Internet DRAFT - draft-ietf-core-problem-details
draft-ietf-core-problem-details
CoRE Working Group T. Fossati
Internet-Draft arm
Intended status: Standards Track C. Bormann
Expires: 7 January 2023 Universität Bremen TZI
6 July 2022
Concise Problem Details For CoAP APIs
draft-ietf-core-problem-details-08
Abstract
This document defines a concise "problem detail" as a way to carry
machine-readable details of errors in a REST response to avoid the
need to define new error response formats for REST APIs for
constrained environments. The format is inspired by, but intended to
be more concise than, the Problem Details for HTTP APIs defined in
RFC 7807.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-core-problem-details/.
Discussion of this document takes place on the Constrained RESTful
Environments Working Group mailing list (mailto:core@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/core/.
Source for this draft and an issue tracker can be found at
https://github.com/core-wg/core-problem-details.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 7 January 2023.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology and Requirements Language . . . . . . . . . . 3
2. Basic Problem Details . . . . . . . . . . . . . . . . . . . . 4
3. Extending Concise Problem Details . . . . . . . . . . . . . . 6
3.1. Standard Problem Detail Entries . . . . . . . . . . . . . 7
3.1.1. Standard Problem Detail Entry: Unprocessed CoAP
Option . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Custom Problem Detail Entries . . . . . . . . . . . . . . 9
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6.1. Standard Problem Detail Key registry . . . . . . . . . . 12
6.2. Custom Problem Detail Key registry . . . . . . . . . . . 14
6.3. Media Type . . . . . . . . . . . . . . . . . . . . . . . 16
6.4. Content-Format . . . . . . . . . . . . . . . . . . . . . 16
6.5. CBOR Tag 38 . . . . . . . . . . . . . . . . . . . . . . . 17
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Normative References . . . . . . . . . . . . . . . . . . 17
7.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Language-Tagged Strings . . . . . . . . . . . . . . 19
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 20
A.2. Detailed Semantics . . . . . . . . . . . . . . . . . . . 20
A.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix B. Interworking with RFC 7807 . . . . . . . . . . . . . 22
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 23
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
REST response status information such as CoAP response codes
(Section 5.9 of [RFC7252]) is sometimes not sufficient to convey
enough information about an error to be helpful. This specification
defines a simple and extensible framework to define CBOR [STD94] data
items to suit this purpose. It is designed to be reused by REST
APIs, which can identify distinct "shapes" of these data items
specific to their needs. Thus, API clients can be informed of both
the high-level error class (using the response code) and the finer-
grained details of the problem (using the vocabulary defined here).
This pattern of communication is illustrated in Figure 1.
.--------. .--------.
| CoAP | | CoAP |
| Client | | Server |
'----+---' '---+----'
| |
| Request |
o----------------->|
| | (failure)
|<-----------------o
| Error Response |
| with a CBOR |
| data item giving |
| Problem Details |
| |
Figure 1: Problem Details: Example with CoAP
The framework presented is largely inspired by the Problem Details
for HTTP APIs defined in [RFC7807]. Appendix B discusses
applications where interworking with [RFC7807] is required.
1.1. Terminology and Requirements Language
The terminology from [RFC7252], [STD94], and [RFC8610] applies; in
particular CBOR diagnostic notation is defined in Section 8 of
[STD94] and Appendix G of [RFC8610]. Readers are also expected to be
familiar with the terminology from [RFC7807].
In this document, the structure of data is specified in CDDL
[RFC8610] [RFC9165].
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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. Basic Problem Details
A Concise Problem Details data item is a CBOR data item with the
following structure (rules named starting with tag38 are defined in
Appendix A):
problem-details = non-empty<{
? &(title: -1) => oltext
? &(detail: -2) => oltext
? &(instance: -3) => ~uri
? &(response-code: -4) => uint .size 1
? &(base-uri: -5) => ~uri
? &(base-lang: -6) => tag38-ltag
? &(base-rtl: -7) => tag38-direction
standard-problem-detail-entries
custom-problem-detail-entries
}>
standard-problem-detail-entries = (
* nint => any
)
custom-problem-detail-entries = (
* (uint/~uri) => { + any => any }
)
non-empty<M> = (M) .and ({ + any => any })
oltext = text / tag38
Figure 2: Structure of Concise Problem Details Data Item
(Examples of elaborated Concise Problem Details data items can be
found later in the document, e.g., Figure 3.)
A number of problem detail entries, the Standard Problem Detail
entries, are predefined (more predefined details can be registered,
see Section 3.1).
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Note that, unlike [RFC7807], Concise Problem Details data items have
no explicit "problem type". Instead, the category (or, one could
say, Gestalt) of the problem can be understood from the shape of the
problem details offered. We talk of a "problem shape" for short.
The title (key -1):
A short, human-readable summary of the problem shape. Beyond the
shape of the problem, it is not intended to summarize all the
specific information given with the problem details. For
instance, the summary might include that an account does not have
enough money for a transaction to succeed, but not the detail
information such as the account number, how much money that
account has, and how much would be needed.
The detail (key -2):
A human-readable explanation specific to this occurrence of the
problem.
The instance (key -3):
A URI reference that identifies the specific occurrence of the
problem. It may or may not yield further information if
dereferenced.
The response-code (key -4):
The CoAP response code (Sections 5.9 and 12.1.2 of [RFC7252])
generated by the origin server for this occurrence of the problem.
The base-uri (key -5):
The base URI (Section 5.1 of [STD66]) that should be used to
resolve relative URI references embedded in this Concise Problem
Details data item.
The base-lang (key -6):
The language-tag (tag38-ltag) that applies to the presentation of
unadorned text strings (not using tag 38) in this Concise Problem
Details data item, see Appendix A.
The base-rtl (key -7):
The writing-direction (tag38-direction) that applies to the
presentation of unadorned text strings (not using tag 38) in this
Concise Problem Details data item, see Appendix A.
Both "title" and "detail" can use either an unadorned CBOR text
string (text) or a language-tagged text string (tag38); see
Appendix A for the definition of the latter. Language tag and
writing direction information for unadorned text strings are intended
to be obtained from context; if that context needs to be saved or
forwarded with a Concise Problem Details data item, "base-lang" and
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"base-rtl" can be used for that. If no such (explicitly saved or
implicit) context information is available, unadorned text is
interpreted with language-tag "en" and writing-direction "false"
(ltr).
The "title" string is advisory and included to give consumers a
shorthand for the category (problem shape) of the error encountered.
The "detail" member, if present, ought to focus on helping the client
correct the problem, rather than giving extensive server-side
debugging information. Consumers SHOULD NOT parse the "detail"
member for information; extensions (see Section 3) are more suitable
and less error-prone ways to obtain such information. Note that the
"instance" URI reference may be relative; this means that it must be
resolved relative to the representation's base URI, as per Section 5
of [STD66].
The "response-code" member, if present, is only advisory; it conveys
the CoAP response code used for the convenience of the consumer.
Generators MUST use the same response code here as in the actual CoAP
response; the latter is needed to assure that generic CoAP software
that does not understand the problem-details format still behaves
correctly. Consumers can use the response-code member to determine
what the original response code used by the generator was, in cases
where it has been changed (e.g., by an intermediary or cache), and
when message bodies persist without CoAP information (e.g., in an
events log or analytics database). Generic CoAP software will still
use the CoAP response code. To support the use case of message body
persistence without support by the problem-details generator, the
entity that persists the Concise Problem Details data item can copy
over the CoAP response code that it received on the CoAP level. Note
that the "response-code" value is a numeric representation of the
actual code (see Section 3 of [RFC7252]), so it does not take the
usual presentation form that resembles an HTTP status code -- 4.04
Not found is represented by the number 132.
The "base-uri" member is usually not present in the initial request-
response communication as it can be inferred as per Section 5.1.3 of
[STD66]. An entity that stores a Concise Problem Details data item
or otherwise makes it available for consumers without this context
might add in a base-uri member to allow those consumers to perform
resolution of any relative URI references embedded in the data item.
3. Extending Concise Problem Details
This specification defines a generic problem details container with
only a minimal set of attributes to make it usable.
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It is expected that applications will extend the base format by
defining new attributes.
These new attributes fall into two categories: generic and
application specific.
Generic attributes will be allocated in the standard-problem-detail-
entries slot according to the registration procedure defined in
Section 3.1.
Application-specific attributes will be allocated in the custom-
problem-detail-entries slot according to the procedure described in
Section 3.2.
Consumers of a Concise Problem Details data item MUST ignore any
Standard or Custom Problem Detail entries, or keys inside the Custom
Problem Detail entries, that they do not recognize ("ignore-unknown
rule"); this allows problem details to evolve. When storing the data
item for future use or forwarding it to other consumers, it is
strongly RECOMMENDED to retain the unrecognized entries; exceptions
might be when storage/forwarding occurs in a different format/
protocol that cannot accommodate them, or when the storage/forwarding
function needs to filter out privacy-sensitive information and for
that needs to assume unrecognized entries might be privacy-sensitive.
3.1. Standard Problem Detail Entries
Beyond the Standard Problem Detail keys defined in Figure 2,
additional Standard Problem Detail keys can be registered for use in
the standard-problem-detail-entries slot (see Section 6.1).
Standard Problem Detail keys are negative integers, so they can never
conflict with Custom Problem Detail keys defined for a specific
application domain (which are unsigned integers or URIs.)
In summary, the keys for Standard Problem Detail entries are in a
global namespace that is not specific to a particular application
domain.
3.1.1. Standard Problem Detail Entry: Unprocessed CoAP Option
Section 2 provides a number of generally applicable Standard Problem
Detail Entries. The present section both registers another useful
Standard Problem Detail entry and serves as an example of a Standard
Problem Detail Entry registration, in the registration template
format that would be ready for registration.
| Key Value: TBD (assigned at registration)
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|
| Name: unprocessed-coap-option
|
| CDDL type: one-or-more<uint>, where
|
| one-or-more<T> = T / [ 2* T ]
|
| Brief description: Option number(s) of CoAP option(s) that were
| not understood
|
| Specification reference: Section 3.1.1 of RFC XXXX
// RFC Editor: please replace RFC XXXX with the RFC number of this
// RFC and remove this note.
The specification of the Standard Problem Detail entry referenced by
the above registration template follows:
The Standard Problem Detail entry unprocessed-coap-option provides
the option number(s) of CoAP option(s) present in the request that
could not be processed by the server.
This may be a critical option that the server is unaware of, or an
option the server is aware of but could not process (and chose not
to, or was not allowed to, ignore it).
The Concise Problem Details data item including this Standard Problem
Detail Entry can be used in fulfillment of the "SHOULD" requirement
in Section 5.4.1 of [RFC7252].
Several option numbers may be given in a list (in no particular
order), without any guarantee that the list is a complete
representation of all the problems in the request (as the server
might have stopped processing already at one of the problematic
options). If an option with the given number was repeated, there is
no indication which of the values caused the error.
Clients need to expect seeing options in the list they did not send
in the request; this can happen if the request traversed a proxy that
added the option but did not act on the problem details response
being returned by the origin server.
Note that for a few special values of unprocessed CoAP options (such
as Accept or Proxy-Uri), there are special response codes (4.06 Not
Acceptable, 5.05 Proxying Not Supported, respectively) to be sent
instead of 4.02 Bad Option.
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3.2. Custom Problem Detail Entries
Applications may extend the Problem Details data item with additional
entries to convey additional, application-specific information.
Such new entries are allocated in the custom-problem-detail-entries
slot, and carry a nested map specific to that application. The map
key can either be an (absolute!) URI (under control of the entity
defining this extension), or an unsigned integer. Only the latter
needs to be registered (Section 6.2).
Within the nested map, any number of attributes can be given for a
single extension. The semantics of each custom attribute MUST be
described in the documentation for the extension; for extensions that
are registered (i.e., are identified by an unsigned int) that
documentation goes along with the registration.
The unsigned integer form allows a more compact representation. In
exchange, authors are expected to comply with the required
registration and documentation process. In comparison, the URI form
is less space-efficient but requires no registration. It is
therefore useful for experimenting during the development cycle and
for applications deployed in environments where producers and
consumers of Concise Problem Details are more tightly integrated.
(The URI form thus covers the potential need we might otherwise have
for a "private use" range for the unsigned integers.)
Note that the URI given for the extension is for identification
purposes only and, even if dereferenceable in principle, it MUST NOT
be dereferenced in the normal course of handling problem details
(i.e., outside diagnostic/debugging procedures involving humans).
Figure 3 shows an example (in CBOR diagnostic notation) of a custom
extension using a (made-up) URI as custom-problem-detail-entries key.
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{
/ title / -1: "title of the error",
/ detail / -2: "detailed information about the error",
/ instance / -3: "coaps://pd.example/FA317434",
/ response-code / -4: 128, / 4.00 /
"tag:3gpp.org,2022-03:TS29112": {
/ cause / 0: "machine-readable error cause",
/ invalidParams / 1: [
[
/ param / "first parameter name",
/ reason / "must be a positive integer"
],
[
/ param / "second parameter name"
]
],
/ supportedFeatures / 2: "d34db33f"
}
}
Figure 3: Example Extension with URI key
Obviously, an SDO like 3GPP can also easily register such a custom
problem detail entry to receive a more efficient unsigned integer
key; Figure 4 shows how the same example would look like using a
(made-up) registered unsigned int as custom-problem-detail-entries
key:
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{
/ title / -1: "title of the error",
/ detail / -2: "detailed information about the error",
/ instance / -3: "coaps://pd.example/FA317434",
/ response-code / -4: 128, / 4.00 /
/4711 is made-up example key that is not actually registered:/
4711: {
/ cause / 0: "machine-readable error cause",
/ invalidParams / 1: [
[
/ param / "first parameter name",
/ reason / "must be a positive integer"
],
[
/ param / "second parameter name"
]
],
/ supportedFeatures / 2: "d34db33f"
}
}
Figure 4: Example Extension with unsigned int (registered) key
In summary, the keys for the maps used inside Custom Problem Detail
entries are defined specifically to the identifier of that Custom
Problem Detail entry, the documentation of which defines these
internal entries, typically chosen to address a given application
domain.
When there is a need to evolve a Custom Problem Detail entry
definition, the "ignore-unknown rule" discussed in the introduction
to Section 3 provides an easy way to include additional information.
The assumption is that this is done in a backward and forward
compatible way. Sometimes, Custom Problem Detail entries may need to
evolve in a way where forward compatibility by applying the "ignore-
unknown rule" would not be appropriate: e.g., when adding a "must-
understand" member, which can only be ignored at the peril of
misunderstanding the Concise Problem Details data item ("false
interoperability"). In this case, a new Custom Problem Detail key
can simply be registered for this case, keeping the old key backward
and forward compatible.
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4. Privacy Considerations
Problem details may unintentionally disclose information. This can
lead to both privacy and security problems. See Section 5 for more
details that apply to both domains; particular attention needs to be
given to unintentionally disclosing Personally Identifiable
Information (PII).
5. Security Considerations
Concise Problem Details can contain URIs that are not intended to be
dereferenced (Section 3.2, Paragraph 5). One reason is that
dereferencing these can lead to information disclosure (tracking).
Information disclosure can also be caused by URIs in problem details
that _are_ intended for dereferencing, e.g., the "instance" URI.
Implementations need to consider which component of a client should
perform the dereferencing, and which servers are trusted with serving
them. In any case, the security considerations of Section 7 of
[STD66] apply.
The security and privacy considerations outlined in Section 5 of
[RFC7807] apply in full. While these are phrased in terms of
security considerations for new RFC 7807 problem types, they equally
apply to the problem detail entry definitions used here Section 3; in
summary: both when defining new detail entries, and when actually
generating a Concise Problem Details data item, care needs to be
taken that they do not leak sensitive information. Entities storing
or forwarding Concise Problem Details data items need to consider
whether this leads to information being transferred out of the
context within which access to sensitive information was acceptable.
See also Section 3, Paragraph 6 (the last paragraph of the
introduction to that section). Privacy-sensitive information in the
problem details SHOULD NOT be obscured in ways that might lead to
misclassification as non-sensitive (e.g., by base64-encoding).
6. IANA Considerations
// RFC Editor: please replace RFC XXXX with the RFC number of this
// RFC and remove this note.
6.1. Standard Problem Detail Key registry
This specification defines a new sub-registry for Standard Problem
Detail Keys in the CoRE Parameters registry [IANA.core-parameters],
with the policy "specification required" (Section 4.6 of [RFC8126]).
Each entry in the registry must include:
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Key value:
a negative integer to be used as the value of the key
Name:
a name that could be used in implementations for the key
CDDL type:
type of the data associated with the key in CDDL notation
Brief description:
a brief description
Change Controller:
(see Section 2.3 of [RFC8126])
Reference:
a reference document
The expert is requested to assign the shortest key values (1+0 and
1+1 encoding) to registrations that are likely to enjoy wide use and
can benefit from short encodings.
To be immediately useful in CDDL and programming language contexts, a
name consists of a lower-case ASCII letter (a-z) and zero or more
additional ASCII characters that are either lower-case letters,
digits, or a hyphen-minus, i.e., it matches [a-z][-a-z0-9]*. As with
the key values, names need to be unique.
The specification in the reference document needs to provide a
description of the Standard Problem Detail entry, replicating the
CDDL description in "CDDL type", and describing the semantics of the
presence of this entry and the semantics of the value given with it.
Initial entries in this sub-registry are as follows:
+=======+==============+=================+=============+===========+
| Key | Name | CDDL Type | Brief | Reference |
| value | | | description | |
+=======+==============+=================+=============+===========+
| -1 | title | text / tag38 | short, | RFC XXXX |
| | | | human- | |
| | | | readable | |
| | | | summary of | |
| | | | the problem | |
| | | | shape | |
+-------+--------------+-----------------+-------------+-----------+
| -2 | detail | text / tag38 | human- | RFC XXXX |
| | | | readable | |
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| | | | explanation | |
| | | | specific to | |
| | | | this | |
| | | | occurrence | |
| | | | of the | |
| | | | problem | |
+-------+--------------+-----------------+-------------+-----------+
| -3 | instance | ~uri | URI | RFC XXXX |
| | | | reference | |
| | | | identifying | |
| | | | specific | |
| | | | occurrence | |
| | | | of the | |
| | | | problem | |
+-------+--------------+-----------------+-------------+-----------+
| -4 | response- | uint .size 1 | CoAP | RFC XXXX |
| | code | | response | |
| | | | code | |
+-------+--------------+-----------------+-------------+-----------+
| -5 | base-uri | ~uri | Base URI | RFC XXXX |
+-------+--------------+-----------------+-------------+-----------+
| -6 | base-lang | tag38-ltag | Base | RFC XXXX |
| | | | language | |
| | | | tag (see | |
| | | | Appendix A) | |
+-------+--------------+-----------------+-------------+-----------+
| -7 | base-rtl | tag38-direction | Base | RFC XXXX |
| | | | writing | |
| | | | direction | |
| | | | (see | |
| | | | Appendix A) | |
+-------+--------------+-----------------+-------------+-----------+
| TBD | unprocessed- | one-or- | Option | RFC XXXX, |
| | coap-option | more<uint> | number(s) | Section |
| | | | of CoAP | 3.1.1 |
| | | | option(s) | |
| | | | that were | |
| | | | not | |
| | | | understood | |
+-------+--------------+-----------------+-------------+-----------+
Table 1: Initial Entries in the Standard Problem Detail Key registry
6.2. Custom Problem Detail Key registry
This specification defines a new sub-registry for Custom Problem
Detail Keys in the CoRE Parameters registry [IANA.core-parameters],
with the policy "expert review" (Section 4.5 of [RFC8126]).
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The expert is instructed to attempt making the registration
experience as close to first-come-first-served as reasonably
achievable, but checking that the reference document does provide a
description as set out below. (This requirement is a relaxed version
of "specification required" as defined in Section 4.6 of [RFC8126].)
Each entry in the registry must include:
Key value:
an unsigned integer to be used as the value of the key
Name:
a name that could be used in implementations for the key
Brief description:
a brief description
Change Controller:
(see Section 2.3 of [RFC8126])
Reference:
a reference document that provides a description of the map,
including a CDDL description, that describes all inside keys and
values
The expert is requested to assign the shortest key values (1+0 and
1+1 encoding) to registrations that are likely to enjoy wide use and
can benefit from short encodings.
To be immediately useful in CDDL and programming language contexts, a
name consists of a lower-case ASCII letter (a-z) and zero or more
additional ASCII characters that are either lower-case letters,
digits, or a hyphen-minus, i.e., it matches [a-z][-a-z0-9]*. As with
the key values, names need to be unique.
Initial entries in this sub-registry are as follows:
+=======+=============+===========================+===========+
| Key | Name | Brief description | Reference |
| value | | | |
+=======+=============+===========================+===========+
| 7807 | tunnel-7807 | Carry RFC 7807 problem | RFC XXXX, |
| | | details in a Concise | Appendix |
| | | Problem Details data item | B |
+-------+-------------+---------------------------+-----------+
Table 2: Initial Entries in the Custom Problem Detail Key
registry
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6.3. Media Type
IANA is requested to add the following Media-Type to the "Media
Types" registry [IANA.media-types].
+============================+============================+=========+
|Name |Template |Reference|
+============================+============================+=========+
|concise-problem-details+cbor|application/concise-problem-|RFC XXXX,|
| |details+cbor |Section |
| | |6.3 |
+----------------------------+----------------------------+---------+
Table 3: New Media Type application/concise-problem-details+cbor
Type name: application
Subtype name: concise-problem-details+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary (CBOR data item)
Security considerations: Section 5 of RFC XXXX
Interoperability considerations: none
Published specification: Section 6.3 of RFC XXXX
Applications that use this media type: Clients and servers in the
Internet of Things
Fragment identifier considerations: The syntax and semantics of
fragment identifiers is as specified for "application/cbor". (At
publication of RFC XXXX, there is no fragment identification
syntax defined for "application/cbor".)
Person & email address to contact for further information: CoRE WG
mailing list (core@ietf.org), or IETF Applications and Real-Time
Area (art@ietf.org)
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IETF
Provisional registration: no
6.4. Content-Format
IANA is requested to register a Content-Format number in the "CoAP
Content-Formats" sub-registry, within the "Constrained RESTful
Environments (CoRE) Parameters" Registry [IANA.core-parameters], as
follows:
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+==============================+================+======+===========+
| Content-Type | Content Coding | ID | Reference |
+==============================+================+======+===========+
| application/concise-problem- | - | TBD1 | RFC XXXX |
| details+cbor | | | |
+------------------------------+----------------+------+-----------+
Table 4: New Content-Format
TBD1 is to be assigned from the space 256..999.
In the registry as defined by Section 12.3 of [RFC7252] at the time
of writing, the column "Content-Type" is called "Media type" and the
column "Content Coding" is called "Encoding".
// This paragraph to be removed by RFC editor.
6.5. CBOR Tag 38
In the registry "CBOR Tags" [IANA.cbor-tags], IANA has registered
CBOR Tag 38. IANA is requested to replace the reference for this
registration with Appendix A, RFC XXXX.
7. References
7.1. Normative References
[IANA.cbor-tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
19 September 2013,
<https://www.iana.org/assignments/cbor-tags>.
[IANA.core-parameters]
IANA, "Constrained RESTful Environments (CoRE)
Parameters", 8 June 2012,
<https://www.iana.org/assignments/core-parameters>.
[IANA.media-types]
IANA, "Provisional Standard Media Type Registry", 20 July
2012, <https://www.iana.org/assignments/provisional-
standard-media-types>.
[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>.
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[RFC4647] Phillips, A., Ed. and M. Davis, Ed., "Matching of Language
Tags", BCP 47, RFC 4647, DOI 10.17487/RFC4647, September
2006, <https://www.rfc-editor.org/info/rfc4647>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[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>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/info/rfc7807>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC9165] Bormann, C., "Additional Control Operators for the Concise
Data Definition Language (CDDL)", RFC 9165,
DOI 10.17487/RFC9165, December 2021,
<https://www.rfc-editor.org/info/rfc9165>.
[STD66] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[STD94] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
7.2. Informative References
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[I-D.ietf-httpapi-rfc7807bis]
Nottingham, M., Wilde, E., and S. Dalal, "Problem Details
for HTTP APIs", Work in Progress, Internet-Draft, draft-
ietf-httpapi-rfc7807bis-03, 25 May 2022,
<https://www.ietf.org/archive/id/draft-ietf-httpapi-
rfc7807bis-03.txt>.
[RDF] Cyganiak, R., Wood, D., and M. Lanthaler, "RDF 1.1
Concepts and Abstract Syntax", W3C Recommendation, 25
February 2014,
<http://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC6082] Whistler, K., Adams, G., Duerst, M., Presuhn, R., Ed., and
J. Klensin, "Deprecating Unicode Language Tag Characters:
RFC 2482 is Historic", RFC 6082, DOI 10.17487/RFC6082,
November 2010, <https://www.rfc-editor.org/info/rfc6082>.
[Unicode-14.0.0]
The Unicode Consortium, "The Unicode Standard, Version
14.0.0", Mountain View: The Unicode Consortium,
ISBN 978-1-936213-29-0, September 2021,
<https://www.unicode.org/versions/Unicode14.0.0/>. Note
that while this document references a version that was
recent at the time of writing, the statements made based
on this version are expected to remain valid for future
versions.
[Unicode-14.0.0-bidi]
The Unicode Consortium, "Unicode® Standard Annex #9 ---
Unicode Bidirectional Algorithm", 27 August 2021,
<https://www.unicode.org/reports/
tr9/#Markup_And_Formatting>. Note that while this
document references a version that was recent at the time
of writing, the statements made based on this version are
expected to remain valid for future versions.
Appendix A. Language-Tagged Strings
This appendix serves as the archival documentation for CBOR Tag 38, a
tag for serializing language-tagged text strings in CBOR. The text
of this appendix is adapted from the specification text supplied for
its initial registration. It has been extended to allow
supplementing the language tag by a direction indication.
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As with any IANA-registered item, a specification that further
updates this registration needs to update the reference column of the
IANA registry (see Section 6.5). Future specifications may update
this appendix, other parts of this document, or both. (When updating
this appendix, keep in mind that applications beyond concise problem
details may adopt the tag defined here.) Users of this tag are
advised to consult the registry to obtain the most recent update for
this appendix.
A.1. Introduction
In some cases it is useful to specify the natural language of a text
string. This specification defines a tag that does just that. One
technology that supports language-tagged strings is the Resource
Description Framework (RDF) [RDF].
A.2. Detailed Semantics
A language-tagged string in CBOR has the tag 38 and consists of an
array with a length of 2 or 3.
The first element is a well-formed language tag under Best Current
Practice 47 ([RFC5646] and [RFC4647]), represented as a UTF-8 text
string (major type 3).
The second element is an arbitrary UTF-8 text string (major type 3).
Both the language tag and the arbitrary string can optionally be
annotated with CBOR tags; this is not shown in the CDDL below.
The optional third element, if present, represents a ternary value
that indicates a direction, as follows:
* false: left-to-right direction ("ltr"). The text is expected to
be displayed with left-to-right base direction if standalone, and
isolated with left-to-right direction (as if enclosed in LRI ...
PDI or equivalent, see [Unicode-14.0.0-bidi]) in the context of a
longer string or text.
* true: right-to-left direction ("rtl"). The text is expected to be
displayed with right-to-left base direction if standalone, and
isolated with right-to-left direction (as if enclosed in RLI ...
PDI or equivalent, see [Unicode-14.0.0-bidi]) in the context of a
longer string or text.
* null indicates that no indication is made about the direction
("auto"), enabling an internationalization library to make an
auto-detection decision such as treating the string as if enclosed
in FSI ... PDI or equivalent, see [Unicode-14.0.0-bidi].
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If the third element is absent, directionality context may be
applying (e.g., base directionality information for an entire CBOR
message or part thereof). If there is no directionality context
applying, the default interpretation is the same as for null
("auto").
In CDDL:
tag38 = #6.38([tag38-ltag, text, ?tag38-direction])
tag38-ltag = text .regexp "[a-zA-Z]{1,8}(-[a-zA-Z0-9]{1,8})*"
tag38-direction = &(ltr: false, rtl: true, auto: null)
NOTE: Language tags of any combination of case are allowed. But
Section 2.1.1 of [RFC5646], part of Best Current Practice 47,
recommends a case combination for language tags that encoders that
support tag 38 may wish to follow when generating language tags.
Data items with tag 38 that do not meet the criteria above are not
valid (see Section 5.3.2 of [STD94]).
NOTE: The Unicode Standard [Unicode-14.0.0] includes a set of
characters designed for tagging text (including language tagging), in
the range U+E0000 to U+E007F. Although many applications, including
RDF, do not disallow these characters in text strings, the Unicode
Consortium has deprecated these characters and recommends annotating
language via a higher-level protocol instead. See the section
"Deprecated Tag Characters" in Section 23.9 of [Unicode-14.0.0], as
well as [RFC6082].
A.3. Examples
Examples in this section are given in CBOR diagnostic notation first
and then as a pretty-printed hexadecimal representation of the
encoded item.
The following example shows how the English-language string "Hello"
is represented.
38(["en", "Hello"])
D8 26 # tag(38)
82 # array(2)
62 # text(2)
656E # "en"
65 # text(5)
48656C6C6F # "Hello"
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The following example shows how the French-language string "Bonjour"
is represented.
38(["fr", "Bonjour"])
D8 26 # tag(38)
82 # array(2)
62 # text(2)
6672 # "fr"
67 # text(7)
426F6E6A6F7572 # "Bonjour"
The following example shows how the Hebrew-language string "שלום"
(HEBREW LETTER SHIN, HEBREW LETTER LAMED, HEBREW LETTER VAV, HEBREW
LETTER FINAL MEM, U+05E9 U+05DC U+05D5 U+05DD) is represented. Note
the rtl direction expressed by setting the third element in the array
to "true".
38(["he", "שלום", true])
D8 26 # tag(38)
83 # array(3)
62 # text(2)
6865 # "he"
68 # text(8)
D7A9D79CD795D79D # "שלום"
F5 # primitive(21)
Appendix B. Interworking with RFC 7807
On certain occasions, it will be necessary to carry ("tunnel")
[RFC7807] problem details in a Concise Problem Details data item.
This appendix defines a Custom Problem Details entry for that
purpose. This is assigned Custom Problem Detail key 7807 in
Section 6.2. Its structure is:
tunnel-7807 = {
? &(type: 0) => ~uri
? &(status: 1) => 0..999
* text => any
}
To carry an [RFC7807] problem details JSON object in a Concise
Problem Details data item, first convert the JSON object to CBOR as
per Section 6.2 of [STD94]. Create an empty Concise Problem Details
data item.
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Move the values for "title", "detail", and "instance", if present,
from the [RFC7807] problem details to the equivalent Standard Problem
Detail entries. Create a Custom Problem Details entry with key 7807.
Move the values for "type" and "status", if present, to the
equivalent keys 0 and 1 of the Custom Problem Details entry. Move
all remaining key/value pairs (additional members as per Section 3.2
of [RFC7807]) in the converted [RFC7807] problem details object to
the Custom Problem Details map unchanged.
The inverse direction, carrying Concise Problem Details in a Problem
Details JSON object requires the additional support provided by
[I-D.ietf-httpapi-rfc7807bis], which is planned to create the HTTP
Problem Types Registry. An HTTP Problem Type can then be registered
that extracts top-level items from the Concise Problem Details data
item in a similar way to the conversion described above, and which
carries the rest of the Concise Problem Details data item in an
additional member via base64url encoding without padding (Section 5
of [RFC4648]). Details can be defined in a separate document when
the work on [I-D.ietf-httpapi-rfc7807bis] is completed.
Acknowledgments
Mark Nottingham and Erik Wilde, authors of RFC 7807. Klaus Hartke
and Jaime Jiménez, co-authors of an earlier generation of this
specification. Christian Amsüss, Marco Tiloca, Ari Keränen and
Michael Richardson for review and comments on this document.
Francesca Palombini for her review (and support) as responsible AD,
and Joel Jaeggli for his OPSDIR review, both of which brought
significant additional considerations to this document.
For Appendix A, John Cowan and Doug Ewell are also to be
acknowledged. The content of an earlier version of this appendix was
also discussed in the "apps-discuss at ietf.org" and "ltru at
ietf.org" mailing lists. More recently, the authors initiated a
discussion about the handling of writing direction information in
conjunction with language tags. That led to discussions within the
W3C Internationalization Core Working Group. The authors would like
to acknowledge that cross-organization cooperation and particular
contributions from John Klensin and Addison Phillips, and specific
text proposals by Martin Dürst.
Contributors
Peter Occil
Email: poccil14 at gmail dot com
URI: http://peteroupc.github.io/CBOR/
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Peter defined CBOR tag 38, basis of Appendix A.
Christian Amsüss
Email: christian@amsuess.com
Christian contributed what became Section 3.1.1.
Authors' Addresses
Thomas Fossati
arm
Email: thomas.fossati@arm.com
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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