Network Working Group L. Masinter
Request for Comments: 2324 1 April 1998
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 (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.
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
HTCPCP on HTTP.
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
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.
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
188.8.131.52 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"
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
2.2.2 New header fields
184.108.40.206 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 = ( "*"
) *( ";" 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
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 )
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
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
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.
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.
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
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068,
[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
[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
Xerox Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto, CA 94304
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