glm-5.1
b47a6fe70b
Resolve blocking one-way door decisions: - ADR-007: BiStream is a trait, handlers receive Connection not BiStream - ADR-008: Secret service is CLI-embedded, exposed via call protocol - ADR-009: One-way door decision framework (classify by reversal cost) Update existing documents: - overview.md: add design principles, revise ProtocolHandler signature, update shared types, add WASM as design constraint - open-questions.md: add door-type classifications, resolve OQ-01/OQ-08, move OQ-09/OQ-10 to deferred section, mark two-way doors as impl-deferred - README.md: reflect resolved questions, remove crate spec stubs from index - ADR-002: cross-reference ADR-007 for signature revision Clean up premature artifacts: - Remove 11 empty crate spec stubs (16-28 lines each, no unique content) - Specs will be created when each crate enters Phase 1
58 lines
3.9 KiB
Markdown
58 lines
3.9 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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```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 bidirectional QUIC stream
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async fn handle(&self, stream: BiStream, 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 `BiStream` (a joined `(SendStream, RecvStream)` implementing `AsyncRead + AsyncWrite`) and an `AuthContext` carrying the authenticated identity, and 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-004, 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-004: Auth as shared core (IdentityProvider)
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- ADR-007: 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 |