[RFC Home] [TEXT|PDF|HTML] [Tracker] [IPR] [Errata] [Info page]

Updated by: 7168 Errata Exist
Network Working Group                                       L. Masinter
Request for Comments: 2324                                 1 April 1998
Category: Informational

          Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.


   This document describes HTCPCP, a protocol for controlling,
   monitoring, and diagnosing coffee pots.

1. Rationale and Scope

   There is coffee all over the world. Increasingly, in a world in which
   computing is ubiquitous, the computists want to make coffee. Coffee
   brewing is an art, but the distributed intelligence of the web-
   connected world transcends art.  Thus, there is a strong, dark, rich
   requirement for a protocol designed espressoly for the brewing of
   coffee. Coffee is brewed using coffee pots.  Networked coffee pots
   require a control protocol if they are to be controlled.

   Increasingly, home and consumer devices are being connected to the
   Internet. Early networking experiments demonstrated vending devices
   connected to the Internet for status monitoring [COKE]. One of the
   first remotely _operated_ machine to be hooked up to the Internet,
   the Internet Toaster, (controlled via SNMP) was debuted in 1990

   The demand for ubiquitous appliance connectivity that is causing the
   consumption of the IPv4 address space. Consumers want remote control
   of devices such as coffee pots so that they may wake up to freshly
   brewed coffee, or cause coffee to be prepared at a precise time after
   the completion of dinner preparations.

Masinter                     Informational                      [Page 1]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   This document specifies a Hyper Text Coffee Pot Control Protocol
   (HTCPCP), which permits the full request and responses necessary to
   control all devices capable of making the popular caffeinated hot

   HTTP 1.1 ([RFC2068]) permits the transfer of web objects from origin
   servers to clients. The web is world-wide.  HTCPCP is based on HTTP.
   This is because HTTP is everywhere. It could not be so pervasive
   without being good. Therefore, HTTP is good. If you want good coffee,
   HTCPCP needs to be good. To make HTCPCP good, it is good to base

   Future versions of this protocol may include extensions for espresso
   machines and similar devices.

2. HTCPCP Protocol

   The HTCPCP protocol is built on top of HTTP, with the addition of a
   few new methods, header fields and return codes.  All HTCPCP servers
   should be referred to with the "coffee:" URI scheme (Section 4).

2.1 HTCPCP Added Methods

2.1.1 The BREW method, and the use of POST

   Commands to control a coffee pot are sent from client to coffee
   server using either the BREW or POST method, and a message body with
   Content-Type set to "application/coffee-pot-command".

   A coffee pot server MUST accept both the BREW and POST method
   equivalently.  However, the use of POST for causing actions to happen
   is deprecated.

   Coffee pots heat water using electronic mechanisms, so there is no
   fire. Thus, no firewalls are necessary, and firewall control policy
   is irrelevant. However, POST may be a trademark for coffee, and so
   the BREW method has been added. The BREW method may be used with
   other HTTP-based protocols (e.g., the Hyper Text Brewery Control

2.1.2 GET method

   In HTTP, the GET method is used to mean "retrieve whatever
   information (in the form of an entity) identified by the Request-
   URI." If the Request-URI refers to a data-producing process, it is
   the produced data which shall be returned as the entity in the
   response and not the source text of the process, unless that text
   happens to be the output of the process.

Masinter                     Informational                      [Page 2]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   In HTCPCP, the resources associated with a coffee pot are physical,
   and not information resources. The "data" for most coffee URIs
   contain no caffeine.

2.1.3 PROPFIND method

   If a cup of coffee is data, metadata about the brewed resource is
   discovered using the PROPFIND method [WEBDAV].

2.1.4 WHEN method

   When coffee is poured, and milk is offered, it is necessary for the
   holder of the recipient of milk to say "when" at the time when
   sufficient milk has been introduced into the coffee. For this
   purpose, the "WHEN" method has been added to HTCPCP. Enough? Say

2.2 Coffee Pot Header fields

   HTCPCP recommends several HTTP header fields and defines some new

2.2.1 Recommended header fields The "safe" response header field.

   [SAFE] defines a HTTP response header field, "Safe", which can be
   used to indicate that repeating a HTTP request is safe. The inclusion
   of a "Safe: Yes" header field allows a client to repeat a previous
   request if the result of the request might be repeated.

   The actual safety of devices for brewing coffee varies widely, and
   may depend, in fact, on conditions in the client rather than just in
   the server. Thus, this protocol includes an extension to the "Safe"
   response header:

          Safe                = "Safe" ":" safe-nature
          safe-nature         = "yes" | "no" | conditionally-safe
          conditionally-safe  = "if-" safe-condition
          safe-condition      = "user-awake" | token

   indication will allow user agents to handle retries of some safe
   requests, in particular safe POST requests, in a more user-friendly

Masinter                     Informational                      [Page 3]

RFC 2324                       HTCPCP/1.0                   1 April 1998

2.2.2 New header fields The Accept-Additions header field

   In HTTP, the "Accept" request-header field is used to specify media
   types which are acceptable for the response. However, in HTCPCP, the
   response may result in additional actions on the part of the
   automated pot. For this reason, HTCPCP adds a new header field,

       Accept-Additions = "Accept-Additions" ":"
                          #( addition-range [ accept-params ] )

        addition-type   = ( "*"
                          | milk-type
                          | syrup-type
                          | sweetener-type
                          | spice-type
                          | alcohol-type
                          ) *( ";" parameter )
        milk-type       = ( "Cream" | "Half-and-half" | "Whole-milk"
                          | "Part-Skim" | "Skim" | "Non-Dairy" )
        syrup-type      = ( "Vanilla" | "Almond" | "Raspberry"
                          | "Chocolate" )
        alcohol-type    = ( "Whisky" | "Rum" | "Kahlua" | "Aquavit" )

2.2.3 Omitted Header Fields

   No options were given for decaffeinated coffee. What's the point?

2.3 HTCPCP return codes

   Normal HTTP return codes are used to indicate difficulties of the
   HTCPCP server. This section identifies special interpretations and
   new return codes.

2.3.1 406 Not Acceptable

   This return code is normally interpreted as "The resource identified
   by the request is only capable of generating response entities which
   have content characteristics not acceptable according to the accept
   headers sent in the request. In HTCPCP, this response code MAY be
   returned if the operator of the coffee pot cannot comply with the
   Accept-Addition request. Unless the request was a HEAD request, the
   response SHOULD include an entity containing a list of available
   coffee additions.

Masinter                     Informational                      [Page 4]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   In practice, most automated coffee pots cannot currently provide

2.3.2 418 I'm a teapot

   Any attempt to brew coffee with a teapot should result in the error
   code "418 I'm a teapot". The resulting entity body MAY be short and

3. The "coffee" URI scheme

   Because coffee is international, there are international coffee URI
   schemes.  All coffee URL schemes are written with URL encoding of the
   UTF-8 encoding of the characters that spell the word for "coffee" in
   any of 29 languages, following the conventions for
   internationalization in URIs [URLI18N].

coffee-url  =  coffee-scheme ":" [ "//" host ]
                ["/" pot-designator ] ["?" additions-list ]

coffee-scheme = ( "koffie"                      ; Afrikaans, Dutch
                  | "q%C3%A6hv%C3%A6"          ; Azerbaijani
                  | "%D9%82%D9%87%D9%88%D8%A9" ; Arabic
               | "akeita"                   ; Basque
               | "koffee"                   ; Bengali
               | "kahva"                    ; Bosnian
               | "kafe"                     ; Bulgarian, Czech
               | "caf%C3%E8"                ; Catalan, French, Galician
                  | "%E5%92%96%E5%95%A1"       ; Chinese
                  | "kava"                     ; Croatian
               | "k%C3%A1va                 ; Czech
               | "kaffe"                    ; Danish, Norwegian, Swedish
               | "coffee"                   ; English
               | "kafo"                     ; Esperanto
                  | "kohv"                     ; Estonian
               | "kahvi"                    ; Finnish
               | "%4Baffee"                 ; German
               | "%CE%BA%CE%B1%CF%86%CE%AD" ; Greek
               | "%E0%A4%95%E0%A5%8C%E0%A4%AB%E0%A5%80" ; Hindi
               | "%E3%82%B3%E3%83%BC%E3%83%92%E3%83%BC" ; Japanese
               | "%EC%BB%A4%ED%94%BC"       ; Korean
               | "%D0%BA%D0%BE%D1%84%D0%B5" ; Russian
               | "%E0%B8%81%E0%B8%B2%E0%B9%81%E0%B8%9F" ; Thai

   pot-designator = "pot-" integer  ; for machines with multiple pots
   additions-list = #( addition )

Masinter                     Informational                      [Page 5]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   All alternative coffee-scheme forms are equivalent.  However, the use
   of coffee-scheme in various languages MAY be interpreted as an
   indication of the kind of coffee produced by the coffee pot.  Note
   that while URL scheme names are case-independent, capitalization is
   important for German and thus the initial "K" must be encoded.

4. The "message/coffeepot" media type

   The entity body of a POST or BREW request MUST be of Content-Type
   "message/coffeepot". Since most of the information for controlling
   the coffee pot is conveyed by the additional headers, the content of
   "message/coffeepot" contains only a coffee-message-body:

   coffee-message-body = "start" | "stop"

5. Operational constraints

   This section lays out some of the operational issues with deployment
   of HTCPCP ubiquitously.

5.1 Timing Considerations

   A robust quality of service is required between the coffee pot user
   and the coffee pot service.  Coffee pots SHOULD use the Network Time
   Protocol [NTP] to synchronize their clocks to a globally accurate
   time standard.

   Telerobotics has been an expensive technology. However, with the
   advent of the Cambridge Coffee Pot [CAM], the use of the web (rather
   than SNMP) for remote system monitoring and management has been
   proven.  Additional coffee pot maintenance tasks might be
   accomplished by remote robotics.

   Web data is normally static. Therefore to save data transmission and
   time, Web browser programs store each Web page retrieved by a user on
   the user's computer. Thus, if the user wants to return to that page,
   it is now stored locally and does not need to be requested again from
   the server. An image used for robot control or for monitoring a
   changing scene is dynamic. A fresh version needs to be retrieved from
   the server each time it is accessed.

5.2 Crossing firewalls

   In most organizations HTTP traffic crosses firewalls fairly easily.
   Modern coffee pots do not use fire. However, a "firewall" is useful
   for protection of any source from any manner of heat, and not just
   fire. Every home computer network SHOULD be protected by a firewall
   from sources of heat. However, remote control of coffee pots is

Masinter                     Informational                      [Page 6]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   important from outside the home. Thus, it is important that HTCPCP
   cross firewalls easily.

   By basing HTCPCP on HTTP and using port 80, it will get all of HTTP's
   firewall-crossing virtues. Of course, the home firewalls will require
   reconfiguration or new versions in order to accommodate HTCPCP-
   specific methods, headers and trailers, but such upgrades will be
   easily accommodated. Most home network system administrators drink
   coffee, and are willing to accommodate the needs of tunnelling

6. System management considerations

   Coffee pot monitoring using HTTP protocols has been an early
   application of the web.  In the earliest instance, coffee pot
   monitoring was an early (and appropriate) use of ATM networks [CAM].

   The traditional technique [CAM] was to attach a frame-grabber to a
   video camera, and feed the images to a web server. This was an
   appropriate application of ATM networks. In this coffee pot
   installation, the Trojan Room of Cambridge University laboratories
   was used to give a web interface to monitor a common coffee pot.  of
   us involved in related research and, being poor, impoverished
   academics, we only had one coffee filter machine between us, which
   lived in the corridor just outside the Trojan Room. However, being
   highly dedicated and hard-working academics, we got through a lot of
   coffee, and when a fresh pot was brewed, it often didn't last long.

   This service was created as the first application to use a new RPC
   mechanism designed in the Cambridge Computer Laboratory - MSRPC2. It
   runs over MSNL (Multi-Service Network Layer) - a network layer
   protocol designed for ATM networks.

   Coffee pots on the Internet may be managed using the Coffee Pot MIB

7. Security Considerations

   Anyone who gets in between me and my morning coffee should be

   Unmoderated access to unprotected coffee pots from Internet users
   might lead to several kinds of "denial of coffee service" attacks.
   The improper use of filtration devices might admit trojan grounds.
   Filtration is not a good virus protection method.

Masinter                     Informational                      [Page 7]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   Putting coffee grounds into Internet plumbing may result in clogged
   plumbing, which would entail the services of an Internet Plumber
   [PLUMB], who would, in turn, require an Internet Plumber's Helper.

   Access authentication will be discussed in a separate memo.

8. Acknowledgements

   Many thanks to the many contributors to this standard, including Roy
   Fielding, Mark Day, Keith Moore, Carl Uno-Manros, Michael Slavitch,
   and Martin Duerst.  The inspiration of the Prancing Pony, the CMU
   Coke Machine, the Cambridge Coffee Pot, the Internet Toaster, and
   other computer controlled remote devices have led to this valuable

9. References

   [RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
   Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068,
   January 1997.

   [RFC2186] Wessels, D., and K. Claffy, "Internet Cache Protocol (ICP),
   version 2," RFC 2186, September 1997

   [CPMIB] Slavitch, M., "Definitions of Managed Objects for Drip-Type
   Heated Beverage Hardware Devices using SMIv2", RFC 2325, 1 April

   [HTSVMP] Q. Stafford-Fraser, "Hyper Text Sandwich Van Monitoring
   Protocol, Version 3.2". In preparation.

   [RFC2295] Holtman, K., and A. Mutz, "Transparent Content Negotiation
   in HTTP", RFC 2295, March 1998.

   [SAFE] K. Holtman. "The Safe Response Header Field", September 1997.

   [CAM] "The Trojan Room Coffee Machine", D. Gordon and M. Johnson,
   University of Cambridge Computer Lab,

   [CBIO] "The Trojan Room Coffee Pot, a (non-technical) biography", Q.
   Stafford-Fraser, University of Cambridge Computer Lab,

   [RFC2235] Zakon, R., "Hobbes' Internet Timeline", FYI 32, RFC 2230,
   November 1997.  See also

Masinter                     Informational                      [Page 8]

RFC 2324                       HTCPCP/1.0                   1 April 1998

   [NTP] Mills, D., "Network Time Protocol (Version 3) Specification,
   Implementation and Analysis", RFC 1305, March 1992.

   [URLI18N] Masinter, L., "Using UTF8 for non-ASCII Characters in
   Extended URIs" Work in Progress.

   [PLUMB] B. Metcalfe, "Internet Plumber of the Year: Jim Gettys",
   Infoworld, February 2, 1998.

   [COKE] D. Nichols, "Coke machine history", C. Everhart, "Interesting
   uses of networking", <http://www-

10. Author's Address

   Larry Masinter
   Xerox Palo Alto Research Center
   3333 Coyote Hill Road
   Palo Alto, CA 94304

   EMail: masinter@parc.xerox.com

Masinter                     Informational                      [Page 9]

RFC 2324                       HTCPCP/1.0                   1 April 1998

11.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

Masinter                     Informational                     [Page 10]