Markdown Version | Session Recording

Session Date/Time: 08 Jun 2022 14:00

CORE

Summary

This interim meeting of the CORE WG focused on two key documents: "Problem Details for HTTP APIs (CBOR)" (currently in Last Call) and "CBOR URI Reference (Href)", with a particular focus on CURIEs. Discussions for "Problem Details" revolved around clarifying the title field, handling human-readable text without language tags, and processing unknown entries. For "Href", the conversation highlighted the complexities of CURIEs in a CBOR context and the need for a structural alternative.

Key Discussion Points

Problem Details for HTTP APIs (CBOR)

• title Field Semantics:
  • The document's definition of title as "not varying across instances" was discussed. In RFC 7807, this tied to the problem type, which is now deprecated.
  • A suggestion was made to remove the second sentence regarding invariance or clarify its intent: title should describe the kind of problem, not a specific instance (e.g., "not enough money" vs. "you have 54 euros").
  • A sense of those present indicated that the title should be a "short, human-readable summary of the problem shape" without duplicating instance-specific details. An example contrasting generic vs. specific problem descriptions was requested for inclusion.
• Language Tags for Human-Readable Text (title, detail):
  • Francesca asked why unadorned text (without a language tag) is allowed, given its human-readable nature.
  • Three options were considered:
    1. Make English the default.
    2. Make the default depend on context, observing that CoAP currently lacks a standard for language negotiation.
    3. Require a language tag (no unadorned text).
  • The discussion leaned towards option 2, with a fallback to a specified default (e.g., RFC 3864 "en-US") in the absence of context. This would need consultation with the Internationalization Directorate.
  • The overhead of adding a language tag (approx. 6 bytes for "en-US") was deemed acceptable in the grand scheme.
• Examples in Section 3.1:
  • Francesca suggested more examples of standard problem detail entries.
  • Concerns were raised that additional examples might lead implementers to copy values directly without registering them, causing issues. A decision was made to keep the current single example.
• Handling Unknown Entries:
  • Joel's Ops Directorate review noted that the document only addressed unknown entries for consumers, not for forwarders or storers.
  • The proposed solution was to add a "should recommended" to retain unknown entries when storing or forwarding, with exceptions for cases where it's "unbearably difficult" (e.g., format conversion) or if the forwarder's role is to filter/redact information.
• Publication Status:
  • The document is in Last Call, with AD reviews underway. Publication in June is still possible but requires efficient processing of reviews and AD ballots.
  • The Internationalization Directorate review is anticipated.

CBOR URI Reference (Href) and CURIEs

• CURIEs in CBOR Pact:
  • The new CBOR Pact environment allows powerful function tags, which could enable structural CURIE definitions.
  • A proposed function tag could combine a base URI with a relative URI (e.g., /foo/ + /bar/ -> /foo/bar/).
  • Challenges: The semantics of CURIEs are deeply tied to URI syntax, leading to "weird cases" where simple concatenation doesn't work as expected (e.g., http: + //example.com, or combining parts into a fragment identifier or hostname).
  • This often necessitates converting CRIS back to URI strings, concatenating, and then converting back to CRIS, which undermines the purpose of using CRIS.
  • A desire was expressed to operate semantically on CI/CI references directly.
• Subset of CURIEs:
  • The idea of defining a "sane" subset of CURIEs was discussed, possibly by developing a corpus of existing CURIE uses.
  • The fundamental problem of CURIEs being "lexical" (like C preprocessor macros) was highlighted, leading to management difficulties.
  • A "structural better CURIE" concept was proposed, fitting the CI paradigm and ideally backportable to URI space as a subset of lexical CURIEs.
• Scope for Href:
  • Given the complexity, a sense of those present indicated that the full problem of CURIE definition and structural alternatives should be spun off as a separate project and not addressed in the base CI/Href spec.
  • The powerful nature of CBOR Pact function tags means the current Href document is unlikely to create future roadblocks.
  • The work might become relevant for future CoRAL (CoAP Resource Abstract Layer) compression, particularly for expanding prefixes in dictionaries.

AOB (Any Other Business)

• The next CORE WG meeting will be a 2-hour session at IETF 113.
• RFC 9193 ("Terminology for Well-Known URIs") has been published, resolving a long-standing dependency and defining terms and ABNF for media types and content formats, which should streamline future document writing.
• The cbor.me tool was temporarily down, highlighting its importance to the community.

Decisions and Action Items

Problem Details for HTTP APIs (CBOR)

• Decision: Refine the description of the title field to be a "short human-readable summary of the problem shape without duplicating instant-specific details contained in the other problem detail entries." Include a clarifying example.
• Decision: For title and detail fields, allow language-tagged text; in the absence of context (for unadorned text), assume RFC 3864 "en-US" as a default. This decision will be cross-checked with the Internationalization Directorate.
• Decision: No additional examples will be added to Section 3.1 to avoid misinterpretation of example numbers.
• Decision: Add "should recommended" text to retain unknown entries when storing or forwarding problem details, except when "unbearably difficult" or for filtering/security purposes.
• Action Item: Continue processing AD reviews and prepare for Telechat approval, targeting June publication.

CBOR URI Reference (Href) and CURIEs

• Decision: The development of a "structural better CURIE" and the comprehensive definition of CURIE semantics for CBOR are to be spun off as a separate future project. This work will not block the current Href document.
• Action Item: The working group will explore "structural CURIEs" as a separate effort, potentially in the context of CoRAL or other applications needing URI compression/expansion.

Other

• Action Item: Carsten Bormann will provide a tutorial or wiki entry on generating RFC index entries, particularly for Markdown/Cramdown sources.

Next Steps

• Complete the Last Call process for "Problem Details for HTTP APIs (CBOR)".
• Continue work on "CBOR URI Reference (Href)".
• Prepare for the CORE WG meeting at IETF 113.
• Initiate discussions or a new effort on "structural CURIEs" as a separate work item.