urus/ROADMAP.md

urus — Roadmap

Companion to urus-spec.md (artefact store, URUS project). v1 shipped 2026-05-26, built against pre-v0.4 smarm — before cancellation, supervisors, links, gen_server, registry, select, and the slot-slab runtime existed. smarm is now at v0.8. This roadmap covers catching up, then extending.

State assessment (2026-06-11)

Verified against smarm master (393cdd0: v0.8 slot slab + park-epoch + select, plus RFC 008 phase 1 fd arms / timed fd waits):

• Builds clean, 24/24 tests pass. The scheduler surface urus consumes (spawn, wait_readable, wait_writable, sleep, init, Config, run, JoinHandle) survived the v0.5–v0.8 runtime rework unchanged.
• Timeouts are decorative. Config::{request_timeout, keep_alive_timeout} are threaded into ConnLimits and never read. read_some parks in wait_readable with no deadline → an idle keep-alive connection pins its actor (and its 64 KiB+ of buffers) forever. Slowloris-shaped.
• No supervision. Spec §2.1 calls for a supervised listener pool; v1 predates Strategy/ChildSpec and uses bare spawn + join. A panicking listener silently shrinks the accept pool.
• No graceful shutdown. Spec deferred it; smarm now has the pieces: request_stop + sentinel unwind, and the 06-10 io fix (deregister a stopped actor's fd wait on the unwind path) makes stopping an actor parked in wait_readable safe. The OwnedFd-drops-on-unwind discipline in conn_actor.rs already composes with this.
• No streaming response path. RespBody is Empty | Bytes. Blocks SSE (a spec v1 goal that slipped) and chunked responses.
• Full-duplex constraint (matters for WebSocket). smarm's epoll model is one waiter per RawFd (AlreadyExists, now surfaced as Err via the try_select twins) and one direction per parked actor. RFC 008 phase 1 (landed 393cdd0) gives first-of(fd, channel) via fd arms in select — the duplex options in v0.4-3 are both open now. Decide in v0.4 design, before the frame codec.

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v0.2 — OTP refresh ✅ (landed 2026-06, chunks 1-4 / commits 5fe6969..HEAD)

Adopt the primitives urus predates. No protocol surface changes; Plug/Conn untouched. Chunks are independently landable, in order:

1. Supervised listener pool ✅

Landed: serve_with runs a Strategy::OneForOne supervisor on the root actor, one ChildSpec per dup'd listener fd, Restart::Permanent. A listener panic (or a transient wait_readable failure, which now exits and restarts instead of being fatal) restarts that listener; the pool never silently shrinks. Connection actors stay unsupervised bare spawns (per spec: a connection is cheap and its failure is local — a 500 path, not a restart path); spawn parents them under the listener, which has no supervisor channel, so their deaths are invisible to the pool supervisor by construction.

Open question resolved as leaned: the ChildSpec factory owns the fd via Arc<OwnedFd> (OwnedFd gained Sync for this) and every (re)start reuses it. No re-dup, no window where a pool slot has no fd. Covered by tests/integration.rs::panicking_listener_restarts (pool of 1, panic injected before accept so the pending connection must survive into the restarted listener).

2. Graceful shutdown ✅

Landed (c658ac0): serve_with_shutdown(config, pipeline, signal) + shutdown_handle(). Drain-then-stop as decided below; design details in the commit body. serve_with keeps v1 run-forever semantics by dropping its own Handle. serve_with gains a shutdown signal (an urus::Handle with .shutdown(), backed by a channel + request_stop fan-out):

1. Stop listeners (no new accepts; listener fds close).
2. Decided: drain-then-stop with a deadline — in-flight requests get to finish; request_stop after the deadline (unwind closes fds cleanly via OwnedFd::drop). Drain also keeps the door open for an apache-reload-style restart later.
3. Supervisor winds down; rt.run returns; serve_with returns.

Requires tracking live connection pids. Cheapest honest version: a gen_server connection registry — listener casts {Started, pid}, conn actor monitors-free self-deregisters via a drop guard cast. Pid set only (no activity stamps — chunk 3 went per-conn timed waits, no reaper); still the future ws/channels introspection point, so build it once here.

3. Enforce the timeouts we advertise ✅

Landed (a60687b): timed waits as decided below; the leaning held — a per-request Instant deadline keeps request_timeout an honest whole-request wall clock (mid-head expiry: best-effort non-parking 408; mid-body: close). Details in the commit body. Decided: smarm-native timed waits (the fork's option (a), a reaper in urus, died when RFC 008 landed at 393cdd0 — wait_readable_timeout / wait_writable_timeout exist upstream now, so there is nothing for the reaper to be the stopgap for):

read_some parks in wait_readable_timeout instead of wait_readable; Ok(false) means the deadline passed and the conn actor closes. Per-conn semantics, no activity stamping, no sweep ticker. Semantics note: a timed read wait enforces idle-between-reads — keep_alive_timeout between requests, and slowloris dies because each stalled read has a deadline. request_timeout as a whole-request wall clock is NOT what this gives; decide in implementation whether to track a per-request deadline across reads (cheap: one Instant in the conn loop, pass the min of both budgets to each wait) or redefine request_timeout as per-read. Leaning the Instant: it keeps the advertised config honest.

urus is the first real consumer of the timed wrappers — note the RFC 008 reviewer flag (wait_fd wraps in NoPreempt, select arms don't); the crud example under load doubles as that confirmation.

4. Hygiene ✅

Landed: registry names + whereis test (in-runtime probe via a handler — tests are foreign threads), README rewrite, smarm-trace compile verified.

• Registry names: urus.server, urus.listener.{n} via smarm::register (debuggability; whereis in tests).
• README: rewrite Roadmap section to point here; document Handle.
• smarm-trace feature passthrough already exists — verify it still compiles under --features smarm-trace.

Exit criteria: kill -TERM equivalent drains cleanly in the crud example; an idle keep-alive conn is reaped at keep_alive_timeout; a deliberately panicking listener restarts under load without dropped accepts (test each).

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v0.3 — Streaming bodies + SSE ✅ (landed 2026-06, chunks 1-3)

The slipped v1 goal, and the WebSocket prerequisite (an upgraded connection is "a response that never ends").

1. RespBody::Stream(StreamBody) ✅ — decided: pull (user call at the v0.3 design fork): the handler hands back a smarm::Receiver<Vec<u8>> and the producer is an actor the handler spawned; the conn actor pumps (pump_stream) and keeps sole ownership of the socket and write deadlines. The recv() park between chunks is stoppable by the draining registry, so infinite streams die at the drain deadline with no polling. HTTP/1.1: chunked TE, keep-alive after the terminator; HTTP/1.0: raw bytes, forced close, EOF-delimited. End of stream = every Sender dropped = 0-chunk. Timeout split (handoff Q3, as proposed): request_timeout covers the READ phase only; new Config.write_timeout (default 30s) bounds every response write — fresh budget per streamed chunk, and the fixed-body + error-response writes went deadline-bounded too (write-side slowloris closed).
2. Chunked request bodies ✅ — read_chunked_body decodes incrementally on the request deadline; extensions ignored, trailers consumed + discarded, decoded size capped at max_body_bytes (413), size-line/trailer spam capped (400). CL + TE: chunked, or chunked on HTTP/1.0, rejected 400 at parse (smuggling ambiguity). Keep-alive drain accounts RAW framing length, so pipelined requests behind a chunked body land exactly.
3. SSE sugar ✅ — Conn::sse() / sse_with_heartbeat → EventSender (send(event, data) / data / comment, Clone, Err(SseClosed) once the stream is gone). Heartbeat lives in the pump as leaned: with StreamBody.heartbeat set, the chunk wait is recv_timeout(interval) and expiry writes a : keep-alive comment chunk. Liveness from the ping (dead client = heartbeat write stalls past write_timeout), not from any request clock.

Exit criteria (verified): chunked round-trips both directions with keep-alive and pipelining intact; an infinite SSE stream heartbeats while silent, is killed by write_timeout when the client stops reading, and is force-stopped at the drain deadline on shutdown; full suite green.

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v0.4 — WebSocket upgrade path ✅ (landed 2026-06, chunks 1-3)

1. Handshake ✅ (49538cc) — Conn::upgrade() (handler arg comes with chunk 3): §4.2.1 validation, 101 + accept key, marker field on Conn, actor leaves the HTTP loop (fd drops until chunk 3 takes over). Rejections stay plain HTTP (400 / 426 + version header) with keep-alive intact. Dep decision changed at the design pass: SHA-1 is sha1_smol (zero transitive deps) — dep #3 SPENT, no hand-rolled crypto (user call). The v0.6 JSON question is therefore a dep #4 question now. Base64 stays in-tree, encode-only.
2. Frame codec ✅ (2869153) — pure ws::frame: incremental decode (mask-required server mode), minimal-length + RSV + control rules enforced, header-derived cap check before payload buffering, close-code wire validation, Assembler for fragmentation with whole-message UTF-8 check, FrameError→close-code map (1002/1009/1007). §5.7 examples pinned verbatim.
3. Duplex wiring ✅ — topology decision: (b) one actor, RFC 008 fd arms (urus exists to put smarm through its paces; first fd-arm consumer is the point). As landed:
   • ws::duplex::run_duplex replaces the HTTP loop after the 101: try_select(&[&outbound_rx, &FdArm::readable(fd)]) per iteration — outbound at index 0 (select is priority-ordered: owed writes drain before reading more). Accepted gap documented: mid-write of a large outbound frame the actor isn't reading.
   • Handler API (the deferred questions, as answered): in-actor callbacks — WsHandler { on_message, on_close } runs inside the select loop; concurrency = spawn your own actor with a WsSender clone (the SSE-producer pattern). Conn::upgrade(self, handler) flat signature (builder deferred until per-upgrade options exist, e.g. subprotocols). WsSender: Clone, send/text/binary/ping/ close → Err(WsClosed), unbounded channel like SSE (slow client bounded by write_timeout). Control frames invisible v1: auto-pong inline (§5.5.2), peer close auto-echoed (§5.5.1, server closes TCP first per §7.1.1) surfacing only as on_close(Some(code), reason); wordless endings (EOF, write failure, handshake timeout) = on_close(None, ""). on_ping/on_pong can land later as default trait methods, non-breaking.
   • Server-initiated close (WsSender::close or FrameError→1002/1009/ 1007, handler panic→1011): close frame out, then a bounded drain (one write_timeout budget) for the peer's echo, discarding data (§1.4). Handler panics re-raise smarm's stop sentinel before being treated as panics — the pipeline's catch_unwind dance, replicated.
   • Caps: Config.max_frame_payload (1 MiB) / max_message_bytes (4 MiB) — Config fields per the max_body_bytes precedent; header cap checked before payload buffers.
   • Buf handover: bytes pipelined past the upgrade head carry into the duplex loop (tested).
   • Registry: conn stays Busy for the ws lifetime (an open ws is in-flight work); graceful shutdown force-stops it out of the select park at the drain deadline (tested — the in-runtime request_stop wake covers select parks, not just channel recv).
   • Validated against a real client (python websocket-client): echo, ping/pong payload, close handshake. examples/ws_echo.rs shows both handler shapes (/echo in-actor, /clock producer-spawning).
4. Handler API ✅ — folded into chunk 3 above (was: settle in design pass; settled: gen_server-shaped trait + WsSender handle).

v0.5 — PubSub ✅ (landed 2026-06, chunks 1-2)

urus::pubsub, phoenix_pubsub-shaped, local node only (no distribution — smarm has none). All six design questions ratified by the user pre-code ("push" on the stated leans); as-landed:

• Generic PubSub<M> per instance (Q1); heterogeneous buses are an app-side enum. Arc<M> payloads: one allocation per broadcast.
• subscribe(topic) -> Receiver<Arc<M>> (Q2), fresh channel per subscription; subscribe_as(pid, ..) pins lifetime to an explicit pid for relay shapes. Sender-passing fan-in (subscribe_with) deliberately deferred — compatible addition.
• Unbounded mailboxes (Q3): broadcast never blocks the table. Cleanup is monitor Down (eager, on subscriber death) + prune-on-send-failure (lazy, dropped receivers). Bench before sharding.
• User-owned handle (Q4). The ratified register-by-name helper turned out NOT implementable: smarm's registry maps name → Pid and a Pid can't be turned back into a ServerRef. Deferred pending smarm support (or a type-erased global, rejected). pid() exposed.
• Unique per (pid, topic) (Q5): subscribe idempotent (replaces the sender; the stale receiver closes). One monitor per live pid. handle_down is a full table scan as ratified; pid→topics reverse index is the documented optimization if deaths measure hot.
• Table: gen_server HashMap<Topic, HashMap<Pid, Sender<Arc<M>>>> — single server, not sharded (bench first). subscriber_count(topic) added (tests need to observe async cleanup; legitimate API).

Discoveries this cycle:

• PubSub::new() is in-runtime only (spawns the table actor) but pipelines are built pre-runtime → the composition pattern is a NON-static Arc<OnceLock<PubSub<M>>> in the route closure. Non-static is load-bearing: the drained pipeline drops the cell in-runtime, the table's inbox closes, the table exits, AllDone is reachable. A static (crud's store shape) hangs serve_with_shutdown. Corollary: relays hold Receiver only, never a PubSub clone (mutual-keepalive cycle). Proven by shutdown_with_open_chat_terminates.
• WsHandler::on_open(&mut self, sender) added (defaulted, non-breaking): without it a listen-only ws client can never be subscribed (on_message never fires). Same panic contract as on_message (1011, no on_close). The 101 reaches the client before on_open runs — subscription liveness needs an app-level ack (documented; the integration tests use a sync/synced ack).
• hammer.sh default subset now includes ws_.

Chunk 2's ws_chat: rooms as topics, on_open subscribes (conn-actor pid) + spawns the relay, broadcast_from(self_pid(), ..) for no-echo.

v0.6 — Channels — DONE (2026-06-12)

Join/leave/event protocol over WebSocket transport, PubSub underneath. Design decisions ratified pre-code (2026-06-12):

Feature flags. Two additive features:

• "channels" — the Channel trait, TopicRouter trait, PrefixRouter, ChannelSocket, session machinery. Zero new deps; pubsub is already always-on (it only exists because channels needs it).
• "phoenix" — implies "channels" + serde/serde_json + the V2 frame codec. Opt-in phoenix.js interop; users who want protobuf or any other wire format take "channels" only and supply their own codec.

Payload generics. The Channel trait is generic over payload: P: Encode + Decode where Encode/Decode are urus codec traits (one method each). The "phoenix" feature provides a JsonCodec blanket impl via serde. No JSON anywhere in the "channels" surface.

Channel trait shape.

trait Channel<P>: Send + 'static {
    fn join(topic: &str, payload: P, socket: &ChannelSocket<P>) -> Result<P, P>;
    fn handle_in(&mut self, event: &str, payload: P, socket: &ChannelSocket<P>);
    fn terminate(&mut self) {}
}

handle_out deferred — can land as a defaulted method, non-breaking.

ChannelSocket. Newtype over WsSender + a PubSub handle. Exposes reply(ref, status, payload), push(event, payload), broadcast(topic, payload). The ref from the incoming frame is threaded in by the channel actor loop, invisible to the impl. Coupling to PubSub is intentional: channels owns pubsub, and broadcast is the core use case.

Topic router. TopicRouter trait: fn route(&self, topic: &str) -> Option<Box<dyn ChannelFactory<P>>>. Factory receives the full raw topic string so wildcard-segment extraction is always possible. urus ships PrefixRouter as the default impl: scan to '*', discard the rest, single HashMap lookup on the prefix. No regex dep, no glob machinery — users who need that implement TopicRouter themselves.

Channel actor lifetime + session persistence. Default: channel actor linked to the ws connection actor, cold-start on every reconnect (phoenix-server-compatible behavior). Opt-in persistence via a ChannelSession trait:

trait ChannelSession: Send + 'static {
    type Key: Eq + Hash + Send + 'static;
    fn session_key(topic: &str, join_payload: &P) -> Self::Key;
    fn buffer_cap() -> usize { 128 }
    fn ttl() -> Duration { Duration::from_secs(30) }
}

When implemented, the router consults a session registry (gen_server, same pattern as the connection registry) before spawning: an existing actor is reattached, and buffered outbound messages (Vec<Arc<M>>, no re-serialisation) are drained to the reconnecting transport. Buffer full or TTL expired → actor tears down; next join is a cold start. This diverges from Phoenix server conventions (client-re-syncs) but is invisible to phoenix.js at the wire level. Zero-copy drain is the smarm motivation: messages are Arc<M> in the buffer and in the PubSub relay path, one allocation per broadcast regardless of subscriber count or reconnect cycles.

Presence: explicitly out of scope until distribution exists.

As-landed (2026-06-12), beyond the ratified text — veto by diff:

• chunk 1: Channel::join takes &mut self (state from join, and session rejoins need the same instance); the in-flight ref is threaded invisibly through the socket; broadcast gained an event parameter; TopicRouter::route returns Option<Arc<dyn ChannelFactory>>.
• chunk 2: the serde blanket lives behind the Json<T> newtype (a blanket on bare P: Serialize is coherence poison under additive features); encode failure panics into the linked-teardown contract.
• chunk 3: ChannelFactory gained a #[doc(hidden)] deploy() seam (default = the ephemeral linked actor); every attach re-calls join() (re-entrant by contract); rejected rejoin / explicit leave / cap / TTL all end the session; second transport evicts the first; Key: Clone (registry's pid→key reverse index); registry spawns eagerly at registration (in-runtime law, same as ChannelHub::new); shutdown composes linklessly via the registry-drop chain — proven by shutdown_with_detached_session_terminates.

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Known bugs

• HTTP/1.0 keep-alive: server honors but never advertises FIXED (2026-06-12, same session it was found). As-landed decisions: serialise_response now echoes connection: keep-alive on a kept-alive 1.0 response (1.1 keep-alive stays implicit); error statuses (>=400) on 1.0 force close — no keep-alive advertised on a 4xx/5xx where reuse is opt-in (conn_actor, alongside the existing 1.0-stream force-close); HEAD needs nothing special (header echo only, framing untouched); parse-error responses already carried connection: close. Validated against the original repro: ab -k -n 5000 -c 50 on GET /users now reports 5000/5000 keep-alive requests, 0 failed, ~63k req/s (vs ~18.9k no-keep-alive baseline, same box). Watch out benching: ab counts a response toward "Non-2xx" silently — a 404'd route still shows "Failed requests: 0" with great rps; check the route first.

Later / icebox

• HTTP/2 — spec §2.2 already designs the stream-actor demux (zero-copy ownership transfer, conn actor owns HPACK + flow control, stream actors run the pipeline). Big: HPACK, flow control, priorities. The Stressgrid constraint (no stream-actor cost on HTTP/1.1) stays law.
• SSE ergonomics round 2 — auto-reconnect support (Last-Event-ID), event-id bookkeeping, backpressure policy on slow consumers.
• TLS — still deferred; acceptor design still must not preclude it.
• Middleware ecosystem — compression, static files, auth plugs.
• Bench suite — urus-bench-spec.md exists in the artefact store; wire it up once v0.2 lands (supervision changes the hot path not at all, but prove it).
• Operator introspection via typed names — the v0.2-era urus.server / urus.listener.{i} pid tags were dropped in the RFC 014 port (names are messageable endpoints now, self-registered with a real Sender<M>). If wanted back, do it properly: register the serve loop's shutdown/control channel under a typed urus.server name instead of faking pid tags with unit channels.