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This document was published by the RFC Editor on Apr 1, 2014.
Request for Comments: 7168
The Hyper Text Coffee Pot Control Protocol (HTCPCP) specification does not allow for the brewing of tea, in all its variety and complexity. This paper outlines an extension to HTCPCP to allow for pots to provide networked tea-brewing facilities.
Status of This Memo
This document is not an Internet Standards Track specification; it is published for informational purposes.
This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
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As noted in the Hyper Text Coffee Pot Control Protocol, coffee is renowned worldwide as an artfully brewed caffeinated beverage, but coffee shares this quality with many other varied preparations based on the filtration of plant material. Foremost, among these are the category of brews based on the straining of water through prepared leaves from a tea tree: the lineage and history of the tea genus will not be recounted as part of this paper, but evidence shows that the production of tea existed many thousands of years ago.
The deficiency of HTCPCP in addressing the networked production of such a venerable beverage as tea is noteworthy: indeed, the only provision given for networked teapots is that they not respond to requests for the production of coffee, which, while eminently reasonable, does not allow for communication with the teapot for its intended purpose.
This paper specifies an extension to HTCPCP to allow communication with networked tea production devices and teapots. The additions to the protocol specified herein permit the requests and responses necessary to control all devices capable of making, arguably, the most popular caffeinated hot beverage.
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in RFC 2119.
2. HTCPCP-TEA Protocol Additions
The TEA extension to HTCPCP adapts the operation of certain HTCPCP methods.
Control of a TEA-capable pot is performed, as described in the base
HTCPCP specification, through the sending of
requests are treated equivalently, but they remain deprecated. Tea
production differs from coffee, however, in that a choice of teas is
often provided for client selection before the tea is brewed. To
this end, a TEA-capable pot that receives a
BREW message of content
message/teapot MUST respond in accordance with the URI
requested, as below.
For the URI
/, brewing will not commence. Instead, an
header as defined in RFC 2295 MUST be sent, with the
available tea bags and/or leaf varieties as entries. An example of
such a response is as follows:
The following example demonstrates the possibility of interoperability of a TEA-capable pot that also complies with the base HTCPCP specification:
TEA-capable HTCPCP clients MUST check the contents of the
header returned by a
BREW request, and provide a specific URI for
subsequent requests of the
A request to the
/ URI with a
Content-Type header of
message/coffeepot SHOULD also be responded to with an
header in the above format, to allow TEA-capable clients the
opportunity to present the selection of teas to the user if inferior
caffeinated beverages have initially been requested.
2.1.2. Variety-Specific URIs
TEA-capable pots follow the base HTCPCP specification when presented
BREW request for a specific variety of tea. Pots SHOULD
follow the recommendations for brewing strength given by each
variety, and stop brewing when this strength is reached; it is
suggested that the strength be measured by detection of the opacity
of the beverage currently under brew by the pot.
TEA-capable clients SHOULD indicate the end of brewing by sending a
BREW request with an entity body containing
stop; the pot MAY
continue brewing beyond the recommended strength until this is
received. If the
stop request is not sent by the client, this may
result in a state inversion in the proportion of tea to water in the
brewing pot, which may be reported by some pots as a negative
BREW command with an entity body containing
stop is received
before the recommended strength is achieved, the pot MUST abort
brewing and serve the resultant beverage at lesser strength. Finding
the preferred strength of beverage when using this override is a
function of the time between the TEA-capable pot receiving a
request and the subsequent
stop. Clients SHOULD be prepared to
make multiple attempts to reach the preferred strength.
2.2. Modified Header Fields
HTCPCP-TEA modifies the definition of one header field from the base HTCPCP specification.
Accept-Additions Header Field
It has been observed that some users of blended teas have an
occasional preference for teas brewed as an emulsion of cane sugar
with hints of water. To allow for this circumstance, the
header field defined in the base HTCPCP specification is
updated to allow the following options:
Implementers should be aware that excessive use of the
may cause the
BREW request to exceed the segment size allowed by the
transport layer, causing fragmentation and a delay in brewing.
2.3. Response Codes
HTCPCP-TEA makes use of normal HTTP error codes and those defined in the base HTCPCP specification.
2.3.1. 300 Multiple Options
BREW request to the
/ URI, as defined in Section 2.1.1, will
Alternates header indicating the URIs of the available
varieties of tea to brew. It is RECOMMENDED that this response be
served with a status code of 300, to indicate that brewing has not
commenced and further options must be chosen by the client.
2.3.2. 403 Forbidden
Services that implement the
Accept-Additions header field MAY return
a 403 status code for a
BREW request of a given variety of tea, if
the service deems the combination of additions requested to be
contrary to the sensibilities of a consensus of drinkers regarding
the variety in question.
A method of garnering and collating consensus indicators of the most viable combinations of additions for each variety to be served is outside the scope of this document.
2.3.3. 418 I'm a Teapot
TEA-capable pots that are not provisioned to brew coffee may return either a status code of 503, indicating temporary unavailability of coffee, or a code of 418 as defined in the base HTCPCP specification to denote a more permanent indication that the pot is a teapot.
message/teapot Media Type
To distinguish messages destined for TEA-capable HTCPCP services from
pots compliant with the base HTCPCP specification, a new MIME media
type is defined by this document. The
Content-Type header of a
BREW request sent to a TEA-capable pot MUST be
tea is to be requested.
4. Environmental Considerations
As noted in Section 2.1, a
BREW request with a
message/teapot to a TEA-capable pot will result in an
Alternates header being sent with the response, and a pot will not be
brewed. However, if the
BREW request has a
message/coffeepot, and the pot is capable of brewing coffee, the
service's behavior will fall back to the base HTCPCP specification
and a pot will be brewed.
If the entity returned by the server when brewing commences contains
Alternates header indicating
the client does not want coffee, the client SHOULD then send a
request with an entity body containing
stop. This will result in
wasted coffee; whether this is regarded as a bad thing is user-
Such waste can be prevented by TEA-capable clients, by first
BREW of type
message/teapot and then allowing
selection of an available beverage.
5. Security Considerations
As with the base HTCPCP specification, most TEA-capable pots are expected to heat water through the use of electric elements, and as such will not be in proximity to fire. Therefore, no firewalls are necessary for communication with these pots to proceed.
This extension does support communication with fired pots, however, which may require heat retention and control policies. Care should be taken so that coal-fired pots and electrically heated kettles are not connected to the same network, to prevent pots from referring to any kettles on the network as darkened or otherwise smoke driven.
This extension to the HTCPCP specification would not be possible without the base specification, and research on networked beverage production leading up thereto. In that vein, the author wishes to acknowledge the sterling work of Larry Masinter in the development of the leading protocol for coffee pot communication.
Many thanks also to Kevin Waterson and Pete Davis, for providing guidance and suggestions during the drafting of this document.