CoRE Z. Shelby
Internet-Draft Sensinode
Intended status: Standards Track January 2, 2012
Expires: July 5, 2012
CoRE Interfaces
draft-shelby-core-interfaces-00
Abstract
This document defines well-known interface descriptions for Batch,
Sensor, Parameter and Actuator types for use in contrained web
servers using the CoRE Link Format. A short reference is provided
for each type that can be efficiently included in the interface
description attribute of the CoRE Link Format.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 5, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Shelby Expires July 5, 2012 [Page 1]
Internet-Draft CoRE Interfaces January 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Interface Descriptions . . . . . . . . . . . . . . . . . . . . 3
3.1. Batch . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Parameter . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Actuator . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Future Interfaces . . . . . . . . . . . . . . . . . . . . 7
3.6. WADL Description . . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Shelby Expires July 5, 2012 [Page 2]
Internet-Draft CoRE Interfaces January 2012
1. Introduction
The Constrained RESTful Environments (CoRE) working group aims at
realizing the REST architecture in a suitable form for the most
constrained nodes (e.g. 8-bit microcontrollers with limited RAM and
ROM) and networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-
machine (M2M) applications such as smart energy and building
automation.
The discovery of resources offered by a constrained server is very
important in machine-to-machine applications where there are no
humans in the loop and static interfaces result in fragility. The
discovery of resources provided by an HTTP Web Server is typically
called Web Linking [RFC5988]. The use of Web Linking for the
description and discovery of resources hosted by constrained web
servers is specified by the CoRE Link Format
[I-D.ietf-core-link-format] and can be used by CoAP
[I-D.ietf-core-coap] or HTTP servers. The CoRE Link Format defines
an attribute that can be used to describe the REST interface of a
resource, and may include a link to a description document. This
document defines well-known interface descriptions for Batch, Sensor,
Parameter and Actuator types for use in contrained web servers. A
short reference is provided for each type that can be efficiently
included in the interface description (if=) attribute of the CoRE
Link Format.
2. Terminology
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 [RFC2119].
This specification requires readers to be familiar with all the terms
and concepts that are discussed in [RFC5988] and
[I-D.ietf-core-link-format].
3. Interface Descriptions
This section defines REST interfaces for Batch, Sensor, Parameter and
Actuator resources. Each type is described along with its Interface
Description attribute value, recommended path pattern and valid
methods. These are defined for each interface in the table below.
These interfaces can support plain text and/or SenML Media types.
The if= column defines the Interface Description (if=) attribute
value to be used in the CoRE Link Format for a resource conforming to
Shelby Expires July 5, 2012 [Page 3]
Internet-Draft CoRE Interfaces January 2012
that interface. When this value appears in the if= attribute of a
link, the resource MUST support the corresponding REST interface
described in this section. The resource MAY support additional
functionality, which is out of scope for this specification.
Although these interface descriptions are intended to be used with
the CoRE Link Format, they are applicable for use in any REST
interface definition.
The Path column defines an example path pattern that a resource of
this type might use for simple end-points. These interfaces are
expected to be used in other path patterns. In any case, resource
paths SHOULD be discoverable as described in
[I-D.ietf-core-link-format].
The Methods column defines the methods supported by that interface,
which are described in more detail below.
+-----------+--------+--------------+-----------------------------+
| Interface | if= | Path Example | Methods |
+-----------+--------+--------------+-----------------------------+
| Batch | core#b | /s,/p,/a | GET, PUT (where applicable) |
| Sensor | core#s | /s/{name} | GET |
| Parameter | core#p | /p/{name} | GET, PUT |
| Actuator | core#a | /a/{name} | GET, PUT |
+-----------+--------+--------------+-----------------------------+
The following is an example of links in the CoRE Link Format using
these interface descriptions. These links are used in the subsequent
examples below.
Req: GET /.well-known/core
Res: 2.05 Content (application/link-format)
</s>;if="core#b",
</s/light>;if="core#s",
</s/temp>;if="core#s",
</s/humidity>;if="core#s",
</p/name>;if="core#p",
</a>;if="core#b",
</a/led1>;if="core#a",
</a/led2>;if="core#a"
3.1. Batch
The Batch interface is used to manipulate a collection of sub-
resources at the same time. The Batch interface type supports the
same methods as its sub-resources, and can be used to read (GET) or
set (PUT) the values of those sub-resource with a single resource
Shelby Expires July 5, 2012 [Page 4]
Internet-Draft CoRE Interfaces January 2012
representation. The sub-resources of a Batch MAY be heterogeneous, a
method used on the Batch only applies to sub-resources that support
it. For example Sensor interfaces do not support PUT, and thus a PUT
request to a Sensor member of that Batch would be ignored. A batch
requires the use of SenML Media types in order to support multiple
sub-resources.
The following example interacts with a Batch /s with Sensor sub-
resources /s/light, /s/temp and /s/humidity.
Req: GET /s
Res: 2.05 Content (application/senml+json)
{"e":[
{ "n": "light", "v": 123, "u": "lx" },
{ "n": "temp", "v": 27.2, "u": "degC" },
{ "n": "humidity", "v": 80, "u": "%RH" }],
}
3.2. Sensor
The Sensor interface allows the value of a sensor resource to be read
(GET). The Media type of the resource can be either plain text or
SenML. Plain text MAY be used for a single measurement that does not
require meta-data. For a measurement with meta-data such as a unit
or time stamp, SenML SHOULD be used. A resource with this interface
MAY use SenML to return multiple measurements in the same
representation, for example a list of recent measurements.
The following are examples of Sensor interface requests in both text/
plain and application/senml+json.
Req: GET /s/humidity (Accept: text/plain)
Res: 2.05 Content (text/plain)
80
Req: GET /s/humidity (Accept: application/senml+json)
Res: 2.05 Content (application/senml+json)
{"e":[
{ "n": "humidity", "v": 80, "u": "%RH" }],
}
Shelby Expires July 5, 2012 [Page 5]
Internet-Draft CoRE Interfaces January 2012
3.3. Parameter
The Parameter interface allows configurable parameters and other
information to be modeled as a resource. The value of the parameter
can be read (GET) or set (PUT). The PUT method is not required, and
thus a parameter can be made read-only. Plain text or SenML Media
types MAY be returned from this type of interface.
The following example shows request for reading and setting a
parameter.
Req: GET /p/name
Res: 2.05 Content (text/plain)
node5
Req: PUT /p/name (text/plain)
outdoor
Res: 2.04 Changed
3.4. Actuator
The Actuator interface is used by resources that model different
kinds of actuators (changing its value has an effect on its
environment). Examples of actuators include for example LEDs,
relays, motor controllers and light dimmers. The current value of
the actuator can be read (GET) or a new actuator value set (PUT).
Plain text or SenML Media types MAY be returned from this type of
interface. A resource with this interface MAY use SenML to include
multiple measurements in the same representation, for example a list
of recent actuator values or a list of values to set.
The following example shows request for reading and setting an
actuator (turning on a led).
Req: GET /a/led1
Res: 2.05 Content (text/plain)
0
Req: PUT /a/led1 (text/plain)
1
Res: 2.04 Changed
Shelby Expires July 5, 2012 [Page 6]
Internet-Draft CoRE Interfaces January 2012
3.5. Future Interfaces
It is expected that further interface descriptions will be defined in
this and other specifications. Potential interfaces to be considered
for this specifications include:
Batch of Links: This resource would contain a list of links,
pointing to resources that will be manipulated by requesting a
method on that resource.
Collection: This resource would be a container that allows sub-
resources to be added or removed.
3.6. WADL Description
This section defines the formal Web Application Description Langauge
(WADL) definition of these CoRE interface descriptions.
<?xml version="1.0" standalone="yes"?>
<application xmlns="http://research.sun.com/wadl/2006/10"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<grammars>
<include href="http://tools.ietf.org/html/draft-jennings-senml"/>
</grammars>
<doc title="CoRE Interfaces"/>
<resource_type id="b">
<doc title="Batch of sub-resources type. The method is applied
to each sub-resource of the requested resource that
supports it. Mixed sub-resource types can be supported."/>
<method id="b_request" name="GET">
<doc>Retrieve the representations of all resources under
this collection in a single request.</doc>
<request/>
<response status="200">
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</response>
</method>
<method id="b_update" name="PUT">
<doc>Update the representations of all resources under
this collection in a single request that support
PUT.</doc>
Shelby Expires July 5, 2012 [Page 7]
Internet-Draft CoRE Interfaces January 2012
<request>
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</request>
<response/>
</method>
</resource_type>
<resource_type id="s">
<doc title="Sensor resource type"/>
<method id="s_request" name="GET">
<doc>Retrieve the value of the sensor</doc>
<request/>
<response status="200">
<representation mediaType="text/plain"/>
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</response>
</method>
</resource_type>
<resource_type id="p">
<doc title="Parameter resource type"/>
<method id="p_request" name="GET">
<doc>Retrieve the value of the parameter</doc>
<request/>
<response status="200">
<representation mediaType="text/plain"/>
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</response>
</method>
<method id="p_update" name="PUT">
<doc>Update to the parameter value</doc>
<request>
<representation mediaType="text/plain"/>
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</request>
<response/>
</method>
</resource_type>
<resource_type id="a">
Shelby Expires July 5, 2012 [Page 8]
Internet-Draft CoRE Interfaces January 2012
<doc title="Actuator resource type"/>
<method id="a_request" name="GET">
<doc>Retrieve the value of the actuator</doc>
<request/>
<response status="200">
<representation mediaType="text/plain"/>
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</response>
</method>
<method id="a_actuate" name="PUT">
<doc>Control the actuator with a new value or command</doc>
<request>
<representation mediaType="text/plain"/>
<representation mediaType="application/senml+exi"/>
<representation mediaType="application/senml+xml"/>
<representation mediaType="application/senml+json"/>
</request>
<response/>
</method>
</resource_type>
</application>
4. Security Considerations
An implementation of a client needs to be prepared to deal with
responses to a request that differ from what is specified in this
document. A server implementing what the client thinks is a resource
with one of these interface descriptions could return malformed
representations and response codes either by accident or maliciously.
A server sending maliciously malformed responses could attempt to
take advantage of a poorly implemented client for example to crash
the node or perform denial of service.
5. IANA Considerations
To be determined if a registry of interface descriptions should be
created for CoRE, allowing other interface descriptions to be
registered by other specifications (and if this document is the place
to create such a registry).
Shelby Expires July 5, 2012 [Page 9]
Internet-Draft CoRE Interfaces January 2012
6. Acknowledgments
Acknowledgement is given to colleagues from the SENSEI project who
were critical in the initial development of the well-known REST
interface conept, and to Szymon Sasin and Carsten Bormann who have
provided useful discussion and input to the concepts in this
document.
Special thanks to Matthieu Vial for helping develop ideas for the
batch, link batch and collection resources and for providing useful
comments and the document.
7. Changelog
8. References
8.1. Normative References
[I-D.ietf-core-link-format]
Shelby, Z., "CoRE Link Format",
draft-ietf-core-link-format-09 (work in progress),
November 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
8.2. Informative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-08 (work in progress), October 2011.
Shelby Expires July 5, 2012 [Page 10]
Internet-Draft CoRE Interfaces January 2012
Author's Address
Zach Shelby
Sensinode
Kidekuja 2
Vuokatti 88600
FINLAND
Phone: +358407796297
Email: zach@sensinode.com
Shelby Expires July 5, 2012 [Page 11]