Error 418 – I’m A Teapot

Error 418 - I'm A Teapot

Once upon a time, there was a little known thing called the internet. Most everyone knows that TCP/IP (Transmission Control Protocol/Internet Protocol) was created by the US military in an attempt to be able to relay messages and other important documents from one military installation to another in a quick – or at least quicker – manner vs carrier pigeon.

Once this marvelous technology became known, it was obvious that everyone wanted to get their hands on it, and who wouldn’t. At the time, inventions of all sorts were being created.

While most of the world was still coming out of the dark ages from new inventions like frozen food, toasters, etc in the 1950’s, there were groups of engineers like myself, either being born or camped-out in a garage somewhere figuring out the next greatest invention.

In the 1960’s and into the 1970’s, there were now companies of all sizes trying to figure out the next greatest gizmo, or any gizmo’s that would be able to communicate with each other.

During the big bang of the early 1980’s and into the late 1990’s, the TCP/IP standard was already in full swing. Companies now were hot on the trail of making anything that could connect to this new thing called the internet.

As to be expected, so were the CEO’s of these companies racing to get their engineering teams to push forward as fast as possible to beat the competition that lie in wait in the next building to theirs.

Hence, as universities, engineers and all walks of life that had an interest in this new internet technology, were spending countless hours at the office, school, etc, and as to be expected, after so many hours of rattling one’s brain, you get to be a little loopy to say the least.

One such outcome of being loopy is the “Error 418 – I’m a teapot”. With all of the new technologies, there also have to be a governing body to keep track of all of it as well as receive input from others in order to improve whatever technology one might be working on.

Hence the RFC was created. The Request for Comments is a publication from the Internet Society and its associated bodies, most prominently the Internet Engineering Task Force, the principal technical development and standards-setting bodies for the Internet.

Not to be out witted, one such engineer, came up with the “Hyper Text Coffee Pot Control Protocol” and submitted it to the RFC and it remains to this day. It is by far a unique blend of engineering humor.

Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)
RFC 2324 HTCPCP/1.0 1 April 1998

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

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).

HTCPCP Added Methods

2.1 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.

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

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.

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

  1. 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.

  1. 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”

  2. 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 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 tunneling

  1. 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

  2. Security Considerations Anyone who gets in between me and my morning coffee should be insecure. 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.

  3. 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 creation.

[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

[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”,

10.Author’s Address
Larry Masinter
Xerox Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto, CA 94304

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 English. 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