Session Date/Time: 23 Feb 2022 15:00

CBOR

Summary

The CBOR Working Group meeting discussed several key topics including the use of CDDL for QUIC-EX, proposals for notable tags, the introduction of tags for Extended Diagnostic Notation (EDN), and a broader concept of annotations within CBOR. Action items were assigned for further development and review of proposals.

Key Discussion Points

Administrative Items:
- Francesca was confirmed as the responsible AD for CBOR documents, including the file magic document.
- Carsten noted he would look into the shepherd review notes for the file magic document.
CDDL for QUIC-EX:
- A QUIC-EX implementer raised pertinent questions regarding CDDL usage.
- Carsten plans to capture the guidance provided in an Internet-Draft titled "Using CDDL" or similar, based on this interaction.
- The implementers did not encounter limits of CDDL itself, but rather questions on best practices for including CDDL in RFCs.
- The need for better documentation on best practices for integrating CDDL into RFCs was identified.
- A fully working CDDL tool remains a desire, with Carsten providing an update on his ongoing development of version 2, which aims to provide validation and instance generation, though currently lacking full coverage in generated instances.
- The discussion touched on the idea of accepting CDDL as a formal language to facilitate automated verification tooling.
Notable Tags:
- Carsten updated the group on a proposal for tags for compiler-managed alternative data items, stemming from the Haskell community.
- This proposal was added to the Notable Tags document, with an initial tag request (101) being corrected.
- More eyes are requested on this proposal before an IANA request is submitted.
- Jacques' long-standing problem statement tag proposal was also mentioned as needing attention.
- Michael suggested adding text to the notable tags document about the stability guarantees of compiler-assigned numbers, which could range from being specific to a particular build to being part of a protocol.
- A brief, off-topic discussion occurred on tunneling CBOR through JSON, revealing a hidden feature in the CBOR diagnostic tools. Carsten submitted an updated version of the tools but is not currently proposing standardization for this until more experience is gathered.
Extended Diagnostic Notation (EDN) Tags:
- Carsten proposed two new tags (887 and 888) for EDN, specifically to represent dot dot notation and Uniform Resource Identifiers (URIs/CRIs) within CBOR structures.
- Tag 887 would encapsulate a URI string, preserving its semantic information, primarily for diagnostic tools.
- Tag 888 would embed a literal text string as it appears in diagnostic notation.
- The use case is to help tools that process CBOR in both directions but might lack a specific schema, allowing EDN components to be preserved and passed through.
- Concerns were raised about the potential "harm" or unexpected behavior if these tags were encountered in live protocol exchanges not intended for diagnostic output. Generic processors might need to "scream" or be explicitly configured to accept them.
CBOR Annotations and Metadata:
- The discussion on EDN tags evolved into a broader concept for general annotations in CBOR.
- The idea is to have a mechanism for "elective" or "can ignore" tags that provide additional information for diagnostic tools, statistics, or other applications, without affecting the primary application's processing of the CBOR data.
- This concept is analogous to "must process vs. can ignore" or "critical vs. elective" aspects of tags.
- Carsten noted that his CDDL tool version 2 already builds a parallel tree for annotations.
- The group considered looking at how YAML processors handle serialization metadata and explored existing patterns like YANG metadata (though XML-specific) and SDF mapping files (using separate metadata files).

Decisions and Action Items

Michael: Send a mail to the mailing list proposing text on the stability guarantees for compiler-assigned notable tags.
Carsten: Proceed with writing an Internet-Draft on "Using CDDL," drawing from the recent QUIC-EX implementer interaction.
WG Participants: Review the notable tags proposal for compiler-managed alternative data items before an IANA request is sent.

Next Steps

Continue the development of Carsten's CDDL tool version 2.
Further discussion on a general mechanism for CBOR annotations and metadata, considering existing solutions and best practices.
The next scheduled WG meeting is on the 9th. There will be no official CBOR WG meeting at IETF 113.