WEBTRANS

Summary

The WEBTRANS working group met at IETF 125 to discuss the progress of the core protocol specifications and interop status. The W3C WebTransport API is nearing a candidate recommendation with a target release in late 2026 and has been selected for the "Interop 2026" focus area. On the IETF side, the working group has entered Working Group Last Call (WGLC) for its three main documents. Discussion focused on refining HTTP status code responses for unsupported WebTransport requests and coordinating with the HTTP Directorate.

Key Discussion Points

W3C WebTransport Update

Will Law presented the W3C WebTransport group update (Slides 3-8).

Status: A new working draft was published on February 4th. The charter is extended to June 30th, with a release target of August 2026.
Fetch Integration: WebTransport now integrates at the highest level of Fetch, enabling header support in the constructor and inheritance of future Fetch improvements.
Stats & Security: New statistics for bytes acknowledged were added. Content Security Policy (CSP) now includes unsafe-webtransport-hashes.
Interop: WebTransport is now a focus area for "Interop 2026," ensuring deep cross-browser implementation commitment.

IETF Draft Updates

Eric Kinnear provided updates on the active IETF drafts (Slides 9-19).

draft-ietf-webtrans-overview: Editorial cleanup only. The document is in WGLC.
draft-ietf-webtrans-http3:
- Updated security considerations regarding server-initiated stream limits.
- "Max sessions" was removed; WebTransport support is now indicated by the server via a setting (though clients still send it for draft version negotiation).
- New error codes: ALPN Error (mismatched protocol) and WebTransport Requirements Not Met (missing mandatory features like datagrams).
- Clarified that capsule-based protocols should be avoided over HTTP/3 in favor of native WebTransport streams.
draft-ietf-webtrans-http2:
- Parallel security and flow control updates to the H3 draft.
- Split settings for initial max stream data into local and remote initiated bidirectional streams to align with QUIC.
- Disallowed large error codes to maintain consistency with HTTP/3.

Technical Discussion: HTTP Status Codes

The group discussed which status code to return when a resource exists but does not support WebTransport.

Lucas Pardue questioned the current use of 406 (Not Acceptable), noting it traditionally refers to media types.
Mike Bishop and Eric Kinnear discussed 405 (Method Not Allowed), but noted ambiguity regarding whether "Method" refers to CONNECT or the extended protocol.
Ben Schwartz suggested following HTTP Directorate advice to use generic 4xx categories rather than mandating specific codes.
Ted Hardie expressed concern that without a specific code or header, clients cannot distinguish between a missing method and missing WebTransport support.
Lucas Pardue suggested looking into "Problem Details" (RFC 9457) or a specific protocol pseudo-header extension to provide a unique signal to the client.

Interoperability Status

Marten Seemann updated the group on the WebTransport Interop Runner (Slide 20).

Four implementations are currently participating: Chrome, Firefox, WebTransport-go, and a second server implementation.
Current tests cover handshakes, ALPN negotiation, unidirectional/bidirectional streams, and datagrams.
Future tests will include multiplexing and stream resets (including partially reliable resets).

Decisions and Action Items

Status Codes: The editors will consult with the HTTP Directorate to determine the best approach for signaling unsupported WebTransport on an existing resource (e.g., status code vs. header field vs. problem types).
Draft Dependencies: The chairs noted that draft-ietf-webtrans-http3 has a dependency on the "Reliable Stream Resets" work in the QUIC WG. These will likely progress to the IESG together.

Next Steps

Working Group Last Call (WGLC): Participants are urged to review the full text of draft-ietf-webtrans-overview, draft-ietf-webtrans-http3, and draft-ietf-webtrans-http2.
Implementation: Implementers are encouraged to join Marten Seemann’s interop runner to validate the latest draft changes, particularly regarding flow control and settings.
Publication: Pending the resolution of the status code issue and completion of WGLC, the chairs will move the documents toward IESG submission.

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