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a3cb44968e571857c15055da86d2d7f126e281ba
alknet/docs/architecture/questions/065-websocket-carrying-channels.md
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glm-5.2 a3cb44968e docs(adr): 093 — channels pure channel multiplexing (8-byte header, no stream_type) 
Prune the channels spec to reflect the stream-unification resolution
(docs/research/stream-unification/findings.md): the channels wire format
goes from 9 bytes to 8 bytes, the channels layer no longer carries a
stream_type concept, into_sub_streams() is removed, and TTY always uses
its 5-byte format (carried transparently in the channels payload).

ADR-093 is the umbrella decision (the channels-layer consequence of
ADR-092's BiStream handler leaf): every channel is a BiStream, the
handler owns its sub-stream multiplexing, the channels layer routes by
channel_id only. Amends ADR-071 (8-byte header, no stream_type),
ADR-074 (into_sub_streams removed, accept_bi yields BiStream), reverses
ADR-077 (TTY always 5-byte), and the channels-facing clauses of
ADR-072/073/075/076/080/081. Adds ADR-092 forward-reference note
(into_sub_streams preservation subsequently reversed by ADR-093) and
the missing ADR-092 cross-reference on ADR-070.

Adds OQ-68 (add/strip API shape — built-in vs utility; the contract is
decided in ADR-093, the function surface is open; two-way door, low
priority, decision-ready when the channels crate's implementation
begins).

Rewrites the 7 channels spec docs (README, overview, channels-wire,
channels-connection, channels-adapter, channel-operations, channel-client)
to describe the post-amendment shape as current, with the 8-byte header,
the add/strip composition, single accept_bi accessor, BiStream per
channel, and TTY-always-5-byte.

Touch-up cross-references in hub README, client README, ADR-085, and
the OQ-45/47/65 question files (TTY-internal stream_type 3 →
STREAM_CTRL_IN; channels 9-byte → 8-byte).
2026-07-18 18:10:17 +00:00

4.7 KiB
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OQ-65: Should WebSocket Carry the Channels Protocol (Not Just the Call Protocol)?

  • Origin: docs/architecture/crates/http/websocket.md (ADR-048 specifies WebSocket carries the native call-protocol session — the EventEnvelope wire format over a WebSocket text/binary frame stream); docs/architecture/decisions/086-endpoint-types-and-entry-points.md §3 (the web config advertises alknet/channels for the WebSocket-carrying-channels path — a path ADR-048 does not specify).

  • Status: open

  • Door type: one-way (this supersedes or extends ADR-048's "WebSocket carries the native call-protocol session" decision. If WebSocket carries channels, a browser opens one WebSocket and gets the full channels substrate — channel/open, data-channel ALPNs, the relay path through the hub — instead of only the call-protocol session. This is a browser-wire-format one-way door: once browsers depend on the channels-over-WebSocket framing, changing it is a breaking change for every browser client.)

  • Priority: medium (the browser story works without this — ADR-048's call-protocol-only WebSocket is functional — but channels-over-WebSocket makes the browser a first-class channels participant, which simplifies the hub relay and the browser's access to data-channel ALPNs like TTY and tunnels. The question is whether the simplification is worth the one-way-door commitment now, or whether the call-protocol-only path suffices until a concrete browser-needs-a-data-channel use case arrives.)

  • Impacts: Does not block the browser path (ADR-048 works). Would simplify the hub relay (one model, not two) and unblock browser access to data-channel ALPNs (TTY, tunnels) over a single WebSocket if resolved to "WebSocket carries channels."

  • Resolution: Not yet decided. The two options:

    Option A — WebSocket carries call only (ADR-048 unchanged). The browser opens a WebSocket and gets a call-protocol session (EventEnvelope over WebSocket frames). Data-channel ALPNs (TTY, tunnels) are not accessible from the browser — the browser can invoke call operations but cannot open a alknet/tty channel. A browser needing a TTY would use a separate WebSocket per session, each carrying the TTY wire format directly (not via channel/open). Simpler; the browser is a call-protocol client, not a channels client.

    Option B — WebSocket carries channels (extends/supersedes ADR-048). The browser opens a WebSocket and gets a channels connection — the 8-byte chunk format (ADR-071, as amended by ADR-093) over WebSocket binary frames, with channel 0 as alknet/call and data channels opened via channel/open. The browser is a full channels participant: it can open TTY channels, tunnels, etc. through the same WebSocket. The hub relay (ADR-079) works unchanged — the browser leg is a channels connection, same as a native leg. This is the "browser as channels client" path.

    The trade-off: Option B commits to the channels-over-WebSocket framing as a browser wire format (one-way door), but makes the browser a first-class channels participant and simplifies the hub (one relay model, not two). Option A keeps the browser simpler but means the browser cannot use data-channel ALPNs over the same connection — each data-channel ALPN needs its own WebSocket and its own browser-side implementation.

    This question is decision-ready when the first browser-needs-a- data-channel use case arrives (e.g., a browser-based terminal that needs alknet/tty over the hub). Until then, ADR-048's call-protocol-only path is the implemented browser path, and the web config advertises alknet/channels by default (per ADR-086 §3, so the hub is ready for Option B if chosen).

    Note: this is distinct from the WebTransport path (deferred per ADR-044). WebTransport, when revived, would carry channels natively (a WT bidi stream = a channels connection). WebSocket-carrying- channels is the WebSocket equivalent — same substrate, different transport. If Option B is chosen, the WebSocket-channels framing and the WebTransport-channels framing share the channels wire format (ADR-071); only the transport differs.

  • Cross-references: ADR-048 (WebSocket carries the native call-protocol session — the current decision this OQ may supersede or extend), ADR-071 (channels wire format — the 8-byte chunk format that would ride over WebSocket binary frames, as amended by ADR-093), ADR-093 (channels pure channel multiplexing — the umbrella decision), ADR-079 (hub relay — unchanged if the browser is a channels client), ADR-086 §3 (the web config advertises alknet/channels for this path), ADR-044 (WebTransport deferred; WebSocket is the v1 browser path)

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