RFC 2227            Hit-Metering and Usage-Limiting         October 1997


3.2 Format of the Meter header

   The Meter header is used to carry zero or more directives.  Multiple
   Meter headers may occur in an HTTP message, but according to the
   rules in section 4.2 of the HTTP/1.1 specification [4], they may be
   combined into a single header (and should be so combined, to reduce
   overhead).

   For example, the following sequence of Meter headers

       Meter: max-uses=3
       Meter: max-reuses=10
       Meter: do-report

   may be expressed as

       Meter: max-uses=3, max-reuses=10, do-report

3.3 Negotiation of hit-metering and usage-limiting

   An origin server that wants to collect hit counts for a resource, by
   simply forcing all requests to bypass any proxy caches, would respond
   to requests on the resource with "Cache-control: s-maxage=0".  (An
   origin server wishing to prevent HTTP/1.0 proxies from improperly
   caching the response could also send both "Expires: ", to
   prevent such caching, and "Cache-control: max-age=NNNN", to allow
   newer proxies to cache the response).

   The purpose of the Meter header is to obviate the need for "Cache-
   control: s-maxage=0" within a metering subtree.  Thus, any proxy may
   negotiate the use of hit-metering and/or usage-limiting with the
   next-hop server.  If this server is the origin server, or is already
   part of a metering subtree (rooted at the origin server), then it may
   complete the negotiation, thereby extending the metering subtree to
   include the new proxy.

   To start the negotiation, a proxy sends its request with one of the
   following Meter directives:

   will-report-and-limit
                   indicates that the proxy is willing and able to
                   return usage reports and will obey any usage-limits.

   wont-report     indicates that the proxy will obey usage-limits but
                   will not send usage reports.

   wont-limit      indicates that the proxy will not obey usage-limits
                   but will send usage reports.




 
RFC 2227            Hit-Metering and Usage-Limiting         October 1997


   A proxy willing to neither obey usage-limits nor send usage reports
   MUST NOT transmit a Meter header in the request.

   By definition, an empty Meter header:

       Meter:

   is equivalent to "Meter: will-report-and-limit", and so, by the
   definition of the Connection header (see section 14.10 of the
   HTTP/1.1 specification [4]), a request that contains

       Connection: Meter

   and no explicit Meter header is equivalent to a request that contains

       Connection: Meter
       Meter: will-report-and-limit

   This makes the default case more efficient.

   An origin server that is not interested in metering or usage-limiting
   the requested resource simply ignores the Meter header.

   If the server wants the proxy to do hit-metering and/or usage-
   limiting, its response should include one or more of the following
   Meter directives:

   For hit-metering:

   do-report       specifies that the proxy MUST send usage reports to
                   the server.

   dont-report     specifies that the proxy SHOULD NOT send usage
                   reports to the server.