core K. Li
Internet-Draft B. Greevenbosch
Intended status: Standards Track R. Sun
Expires: June 19, 2015 Huawei Technologies
December 16, 2014
Representing CoRE Link Collections in CBOR
draft-li-core-links-cbor-01
Abstract
Web Linking (RFC5988) provides a way to represent links between Web
resources as well as the relations expressed by them and attributes
of such a link. In constrained networks, a collection of Web links
can be exchanged in the CoRE link format (RFC6690).
This specification defines a common format for representing Web links
in CBOR format (RFC7049).
Note
Discussion and suggestions for improvement are requested, and should
be sent to core@ietf.org.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 19, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Information Model . . . . . . . . . . . . . . . . . . . . . . 3
3. Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Web Links in CBOR . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Web Linking [RFC5988] provides a way to represent links between Web
resources as well as the relations expressed by them and attributes
of such a link. In constrained networks, a collection of Web links
can be exchanged in the CoRE link format [RFC6690] to enable resource
discovery, for instance by using the CoAP protocol [RFC7252].
[I-D.ietf-core-links-json] defines a common format for representing
Web links in JSON format.
The Concise Binary Object Representation (CBOR) [RFC7049] is a data
format whose design goals include the possibility of extremely small
code size, fairly small message size, and extensibility without the
need for version negotiation.
When converting between CORE Link Format and CBOR, as usual, many
samll decisions have to be made. If left without guidance, it is
likely that a number of slightly incompatible dialects will emerge.
This specification defines a common format for representing Web Links
in the CBOR format.
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1.1. 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].
2. Information Model
This section discusses the information model underlying the CORE Link
Format payload.
An application/link-format document is a collection of web links
("link-value"), each of which is a collection of attributes ("link-
param") applied to a "URI-Reference".
The URI-Reference is represented as a name/value pair with the name
"href" and the URI-Reference as the value.
The link attributes are also represented as name/value pairs with
attribute names and attribute values.
The information model of the CoRE Link Format can be summarized
below:
+------------------+--------------------+
| name | value |
+------------------+--------------------+
| href | resource URI |
+------------------+--------------------+
| attribute name 1 | attribute value 1 |
+------------------+--------------------+
| attribute name 2 | attribute value 2 |
+------------------+--------------------+
| ... | ... |
+------------------+--------------------+
| attribute name n | attribute value n |
+------------------+--------------------+
Figure 1: CoRE Link Format Information Model
3. Encoding
To reduce message size, it would be beneficial to encode "href" and
the standardized attribute names specified in [RFC5988] and [RFC6690]
as integers.
The encoding is summarized below:
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+----------+---------------+
| name | encoded value |
+----------+---------------+
| href | 1 |
+----------+---------------+
| rel | 2 |
+----------+---------------+
| anchor | 3 |
+----------+---------------+
| rev | 4 |
+----------+---------------+
| hreflang | 5 |
+----------+---------------+
| media | 6 |
+----------+---------------+
| title | 7 |
+----------+---------------+
| type | 8 |
+----------+---------------+
| rt | 9 |
+----------+---------------+
| if | 10 |
+----------+---------------+
| sz | 11 |
+----------+---------------+
| ct | 12 |
+----------+---------------+
Figure 2: Link Attributes Encoding
4. Web Links in CBOR
The objective of the CBOR mapping defined in this document is to
contain information of the formats specified in [RFC5988] and
[RFC6690].
We straightforwardly map:
o the outer collection to an array of links (Major type 4)
o each link to a map of pairs of data items (Major type 5)
In the object representing a "link-value", each target attribute or
other parameter ("link-param") is represented by a CBOR pair of data
items.
The URI-Reference is represented as a name/value pair with the name
"href" and the URI-Reference as the value.
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4.1. Examples
</sensors>;ct=40;title="Sensor Index",
</sensors/temp>;rt="temperature-c";if="sensor",
</sensors/light>;rt="light-lux";if="sensor",
<http://www.example.com/sensors/t123>;anchor="/sensors/temp"
;rel="describedby",
</t>;anchor="/sensors/temp";rel="alternate"
Figure 3: Example from page 15 of [RFC6690]
becomes
85 # array(number of data items:5)
a3 # map(number of pairs of data items:3)
01 # unsigned integer(value:1, "href")
68 # text string(8 bytes)
2f73656e736f7273 # "/sensors"
0c # unsigned integer(value:12,"ct")
18 28 # unsigned integer(value:40)
07 # unsigned integer(value:7,"title")
6c # text string(12 bytes)
53656e736f7220496e646578 # "Sensor Index"
a3 # map(number of pairs of data items:3)
01 # unsigned integer(value:1,"href")
6d # text string(13 bytes)
2f73656e736f72732f74656d70 # "/sensors/temp"
09 # unsigned integer(value:9,"rt")
6d # text string(13 bytes)
74656d70657261747572652d63 # "temperature-c"
0a # unsigned integer(value:10,"if")
66 # text string(6 bytes)
73656e736f72 # "sensor"
a3 # map(number of pairs of data items:3)
01 # unsigned integer(value:1,"href")
6e # text string(14 bytes)
2f73656e736f72732f6c69676874 # "/sensors/light"
09 # unsigned integer(value:9,"rt")
69 # text string(9 bytes)
6c696768742d6c7578 # "light-lux"
0a # unsigned integer(value:10,"if")
66 # text string(6 bytes)
73656e736f72 # "sensor"
a3 # map(number of pairs of data items:3)
01 # unsigned integer(value:1,"href")
78 23 # text string(35 bytes)
687474703a2f2f7777772e6578616d706c652e636f6d2f73656e736f72732f74313233
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# "http://www.example.com/sensors/t123"
03 # unsigned integer(value:3,"anchor")
6d # text string(13 bytes)
2f73656e736f72732f74656d70 # "/sensors/temp"
02 # unsigned integer(value:2,"rel")
6b # text string(11 bytes)
6465736372696265646279 # "describedby"
a3 # map(number of pairs of data items:3)
01 # unsigned integer(value:1,"href")
62 # text string(12 bytes)
2f74 # "/t"
03 # unsigned integer(value:3,"anchor")
6d # text string(13 bytes)
2f73656e736f72732f74656d70 # "/sensors/temp"
02 # unsigned integer(value:2,"rel")
69 # text string(9 bytes)
616c7465726e617465 # "alternate"
Figure 4: Links Encoded in CBOR
5. IANA Considerations
This specification registers the following additional Internet Media
Types:
Type name: application
Subtype name: link-format+cbor
Required parameters: None
Optional parameters: None
Encoding considerations: Resources that use the "application/ link-
format+cbor" media type are required to conform to the "application/
cbor" Media Type and are therefore subject to the same encoding
considerations specified in [RFC7159], Section 6.
Security considerations: As defined in this specification
Published specification: This specification.
Applications that use this media type: None currently known.
Additional information:
--Magic number(s): N/A
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--File extension(s): N/A
--Macintosh file type code(s): TEXT
Person & email address to contact for further information: Kepeng Li
<likepeng@huawei.com>
Intended usage: COMMON
Change controller: IESG
6. Security Considerations
The security considerations of [RFC6690] and [RFC7049] apply.
7. Acknowledgements
TBD.
8. References
8.1. Normative References
[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.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, August 2012.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, October 2013.
8.2. Informative References
[I-D.ietf-core-links-json]
Bormann, C., "Representing CoRE Link Collections in JSON",
draft-ietf-core-links-json-02 (work in progress), July
2014.
Authors' Addresses
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Kepeng Li
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
P. R. China
Phone: +86-755-28974259
Email: likepeng@huawei.com
Bert Greevenbosch
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
P. R. China
Email: bert.greevenbosch@huawei.com
Ruinan Sun
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen, Guangdong 518129
P. R. China
Phone: +86-755-28970171
Email: sunruinan@huawei.com
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