Bus input: serve envelopes from yukart/vehicle/+ and yukart/host/+

Newest per signal, stale after 5 s or when only the retained copy is known.
Bus or mock, never both; hello says which (source bus|mock|none).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

Cargo.lock

@@ -75,6 +75,54 @@ dependencies = [
  "crypto-common",
 ]
 
+[[package]]
+name = "fixedbitset"
+version = "0.5.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d674e81391d1e1ab681a28d99df07927c6d4aa5b027d7da16ba32d1d21ecd99"
+
+[[package]]
+name = "flume"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da0e4dd2a88388a1f4ccc7c9ce104604dab68d9f408dc34cd45823d5a9069095"
+dependencies = [
+ "futures-core",
+ "futures-sink",
+ "spin",
+]
+
+[[package]]
+name = "futures-core"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92d699e522242e69e3003b94ecc1f960f3a5e015aa7c5d7486e65ad01dd94f5e"
+
+[[package]]
+name = "futures-sink"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1944426bf7d03f1d14f708785e4b33efd750b36d48a157b836b3efc15ede8e1d"
+
+[[package]]
+name = "futures-task"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cd417de3d1d015fc3bfd2b1ea46dfc7bab72ef86f1cc7cc9c78e728b34a6d1fd"
+
+[[package]]
+name = "futures-util"
+version = "0.3.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d50a92467f8ba5dd6e3ee5d4bd04d73ab2e4e1c44474a0674821dfce14b79bc"
+dependencies = [
+ "futures-core",
+ "futures-sink",
+ "futures-task",
+ "pin-project-lite",
+ "slab",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.4.3"
@@ -124,6 +172,15 @@ version = "0.2.190"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ce5d3ddc6d3fa000eb1536d85e147bfe31aacaba692ed6a876f95cb7c855be78"
 
+[[package]]
+name = "lock_api"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "224399e74b87b5f3557511d98dff8b14089b3dadafcab6bb93eab67d3aace965"
+dependencies = [
+ "scopeguard",
+]
+
 [[package]]
 name = "log"
 version = "0.4.34"
@@ -136,6 +193,23 @@ version = "2.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
 
+[[package]]
+name = "mio"
+version = "1.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1788edb87fdc09c7e26304471e2f5be8cdefb1b6930d6e3985fc02ff53bf86ee"
+dependencies = [
+ "libc",
+ "wasi",
+ "windows-sys",
+]
+
+[[package]]
+name = "pin-project-lite"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.107"
@@ -177,6 +251,29 @@ version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "63b8176103e19a2643978565ca18b50549f6101881c443590420e4dc998a3c69"
 
+[[package]]
+name = "rumqttc"
+version = "0.25.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0feff8d882bff0b2fddaf99355a10336d43dd3ed44204f85ece28cf9626ab519"
+dependencies = [
+ "bytes",
+ "fixedbitset",
+ "flume",
+ "futures-util",
+ "log",
+ "thiserror",
+ "tokio",
+ "tokio-stream",
+ "tokio-util",
+]
+
+[[package]]
+name = "scopeguard"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
+
 [[package]]
 name = "serde"
 version = "1.0.229"
@@ -230,11 +327,37 @@ dependencies = [
  "digest",
 ]
 
+[[package]]
+name = "slab"
+version = "0.4.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c790de23124f9ab44544d7ac05d60440adc586479ce501c1d6d7da3cd8c9cf5"
+
+[[package]]
+name = "socket2"
+version = "0.6.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d1e2c7f27f8d4cb10542a02c49005dbd6e93095799d6f3be745fae9f8fedd4"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "spin"
+version = "0.9.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3763264f6b73151db08c50ff20d7d8a0b8796e021cdea7ceedad07b80155fa0e"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "svc-gw"
 version = "0.1.0"
 dependencies = [
  "libc",
+ "rumqttc",
  "serde_json",
  "tungstenite",
 ]
@@ -270,6 +393,57 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "tokio"
+version = "1.53.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e95f91fcc7a621e8b030f6aa23c71fe9838ae2fb4d8118b75602a328f5144044"
+dependencies = [
+ "bytes",
+ "libc",
+ "mio",
+ "pin-project-lite",
+ "socket2",
+ "tokio-macros",
+ "windows-sys",
+]
+
+[[package]]
+name = "tokio-macros"
+version = "2.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78773a2a397f451582ce068015985c33193cf6dea8b74d2a639fe457b2f07b0e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "tokio-stream"
+version = "0.1.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a3d06f0b082ba57c26b79407372e57cf2a1e28124f78e9479fe80322cf53420b"
+dependencies = [
+ "futures-core",
+ "pin-project-lite",
+ "tokio",
+]
+
+[[package]]
+name = "tokio-util"
+version = "0.7.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e464cf451ba96ebfc6f9b6542f17ee8b8956e33f1e40d9690624e59d7a7f8a4b"
+dependencies = [
+ "bytes",
+ "futures-core",
+ "futures-sink",
+ "libc",
+ "pin-project-lite",
+ "tokio",
+]
+
 [[package]]
 name = "tungstenite"
 version = "0.30.0"
@@ -298,6 +472,27 @@ version = "1.0.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d245f478577f809a851594d02313b640fb437e0bb33866753cff937863096954"
 
+[[package]]
+name = "wasi"
+version = "0.11.1+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "zmij"
 version = "1.0.23"

Cargo.toml

@@ -7,6 +7,7 @@ publish = false
 
 [dependencies]
 libc = "0.2"
+rumqttc = { version = "0.25", default-features = false }
 serde_json = "1"
 tungstenite = { version = "0.30", default-features = false, features = ["handshake"] }
 

deploy/yukart-gw.service

@@ -1,6 +1,8 @@
 [Unit]
 Description=Yukart gateway: the display boundary (svc-gw)
 Documentation=gitea:yukart/svc-gw
+# Tier 3. Ordered after the broker and nothing else; it reconnects by itself if the broker restarts.
+After=mosquitto.service
 StartLimitIntervalSec=0
 
 [Service]

docs/impl/plans/INITIAL.md

@@ -1,7 +1,7 @@
 ---
 type: plan
 status: active
-updated: 2026-10-09
+updated: 2026-10-12
 ---
 # Initial plan
 
@@ -23,6 +23,9 @@ directly.
 0. **Boundary v0** — in place: WebSocket on `:7700`, hello, heartbeats both ways,
    `mark` forwarded to the recorder's control socket, mock state behind `--mock`.
    Protocol in contracts [`docs/BOUNDARY.md`](gitea:yukart/contracts).
+   **Bus input** — in place (2026-10-12): subscribes to `yukart/vehicle/+` and
+   `yukart/host/+`, keeps the newest envelope per signal, marks stale after 5 s
+   or when known only from a retained copy. Bus or mock, never both.
 1. Static file serving for the basemap — smallest useful thing, unblocks the map.
 2. Nav HTTP proxy to [svc-nav](gitea:yukart/svc-nav).
 3. Aggregation and rate limiting, once there is real CAN traffic to aggregate.

src/bus.rs

@@ -0,0 +1,88 @@
+//! The real input: envelopes from the bus, latest per signal.
+//!
+//! Subscribes to the envelope topics and keeps the newest envelope of each signal,
+//! keyed by the topic's last segment (the signal name, contracts guideline 1).
+//! Staleness is judged here, by arrival: a signal not refreshed within `STALE`,
+//! or known only from the broker's retained copy (it may predate a reboot), is
+//! sent with `quality: "stale"`. Signals are never dropped once seen; an old value
+//! shown stale is the honest picture.
+
+use std::collections::HashMap;
+use std::sync::{Arc, Mutex};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use rumqttc::{Client, Event, MqttOptions, Packet, QoS};
+use serde_json::{json, Map, Value};
+
+const TOPICS: [&str; 2] = ["yukart/vehicle/+", "yukart/host/+"];
+const STALE: Duration = Duration::from_secs(5);
+
+struct Entry {
+    envelope: Value,
+    at: Instant,
+    retained: bool,
+}
+
+#[derive(Clone)]
+pub struct Bus {
+    latest: Arc<Mutex<HashMap<String, Entry>>>,
+}
+
+impl Bus {
+    /// Connects in the background and reconnects forever; never blocks the caller.
+    pub fn start(host: &str, port: u16) -> Self {
+        let bus = Bus { latest: Arc::default() };
+        let mut opts = MqttOptions::new("svc-gw", host, port);
+        opts.set_keep_alive(Duration::from_secs(5));
+        let (client, mut connection) = Client::new(opts, 64);
+        let latest = bus.latest.clone();
+        thread::spawn(move || {
+            let mut up = false;
+            for ev in connection.iter() {
+                match ev {
+                    Ok(Event::Incoming(Packet::ConnAck(_))) => {
+                        up = true;
+                        eprintln!("bus: connected; subscribing to {}", TOPICS.join(", "));
+                        // A clean session forgets subscriptions: renew them on every connect.
+                        for t in TOPICS {
+                            let _ = client.try_subscribe(t, QoS::AtMostOnce);
+                        }
+                    }
+                    Ok(Event::Incoming(Packet::Publish(p))) => {
+                        let Some(name) = p.topic.rsplit('/').next() else { continue };
+                        let Ok(envelope) = serde_json::from_slice::<Value>(&p.payload) else { continue };
+                        if !envelope.is_object() {
+                            continue;
+                        }
+                        let entry = Entry { envelope, at: Instant::now(), retained: p.retain };
+                        latest.lock().unwrap().insert(name.to_string(), entry);
+                    }
+                    Ok(_) => {}
+                    Err(e) => {
+                        if std::mem::take(&mut up) {
+                            eprintln!("bus: {e}; retrying");
+                        }
+                        thread::sleep(Duration::from_secs(1));
+                    }
+                }
+            }
+        });
+        bus
+    }
+
+    /// Every signal seen, newest envelope each, marked stale where it is.
+    pub fn snapshot(&self) -> Map<String, Value> {
+        let latest = self.latest.lock().unwrap();
+        latest
+            .iter()
+            .map(|(name, e)| {
+                let mut env = e.envelope.clone();
+                if (e.retained || e.at.elapsed() > STALE) && env.get("quality").is_none() {
+                    env["quality"] = json!("stale");
+                }
+                (name.clone(), env)
+            })
+            .collect()
+    }
+}

src/main.rs

@@ -2,8 +2,10 @@
 //! hello, heartbeats, state snapshots down and acknowledged commands up.
 //! Defined in contracts `docs/BOUNDARY.md`.
 //!
-//! v0 has no bus input yet: without `--mock` it sends hello and heartbeats only.
+//! State comes from the bus (`bus.rs`), or from the mock with `--mock`: one input
+//! or the other, never both, so mock data cannot mix into real data.
 
+mod bus;
 mod client;
 mod hub;
 mod mock;
@@ -20,7 +22,8 @@ use serde_json::json;
 const USAGE: &str = "\
 usage: svc-gw [options]
   --listen ADDR       WebSocket listen address              (0.0.0.0:7700)
-  --mock              synthesise vehicle state, flagged as mock in every message
+  --mock              synthesise vehicle state, flagged as mock in every message (no bus)
+  --broker HOST:PORT  MQTT broker; '' for none                (127.0.0.1:1883)
   --recorder-ctl PATH recorder control socket, for 'mark'   (/run/yukart-recorder/ctl.sock)";
 
 pub fn now_us() -> i64 {
@@ -50,12 +53,14 @@ fn main() -> ExitCode {
     let mut listen = "0.0.0.0:7700".to_string();
     let mut mock = false;
     let mut recorder_ctl = "/run/yukart-recorder/ctl.sock".to_string();
+    let mut broker = "127.0.0.1:1883".to_string();
     let mut args = std::env::args().skip(1);
     while let Some(a) = args.next() {
         match a.as_str() {
             "--mock" => mock = true,
             "--listen" => listen = args.next().unwrap_or_default(),
             "--recorder-ctl" => recorder_ctl = args.next().unwrap_or_default(),
+            "--broker" => broker = args.next().unwrap_or_default(),
             _ => {
                 eprintln!("svc-gw: unknown option {a}\n{USAGE}");
                 return ExitCode::from(2);
@@ -64,6 +69,18 @@ fn main() -> ExitCode {
     }
 
     let registry = signals::Registry::load();
+    let bus = if mock || broker.is_empty() {
+        None
+    } else {
+        match broker.rsplit_once(':').and_then(|(h, p)| Some((h, p.parse::<u16>().ok()?))) {
+            Some((host, port)) => Some(bus::Bus::start(host, port)),
+            None => {
+                eprintln!("svc-gw: --broker must be HOST:PORT\n{USAGE}");
+                return ExitCode::from(2);
+            }
+        }
+    };
+    let source = if mock { "mock" } else if bus.is_some() { "bus" } else { "none" };
     let hub = hub::Hub::default();
     let ctx = Arc::new(client::Ctx {
         hub: hub.clone(),
@@ -72,7 +89,7 @@ fn main() -> ExitCode {
             "proto": 0,
             "server": concat!("svc-gw ", env!("CARGO_PKG_VERSION")),
             "host": std::fs::read_to_string("/proc/sys/kernel/hostname").unwrap_or_default().trim(),
-            "source": if mock { "mock" } else { "none" },
+            "source": source,
             "mock": mock,
             "hb_ms": client::HEARTBEAT.as_millis() as u64,
             "timeout_ms": client::TIMEOUT.as_millis() as u64,
@@ -88,7 +105,7 @@ fn main() -> ExitCode {
             return ExitCode::from(1);
         }
     };
-    eprintln!("svc-gw {} on ws://{listen}{}", env!("CARGO_PKG_VERSION"), if mock { " — MOCK DATA" } else { "" });
+    eprintln!("svc-gw {} on ws://{listen}, source {source}{}", env!("CARGO_PKG_VERSION"), if mock { " — MOCK DATA" } else { "" });
 
     // Steady state is reached with zero clients: the producer runs regardless.
     thread::spawn(move || {
@@ -100,9 +117,14 @@ fn main() -> ExitCode {
             thread::sleep(Duration::from_millis(200));
             let dt = last.elapsed().as_secs_f64();
             last = Instant::now();
-            if mock {
+            let signals = match &bus {
+                Some(b) => Some(b.snapshot()).filter(|s| !s.is_empty()),
+                None if mock => Some(m.step(&registry, dt)),
+                None => None,
+            };
+            if let Some(signals) = signals {
                 seq += 1;
-                let state = json!({ "t": "state", "seq": seq, "mock": true, "signals": m.step(&registry, dt) });
+                let state = json!({ "t": "state", "seq": seq, "mock": mock, "signals": signals });
                 hub.broadcast(&state.to_string());
             }
             if last_hb.elapsed() >= client::HEARTBEAT {