Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track M. Mohajer
Expires: June 29, 2020 u-blox UK
December 27, 2019
FETCH & PATCH with Sensor Measurement Lists (SenML)
draft-ietf-core-senml-etch-06
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 FETCH, PATCH, and iPATCH
methods enable accessing and updating parts of a resource or multiple
resources with one request. This document defines new media types
for the CoAP FETCH, PATCH, and iPATCH methods for resources
represented with the SenML data model.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 29, 2020.
Copyright Notice
Copyright (c) 2019 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
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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 . . . . . . . . . . . . . . . . . . . . . 5
4. Fragment Identification . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. CoAP Content-Format Registration . . . . . . . . . . . . 7
6.2. senml-etch+json Media Type . . . . . . . . . . . . . . . 7
6.3. senml-etch+cbor Media Type . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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::2/3311/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
{"n":"5750", "vs":"Ceiling light"}
]
Here three resources "3311/0/5850", "3311/0/5851", and "3311/0/5750",
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::2/3311/0/", hence full names for resources
are "2001:db8::2/3311/0/5850", etc.
The CoAP [RFC7252] FETCH, PATCH, and iPATCH methods [RFC8132] enable
accessing and updating parts of a resource or multiple resources with
one request.
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This document defines two new media types, one using the JavaScript
Object Notation (JSON) [RFC8259] and one using the Concise Binary
Object Representation (CBOR) [RFC7049], which can be used with the
CoAP FETCH, PATCH, and iPATCH methods for resources represented with
the SenML data model. The rest of the document uses term "(i)PATCH"
when referring to both methods as the semantics of the new media
types are the same for the CoAP PATCH and iPATCH 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]. The following additional 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 matches the selection
criteria of a Fetch or Patch Record and hence is a target for a
Fetch or Patch operation.
Target Pack: A SenML Pack that 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.
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The key differences to the SenML media type are allowing the use of a
"null" value for removing records with the (i)PATCH method and lack
of value fields in Fetch Records. Also the Fetch and Patch Records
do not have default time or base version when the fields are omitted.
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 Target 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].
A Fetch Pack MUST contain at least one Fetch Record. A Fetch Record
MUST contain a name and/or a base name field.
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::2/3311/0/", "n":"5850"},
{"n":"5851"}
]
The result to a FETCH request with the example above would be:
[
{"bn":"2001:db8::2/3311/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
]
The SenML time and unit fields can be used in a Fetch Record to
further narrow the selection of matched SenML Records. When no time
or unit 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 the SenML Records (if any) with equal
resolved time value and name are matched. Similarly, when unit is
given, only the SenML Records with equal resolved unit and name are
matched. If both time and unit are given in the Fetch Record, both
MUST to match for the SenML Record to match.
For example, if the IPSO resource "5850" would have multiple sensor
readings (SenML Records) with different time values, the following
Fetch Pack can be used to retrieve the Record with time
"1.276020091e+09":
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[
{"bn":"2001:db8::2/3311/0/", "n":"5850", "t":1.276020091e+09}
]
The resolved form of records (Section 4.6 of [RFC8428]) is used when
comparing the names, times, and units of the Target and Fetch Records
to accommodate for differences in use of the base values. In
resolved form the SenML name in the example above becomes
"2001:db8::2/3311/0/5850". Since there is no base time in the Pack,
the time in resolved form is equal to the time in the example.
If no SenML Records match, empty SenML Pack (i.e., array with no
elements) is returned as a response.
All other Fetch Record fields than name, base name, time, base time,
unit, and base unit MUST be ignored.
3.2. SenML (i)PATCH
The (i)PATCH method can be used to change the fields of SenML
Records, to add new Records, and to remove existing Records. The
names, times, and units of the Patch Records are given and matched in
same way as for the Fetch Records, except each Patch Record MUST
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; hence PATCH and iPATCH methods for SenML Packs
are equivalent.
When the name in a Patch Record matches with the name in an existing
Record, the resolved time values and units (if any) are compared. If
the time values and units either do not exist in both Records or are
equal, the Target Record is replaced with the contents of the Patch
Record. All Patch Records MUST contain at least a SenML Value or Sum
field. A Patch Pack with invalid Records MUST be rejected.
If a Patch Record contains a name, or combination of a time value,
unit, 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 ("v") field with value null, it MUST
NOT be added but the matched Record (if any) is removed from the
Target Pack.
For example, the following document could be given as an (i)PATCH
payload to change/set values of two SenML Records for the example in
Section 1:
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[
{"bn":"2001:db8::2/3311/0/", "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::2/3311/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10},
{"n":"5750", "vs":"Ceiling light"}
]
As another example, the following document could be given as an
(i)PATCH payload to remove the two SenML Records:
[
{"bn":"2001:db8::2/3311/0/", "n":"5850", "v":null},
{"n":"5851", "v":null}
]
4. Fragment Identification
Fragment identification for Records of Fetch and Patch Packs uses the
same mechanism as SenML JSON/CBOR fragment identification (see
Section 9 of [RFC8428]), i.e., "rec" scheme followed by a comma-
separated list of Record positions or range(s) of Records. For
example, to select the 3rd and 5th Record of a Fetch or Patch Pack, a
fragment identifier "rec=3,5" can be used in the URI of the Fetch or
Patch Pack resource.
5. Security Considerations
The security and privacy considerations of SenML apply also with the
FETCH and (i)PATCH methods. CoAP's security mechanisms are used to
provide security for 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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6. 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.
6.1. 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]. The
assigned IDs are shown in Table 1.
+-----------------------------+----------+---------+
| Media type | Encoding | ID |
+-----------------------------+----------+---------+
| application/senml-etch+json | - | TBD-320 |
| | | |
| application/senml-etch+cbor | - | TBD-322 |
+-----------------------------+----------+---------+
Table 1: CoAP Content-Format IDs
6.2. senml-etch+json Media Type
Type name: application
Subtype name: senml-etch+json
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: See Section 5 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.
Published specification: RFC-AAAA
Applications that use this media type: Applications that use the
SenML media type for resource representation.
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Fragment identifier considerations: Fragment identification for
application/senml-etch+json is supported by using fragment
identifiers as specified by RFC AAAA.
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): senml-etchj
Windows Clipboard Name: "SenML FETCH/PATCH format"
Macintosh file type code(s): N/A
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: N/A
Author: Ari Keranen ari.keranen@ericsson.com
Change controller: IESG
6.3. senml-etch+cbor Media Type
Type name: application
Subtype name: senml-etch+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: See Section 5 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: Fragment identification for
application/senml-etch+cbor is supported by using fragment
identifiers as specified by RFC AAAA.
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): senml-etchc
Macintosh file type code(s): N/A
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: N/A
Author: Ari Keranen ari.keranen@ericsson.com
Change controller: IESG
7. 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, Michael Richardson, and other participants from the
IETF CoRE and OMA SpecWorks DMSE working groups who have contributed
ideas and reviews.
8. References
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8.1. Normative References
[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>.
8.2. Informative References
[IPSO] IPSO, "IPSO Light Control Smart Object", 2018,
<http://www.openmobilealliance.org/tech/profiles/
lwm2m/3311.xml>.
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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