timeout=NNN     sets a metering timeout of NNN minutes, from the time
                   that this response was originated, for the reporting
                   of a hit-count.  If the proxy has a non-zero hit
                   count for this response when the timeout expires, it
                   MUST send a report to the server at or before that
                   time.  Implies "do-report".

   By definition, an empty Meter header in a response, or any Meter
   header that does not contain "dont-report", means "Meter: do-report";
   this makes a common case more efficient.







 
RFC 2227            Hit-Metering and Usage-Limiting         October 1997


      Note: an origin server using the metering timeout mechanism to
      bound the collection period over which hit-counts are obtained
      should adjust the timeout values in the responses it sends so that
      all responses generated within that period reach their metering
      timeouts at or before the end of that period.

      If the origin server simply sends a constant metering timeout T
      with each response for a resource, the reports that it receives
      will reflect activity over a period whose duration is between T
      and N*T (in the worst case), where N is the maximum depth of the
      metering subtree.

   For usage-limiting

   max-uses=NNN    sets an upper limit of NNN "uses" of the response,
                   not counting its immediate forwarding to the
                   requesting end-client, for all proxies in the
                   following subtree taken together.

   max-reuses=NNN  sets an upper limit of NNN "reuses" of the response
                   for all proxies in the following subtree taken
                   together.

   When a proxy has exhausted its allocation of "uses" or "reuses" for a
   cache entry, it MUST revalidate the cache entry (using a conditional
   request) before returning it in a response.  (The proxy SHOULD use
   this revalidation message to send a usage report, if one was
   requested and it is time to send it.  See sections 3.4 and 3.5.)

   These Meter response-directives apply only to the specific response
   that they are attached to.

      Note that the limit on "uses" set by the max-uses directive does
      not include the use of the response to satisfy the end-client
      request that caused the proxy's request to the server.  This
      counting rule supports the notion of a cache-initiated prefetch: a
      cache may issue a prefetch request, receive a max-uses=0 response,
      store that response, and then return that response (without
      revalidation) when a client makes an actual request for the
      resource.  However, each such response may be used at most once in
      this way, so the origin server maintains precise control over the
      number of actual uses.

   A server MUST NOT send a Meter header that would require a proxy to
   do something that it has not yet offered to do.  A proxy receiving a
   Meter response-directive asking the proxy to do something it did not
   volunteer to do SHOULD ignore that directive.





 
RFC 2227            Hit-Metering and Usage-Limiting         October 1997


   A proxy receiving a Meter header in a response MUST either obey it,
   or it MUST revalidate the corresponding cache entry on every access.
   (I.e., if it chooses not to obey the Meter header in a response, it
   MUST act as if the response included "Cache-control:  s-maxage=0".)

      Note: a proxy that has not sent the Meter header in a request for
      the given resource, and which has therefore not volunteered to
      honor Meter directives in a response, is not required to honor
      them.  If, in this situation, the server does send a Meter header
      in a response, this is a protocol error.  However, based on the
      robustness principle, the proxy may choose to interpret the Meter
      header as an implicit request to include "Cache-control: s-
      maxage=0" when it forwards the response, since this preserves the
      apparent intention of the server.

   A proxy that receives the Meter header in a request may ignore it
   only to the extent that this is consistent with its own duty to the
   next-hop server.  If the received Meter request header is
   inconsistent with that duty, or if no Meter request header is
   received and the response from the next-hop server requests any form
   of metering or limiting, then the proxy MUST add "Cache-control: s-
   maxage=0" to any response it forwards for that request.  (A proxy