. The expiry an expiry date for the log file in hours.
   if the log file data is not retrieved before this time the proxy may
   delete it. The peak option is used to specify a binary mask
   indicating the peak hours of the server. This mask specified as a
   six digit hexadecimal number whose bit positions 0 to 23 correspond
   to the time intervals 0:00 to 0:59 GMT, 1:00 to 1:59 GMT through
   23:00 to 23:59 GMT respectively. A set bit indicates a period during
   which server load is high and log file retrieval should be avoided.
   If specified a peak mask should have at least one clear bit. 

Proxy-Instruction 

   The proxy instruction header is used to reply to a proxy features
   header. It should only be present when a Proxy-Features header was
   present in the corresponding request. 

Phillip M. Hallam-Baker                                                 Page 2



Notification for Proxy Caches                                                 

   
   	Proxy-Instruction   = "Proxy-Instruction" ":" _proxy-name_
   					 1*(; proxy-cmd-option)
   
   	proxy-name	    = dns-name
   	proxy-cmd-option    = "log" | "summary" | "inform"
   
   

   The proxy-name field specifies the proxy for which the instruction
   is intended. Proxies may strip out headers which apply to them when
   passing the message on. 

   Three proxy instructions are defined. These are mutually exclusive.
   The log instruction instructs the proxy to record log data which
   will be retreived later. The summary directive indicates that the
   proxy may opt to provide summary as opposed to full logfiles. The
   inform directive instructs the proxy to perform an If-Modify-Since
   operation on each request. 

Log Exchange Protocol 

   A proxy informs a server that it is willing to inform the server
   when a resource is served from a cache. The server reply indicates
   whether the server is willing to accept summary data and if so what
   type of data is acceptable. If no Proxy-Instruction field is
   specified the proxy will keep no log data on the servers behalf. 

   The server retrieves its log information periodically using a HTTP
   GET method. The server may erase the log file information after
   successfully completion of this operation. Log files are exchanged
   in the  extended log file format [Hallam96]. The data stored in such
   logs should only contain data corresponding to a single server. 

Example 

   
   GET /foo HTTP/1.1
   Accept: text/html
   Proxy-Features: proxy.w3.org; log=http://proxy.w3.org/logs/xxxxx.org; 
expiry=24
   

   
   201 OK
   Proxy-Instruction: proxy.w3.org; log
   Content-Type: text/html
   
   ...text...
   

   The server later retrieves the proxy log information: 

   

Phillip M. Hallam-Baker                                                 Page 3



Notification for Proxy Caches                                                 

   GET /logs HTTP/1.1
   Accept: application/www-extended-log
   

   
   201 O.K.
   Content-Type: application/www-extended-log
   
   #Version: 1.0
   #Start-Date: 1996-02-21 12:00
   #End-Date: 1996-02-21 16:45.34
   #Fields Time URI
   12:02 /foo
   12:03 /foo/bar
   ...
   

Notification Protocol 

   A proxy signals that it can accept the notification protocol using
   the notify proxy option. The server may undertake to provide
   notification in reply using a new notify parameter of the
   Cache-Control header. Notification takes place using the Notify
   method. This takes as its parameter the full URI of the resource
   which has expired. 

Example 

   The proxy proxy.w3.org sends the remote server the following
   request: 

   
   GET /foo HTTP/1.1
   Accept: text/html
   Proxy-Features: proxy.w3.org; notify
   

   The server indicates that it is willing to provide notification: 

   
   201 OK
   Cache-Control: notify
   Content-Type: text/html
   
   ...text...
   

   The server subsequently notifies the proxy that the page has
   expired: 

   
   NOTIFY /foo HTTP/1.1
   

Phillip M. Hallam-Baker                                                 Page 4



Notification for Proxy Caches                                                 

   A server must not generate a cache control notify directive unless
   notification was offered as a proxy feature. 

   Note: servers which are capable of supporting the notification
   protocol are not obliged to provide notification for every request.
   Such a requirement could lead to servers becoming overloaded. It is
   expected that use of this protocol will be restricted to a limited
   number of high load servers and proxies. Clients should not in
   attempt to use this facility as a matter of course. 

   Query: an alternative approach would be to piggyback notifications
   on the back of other requests using a header tag. alternatively the
   notification could also cause the updated page to be pushed at the
   client. This might require a separate update directive. 

Multiple Proxy Configurations 

   The protocols described are believed to operate correctly in
   configurations involving multiple proxies. Additional work is
   required before it is certain that this is the case. 

Security considerations 

   The logging feature is vulnerable to an IP spoofing attack. An
   attacker might use this feature to obtain logfiles. A lightweight
   authentication technique might significantly increase the difficulty
   of such an attack. 

Further Work 

   The proposals made here are intended to describe structure rather
   than implementation. It may be desirable to combine these proposals
   with other extensions relevant to proxies. Header names should
   therefore be considered advisory only. In particular it is likely
   that the standards process will wish to consider PEP [khare96] as a
   basis for implementation. 

   A proxy might perform an auditing service by authenticating the log
   files with a digital signature or other means. 

   
   Phillip M. Hallam-Baker
   hallam@w3.org
   World Wid Web Consortium
   Cambridge MA
   

References 

   [Khare96] 
       R. Khare, _ PEP: An Extension Mechanism for HTTP _
       http://www.w3.org/pub/WWW/TR/WD-http-pep 


Phillip M. Hallam-Baker                                                 Page 5



Notification for Proxy Caches                                                 

   [Luotonen94] 
       A. Luotonen, _World wide Web Proxies_, Proceedings of First
       International World-Wide Web Conference. Geneva 1994. 

   [HTTP-1.0] 
       R. Fielding, H. Frystyk, T. Berners-Lee, _ Hypertext Transfer
       Protocol -- HTTP/1.0_
       http://www.w3.org/pub/WWW/Protocols/HTTP/1.0/spec.html 

   [HTTP-1.1] 
       R. Fielding, H. Frystyk, T. Berners-Lee, _ Hypertext Transfer
       Protocol -- HTTP/1.1_
       http://www.w3.org/pub/WWW/Protocols/HTTP/1.1/spec.html 

   [Hallam96] 
       P. M. Hallam-Baker _ Extended Log File Format _
       http://www.w3.org/pub/WWW/TR/WD-logfile.html 





































Phillip M. Hallam-Baker                                                 Page 6