draft-vixie-icp-htcp-01.txt

-

      |      SPECIFIER      |
      +---------------------+
      |        DETAIL       |
      +---------------------+


   4 - Cache Headers

   HTCP/0.0 CACHE-HDRS are as follows:

   Cache-Vary: <header-name> ...
      The sender of this header has learned that content varies on a set of
      headers different from the set given in the object's Vary: header.
      If Cache-Vary: specifies the null set, then the origin server has
      been found to issue identical results no matter what request headers
      are given to it.







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   Cache-Location: <cache-hostname>:<port> ...
      The sender of this header has learned of one or more proxy caches who
      are holding a copy of this object.  Probing these caches with HTCP
      may result in discovery of new, close-by (preferrable to current)
      HTCP neighbors.

   Cache-Policy: [no-cache] [no-share] [cookie-ok]
      The sender of this header has learned that the object's policy has
      more detail than is given in its response headers.

              ``no-cache'' means that it is uncacheable (no reason given),
                   but may be shareable between simultaneous requestors.
              ``no-share'' means that it is unshareable (no reason given),
                   and per-requestor tunnelling is always required).
              ``cookie-ok'' means that the content is not going to change
                   as a result of different, missing, or even random
                   cookies being included in the request headers, and
                   that caching may be possible.


   Cache-Expiry: <date>
      The sender of this header has learned that this object should be
      considered to have expired at a time different than that indicate by
      its response headers.  The format is the same as HTTP/1.1 Expires:.

   Cache-MD5: <discovered content MD5>
      The sender of this header has computed an MD5 checksum for this
      object which is either different from that given in the object's
      Content-MD5:  header, or is being supplied since the object has no
      Content-MD5 header.  The format is the same as HTTP/1.1 Content-MD5:.

   Cache-to-Origin: <origin>[,<origin>...] <rtt> <samples> <hops>
      The sender of this header has measured the round trip time to a set
      of origin servers (given as a comma separated list of <origin>
      hostnames).  The <rtt> is the average number of seconds, expressed as
      decimal ASCII with arbitrary precision and no exponent.  <Samples> is
      the number of RTT samples which have had input to this average.
      <Hops> is the number of routers between the cache and the origin, or
      0 if the cache doesn't know.









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   6 - Transport Policy Controls

   A set of configuration variables concerning transport characteristics
   should be maintained for each agent which is capable of initiating HTCP
   transactions, perhaps with a set of per-agent global defaults.  These
   variables are:

      Maximum number of unacknowledged transactions before a ``failure'' is
      imputed.

      Maximum interval without a response to some transaction before a
      ``failure'' is imputed.

      Should ICMP-Portunreach be treated as a failure?

      Should RESPONSE=5 && MO=1 be treated as a failure?

      Minimum interval before trying a new transaction after a failure






























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   7 - Operations and their Opcodes

   HTCP/0.* opcodes and their respective OP-DATA are defined below:

   7.1. NOP (OPCODE 0):

   This is an HTCP-level ``ping.''  Responders are encouraged to process
   NOP's with minimum delay since the requestor may be using the NOP RTT
   (round trip time) for configuration or mapping purposes.  The RESPONSE
   code for a NOP is always zero (0).  There is no OP-DATA for a NOP.  NOP
   requests with RD=0 cause no processing to occur at all.

   7.2. TST (OPCODE 1):

   Test for the presence of a specified content entity in a proxy cache.
   TST requests with RD=0 cause no processing to occur at all.

   TST requests have the following OP-DATA:

                    +0 (MSB)                            +1 (LSB)
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      0: |                                                               |
         /                          SPECIFIER                            /
         /                                                               /
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+


   RESPONSE codes for TST are as follows:

          0   entity is present in responder's cache (OP-DATA valid)
          1   entity is not present in responder's cache

   TST responses have the following OP-DATA, if RESPONSE is zero (0):

                    +0 (MSB)                            +1 (LSB)
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      0: |                                                               |
         /                             DETAIL                            /
         /                                                               /
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+


   DETAIL  is a set of cache, entity, and response headers.  The cache
           headers are described above.  Entity and response headers are
           defined by HTTP.



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   7.3. MON (OPCODE 2):

   Monitor activity in a proxy cache (adds, deletes, replacements, etc).
   Since interleaving of HTCP transaction over a single pair of UDP
   endpoints is not supported, it is recommended that a unique UDP endpoint
   be allocated by the requestor for each concurrent MON request.  MON
   requests with RD=0 are equivilent to those with RD=1 and TIME=0; that
   is, they will cancel any outstanding MON transaction.

   MON requests have the following OP-DATA structure:

                     +0 (MSB)
         +---+---+---+---+---+---+---+---+
      0: |             TIME              |
         +---+---+---+---+---+---+---+---+


   TIME  is the number of seconds of monitoring output desired by the
         initiator.  Subsequent MON requests from the same initiator with
         the same MSG-ID should update the time on a ongoing MON
         transaction.  This is called ``overlapping renew.''

   RESPONSE codes for MON are as follows:

            0   accepted, OP-DATA is present and valid
            1   refused (quota error -- too many MON's are active)


   MON responses have the following OP-DATA structure, if RESPONSE is zero
   (0):

                    +0 (MSB)                            +1 (LSB)
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      0: |             TIME              |     ACTION    |     REASON    |
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      2: |                                                               |
         /                            IDENTITY                           /
         /                                                               /
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+


   TIME      is the number of seconds remaining for this MON transaction.

   ACTION    is a numeric code indicating a cache population action.  Codes
             are:



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                     0   an entity has been added to the cache
                     1   an entity in the cache has been refreshed
                     2   an entity in the cache has been replaced
                     3   an entity in the cache has been deleted


   REASON    is a numeric code indicating the reason for an ACTION.  Codes
             are:

                0   some reason not covered by the other REASON codes
                1   a proxy client fetched this entity
                2   a proxy client fetched with caching disallowed
                3   the proxy server prefetched this entity
                4   the entity expired, per its headers
                5   the entity was purged due to caching storage limits


   7.4. SET (OPCODE 3):

   Inform a cache of the identity of an object.  This is a ``push''
   transaction, whereby cooperating caches can share information such as
   updated Age/Date/Expires headers (which might result from an origin
   ``304 Not modified'' response) or updated cache headers (which might
   result from the discovery of non-authoritative ``vary'' conditions or
   from learning of second or third party cache locations for this entity.
   RD is honoured.

   SET requests have the following OP-DATA structure:

         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      0: |                                                               |
         /                            IDENTITY                           /
         /                                                               /
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+


   RESPONSE  codes are as follows:

                    0   identity accepted, thank you
                    1   identity ignored, no reason given, thank you


   SET responses have no OP-DATA.





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   7.5. CLR (OPCODE 4):

   Tell a cache to completely forget about an entity.  RD is honoured.

   CLR requests have the following OP-DATA structure:

         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      0: |                   RESERVED                    |     REASON    |
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      2: |                                                               |
         /                           SPECIFIER                           /
         /                                                               /
         +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+


   REASON    is a numeric code indicating the reason why the requestor is
             asking that this entity be removed.  The codes are as follows:

             0   some reason not better specified by another code
             1   the origin server told me that this entity does not exist


   RESPONSE  codes are as follows:

                     0   i had it, it's gone now
                     1   i had it, i'm keeping it, no reason given.
                     2   i didn't have it


   CLR responses have no OP-DATA.

   Clearing a URL without specifying response, entity, or cache headers
   means to clear all entities using that URL.

   5 - Security Considerations













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   6 - References

   [RFC2068]
      R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T. Berners-Lee,
      ``Hypertext Transfer Protocol -- HTTP/1.1,'' RFC 2068, UC Irvine,
      DEC, MIT/LCS, January 1997

   [RFC2186]
      D. Wessels, K. Claffy, ``Internet Cache Protocol (ICP), version 2,''
      RFC 2186, National Laboratory for Applied Network Research/UCSD,
      September 1997

   7 - Author's Address

         Paul Vixie
            Vixie Enterprises
            950 Charter Street
            Redwood City, CA 94063
            [phone]
            <[e-mail]>




























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