draft-ietf-core-multipart-ct-02.txt   draft-ietf-core-multipart-ct-03.txt 
CoRE T. Fossati CoRE T. Fossati
Internet-Draft Nokia Internet-Draft ARM
Intended status: Standards Track K. Hartke Intended status: Standards Track K. Hartke
Expires: February 8, 2019 Ericsson Expires: September 9, 2019 Ericsson
C. Bormann C. Bormann
Universitaet Bremen TZI Universitaet Bremen TZI
August 07, 2018 March 08, 2019
Multipart Content-Format for CoAP Multipart Content-Format for CoAP
draft-ietf-core-multipart-ct-02 draft-ietf-core-multipart-ct-03
Abstract Abstract
This memo defines application/multipart-core, an application- This memo defines application/multipart-core, an application-
independent media-type that can be used to combine representations of independent media-type that can be used to combine representations of
several different media types into a single CoAP message-body with zero or more different media types into a single message, such as a
minimal framing overhead, each along with a CoAP Content-Format CoAP request or response body, with minimal framing overhead, each
identifier. along with a CoAP Content-Format identifier.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on February 8, 2019. This Internet-Draft will expire on September 9, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Multipart Content-Format Encoding . . . . . . . . . . . . . . 3 2. Multipart Content-Format Encoding . . . . . . . . . . . . . . 3
3. Usage Examples . . . . . . . . . . . . . . . . . . . . . . . 3 3. Usage Examples . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Observing Resources . . . . . . . . . . . . . . . . . . . 3 3.1. Observing Resources . . . . . . . . . . . . . . . . . . . 4
3.2. Implementation hints . . . . . . . . . . . . . . . . . . 4 4. Implementation hints . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. Registration of media type application/multipart-core . . 5 5.1. Registration of media type application/multipart-core . . 5
4.2. Registration of a Content-Format identifier for 5.2. Registration of a Content-Format identifier for
application/multipart-core . . . . . . . . . . . . . . . 6 application/multipart-core . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7 7.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7 7.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
This memo defines application/multipart-core, an application- This memo defines application/multipart-core, an application-
independent media-type that can be used to combine representations of independent media-type that can be used to combine representations of
several different media types into a single CoAP [RFC7252] message- zero or more different media types into a single message, such as a
body with minimal framing overhead, each along with a CoAP Content- CoAP [RFC7252] request or response body, with minimal framing
Format identifier. overhead, each along with a CoAP Content-Format identifier.
This simple and efficient binary framing mechanism can be employed to This simple and efficient binary framing mechanism can be employed to
create application specific request and response bodies which build create application specific request and response bodies which build
on multiple already existing media types. on multiple already existing media types.
Applications using the application/multipart-core Content-Format The individual representations in an application/multipart-core body
define the internal structure of the application/multipart-core occur in a sequence, which may be employed by an application where
representation. such a sequence is natural, e.g. for a number of audio snippets in
different formats to be played out in that sequence.
For example, one way to structure the sub-types specific to an In other cases, an application may be more interested in a bag of
application/multipart-core container is to always include them at the representations, which are distinguished by their Content-Format
same fixed position. This specification allows to indicate that an identifier, such as an audio snippet and a text representation
optional part is not present by substituting a null value for the accompanying it. In such a case, the sequence in which these occur
representation of the part. may not be relevant to the application. This specification allows to
indicate that an optional part is not present by substituting a null
value for the representation of the part.
Optionally, an application might use the general format defined here, A third situation that is common only ever has a single
but also register a new media type and an associated Content-Format representation in the sequence, which is one of a set of formats
identifier -- typically one in the range 10000-64999 -- instead of possible. This kind of union of formats may also make the presence
using application/multipart-core. of the actual representation optional, the omission of which leads to
a zero-length array.
Where these rules are not sufficient for an application, it might
still use the general format defined here, but register a new media
type and an associated Content-Format identifier to associate the
representation with these more specific semantics instead of using
application/multipart-core.
1.1. Requirements Language
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.
2. Multipart Content-Format Encoding 2. Multipart Content-Format Encoding
A representation of media-type application/multipart-core contains a A representation of media-type application/multipart-core contains a
collection of zero or more representations, each along with their collection of zero or more representations, each along with their
respective content format. respective content format.
The collection is encoded as a CBOR [RFC7049] array with an even The collection is encoded as a CBOR [RFC7049] array with an even
number of elements. The second, fourth, sixth, etc. element is a number of elements. The second, fourth, sixth, etc. element is a
byte string containing a representation, or the value "null" if an byte string containing a representation, or the value "null" if an
optional part is indicated as not given. The first, third, fifth, optional part is indicated as not given. The first, third, fifth,
etc. element is an unsigned integer specifying the content format ID etc. element is an unsigned integer specifying the content format ID
of the representation following it. (Future extensions might want to of the representation following it.
include additional alternative ways of specifying the media type of a
representation in such a position.)
For example, a collection containing two representations, one with For example, a collection containing two representations, one with
content format ID 42 and one with content format ID 0, looks like content format ID 42 and one with content format ID 0, looks like
this in CBOR diagnostic notation: this in CBOR diagnostic notation:
[42, h'0123456789abcdef', 0, h'3031323334'] [42, h'0123456789abcdef', 0, h'3031323334']
For illustration, the structure of an application/multipart-core For illustration, the structure of an application/multipart-core
representation can be described by the CDDL [I-D.ietf-cbor-cddl] representation can be described by the CDDL [I-D.ietf-cbor-cddl]
specification in Figure 1: specification in Figure 1:
multipart-core = [* multipart-part] multipart-core = [* multipart-part]
multipart-part = (type: uint .size 2, part: bytes / null) multipart-part = (type: uint .size 2, part: bytes / null)
Figure 1: CDDL for application/multipart-core Figure 1: CDDL for application/multipart-core
This format is intended as a strict specification: An implementation
MUST stop processing the representation if there is a CBOR well-
formedness error, a deviation from the structure defined above, or
any residual data left after processing the CBOR data item. (This
generally means the representation is not processed at all except if
some streaming processing has already happened.)
3. Usage Examples 3. Usage Examples
3.1. Observing Resources 3.1. Observing Resources
When a client registers to observe a resource [RFC7641] for which no When a client registers to observe a resource [RFC7641] for which no
representation is available yet, the server may send one or more 2.05 representation is available yet, the server may send one or more 2.05
(Content) notifications before sending the first actual 2.05 (Content) notifications before sending the first actual 2.05
(Content) or 2.03 (Valid) notification. The possible resulting (Content) or 2.03 (Valid) notification. The possible resulting
sequence of notifications is shown in Figure 1. sequence of notifications is shown in Figure 1.
skipping to change at page 4, line 23 skipping to change at page 4, line 40
Figure 2: Sequence of Notifications: Figure 2: Sequence of Notifications:
The specification of the Observe option requires that all The specification of the Observe option requires that all
notifications carry the same Content-Format. The application/ notifications carry the same Content-Format. The application/
multipart-core media type can be used to provide that Content-Format: multipart-core media type can be used to provide that Content-Format:
e.g., carrying an empty list of representations in the case marked as e.g., carrying an empty list of representations in the case marked as
"Pending" in Figure 2, and carrying a single representation specified "Pending" in Figure 2, and carrying a single representation specified
as the target content-format in the case in the middle of the figure. as the target content-format in the case in the middle of the figure.
3.2. Implementation hints 4. Implementation hints
This section describes the serialization for readers that may be new This section describes the serialization for readers that may be new
to CBOR. It does not contain any new information. to CBOR. It does not contain any new information.
An application/multipart-core representation carrying no An application/multipart-core representation carrying no
representations is represented by an empty CBOR array, which is representations is represented by an empty CBOR array, which is
serialized as a single byte with the value 0x80. serialized as a single byte with the value 0x80.
An application/multipart-core representation carrying a single An application/multipart-core representation carrying a single
representation is represented by a two-element CBOR array, which is representation is represented by a two-element CBOR array, which is
skipping to change at page 4, line 45 skipping to change at page 5, line 13
is an unsigned integer for the Content-Format value, which is is an unsigned integer for the Content-Format value, which is
represented as described in Table 1. The second element is the represented as described in Table 1. The second element is the
object as a byte string, which is represented as a length as object as a byte string, which is represented as a length as
described in Table 2 followed by the bytes of the object. described in Table 2 followed by the bytes of the object.
+----------------+------------+ +----------------+------------+
| Serialization | Value | | Serialization | Value |
+----------------+------------+ +----------------+------------+
| 0x00..0x17 | 0..23 | | 0x00..0x17 | 0..23 |
| 0x18 0xnn | 24..255 | | 0x18 0xnn | 24..255 |
| 0x19 0xnn 0xnn | 256..66535 | | 0x19 0xnn 0xnn | 256..65535 |
+----------------+------------+ +----------------+------------+
Table 1: Serialization of content-format Table 1: Serialization of content-format
+-----------------------------+-------------------+ +-----------------------------+-------------------+
| Serialization | Length | | Serialization | Length |
+-----------------------------+-------------------+ +-----------------------------+-------------------+
| 0x40..0x57 | 0..23 | | 0x40..0x57 | 0..23 |
| 0x58 0xnn | 24..255 | | 0x58 0xnn | 24..255 |
| 0x59 0xnn 0xnn | 256..66535 | | 0x59 0xnn 0xnn | 256..65535 |
| 0x5a 0xnn 0xnn 0xnn 0xnn | 66536..4294967295 | | 0x5a 0xnn 0xnn 0xnn 0xnn | 65536..4294967295 |
| 0x5b 0xnn .. 0xnn (8 bytes) | 4294967296.. | | 0x5b 0xnn .. 0xnn (8 bytes) | 4294967296.. |
+-----------------------------+-------------------+ +-----------------------------+-------------------+
Table 2: Serialization of object length Table 2: Serialization of object length
For example, a single text/plain object (content-format 0) of value For example, a single text/plain object (content-format 0) of value
"Hello World" (11 characters) would be serialized as "Hello World" (11 characters) would be serialized as
0x82 0x00 0x4b H e l l o 0x20 w o r l d 0x82 0x00 0x4b H e l l o 0x20 w o r l d
In effect, the serialization for a single object is done by prefixing In effect, the serialization for a single object is done by prefixing
the object with information about its content-format (here: 0x82 the object with information that there is one object (here: 0x82),
0x00) and its length (here: 0x4b). about its content-format (here: 0x00) and its length (here: 0x4b).
For more than one representation included in an application/ For more than one representation included in an application/
multipart-core representation, the head of the CBOR array is adjusted multipart-core representation, the head of the CBOR array is adjusted
(0x84 for two representations, 0x86 for three, ...) and the sequences (0x84 for two representations, 0x86 for three, ...) and the sequences
of content-format and embedded representations follow. of content-format and embedded representations follow.
4. IANA Considerations 5. IANA Considerations
4.1. Registration of media type application/multipart-core 5.1. Registration of media type application/multipart-core
IANA is requested to register the following media type [RFC6838]: IANA is requested to register the following media type [RFC6838]:
Type name: application Type name: application
Subtype name: multipart-core Subtype name: multipart-core
Required parameters: N/A Required parameters: N/A
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: binary Encoding considerations: binary
Security considerations: See the Security Considerations Section of Security considerations: See the Security Considerations Section of
RFCthis RFCthis
skipping to change at page 6, line 4 skipping to change at page 6, line 18
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: binary Encoding considerations: binary
Security considerations: See the Security Considerations Section of Security considerations: See the Security Considerations Section of
RFCthis RFCthis
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: RFCthis Published specification: RFCthis
Applications that use this media type: Applications that need to Applications that use this media type: Applications that need to
combine representations of potentially several media types into combine representations of zero or more different media types into
one, e.g., EST-CoAP [I-D.ietf-ace-coap-est] one, e.g., EST-CoAP [I-D.ietf-ace-coap-est]
Fragment identifier considerations: N/A Fragment identifier considerations: The syntax and semantics of
fragment identifiers specified for "application/multipart-core" is
as specified for "application/cbor". (At publication of this
document, there is no fragment identification syntax defined for
"application/cbor".)
Additional information: Additional information:
Deprecated alias names for this type: N/A Deprecated alias names for this type: N/A
Magic number(s): N/A Magic number(s): N/A
File extension(s): N/A File extension(s): N/A
Macintosh file type code(s): N/A Macintosh file type code(s): N/A
skipping to change at page 6, line 33 skipping to change at page 7, line 5
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: CoRE WG Author: CoRE WG
Change controller: IESG Change controller: IESG
Provisional registration? (standards tree only): no Provisional registration? (standards tree only): no
4.2. Registration of a Content-Format identifier for application/ 5.2. Registration of a Content-Format identifier for application/
multipart-core multipart-core
IANA is requested to register the following Content-Format to the IANA is requested to register the following Content-Format to the
"CoAP Content-Formats" subregistry, within the "Constrained RESTful "CoAP Content-Formats" subregistry, within the "Constrained RESTful
Environments (CoRE) Parameters" registry, from the Expert Review Environments (CoRE) Parameters" registry, from the Expert Review
space (0..255): space (0..255):
+----------------------------+----------+------+-----------+ +----------------------------+----------+------+-----------+
| Media Type | Encoding | ID | Reference | | Media Type | Encoding | ID | Reference |
+----------------------------+----------+------+-----------+ +----------------------------+----------+------+-----------+
| application/multipart-core | -- | TBD1 | RFCthis | | application/multipart-core | -- | TBD1 | RFCthis |
+----------------------------+----------+------+-----------+ +----------------------------+----------+------+-----------+
5. Security Considerations 6. Security Considerations
The security considerations of [RFC7049] apply. In particular, The security considerations of [RFC7049] apply. In particular,
resource exhaustion attacks may employ large values for the byte resource exhaustion attacks may employ large values for the byte
string size fields, or deeply nested structures of recursively string size fields, or deeply nested structures of recursively
embedded application/multipart-core representations. embedded application/multipart-core representations.
6. References 7. References
6.1. Normative References 7.1. 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 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>. October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
Application Protocol (CoAP)", RFC 7641, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
DOI 10.17487/RFC7641, September 2015, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
<https://www.rfc-editor.org/info/rfc7641>.
6.2. Informative References 7.2. Informative References
[I-D.ietf-ace-coap-est] [I-D.ietf-ace-coap-est]
Stok, P., Kampanakis, P., Kumar, S., Richardson, M., Stok, P., Kampanakis, P., Richardson, M., and S. Raza,
Furuhed, M., and S. Raza, "EST over secure CoAP (EST- "EST over secure CoAP (EST-coaps)", draft-ietf-ace-coap-
coaps)", draft-ietf-ace-coap-est-05 (work in progress), est-10 (work in progress), March 2019.
July 2018.
[I-D.ietf-cbor-cddl] [I-D.ietf-cbor-cddl]
Birkholz, H., Vigano, C., and C. Bormann, "Concise data Birkholz, H., Vigano, C., and C. Bormann, "Concise data
definition language (CDDL): a notational convention to definition language (CDDL): a notational convention to
express CBOR data structures", draft-ietf-cbor-cddl-03 express CBOR and JSON data structures", draft-ietf-cbor-
(work in progress), July 2018. cddl-07 (work in progress), February 2019.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
Acknowledgements Acknowledgements
Most of the text in this draft is from earlier contributions by two Most of the text in this draft is from earlier contributions by two
of the authors, Thomas Fossati and Klaus Hartke. The re-mix in this of the authors, Thomas Fossati and Klaus Hartke. The re-mix in this
document is based on the requirements in [I-D.ietf-ace-coap-est], document is based on the requirements in [I-D.ietf-ace-coap-est],
based on discussions with Michael Richardson, Panos Kampanis and based on discussions with Michael Richardson, Panos Kampanis and
Peter van der Stok. Peter van der Stok.
Authors' Addresses Authors' Addresses
Thomas Fossati Thomas Fossati
Nokia ARM
Email: thomas.fossati@nokia.com Email: thomas.fossati@arm.com
Klaus Hartke Klaus Hartke
Ericsson Ericsson
Torshamnsgatan 23 Torshamnsgatan 23
Stockholm SE-16483 Stockholm SE-16483
Sweden Sweden
Email: klaus.hartke@ericsson.com Email: klaus.hartke@ericsson.com
Carsten Bormann Carsten Bormann
Universitaet Bremen TZI Universitaet Bremen TZI
Postfach 330440 Postfach 330440
Bremen D-28359 Bremen D-28359
Germany Germany
Phone: +49-421-218-63921 Phone: +49-421-218-63921
Email: cabo@tzi.org Email: cabo@tzi.org
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