Internet DRAFT - draft-ietf-httpapi-yaml-mediatypes
draft-ietf-httpapi-yaml-mediatypes
HTTPAPI R. Polli
Internet-Draft Digital Transformation Department, Italian Government
Intended status: Informational E. Wilde
Expires: 2 March 2024 Axway
E. Aro
Mozilla
30 August 2023
YAML Media Type
draft-ietf-httpapi-yaml-mediatypes-10
Abstract
This document registers the application/yaml media type and the +yaml
structured syntax suffix on the IANA Media Types registry, intended
to be used to identify document components serialized according to
the YAML specification.
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-httpapi-yaml-mediatypes/.
Discussion of this document takes place on the HTTPAPI Working Group
mailing list (mailto:httpapi@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/httpapi/. Subscribe at
https://www.ietf.org/mailman/listinfo/httpapi/. Working Group
information can be found at https://datatracker.ietf.org/wg/httpapi/
about/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-httpapi/mediatypes/labels/yaml.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Polli, et al. Expires 2 March 2024 [Page 1]
Internet-Draft YAML Media Type August 2023
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 2 March 2024.
Copyright Notice
Copyright (c) 2023 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
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
1.2. Fragment identification . . . . . . . . . . . . . . . . . 4
1.2.1. Fragment identification via alias nodes . . . . . . . 4
2. Media Type and Structured Syntax Suffix registrations . . . . 5
2.1. Media Type application/yaml . . . . . . . . . . . . . . . 5
2.2. The +yaml Structured Syntax Suffix . . . . . . . . . . . 6
3. Interoperability Considerations . . . . . . . . . . . . . . . 7
3.1. YAML is an Evolving Language . . . . . . . . . . . . . . 7
3.2. YAML streams . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Filename extension . . . . . . . . . . . . . . . . . . . 8
3.4. YAML and JSON . . . . . . . . . . . . . . . . . . . . . . 8
3.5. Fragment identifiers . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
4.1. Arbitrary Code Execution . . . . . . . . . . . . . . . . 10
4.2. Resource Exhaustion . . . . . . . . . . . . . . . . . . . 10
4.3. YAML streams . . . . . . . . . . . . . . . . . . . . . . 11
4.4. Expressing booleans . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . 12
6.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Examples related to fragment identifier
interoperability . . . . . . . . . . . . . . . . . . . . 13
A.1. Unreferenceable nodes . . . . . . . . . . . . . . . . . . 14
Polli, et al. Expires 2 March 2024 [Page 2]
Internet-Draft YAML Media Type August 2023
A.2. Referencing a missing node . . . . . . . . . . . . . . . 14
A.3. Representation graph with anchors and cyclic
references . . . . . . . . . . . . . . . . . . . . . . . 14
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Since draft-ietf-httpapi-yaml-mediatypes-02 . . . . . . . . . . 17
Since draft-ietf-httpapi-yaml-mediatypes-01 . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
YAML [YAML] is a data serialization format that is capable of
conveying one or multiple documents in a single presentation stream
(e.g., a file or a network resource). It is widely used on the
Internet, including in the API sector (e.g., see [OAS]), but a
corresponding media type and structured syntax suffix had not
previously been registered by IANA.
To increase interoperability when exchanging YAML streams, and
leverage content negotiation mechanisms when exchanging YAML
resources, this specification registers the application/yaml media
type and the +yaml structured syntax suffix [MEDIATYPE].
Moreover, it provides security considerations and interoperability
considerations related to [YAML], including its relation with [JSON].
1.1. Notational Conventions
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. These words may also appear in this
document in lower case as plain English words, absent their normative
meanings.
The terms "content", "content negotiation", "resource", and "user
agent" in this document are to be interpreted as in [HTTP].
The terms "fragment" and "fragment identifier" in this document are
to be interpreted as in [URI].
The terms "presentation", "stream", "YAML document", "representation
graph", "tag", "serialization detail", "node", "alias node", "anchor"
and "anchor name" in this document are to be interpreted as in
[YAML].
Polli, et al. Expires 2 March 2024 [Page 3]
Internet-Draft YAML Media Type August 2023
Figures containing YAML code always start with the "%YAML 1.2"
directive to improve readability.
1.2. Fragment identification
A fragment identifies a node in a stream.
A fragment identifier starting with "*" is to be interpreted as a
YAML alias node (see Section 1.2.1).
For single-document YAML streams, a fragment identifier that is empty
or that starts with "/" is to be interpreted as a JSON Pointer
[JSON-POINTER] and is evaluated on the YAML representation graph,
walking through alias nodes; in particular, the empty fragment
identifier references the root node. This syntax can only reference
the YAML nodes that are on a path that is made up of nodes
interoperable with the JSON data model (see Section 3.4).
A fragment identifier is not guaranteed to reference an existing
node. Therefore, applications SHOULD define how an unresolved alias
node ought to be handled.
1.2.1. Fragment identification via alias nodes
This section describes how to use alias nodes (see Section 3.2.2.2
and 7.1 of [YAML]) as fragment identifiers to designate nodes.
A YAML alias node can be represented in a URI fragment identifier by
encoding it into bytes using UTF-8 [UTF-8], but percent-encoding of
those characters is not allowed by the fragment rule in Section 3.5
of [URI].
If multiple nodes would match a fragment identifier, the first
occurrence of such match is selected.
Users concerned with interoperability of fragment identifiers:
* SHOULD limit alias nodes to a set of characters that do not
require encoding to be expressed as URI fragment identifiers: this
is generally possible since anchor names are a serialization
detail;
* SHOULD NOT use alias nodes that match multiple nodes.
Polli, et al. Expires 2 March 2024 [Page 4]
Internet-Draft YAML Media Type August 2023
In the example resource below, the relative reference (see
Section 4.2 of [URI]) file.yaml#*foo identifies the first alias node
*foo pointing to the node with value scalar and not the one in the
second document; whereas the relative reference file.yaml#*document_2
identifies the root node of the second document {one: [a, sequence]}.
%YAML 1.2
---
one: &foo scalar
two: &bar
- some
- sequence
- items
...
%YAML 1.2
---
&document_2
one: &foo [a, sequence]
Figure 1: A YAML stream containing two YAML documents.
2. Media Type and Structured Syntax Suffix registrations
This section describes the information required to register the above
media type according to [MEDIATYPE]
2.1. Media Type application/yaml
The media type for YAML text is application/yaml; the following
information serves as the registration form for this media type.
Type name: application
Subtype name: yaml
Required parameters: N/A
Optional parameters: N/A; unrecognized parameters should be ignored
Encoding considerations: binary
Security considerations: see Section 4 of this document
Interoperability considerations: see Section 3 of this document
Published specification: [YAML], this document
Applications that use this media type: Applications that need a
Polli, et al. Expires 2 March 2024 [Page 5]
Internet-Draft YAML Media Type August 2023
human-friendly, cross language, Unicode based data serialization
language designed around the common native data types of dynamic
programming languages.
Fragment identifier considerations: See Section 1.2 of this document
Additional information:
* Deprecated alias names for this type: application/x-yaml, text/
yaml, text/x-yaml. These names are used, but not registered.
* Magic number(s) N/A
* File extension(s): "yaml" (preferred), "yml". See Section 3.3 of
this document.
* Macintosh file type code(s): N/A
* Windows Clipboard Name: YAML
Person and email address to contact for further information: See the
Authors' Addresses section of this document.
Intended usage: COMMON
Restrictions on usage: None.
Author: See the Authors' Addresses section of this document.
Change controller: IETF
2.2. The +yaml Structured Syntax Suffix
The suffix +yaml MAY be used with any media type whose representation
follows that established for application/yaml. The media type
structured syntax suffix registration form follows. See [MEDIATYPE]
for definitions of each of the registration form headings.
Name: YAML Ain't Markup Language (YAML)
+suffix: +yaml
References: [YAML], this document
Encoding considerations: Same as "application/yaml"
Fragment identifier considerations: Differently from application/
Polli, et al. Expires 2 March 2024 [Page 6]
Internet-Draft YAML Media Type August 2023
yaml, there is no fragment identification syntax defined for
+yaml.
A specific xxx/yyy+yaml media type needs to define the syntax and
semantics for fragment identifiers because the ones defined for
"application/yaml" do not apply unless explicitly expressed.
Interoperability considerations: Same as "application/yaml"
Security considerations: Same as "application/yaml"
Contact: httpapi@ietf.org or art@ietf.org
Author: See the Authors' Addresses section of this document
Change controller: IETF
3. Interoperability Considerations
3.1. YAML is an Evolving Language
YAML is an evolving language and, over time, some features have been
added and others removed.
This [YAML] media type registration is independent of YAML version.
This allows content negotiation of version-independent YAML
resources.
Implementers concerned about features related to a specific YAML
version can specify it in YAML documents using the %YAML directive
(see Section 6.8.1 of [YAML]).
3.2. YAML streams
A YAML stream can contain zero or more YAML documents.
When receiving a multi-document stream, an application that only
expects one-document streams, ought to signal an error instead of
ignoring the extra documents.
Current implementations consider different documents in a stream
independent, similarly to JSON Text Sequences (see [RFC7464]);
elements such as anchors are not guaranteed to be referenceable
across different documents.
Polli, et al. Expires 2 March 2024 [Page 7]
Internet-Draft YAML Media Type August 2023
3.3. Filename extension
The "yaml" filename extension is the preferred one; it is the most
popular and widely used on the web. The "yml" filename extension is
still used. The simultaneous usage of two filename extensions in the
same context might cause interoperability issues (e.g., when both a
"config.yaml" and a "config.yml" are present).
3.4. YAML and JSON
When using flow collection styles (see Section 7.4 of [YAML]) a YAML
document could look like JSON [JSON], thus similar interoperability
considerations apply.
When using YAML as a more efficient format to serialize information
intended to be consumed as JSON, information not reflected in the
representation graph and classified as presentation or serialization
detail (see Section 3.2 of [YAML]) can be discarded. This includes
comments (see Section 3.2.3.3 of [YAML]), directives, and alias nodes
(see Section 7.1 of [YAML]) that do not have a JSON counterpart.
%YAML 1.2
---
# This comment will be lost
# when serializing in JSON.
Title:
type: string
maxLength: &text_limit 64
Name:
type: string
maxLength: *text_limit # Replaced by the value 64.
Figure 2: JSON replaces alias nodes with static values.
Implementers need to ensure that relevant information will not be
lost during the processing. For example, they might consider
acceptable that alias nodes are replaced by static values.
In some cases an implementer may want to define a list of allowed
YAML features, taking into account that the following ones might have
interoperability issues with [JSON]:
* multi-document YAML streams;
Polli, et al. Expires 2 March 2024 [Page 8]
Internet-Draft YAML Media Type August 2023
* non UTF-8 encoding. Before encoding YAML streams in UTF-16 or
UTF-32, it is important to note that Section 8.1 of [JSON]
mandates the use of UTF-8 when exchanging JSON texts between
systems that are not part of a closed ecosystem, and that
Section 5.2 of [YAML] recommends the use of UTF-8;
* mapping keys that are not strings;
* circular references represented using anchor (see Section 4.2 and
Figure 4);
* .inf and .nan float values, since JSON does not support them;
* non-JSON types, including the ones associated with tags like
!!timestamp that were included in the default schema of older YAML
versions;
* tags in general, and specifically the ones that do not map to JSON
types like custom and local tags such as !!python/object and
!mytag (see Section 2.4 of [YAML]);
%YAML 1.2
---
non-json-keys:
0: a number
[0, 1]: a sequence
? {k: v}
: a map
---
non-json-keys:
!date 2020-01-01: a timestamp
non-json-value: !date 2020-01-01
...
Figure 3: Example of mapping keys and values not supported in
JSON in a multi- document YAML stream
3.5. Fragment identifiers
To allow fragment identifiers to traverse alias nodes, the YAML
representation graph needs to be generated before the fragment
identifier evaluation. It is important that this evaluation will not
cause the issues mentioned in Section 3.4 and in Security
considerations (Section 4) such as infinite loops and unexpected code
execution.
Polli, et al. Expires 2 March 2024 [Page 9]
Internet-Draft YAML Media Type August 2023
Implementers need to consider that the YAML version and supported
features (e.g., merge keys) can affect the generation of the
representation graph (see Figure 9).
In Section 2.1, this document extends the use of specifications based
on the JSON data model with support for YAML fragment identifiers.
This is to improve the interoperability of already consolidated
practices, such as the one of writing OpenAPI documents [OAS] in
YAML.
Appendix A provides a non-exhaustive list of examples that could help
understand interoperability issues related to fragment identifiers.
4. Security Considerations
Security requirements for both media type and media type suffix
registrations are discussed in Section 4.6 of [MEDIATYPE].
4.1. Arbitrary Code Execution
Care should be used when using YAML tags, because their resolution
might trigger unexpected code execution.
Code execution in deserializers should be disabled by default, and
only be enabled explicitly. In those cases, the implementation
should ensure - for example, via specific functions - that the code
execution results in strictly bounded time/memory limits.
Many implementations provide safe deserializers addressing these
issues.
4.2. Resource Exhaustion
YAML documents are rooted, connected, directed graphs and can contain
reference cycles, so they can't be treated as simple trees (see
Section 3.2.1 of [YAML]). An implementation that treats them as
simple trees risks going into an infinite loop while traversing the
YAML representation graph. This can happen:
* when trying to serialize it as JSON;
* or when searching/identifying nodes using specifications based on
the JSON data model (e.g., [JSON-POINTER]).
%YAML 1.2
---
x: &x
y: *x
Polli, et al. Expires 2 March 2024 [Page 10]
Internet-Draft YAML Media Type August 2023
Figure 4: A cyclic document
Even if a representation graph is not cyclic, treating it as a simple
tree could lead to improper behaviors (such as the "billion laughs"
or "Exponential Entity Expansion" problem).
%YAML 1.2
---
x1: &a1 ["a", "a"]
x2: &a2 [*a1, *a1]
x3: &a3 [*a2, *a2]
Figure 5: A billion laughs document
This can be addressed using processors limiting the anchor recursion
depth and validating the input before processing it; even in these
cases it is important to carefully test the implementation you are
going to use. The same considerations apply when serializing a YAML
representation graph in a format that does not support reference
cycles (see Section 3.4).
4.3. YAML streams
Incremental parsing and processing of a YAML stream can produce
partial results and later indicate failure to parse the remainder of
the stream; to prevent partial processing, implementers might prefer
validating and processing all the documents in a stream at the same
time.
Repeated parsing and re-encoding of a YAML stream can result in the
addition or removal of document delimiters (e.g., --- or ...) as well
as the modification of anchor names and other serialization details,
which can break signature validation.
4.4. Expressing booleans
Section 10.3.2 of [YAML] specifies that only the scalars matching the
regular expression true|True|TRUE|false|False|FALSE are interpreted
as booleans. Older YAML versions were more tolerant (e.g.,
interpreting NO and N as False, and YES and Y as True). When the
older syntax is used, a YAML implementation could then interpret
{insecure: n} as {insecure: "n"} instead of {insecure: false}. Using
the syntax defined in Section 10.3.2 of [YAML] prevents these issues.
5. IANA Considerations
This specification defines the following new Internet media type
[MEDIATYPE].
Polli, et al. Expires 2 March 2024 [Page 11]
Internet-Draft YAML Media Type August 2023
IANA is asked to update the "Media Types" registry at
https://www.iana.org/assignments/media-types
(https://www.iana.org/assignments/media-types) with the registration
information provided in the section below.
+==================+==================================+
| Media Type | Registration information section |
+==================+==================================+
| application/yaml | Section 2.1 of this document |
+------------------+----------------------------------+
Table 1
IANA is asked to update the "Structured Syntax Suffixes" registry at
https://www.iana.org/assignments/media-type-structured-suffix
(https://www.iana.org/assignments/media-type-structured-suffix) with
the registration information provided in the section below.
+========+==================================+
| Suffix | Registration information section |
+========+==================================+
| +yaml | Section 2.2 of this document |
+--------+----------------------------------+
Table 2
6. References
6.1. Normative References
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[JSON] 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/rfc/rfc8259>.
[JSON-POINTER]
Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
"JavaScript Object Notation (JSON) Pointer", RFC 6901,
DOI 10.17487/RFC6901, April 2013,
<https://www.rfc-editor.org/rfc/rfc6901>.
Polli, et al. Expires 2 March 2024 [Page 12]
Internet-Draft YAML Media Type August 2023
[MEDIATYPE]
Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
[OAS] Darrel Miller, Jeremy Whitlock, Marsh Gardiner, Mike
Ralphson, Ron Ratovsky, and Uri Sarid, "OpenAPI
Specification 3.0.0", 26 July 2017.
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[URI] 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/rfc/rfc3986>.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
[YAML] Oren Ben-Kiki, Clark Evans, Ingy dot Net, Tina Müller,
Pantelis Antoniou, Eemeli Aro, and Thomas Smith, "YAML
Ain't Markup Language Version 1.2", 1 October 2021,
<https://yaml.org/spec/1.2.2/>.
6.2. Informative References
[I-D.ietf-jsonpath-base]
Gössner, S., Normington, G., and C. Bormann, "JSONPath:
Query expressions for JSON", Work in Progress, Internet-
Draft, draft-ietf-jsonpath-base-20, 25 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-
jsonpath-base-20>.
[RFC7464] Williams, N., "JavaScript Object Notation (JSON) Text
Sequences", RFC 7464, DOI 10.17487/RFC7464, February 2015,
<https://www.rfc-editor.org/rfc/rfc7464>.
Appendix A. Examples related to fragment identifier interoperability
Polli, et al. Expires 2 March 2024 [Page 13]
Internet-Draft YAML Media Type August 2023
A.1. Unreferenceable nodes
In this example, a couple of YAML nodes that cannot be referenced
based on the JSON data model since their mapping keys are not
strings.
%YAML 1.2
---
a-map-cannot:
? {be: expressed}
: with a JSON Pointer
0: no numeric mapping keys in JSON
Figure 6: Example of YAML nodes that are not referenceable based
on JSON data model.
A.2. Referencing a missing node
In this example the fragment #/0 does not reference an existing node
%YAML 1.2
---
0: "JSON Pointer `#/0` references a string mapping key."
Figure 7: Example of a JSON Pointer that does not reference an
existing node.
A.3. Representation graph with anchors and cyclic references
In this YAML document, the #/foo/bar/baz fragment identifier
traverses the representation graph and references the string you.
Moreover, the presence of a cyclic reference implies that there are
infinite fragment identifiers #/foo/bat/../bat/bar referencing the
&anchor node.
%YAML 1.2
---
anchor: &anchor
baz: you
foo: &foo
bar: *anchor
bat: *foo
Figure 8: Example of a cyclic reference and alias nodes.
Polli, et al. Expires 2 March 2024 [Page 14]
Internet-Draft YAML Media Type August 2023
Many YAML implementations will resolve the merge key "<<:"
(https://yaml.org/type/merge.html) defined in YAML 1.1 in the
representation graph. This means that the fragment #/book/author/
given_name references the string Federico and that the fragment
#/book/<< will not reference any existing node.
%YAML 1.1
---
# Many implementations use merge keys.
the-viceroys: &the-viceroys
title: The Viceroys
author:
given_name: Federico
family_name: De Roberto
book:
<<: *the-viceroys
title: The Illusion
Figure 9: Example of YAML merge keys.
Acknowledgements
Thanks to Erik Wilde and David Biesack for being the initial
contributors of this specification, and to Darrel Miller and Rich
Salz for their support during the adoption phase.
In addition to the people above, this document owes a lot to the
extensive discussion inside and outside the HTTPAPI workgroup. The
following contributors have helped improve this specification by
opening pull requests, reporting bugs, asking smart questions,
drafting or reviewing text, and evaluating open issues:
Tina (tinita) Müller, Ben Hutton, Carsten Bormann, Manu Sporny and
Jason Desrosiers.
FAQ
This section is to be removed before publishing as an RFC.
Q: Why this document? After all these years, we still lack a proper
media-type for YAML. This has some security implications too (eg.
wrt on identifying parsers or treat downloads)
Q: Why using alias nodes as fragment identifiers? Alias nodes are a
native YAML feature that allows addressing any node in a YAML
document. Since YAML is not limited to string keywords, not all
nodes are addressable using JSON Pointers. Alias nodes are thus
the natural choice for fragment identifiers Section 1.2.
Polli, et al. Expires 2 March 2024 [Page 15]
Internet-Draft YAML Media Type August 2023
Q: Why not use plain names for alias nodes? Why not define plain
names? Using plain name fragments could have limited the ability of
future xxx+yaml media types to define their plain name fragments.
Moreover, alias nodes starts with * so we found no reason to strip
it when using them in fragments.
Preserving * had another positive result: it allows distinguishing
a fragment identifier expressed as an alias node from one
expressed in other formats. In this document we included JSON
Pointer [JSON-POINTER] which is expected to start with /.
Moreover, since JSON Path [I-D.ietf-jsonpath-base] expressions
start with $, this mechanism can be extended to JSON Path too.
Q: Why not just use JSON Pointer as the primary fragment
identifier? Fragment identifiers in YAML always reference YAML
representation graph nodes. JSON Pointer can only rely on string
keywords so it is not able to reference a generic node in the
representation graph.
Since JSON Pointer is a specification unrelated to YAML, we
decided to isolate the impacts of changes in JSON Pointer on YAML
fragments: only fragments starting with "/" are "delegated" to an
external spec, and if [JSON-POINTER] changes, it will only affect
fragments starting with "/".
The current behaviour for empty fragments is the same for both
JSON Pointer and alias nodes. Incidentally, it's the only
sensible behaviour independently of [JSON-POINTER].
Q: Why describe the YAML/JSON so closely? In the context of Web
APIs, YAML is widely used as a more compact way to serialize
content inteded to be consumed according to the JSON data model.
Typical examples are OpenAPI specifications and Kubernetes
manifest files, that can be serialized in both formats. The YAML
media type registration I-D is a spin-off and a building block for
the OpenAPI specification media type registration. The YAML/JSON
section aims at clarifying what developers should expect when
using YAML instead of JSON, and its content arose from common
mistakes and FAQs.
Please note that we are not imposing any normative restriction on
YAML streams; this is because YAML is defined outside this
document. Instead, we only provide Interoperability and Security
considerations that, by their nature, are not normative.
Q: Do we forbid using non-UTF-8 YAML serialization? No. Since
Polli, et al. Expires 2 March 2024 [Page 16]
Internet-Draft YAML Media Type August 2023
[JSON] recommends UTF-8 in interoperability context we suggest
that using UTF-8 is an interoperable behavior. This is aligned
with Section 5.2 of [YAML] that explicitly recommends UTF-8.
Q: Why media type registration information is outside the IANA
Considerations? We decided to follow the style adopted in [HTTP]
where the IANA Considerations in Section 18.8 of [HTTP] references
the multipart/byteranges media type registration form contained in
the specification body Section 14.6 of [HTTP].
Change Log
This section is to be removed before publishing as an RFC.
Since draft-ietf-httpapi-yaml-mediatypes-02
* clarification on fragment identifiers #50.
Since draft-ietf-httpapi-yaml-mediatypes-01
* application/yaml fragment identifiers compatible with JSON Pointer
#41 (#47).
Authors' Addresses
Roberto Polli
Digital Transformation Department, Italian Government
Italy
Email: robipolli@gmail.com
Erik Wilde
Axway
Switzerland
Email: erik.wilde@dret.net
Eemeli Aro
Mozilla
Finland
Email: eemeli@gmail.com
Polli, et al. Expires 2 March 2024 [Page 17]
