glm-5.2
cc470a363a
Port the call + channels architecture documentation from the alknet mono-repo into docs/architecture/, renumbered as alkcall ADR-001..045. Renumbering map (alknet -> alkcall): Core: 001,002,004,006,007,011,065,070,092,014,050,091 -> 001-012 Call: 005,064,012,023,015,022,024,016,049,017,028,029,030,032,066,069,067,068 -> 013-030 Shared: 003,009,013 -> 031-033 Channels: 071,093,072,073,074,075,076,094,079,080,081,089 -> 034-045 3 superseded/reversed ADRs kept for historical trail: - ADR-013 (irpc foundation, superseded by ADR-014) - ADR-023 (peer-scoped filtering, superseded by ADR-024) - ADR-077 (TTY inside channels, reversed by ADR-035 — not ported, TTY-only) Ported docs (11 spec files + README + open-questions): - call-README.md, call-protocol.md, operation-registry.md, client-and-adapters.md - channels-README.md, channels-overview.md, channels-wire.md, channels-connection.md, channels-adapter.md, channel-operations.md, channel-client.md - README.md (index with doc table, ADR table grouped by category, key principles) - open-questions.md (lean — 30 OQs, renumbered OQ-01..030; includes new OQ-22 for the pub/sub gap) Cross-reference rewriting: - All ADR-NNN references rewritten single-pass (no chaining bug) - Markdown link paths fixed - Title lines aligned with filenames - Non-ported ADR refs (052, 082, 086, etc.) left as-is with README note The open-questions.md includes OQ-22 (new): the call protocol pub/sub gap — subscribe exists but pub does not, needed for channels channel/resources/subscribe fan-out. This is the next ADR to write (alkcall ADR-046).
66 lines
4.2 KiB
Markdown
66 lines
4.2 KiB
Markdown
# ADR-002: ProtocolHandler Trait
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## Status
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Accepted
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## Context
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The previous architecture had two separate interface traits: `StreamInterface` (for byte-stream protocols like SSH, raw TCP) and `MessageInterface` (for message-based protocols like DNS, HTTP). This split created complexity — each interface type needed its own listener configuration, its own dispatch path, and its own framing assumptions. The `ListenerConfig` enum had three variants. The server accept loop handled three different listener types.
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In practice, the distinction between "stream" and "message" protocols is artificial at the handler level. SSH starts as a byte stream but internally multiplexes channels and messages. DNS over QUIC is message-based but arrives as a stream of frames. HTTP/2 is both — bidirectional streams with message semantics. Every protocol can be modeled as "receive a byte stream, manage your own wire format."
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iroh's `ProtocolHandler` trait demonstrates this: it takes a bidirectional QUIC stream and the handler is responsible for its own protocol. One trait, one dispatch point.
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## Decision
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A single `ProtocolHandler` trait replaces both `StreamInterface` and `MessageInterface`:
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> **Note**: The signature below was revised by ADR-005. The `handle()` method
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> now receives a `Connection` (not a `BiStream`) — see ADR-005 for the
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> current authoritative signature. The original signature is retained here
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> for historical context.
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```rust
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#[async_trait]
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pub trait ProtocolHandler: Send + Sync + 'static {
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/// The ALPN string this handler claims (e.g. b"alknet/ssh")
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fn alpn(&self) -> &'static [u8];
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/// Handle an incoming connection (revised by ADR-005 to receive
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/// `Connection` instead of `BiStream`)
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async fn handle(&self, connection: Connection, auth: &AuthContext) -> Result<(), HandlerError>;
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}
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```
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- `alpn()` returns a static byte string — the handler's ALPN identifier
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- `handle()` receives a `Connection` (revised by ADR-005 from the original
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`BiStream`) and an `AuthContext` carrying the authenticated identity, and
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returns `HandlerError` on failure
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- Every handler manages its own wire format — no shared framing, no StreamInterface/MessageInterface split
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- The `ListenerConfig` enum is eliminated — ALPN advertisement configuration replaces it
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**AuthContext resolution is hybrid** (see ADR-003, OQ-02 resolution): the endpoint resolves what it can before calling `handle()` (e.g., TLS client certificate fingerprint), and the handler resolves what it must inside `handle()` (e.g., AuthToken in the first frame of a call stream). The `AuthContext` passed to `handle()` may contain partial identity information — the handler is responsible for completing authentication if the endpoint didn't have enough information.
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## Consequences
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**Positive:**
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- One trait, one dispatch point — eliminates the StreamInterface/MessageInterface split and ListenerConfig enum
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- Each handler owns its wire format — no shared framing assumptions that constrain protocol design
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- Adding a new protocol is implementing one trait with two methods
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- Testable in isolation — give a handler a mock BiStream and AuthContext
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- WASM-compatible in principle — handlers that don't need tokio runtime features compile to WASM
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**Negative:**
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- Every handler must implement its own framing — no shared "read a length-prefixed message" utility (mitigated: common utilities can live in alknet-core without mandating their use)
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- Handlers that want message semantics must build them (mitigated: alknet-call provides this as a handler, not a mandatory layer)
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- AuthContext resolution is hybrid — the endpoint resolves what it can (TLS-level auth), but handlers that need protocol-level credential extraction must do so inside handle(). This means AuthContext may be partial when handle() is called. Handlers must not assume AuthContext is fully resolved.
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## References
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- Pivot proposal: `docs/research/pivot/alpn-service-architecture.md`
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- ADR-001: ALPN-based protocol dispatch
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- ADR-003: Auth as shared core (IdentityProvider)
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- ADR-005: BiStream type definition (revised this ADR's signature from BiStream to Connection)
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- iroh ProtocolHandler pattern: `docs/research/references/iroh/`
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- Replaces StreamInterface, MessageInterface, and ListenerConfig |