SHOULD NOT add or change the Expires header or max-age Cache-control
   directive.)

      For example, if proxy A receives a GET request from proxy B for
      URL X with "Connection: Meter", but proxy A's cached response for
      URL does not include any Meter directives, then proxy A may ignore
      the metering offer from proxy B.

      However, if proxy A has previously told the origin server "Meter:
      wont-limit" (implying will-report), and the cached response
      contains "Meter: do-report", and proxy B's request includes
      "Meter:  wont-report", then proxy B's offer is inconsistent with
      proxy A's duty to the origin server.  Therefore, in this case
      proxy A must add "Cache-control: s-maxage=0" when it returns the
      cached response to proxy B, and must not include a Meter header in
      this response.

   If a server does not want to use the Meter mechanism, and will not
   want to use it any time soon, it may send this directive:

   wont-ask        recommends that the proxy SHOULD NOT send any Meter
                   directives to this server.








 
RFC 2227            Hit-Metering and Usage-Limiting         October 1997


   The proxy SHOULD remember this fact for up to 24 hours.  This avoids
   virtually all unnecessary overheads for servers that do not wish to
   use or support the Meter header.  (This directive also implies
   "dont-report".)

3.4 Transmission of usage reports

   To transmit a usage report, a proxy sends the following Meter header
   in a request on the appropriate resource:

       Meter: count=NNN/MMM

   The first integer indicates the count of uses of the cache entry
   since the last report; the second integer indicates the count of
   reuses of the entry (see section 5.3 for rules on counting uses and
   reuses).  The transmission of a "count" directive in a request with
   no other Meter directive is also defined as an implicit transmission
   of a "will-report-and-limit" directive, to optimize the common case.
   (A proxy not willing to honor usage-limits would send "Meter:
   count=NNN/MMM, wont-limit" for its reports.)

   Note that when a proxy forwards a client's request and receives a
   response, the response that the proxy sends immediately to the
   requesting client is not counted as a "use".  I.e., the reported
   count is the number of times the cache entry was used, and not the
   number of times that the response was used.

   A proxy SHOULD NOT transmit "Meter: count=0/0", since this conveys no
   useful information.

   Usage reports MUST always be transmitted as part of a conditional
   request (such as a GET or HEAD), since the information in the
   conditional header (e.g., If-Modified-Since or If-None-Match) is
   required for the origin server to know which instance of a resource
   is being counted.  Proxys forwarding usage reports up the metering
   subtree MUST NOT change the contents of the conditional header, since
   otherwise this would result in incorrect counting.

   A usage report MUST NOT be transmitted as part of a forwarded request
   that includes multiple entity tags in an If-None-Match or If-Match
   header.

      Note: a proxy that offers its willingness to do hit-metering
      (report usage) must count both uses and reuses.  It is not
      possible to negotiate the reporting of one but not the other.







 
RFC 2227            Hit-Metering and Usage-Limiting         October 1997


3.5 When to send usage reports

   A proxy that has offered to send usage reports to its parent in the
   metering subtree MUST send a usage report in each of these
   situations:

      1. When it forwards a conditional GET on the resource
         instance on behalf of one of its clients (if the GET is
         conditional on at most one entity-tag).