feat(core): settle the Store trait (flush, is_empty, conformance suite)

tines-core/Cargo.toml

@@ -14,6 +14,11 @@ categories = ["no-std", "embedded", "network-programming", "science::robotics"]
 [features]
 default = ["alloc"]
 alloc = []
+# A `no_std`-clean conformance suite ([`store_conformance`]) that concrete
+# backends run against themselves to prove they honor the `Store` contract.
+# Std-free so it builds with `--no-default-features`; enabled only by the
+# backend crates that exercise the suite (MemStore, LogStore, CappedStore).
+conformance = []
 
 [dependencies]
 heapless = { version = "0.8", features = ["serde"] }

tines-core/src/lib.rs

@@ -14,6 +14,8 @@ pub mod mem_store;
 pub mod node;
 pub mod observation;
 pub mod store;
+#[cfg(feature = "conformance")]
+pub mod store_conformance;
 pub mod transport;
 mod wire;
 

tines-core/src/mem_store.rs

@@ -479,3 +479,24 @@ mod tests {
         assert!(!s.is_released(&[0u8; 16]));
     }
 }
+
+#[cfg(all(test, feature = "conformance"))]
+mod conformance_tests {
+    use crate::store_conformance;
+
+    use super::MemStore;
+
+    // The whole suite runs against `MemStore` from its own crate.
+    #[test]
+    fn store_conforms() {
+        store_conformance::insert_get(MemStore::new);
+        store_conformance::dedupe(MemStore::new);
+        store_conformance::age_lineage(MemStore::new);
+        store_conformance::saturating_ticks(MemStore::new);
+        store_conformance::release_surviving_get(MemStore::new);
+        store_conformance::sig_round_trip(MemStore::new);
+        store_conformance::trim_order(MemStore::new);
+        store_conformance::no_tombstones(MemStore::new);
+        store_conformance::idempotent_flush(MemStore::new);
+    }
+}

tines-core/src/node.rs

@@ -219,14 +219,15 @@ impl<S: Store, T: Transport> Node<S, T> {
         &self.store
     }
 
-    /// Mutable access to the backing store.
+    /// Best-effort durability flush, advancing each stored observation's age
+    /// up to `now`.
     ///
-    /// Lets a host call backend-specific methods that aren't on the [`Store`]
-    /// trait — e.g. `tines_store::LogStore::flush`, the durability boundary a
-    /// host reaches on its flush schedule. [`Self::trim`] takes `&mut self`;
-    /// this exposes the concrete backend the same way.
-    pub fn store_mut(&mut self) -> &mut S {
-        &mut self.store
+    /// This is the durability boundary a host reaches on its flush schedule —
+    /// delegates to [`Store::flush`], so it is infallible by contract: a failed
+    /// flush is, at worst, a duplicate custodian on the next exchange, never a
+    /// lost message.
+    pub fn flush(&mut self, now: Tick) -> Result<(), StoreError> {
+        self.store.flush(now)
     }
 
     /// Access the transport (e.g. to `connect`/`disconnect` a peer in tests).

tines-core/src/store.rs

@@ -43,7 +43,6 @@ pub enum StoreError {
 /// differ only in age or `observed_at` share an id and dedupe on insert. Ages
 /// are reported as *current* ages, advanced by the elapsed ticks since each
 /// observation was stored.
-#[allow(clippy::len_without_is_empty)]
 pub trait Store {
     /// Insert an observation.
     ///
@@ -62,6 +61,11 @@ pub trait Store {
     /// Number of observations currently stored.
     fn len(&self) -> usize;
 
+    /// `true` if the store holds no observations.
+    fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
     /// Visit every stored observation id.
     fn for_each_id(&self, f: &mut dyn FnMut(&ObservationId));
 
@@ -85,6 +89,10 @@ pub trait Store {
     /// Releasing an id that is not currently stored is a no-op. The mark
     /// persists for the lifetime of the entry (until it is trimmed); a
     /// re-inserted observation starts un-released.
+    ///
+    /// Release is best-effort and infallible: it never returns an error, and a
+    /// failed release is, at worst, a duplicate custodian on the next
+    /// exchange — never a lost message.
     fn release(&mut self, id: &ObservationId);
 
     /// Returns `true` if the observation with `id` has been released.
@@ -98,6 +106,19 @@ pub trait Store {
     /// the number of observations removed. Trimmed ids are not tombstoned:
     /// re-inserting them later is accepted.
     fn trim(&mut self, policy: &TrimPolicy, now: Tick) -> usize;
+
+    /// Best-effort durability flush, advancing each stored observation's age
+    /// up to the caller's `now` and recording `now` as the flush clock.
+    ///
+    /// Flush must not lose messages, must never resurrect a released message,
+    /// and is infallible by contract: a failed flush is, at worst, a
+    /// duplicate custodian on the next exchange — never a lost message.
+    /// Backends that cannot persist more cheaply default to a no-op that
+    /// simply returns `Ok(())`.
+    fn flush(&mut self, now: Tick) -> Result<(), StoreError> {
+        let _ = now;
+        Ok(())
+    }
 }
 
 /// Current (age-adjusted) age of a stored observation at tick `now`.

tines-core/src/store_conformance.rs

@@ -0,0 +1,223 @@
+//! Backend conformance suite.
+//!
+//! A `no_std`-clean set of property tests that any [`Store`] backend can run to
+//! prove it honors the contract in [`Store`](crate::Store). Each public function
+//! exercises exactly one property against a backend produced by a
+//! caller-supplied factory, so the same body runs for [`MemStore`], a
+//! [`LogStore`](crate::store::LogStore) opened on a fresh file per case and
+//! [`CappedStore`] — see the `#[test]` shims in each backend crate.
+//!
+//! The functions build their own [`Observation`]s, including one carrying a
+//! `sig`, which only the crate that owns the `#[non_exhaustive]` type may
+//! construct by struct literal — this is why the suite lives *inside*
+//! `tines-core` rather than as a `tines-core/tests/` file.
+//!
+//! The suite is deliberately free of `std`/`alloc` so it can build under
+//! `--no-default-features` (with this feature on): every call is `heapless`
+//! plus `assert!`.
+
+use crate::observation::Observation;
+use crate::{Payload, SigAlgo, Signature, Store, Topic, TrimPolicy};
+
+/// Build a signed broadcast observation for the suite.
+///
+/// `signature` is a byte string the backend need not understand; the test only
+/// checks it round-trips verbatim, so it is any length `<= MAX_SIG`.
+fn signed_obs(seq: u64, topic: &[u8], signature: &[u8]) -> Observation {
+    let payload = Payload::from_slice(b"pay").expect("payload fits capacity");
+    Observation {
+        observer: [1u8; 16],
+        seq,
+        age_ms: 0,
+        observed_at: None,
+        topic: Topic::from_slice(topic).expect("topic fits capacity"),
+        payload,
+        dest: None,
+        sig: Some(Signature {
+            version: 1,
+            algo: SigAlgo::Ed25519,
+            bytes: heapless::Vec::from_slice(signature).expect("signature fits capacity"),
+        }),
+    }
+}
+
+/// Two observations that carry the *same* id: same content, different age.
+/// The signature is ignored by identity, so an aged copy reuses the id.
+fn same_id(seq: u64, topic: &[u8]) -> (Observation, Observation) {
+    let fresh = signed_obs(seq, topic, &[0u8; 8]);
+    let mut aged = signed_obs(seq, topic, &[0u8; 8]);
+    aged.age_ms = 500;
+    (fresh, aged)
+}
+
+/// A freshly inserted observation must be retrievable by id at `now`.
+pub fn insert_get<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let (obs, _) = same_id(1, b"t");
+    let id = obs.id();
+    assert!(store.insert(obs, 1000).unwrap(), "insert succeeds");
+    let got = store.get(&id, 1000).expect("get after insert");
+    assert_eq!(got.seq, 1);
+    assert_eq!(got.topic.as_slice(), b"t");
+    assert_eq!(got.payload.as_slice(), b"pay");
+}
+
+/// A second insert of an already-held id is a no-op: the entry, its stored age
+/// lineage and its release state are left untouched.
+pub fn dedupe<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    assert!(store.is_empty());
+    let (fresh, aged) = same_id(1, b"t");
+    let id = fresh.id();
+    assert_eq!(id, aged.id(), "an aged copy shares the id");
+    assert!(store.insert(fresh, 1000).unwrap(), "first insert");
+    assert_eq!(store.len(), 1);
+    assert!(
+        !store.insert(aged, 1500).unwrap(),
+        "duplicate is not reinserted"
+    );
+    assert_eq!(store.len(), 1);
+    assert!(store.contains(&id));
+}
+
+/// `get` advances age by elapsed ticks; a deduped insert must not reset the
+/// stored age lineage.
+pub fn age_lineage<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let (fresh, _) = same_id(1, b"t");
+    let id = fresh.id();
+    store.insert(fresh, 1000).unwrap();
+    let first = store.get(&id, 1500).unwrap();
+    assert_eq!(first.age_ms, 500, "age advances to elapsed ticks");
+    // A later insert of the same id must not reset stored_at.
+    store.insert(same_id(1, b"t").0, 3000).unwrap();
+    let second = store.get(&id, 3500).unwrap();
+    assert_eq!(
+        second.age_ms, 2500,
+        "age keeps climbing from the first insert, not the duplicate"
+    );
+}
+
+/// `get` with `now` before the stored tick saturates to zero age — it must not
+/// underflow.
+pub fn saturating_ticks<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let (fresh, _) = same_id(1, b"t");
+    let id = fresh.id();
+    store.insert(fresh, 2000).unwrap();
+    let got = store.get(&id, 1000).unwrap();
+    assert_eq!(got.age_ms, 0, "elapsed underflow saturates at zero");
+}
+
+/// Releasing marks an id but leaves it stored, contained and gettable; it must
+/// not evict the entry.
+pub fn release_surviving_get<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let (fresh, _) = same_id(1, b"t");
+    let id = fresh.id();
+    store.insert(fresh, 1000).unwrap();
+    store.release(&id);
+    assert!(store.is_released(&id));
+    assert!(store.contains(&id), "release does not evict");
+    assert!(
+        store.get(&id, 1000).is_some(),
+        "released id is still gettable"
+    );
+    assert_eq!(store.len(), 1);
+}
+
+/// A signature carried by an observation round-trips through the store intact,
+/// and a different signature over the same content shares the id.
+pub fn sig_round_trip<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let sig_bytes = [7u8; 32];
+    let fresh = signed_obs(1, b"sig", &sig_bytes);
+    let id = fresh.id();
+    store.insert(fresh, 1000).unwrap();
+    let got = store.get(&id, 1000).unwrap();
+    let sig = got
+        .sig
+        .expect("the signature round-trips through the store");
+    assert_eq!(sig.version, 1);
+    assert_eq!(sig.algo, SigAlgo::Ed25519);
+    assert_eq!(&sig.bytes[..], &sig_bytes[..]);
+    // A different signature over identical content must not change identity.
+    let other = signed_obs(1, b"sig", &[9u8; 40]);
+    assert_eq!(other.id(), id, "the signature must not affect identity");
+}
+
+/// With a count cap, `trim` drops the oldest (highest current age) first and
+/// reports how many it removed.
+pub fn trim_order<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    for i in 0..5u64 {
+        let fresh = signed_obs(i, b"t", &[i as u8]);
+        assert!(store.insert(fresh, i * 10).unwrap(), "insert {}", i);
+    }
+    let policy = TrimPolicy {
+        keep_per_topic: None,
+        max_age_ms: None,
+        max_count: Some(2),
+    };
+    assert_eq!(
+        store.trim(&policy, 50),
+        3,
+        "trim returns the number removed"
+    );
+    // The two youngest (seq 3 and 4, lowest current age) survive.
+    for dropped in 0..3u64 {
+        let fresh = signed_obs(dropped, b"t", &[dropped as u8]);
+        assert!(!store.contains(&fresh.id()), "seq {} is trimmed", dropped);
+    }
+    for kept in 3..5u64 {
+        let fresh = signed_obs(kept, b"t", &[kept as u8]);
+        assert!(store.contains(&fresh.id()), "seq {} survives", kept);
+    }
+}
+
+/// A trimmed id is not tombstoned: it can be reinserted and counted again.
+pub fn no_tombstones<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let fresh = signed_obs(1, b"t", &[1u8; 8]);
+    let id = fresh.id();
+    store.insert(fresh, 0).unwrap();
+    let policy = TrimPolicy {
+        keep_per_topic: None,
+        max_age_ms: Some(1),
+        max_count: None,
+    };
+    assert_eq!(store.trim(&policy, 100), 1);
+    assert!(store.is_empty());
+    // The trimmed id is not tombstoned: re-insert it (aged, still same id).
+    let reinserted = signed_obs(1, b"t", &[1u8; 8]);
+    let mut reinserted = reinserted;
+    reinserted.age_ms = 5;
+    assert_eq!(reinserted.id(), id, "an aged re-insert keeps the id");
+    assert!(
+        store.insert(reinserted, 0).unwrap(),
+        "a trimmed id can be reinserted"
+    );
+    assert!(store.contains(&id));
+    assert_eq!(store.len(), 1);
+}
+
+/// Flushing twice is safe: it must not error and must not evict, and age must
+/// keep advancing afterwards.
+pub fn idempotent_flush<S: Store>(mut make: impl FnMut() -> S) {
+    let mut store = make();
+    let fresh = signed_obs(1, b"t", &[1u8; 8]);
+    let id = fresh.id();
+    store.insert(fresh, 1000).unwrap();
+    assert!(
+        store.flush(2000).is_ok(),
+        "the first flush is a best-effort success"
+    );
+    assert!(
+        store.flush(2000).is_ok(),
+        "the second flush is a no-op that still succeeds"
+    );
+    assert!(store.contains(&id), "flush does not evict");
+    assert_eq!(store.len(), 1);
+    let got = store.get(&id, 2500).unwrap();
+    assert_eq!(got.age_ms, 1500, "age keeps advancing past a flush");
+}