Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track M. Mohajer
Expires: September 13, 2019 u-blox UK
March 12, 2019
FETCH & PATCH with Sensor Measurement Lists (SenML)
draft-ietf-core-senml-etch-03
Abstract
The Sensor Measurement Lists (SenML) media type and data model can be
used to send collections of resources, such as batches of sensor data
or configuration parameters. The CoAP iPATCH, PATCH, and FETCH
methods enable accessing and updating parts of a resource or multiple
resources with one request. This document defines new media types
for the CoAP iPATCH, PATCH, and FETCH methods for resources
represented with the SenML data model.
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 September 13, 2019.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Using FETCH and (i)PATCH with SenML . . . . . . . . . . . . . 3
3.1. SenML FETCH . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. SenML (i)PATCH . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. CoAP Content-Format Registration . . . . . . . . . . . . 6
5.2. senml-etch+json Media Type . . . . . . . . . . . . . . . 6
5.3. senml-etch+cbor Media Type . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Sensor Measurement Lists (SenML) media type [RFC8428] and data
model can be used to transmit collections of resources, such as
batches of sensor data or configuration parameters.
An example of a SenML collection is shown below:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
{"n":"5750", "vs":"Ceiling light"}
]
Here three resources "3306/0/5850", "3306/0/5851", and "3306/0/5750",
of an IPSO dimmable light smart object [IPSO] are represented using a
single SenML Pack with three SenML Records. All resources share the
same base name "2001:db8::2/3306/0/", hence full names for resources
are "2001:db8::2/3306/0/5850", etc.
The CoAP [RFC7252] iPATCH, PATCH, and FETCH methods [RFC8132] enable
accessing and updating parts of a resource or multiple resources with
one request.
This document defines two new media types, one using the JavaScript
Object Notation (JSON) [RFC8259] and one using the Concise Binary
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Object Representation (CBOR) [RFC7049], that can be used with the
CoAP iPATCH, PATCH, and FETCH methods for resources represented with
the SenML data model. The semantics of the new media types are the
same for the CoAP PATCH and iPATCH methods. The rest of the document
uses term "(i)PATCH" when referring to both methods.
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 [RFC8132] and [RFC8428]. Also the following terms are used in
this document:
Fetch Record: One set of parameters that is used to match SenML
Record(s).
Fetch Pack: One or more Fetch Records in an array structure.
Patch Record: One set of parameters similar to Fetch Record but also
containing instructions on how to change existing SenML Pack(s).
Patch Pack: One or more Patch Records in an array structure.
Target Record: A Record in a SenML Pack that is matching the
selection criteria of a Fetch or Patch Record and hence is a
target for a Fetch or Patch operation.
(i)PATCH: A term that refers to both CoAP "PATCH" and "iPATCH"
methods when there is no difference in this specification in which
one is used.
3. Using FETCH and (i)PATCH with SenML
The FETCH/(i)PATCH media types for SenML are modeled as extensions to
the SenML media type to enable re-use of existing SenML parsers and
generators, in particular on constrained devices. Unless mentioned
otherwise, FETCH and PATCH Packs are constructed with the same rules
and constraints as SenML Packs.
The key difference to the SenML media type is allowing the use of a
"null" value for removing records with the (i)PATCH method. Also the
Fetch and Patch Records do not have default time or base version when
the fields are omitted.
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3.1. SenML FETCH
The FETCH method can be used to select and return a subset of
records, in sequence, of one or more SenML Packs. The SenML Records
are selected by giving a set of names that, when resolved, match
resolved names in a SenML Pack. The names for a Fetch Pack are given
using the SenML "name" and/or "base name" Fields. The names are
resolved by concatenating the base name with the name field as
defined in [RFC8428].
For example, to select the IPSO resources "5850" and "5851" from the
example in Section 1, the following Fetch Pack can be used:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850"},
{"n":"5851"}
]
The result to a FETCH request with the example above would be:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
]
When SenML Records contain also time values, a name may no longer
uniquely identify a single Record. When no time is given in a Fetch
Record, all SenML Records with the given name are matched (i.e.,
unlike with SenML Records, lack of time field in a Fetch Record does
not imply time value zero). When time is given in the Fetch Record,
only a SenML Record (if any) with equal resolved time value and name
is matched.
The resolved form of records (Section 4.6 of [RFC8428]) is used when
comparing the names and times of the Target and Fetch Records to
accommodate for differences in use of the base values.
3.2. SenML (i)PATCH
The (i)PATCH method can be used to change the values of SenML
Records, to add new Records, and to remove existing Records. The
names and times of the Patch Records are given and matched in same
way as for the Fetch Records, except each Patch Record can match at
most one Target Record. Patch Packs can also include new values and
other SenML Fields for the Records. Application of Patch Packs is
idempotent.
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When the name in a Patch Record matches with the name in an existing
Record, the resolved time values are compared. If the time values
either do not exist in both Records or are equal, the Target Record
is replaced with the contents of the Patch Record.
If a Patch Record contains a name, or combination of a time value and
a name, that do not exist in any existing Record in the Pack, the
given Record, with all the fields it contains, is added to the Pack.
If a Patch Record has a value field with value null, the matched
Record (if any) is removed from the Pack.
For example, the following document could be given as (i)PATCH
payload to change/set values of two SenML Records for the example in
Section 1:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10}
]
If the request is successful, the resulting representation of the
example SenML Pack would be as follows:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10},
{"n":"5750", "vs":"Ceiling light"}
]
4. Security Considerations
The security and privacy considerations of SenML apply also with the
FETCH and (i)PATCH methods.
In FETCH and (i)PATCH requests, the client can pass arbitrary names
to the target resource for manipulation. The resource implementer
must take care to only allow access to names that are actually part
of (or accessible through) the target resource.
If the client is not allowed to do a GET or PUT on the full target
resource (and thus all the names accessible through it), access
control rules must be evaluated for each record in the pack.
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5. IANA Considerations
This document registers two new media types and CoAP Content-Format
IDs for both media types.
Note to RFC Editor: Please replace all occurrences of "RFC-AAAA" with
the RFC number of this document.
5.1. CoAP Content-Format Registration
IANA is requested to assign CoAP Content-Format IDs for the SenML
PATCH and FETCH media types in the "CoAP Content-Formats" sub-
registry, within the "CoRE Parameters" registry [RFC7252]. All IDs
are assigned from the "IETF Review or IESG Approval" range. The
assigned IDs are show in Table 1.
+-----------------------------+-----+
| Media type | ID |
+-----------------------------+-----+
| application/senml-etch+json | TBD |
| | |
| application/senml-etch+cbor | TBD |
+-----------------------------+-----+
Table 1: CoAP Content-Format IDs
5.2. senml-etch+json Media Type
Type name: application
Subtype name: senml-etch+json
Required parameters: none
Optional parameters: none
Encoding considerations: Must be encoded as using a subset of the
encoding allowed in [RFC8259]. This simplifies implementation of a
very simple system and does not impose any significant limitations as
all this data is meant for machine to machine communications and is
not meant to be human readable.
Security considerations: See Section 4 of RFC-AAAA.
Interoperability considerations: Applications MUST ignore any key
value pairs that they do not understand unless the key ends with the
'_' character in which case an error MUST be generated. This allows
backwards compatible extensions to this specification.
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Published specification: RFC-AAAA
Applications that use this media type: Applications that use the
SenML media type for resource representation.
Fragment identifier considerations: N/A
Additional information:
Magic number(s): none
File extension(s): senml-etchj
Windows Clipboard Name: "SenML FETCH/PATCH format"
Macintosh file type code(s): none
Macintosh Universal Type Identifier code: org.ietf.senml-etch-json
conforms to public.text
Person & email address to contact for further information: Ari
Keranen ari.keranen@ericsson.com
Intended usage: COMMON
Restrictions on usage: None
Author: Ari Keranen ari.keranen@ericsson.com
Change controller: IESG
5.3. senml-etch+cbor Media Type
Type name: application
Subtype name: senml-etch+cbor
Required parameters: none
Optional parameters: none
Encoding considerations: Must be encoded as using [RFC7049].
Security considerations: See Section 4 of RFC-AAAA.
Interoperability considerations: Applications MUST ignore any key
value pairs that they do not understand unless the key ends with the
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'_' character in which case an error MUST be generated. This allows
backwards compatible extensions to this specification.
Published specification: RFC-AAAA
Applications that use this media type: Applications that use the
SenML media type for resource representation.
Fragment identifier considerations: N/A
Additional information:
Magic number(s): none
File extension(s): senml-etchc
Macintosh file type code(s): none
Macintosh Universal Type Identifier code: org.ietf.senml-etch-cbor
conforms to public.data
Person & email address to contact for further information: Ari
Keranen ari.keranen@ericsson.com
Intended usage: COMMON
Restrictions on usage: None
Author: Ari Keranen ari.keranen@ericsson.com
Change controller: IESG
6. Acknowledgements
The use of FETCH and (i)PATCH methods with SenML was first introduced
by the OMA SpecWorks LwM2M v1.1 specification. This document
generalizes the use to any SenML representation. The authors would
like to thank Carsten Bormann, Christian Amsuess, Jaime Jimenez,
Klaus Hartke, and other participants from the IETF CoRE and OMA
SpecWorks DMSE working groups who have contributed ideas and reviews.
7. References
7.1. Normative References
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[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>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/info/rfc8132>.
[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>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[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>.
7.2. Informative References
[IPSO] IPSO, "IPSO Smart Object Guidelines", 2018,
<https://www.omaspecworks.org/develop-with-oma-specworks/
ipso-smart-objects/guidelines/>.
Authors' Addresses
Ari Keranen
Ericsson
Email: ari.keranen@ericsson.com
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Mojan Mohajer
u-blox UK
Email: Mojan.Mohajer@u-blox.com
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