Internet DRAFT - draft-keranen-core-senml-data-ct
draft-keranen-core-senml-data-ct
Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track C. Bormann
Expires: January 9, 2020 Universitaet Bremen TZI
July 8, 2019
SenML Data Value Content-Format Indication
draft-keranen-core-senml-data-ct-02
Abstract
The Sensor Measurement Lists (SenML) media type supports multiple
types of values, from numbers to text strings and arbitrary binary
data values. In order to simplify processing of the data values this
document proposes to specify a new SenML field for indicating the
Content-Format of the data.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SenML Content-Format ("ct") Field . . . . . . . . . . . . . . 3
4. Using Content-Type and Content-Coding With the "ct" Field . . 3
5. SenML Base Content-Format ("bct") Field . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Sensor Measurement Lists (SenML) media type [RFC8428] can be used
to send various different kinds of data. In the example given in
Figure 1, a temperature value, an indication whether a lock is open,
and a data value (with SenML field "vd") read from an NFC reader is
sent in a single SenML pack.
[
{"bn":"urn:dev:ow:10e2073a01080063:","n":"temp","u":"Cel","v":7.1},
{"n":"open","vb":false},
{"n":"nfc-reader","vd":"aGkgCg"}
]
Figure 1: SenML pack with unidentified binary data
The receiver is expected to know how to decode the data in the "vd"
field based on the context, e.g., name of the data source and out-of-
band knowledge of the application. However, this context may not
always be easily available to entities processing the SenML pack. To
facilitate automatic decoding it is useful to be able to indicate an
Internet media type and content-coding right in the SenML Record.
The CoAP Content-Format (Section 12.3 in [RFC7252]) provides just
this information; enclosing a Content-Format number (in this case
number 60 as defined for media type application/cbor in [RFC7049]) in
the Record is illustrated in Figure 2. All registered CoAP content
formats are listed in the Content Formats subregistry of the CoRE
Parameters registry [IANA.core-parameters].
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{"n":"nfc-reader", "vd":"gmNmb28YKg", "ct":60}
Figure 2: SenML Record with binary data identified as CBOR
In this example SenML Record the data value contains a string "foo"
and a number 42 encoded in a CBOR [RFC7049] array. Since the example
above uses the JSON format of SenML, the data value containing the
binary CBOR value is base64-encoded. The data value after base64
decoding is shown with CBOR diagnostic notation in Figure 3.
82 # array(2)
63 # text(3)
666F6F # "foo"
18 2A # unsigned(42)
Figure 3: Example Data Value in CBOR diagnostic notation
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers should also be familiar with the terms and concepts discussed
in [RFC8428]. Awareness of terminology issues discussed in
[I-D.bormann-core-media-content-type-format] can also be very
helpful.
3. SenML Content-Format ("ct") Field
When a SenML Record contains a Data Value field ("vd"), the Record
MAY also include a Content-Format indication field. The Content-
Format indication uses label "ct" and an unsigned integer value in
the range of 0-65535 indicating the CoAP Content-Format of the data
(similar to CoRE Link Format [RFC6690] "ct" attribute, except that
the Link Format attribute happens to be encoded as a string).
4. Using Content-Type and Content-Coding With the "ct" Field
Since some Internet media types and their content coding and
parameter alternatives do not have assigned CoAP Content-Format
identifiers, the "ct" field can alternatively be used to indicate the
Content-Type and Content-Coding of the data. If Content-Coding is
not specified with Content-Type, identity (i.e., no) transformation
is used.
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If Content-Coding is used, the content-coding value (e.g., "deflate")
MUST be prefixed with "@" and concatenated with the media type and
parameters (if any). For example: "application/json@deflate".
5. SenML Base Content-Format ("bct") Field
The Base Content-Format Field, label "bct", provides a default value
for the Content-Format Field (label "ct") within its range. The
range of the base field includes the record containing it, up to (but
not including) the next record containing a "bct" field, if any, or
up to the end of the pack otherwise. Resolution (Section 4.6 of
[RFC8428]) of this base field is performed by adding its value with
the label "ct" to all records in this range that carry a "vd" field
but do not already contain a Content-Format ("ct") field.
6. Security Considerations
The indication of a media type in the data does not exempt a
consuming application from properly checking its inputs. Also, the
ability for an attacker to supply crafted SenML data that specify
media types chosen by the attacker may expose vulnerabilities of
handlers for these media types to the attacker.
7. IANA Considerations
IANA is requested to assign new labels in the "SenML Labels"
subregistry of the SenML registry [IANA.senml] (as defined in
[RFC8428]) for the Content-Format indication as per Table 1:
+-----------------+-------+---------------+------------+------------+
| Name | Label | JSON Type | XML Type | Reference |
+-----------------+-------+---------------+------------+------------+
| Base Content- | bct | Number/String | int/string | this |
| Format | | | | document |
| | | | | |
| Content-Format | ct | Number/String | int/string | this |
| | | | | document |
+-----------------+-------+---------------+------------+------------+
Table 1: IANA Registration for new SenML Labels
Acknowledgements
The authors would like to thank Sergio Abreu for the discussions
leading to the design of this extension.
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9. References
9.1. Normative References
[IANA.senml]
IANA, "Sensor Measurement Lists (SenML)",
<http://www.iana.org/assignments/senml>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8428] Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
DOI 10.17487/RFC8428, August 2018,
<https://www.rfc-editor.org/info/rfc8428>.
9.2. Informative References
[I-D.bormann-core-media-content-type-format]
Bormann, C., "On Media-Types, Content-Types, and related
terminology", draft-bormann-core-media-content-type-
format-00 (work in progress), March 2019.
[IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE)
Parameters",
<http://www.iana.org/assignments/core-parameters>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
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Authors' Addresses
Ari Keranen
Ericsson
Jorvas 02420
Finland
Email: ari.keranen@ericsson.com
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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