Merge pull request #2036 from subspace/distinguish-pot-chain-reorg-ex…

…tension

Distinguish between PoT chain reorg and extension during state update

crates/sc-proof-of-time/src/source.rs

@@ -3,7 +3,7 @@ mod state;
 mod timekeeper;
 
 use crate::source::gossip::{GossipProof, PotGossipWorker, ToGossipMessage};
-use crate::source::state::{NextSlotInput, PotState};
+use crate::source::state::{NextSlotInput, PotState, PotStateUpdateOutcome};
 use crate::source::timekeeper::{run_timekeeper, TimekeeperProof};
 use crate::verifier::PotVerifier;
 use core_affinity::CoreId;
@@ -27,7 +27,7 @@ use std::marker::PhantomData;
 use std::sync::Arc;
 use std::thread;
 use subspace_core_primitives::PotCheckpoints;
-use tracing::{debug, error, warn};
+use tracing::{debug, error, trace, warn};
 
 const LOCAL_PROOFS_CHANNEL_CAPACITY: usize = 10;
 const SLOTS_CHANNEL_CAPACITY: usize = 10;
@@ -335,24 +335,54 @@ where
         // This will do one of 3 things depending on circumstances:
         // * if block import is ahead of timekeeper and gossip, it will update next slot input
         // * if block import is on a different PoT chain, it will update next slot input to the
-        //   correct fork
+        //   correct fork (reorg)
         // * if block import is on the same PoT chain this will essentially do nothing
-        if let Some(next_slot_input) = self.state.update(
+        match self.state.update(
             best_slot,
             best_proof,
             Some(subspace_digest_items.pot_parameters_change),
         ) {
-            warn!("Proof of time chain reorg happened");
+            PotStateUpdateOutcome::NoChange => {
+                trace!(
+                    %best_slot,
+                    "Block import didn't result in proof of time chain changes",
+                );
+            }
+            PotStateUpdateOutcome::Extension { from, to } => {
+                warn!(
+                    from_next_slot = %from.slot,
+                    to_next_slot = %to.slot,
+                    "Proof of time chain was extended from block import",
+                );
 
-            if self
-                .to_gossip_sender
-                .try_send(ToGossipMessage::NextSlotInput(next_slot_input))
-                .is_err()
-            {
-                debug!(
-                    next_slot = %next_slot_input.slot,
-                    "Gossip is not able to keep-up with slot production (block import)",
+                if self
+                    .to_gossip_sender
+                    .try_send(ToGossipMessage::NextSlotInput(to))
+                    .is_err()
+                {
+                    debug!(
+                        next_slot = %to.slot,
+                        "Gossip is not able to keep-up with slot production (block import)",
+                    );
+                }
+            }
+            PotStateUpdateOutcome::Reorg { from, to } => {
+                warn!(
+                    from_next_slot = %from.slot,
+                    to_next_slot = %to.slot,
+                    "Proof of time chain reorg happened",
                 );
+
+                if self
+                    .to_gossip_sender
+                    .try_send(ToGossipMessage::NextSlotInput(to))
+                    .is_err()
+                {
+                    debug!(
+                        next_slot = %to.slot,
+                        "Gossip is not able to keep-up with slot production (block import)",
+                    );
+                }
             }
         }
     }

crates/sc-proof-of-time/src/source/state.rs

@@ -73,6 +73,19 @@ impl InnerState {
     }
 }
 
+#[derive(Debug)]
+pub(super) enum PotStateUpdateOutcome {
+    NoChange,
+    Extension {
+        from: NextSlotInput,
+        to: NextSlotInput,
+    },
+    Reorg {
+        from: NextSlotInput,
+        to: NextSlotInput,
+    },
+}
+
 #[derive(Debug)]
 pub(super) struct PotState {
     inner_state: Atomic<InnerState>,
@@ -145,7 +158,7 @@ impl PotState {
         best_slot: Slot,
         best_output: PotOutput,
         maybe_updated_parameters_change: Option<Option<PotParametersChange>>,
-    ) -> Option<NextSlotInput> {
+    ) -> PotStateUpdateOutcome {
         let mut best_state = None;
         // Use `fetch_update` such that we don't accidentally downgrade best slot to smaller value
         let previous_best_state = self
@@ -163,7 +176,51 @@ impl PotState {
             .expect("Callback always returns `Some`; qed");
         let best_state = best_state.expect("Replaced with `Some` above; qed");
 
-        (previous_best_state.next_slot_input != best_state.next_slot_input)
-            .then_some(best_state.next_slot_input)
+        if previous_best_state.next_slot_input == best_state.next_slot_input {
+            return PotStateUpdateOutcome::NoChange;
+        }
+
+        if previous_best_state.next_slot_input.slot < best_state.next_slot_input.slot {
+            let mut slot_iterations = previous_best_state.next_slot_input.slot_iterations;
+            let mut seed = previous_best_state.next_slot_input.seed;
+
+            for slot in u64::from(previous_best_state.next_slot_input.slot)
+                ..u64::from(best_state.next_slot_input.slot)
+            {
+                let slot = Slot::from(slot);
+
+                let Some(checkpoints) = self.verifier.try_get_checkpoints(seed, slot_iterations)
+                else {
+                    break;
+                };
+
+                let next_slot = slot + Slot::from(1);
+
+                // In case parameters change in the next slot, account for them
+                if let Some(Some(parameters_change)) = maybe_updated_parameters_change
+                    && parameters_change.slot == next_slot
+                {
+                    slot_iterations = parameters_change.slot_iterations;
+                    seed = checkpoints.output().seed_with_entropy(&parameters_change.entropy);
+                } else {
+                    seed = checkpoints.output().seed();
+                }
+
+                if next_slot == best_state.next_slot_input.slot
+                    && slot_iterations == best_state.next_slot_input.slot_iterations
+                    && seed == best_state.next_slot_input.seed
+                {
+                    return PotStateUpdateOutcome::Extension {
+                        from: previous_best_state.next_slot_input,
+                        to: best_state.next_slot_input,
+                    };
+                }
+            }
+        }
+
+        PotStateUpdateOutcome::Reorg {
+            from: previous_best_state.next_slot_input,
+            to: best_state.next_slot_input,
+        }
     }
 }