Route burns through the scanner

Cargo.lock

@@ -8670,6 +8670,7 @@ dependencies = [
  "hex",
  "log",
  "parity-scale-codec",
+ "serai-coins-primitives",
  "serai-db",
  "serai-in-instructions-primitives",
  "serai-primitives",

processor/scanner/Cargo.toml

@@ -37,6 +37,7 @@ serai-db = { path = "../../common/db" }
 
 serai-primitives = { path = "../../substrate/primitives", default-features = false, features = ["std"] }
 serai-in-instructions-primitives = { path = "../../substrate/in-instructions/primitives", default-features = false, features = ["std"] }
+serai-coins-primitives = { path = "../../substrate/coins/primitives", default-features = false, features = ["std"] }
 
 messages = { package = "serai-processor-messages", path = "../messages" }
 primitives = { package = "serai-processor-primitives", path = "../primitives" }

processor/scanner/src/db.rs

@@ -6,6 +6,7 @@ use borsh::{BorshSerialize, BorshDeserialize};
 use serai_db::{Get, DbTxn, create_db, db_channel};
 
 use serai_in_instructions_primitives::InInstructionWithBalance;
+use serai_coins_primitives::OutInstructionWithBalance;
 
 use primitives::{EncodableG, Address, ReceivedOutput};
 
@@ -336,9 +337,9 @@ impl<S: ScannerFeed> ScanToEventualityDb<S> {
 }
 
 #[derive(BorshSerialize, BorshDeserialize)]
-pub(crate) struct BlockBoundInInstructions {
+struct BlockBoundInInstructions {
-  pub(crate) block_number: u64,
+  block_number: u64,
-  pub(crate) in_instructions: Vec<InInstructionWithBalance>,
+  in_instructions: Vec<InInstructionWithBalance>,
 }
 
 db_channel! {
@@ -370,3 +371,27 @@ impl<S: ScannerFeed> ScanToReportDb<S> {
     data.in_instructions
   }
 }
+
+db_channel! {
+  ScannerSubstrateEventuality {
+    Burns: (acknowledged_block: u64) -> Vec<OutInstructionWithBalance>,
+  }
+}
+
+pub(crate) struct SubstrateToEventualityDb;
+impl SubstrateToEventualityDb {
+  pub(crate) fn send_burns(
+    txn: &mut impl DbTxn,
+    acknowledged_block: u64,
+    burns: &Vec<OutInstructionWithBalance>,
+  ) {
+    Burns::send(txn, acknowledged_block, burns);
+  }
+
+  pub(crate) fn try_recv_burns(
+    txn: &mut impl DbTxn,
+    acknowledged_block: u64,
+  ) -> Option<Vec<OutInstructionWithBalance>> {
+    Burns::try_recv(txn, acknowledged_block)
+  }
+}

processor/scanner/src/eventuality/db.rs

@@ -11,6 +11,8 @@ create_db!(
   ScannerEventuality {
     // The next block to check for resolving eventualities
     NextToCheckForEventualitiesBlock: () -> u64,
+    // The latest block this task has handled which was notable
+    LatestHandledNotableBlock: () -> u64,
 
     SerializedEventualities: <K: Encode>(key: K) -> Vec<u8>,
   }
@@ -22,16 +24,22 @@ impl<S: ScannerFeed> EventualityDb<S> {
     txn: &mut impl DbTxn,
     next_to_check_for_eventualities_block: u64,
   ) {
-    assert!(
-      next_to_check_for_eventualities_block != 0,
-      "next-to-check-for-eventualities block was 0 when it's bound non-zero"
-    );
     NextToCheckForEventualitiesBlock::set(txn, &next_to_check_for_eventualities_block);
   }
   pub(crate) fn next_to_check_for_eventualities_block(getter: &impl Get) -> Option<u64> {
     NextToCheckForEventualitiesBlock::get(getter)
   }
 
+  pub(crate) fn set_latest_handled_notable_block(
+    txn: &mut impl DbTxn,
+    latest_handled_notable_block: u64,
+  ) {
+    LatestHandledNotableBlock::set(txn, &latest_handled_notable_block);
+  }
+  pub(crate) fn latest_handled_notable_block(getter: &impl Get) -> Option<u64> {
+    LatestHandledNotableBlock::get(getter)
+  }
+
   pub(crate) fn set_eventualities(
     txn: &mut impl DbTxn,
     key: KeyFor<S>,

processor/scanner/src/eventuality/mod.rs

@@ -6,7 +6,10 @@ use primitives::{task::ContinuallyRan, OutputType, ReceivedOutput, Eventuality,
 
 use crate::{
   lifetime::LifetimeStage,
-  db::{OutputWithInInstruction, ReceiverScanData, ScannerGlobalDb, ScanToEventualityDb},
+  db::{
+    OutputWithInInstruction, ReceiverScanData, ScannerGlobalDb, SubstrateToEventualityDb,
+    ScanToEventualityDb,
+  },
   BlockExt, ScannerFeed, KeyFor, SchedulerUpdate, Scheduler, sort_outputs,
   scan::{next_to_scan_for_outputs_block, queue_output_until_block},
 };
@@ -20,6 +23,7 @@ use db::EventualityDb;
 /// only allowed to scan `S::WINDOW_LENGTH - 1` blocks ahead so we can safely schedule keys to
 /// retire `S::WINDOW_LENGTH` blocks out.
 pub(crate) fn latest_scannable_block<S: ScannerFeed>(getter: &impl Get) -> Option<u64> {
+  assert!(S::WINDOW_LENGTH > 0);
   EventualityDb::<S>::next_to_check_for_eventualities_block(getter)
     .map(|b| b + S::WINDOW_LENGTH - 1)
 }
@@ -79,24 +83,81 @@ impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> EventualityTask<D, S, Sch> {
     if EventualityDb::<S>::next_to_check_for_eventualities_block(&db).is_none() {
       // Initialize the DB
       let mut txn = db.txn();
-      // We can receive outputs in `start_block`, but any descending transactions will be in the
+      EventualityDb::<S>::set_next_to_check_for_eventualities_block(&mut txn, start_block);
-      // next block
-      EventualityDb::<S>::set_next_to_check_for_eventualities_block(&mut txn, start_block + 1);
       txn.commit();
     }
 
     Self { db, feed, scheduler }
   }
+
+  // Returns a boolean of if we intaked any Burns.
+  fn intake_burns(&mut self) -> bool {
+    let mut intaked_any = false;
+
+    // If we've handled an notable block, we may have Burns being queued with it as the reference
+    if let Some(latest_handled_notable_block) =
+      EventualityDb::<S>::latest_handled_notable_block(&self.db)
+    {
+      let mut txn = self.db.txn();
+      // Drain the entire channel
+      while let Some(burns) =
+        SubstrateToEventualityDb::try_recv_burns(&mut txn, latest_handled_notable_block)
+      {
+        intaked_any = true;
+
+        let new_eventualities = self.scheduler.fulfill(&mut txn, burns);
+
+        // TODO: De-duplicate this with below instance via a helper function
+        for (key, new_eventualities) in new_eventualities {
+          let key = {
+            let mut key_repr = <KeyFor<S> as GroupEncoding>::Repr::default();
+            assert_eq!(key.len(), key_repr.as_ref().len());
+            key_repr.as_mut().copy_from_slice(&key);
+            KeyFor::<S>::from_bytes(&key_repr).unwrap()
+          };
+
+          let mut eventualities = EventualityDb::<S>::eventualities(&txn, key);
+          for new_eventuality in new_eventualities {
+            eventualities.insert(new_eventuality);
+          }
+          EventualityDb::<S>::set_eventualities(&mut txn, key, &eventualities);
+        }
+      }
+      txn.commit();
+    }
+
+    intaked_any
+  }
 }
 
 #[async_trait::async_trait]
 impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> ContinuallyRan for EventualityTask<D, S, Sch> {
   async fn run_iteration(&mut self) -> Result<bool, String> {
+    // Fetch the highest acknowledged block
+    let Some(highest_acknowledged) = ScannerGlobalDb::<S>::highest_acknowledged_block(&self.db)
+    else {
+      // If we've never acknowledged a block, return
+      return Ok(false);
+    };
+
+    // A boolean of if we've made any progress to return at the end of the function
+    let mut made_progress = false;
+
+    // Start by intaking any Burns we have sitting around
+    made_progress |= self.intake_burns();
+
     /*
-      The set of Eventualities only increase when a block is acknowledged. Accordingly, we can only
+      Eventualities increase upon one of two cases:
-      iterate up to (and including) the block currently pending acknowledgement. "including" is
+
-      because even if block `b` causes new Eventualities, they'll only potentially resolve in block
+        1) We're fulfilling Burns
-      `b + 1`.
+        2) We acknowledged a block
+
+      We can't know the processor has intaked all Burns it should have when we process block `b`.
+      We solve this by executing a consensus protocol whenever a resolution for an Eventuality
+      created to fulfill Burns occurs. Accordingly, we force ourselves to obtain synchrony on such
+      blocks (and all preceding Burns).
+
+      This means we can only iterate up to the block currently pending acknowledgement.
 
       We only know blocks will need acknowledgement *for sure* if they were scanned. The only other
       causes are key activation and retirement (both scheduled outside the scan window). This makes
@@ -113,32 +174,38 @@ impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> ContinuallyRan for EventualityTas
       next_to_scan
     };
 
-    // Fetch the highest acknowledged block
-    let highest_acknowledged = ScannerGlobalDb::<S>::highest_acknowledged_block(&self.db)
-      .expect("EventualityTask run before writing the start block");
-
     // Fetch the next block to check
     let next_to_check = EventualityDb::<S>::next_to_check_for_eventualities_block(&self.db)
       .expect("EventualityTask run before writing the start block");
 
     // Check all blocks
-    let mut iterated = false;
     for b in next_to_check .. exclusive_upper_bound {
-      // If the prior block was notable *and* not acknowledged, break
+      let is_block_notable = ScannerGlobalDb::<S>::is_block_notable(&self.db, b);
-      // This is so if it caused any Eventualities (which may resolve this block), we have them
+      if is_block_notable {
-      {
+        /*
-        // This `- 1` is safe as next to check is bound to be non-zero
+          If this block is notable *and* not acknowledged, break.
-        // This is possible since even if we receive coins in block 0, any transactions we'd make
+
-        // would resolve in block 1 (the first block we'll check under this non-zero rule)
+          This is so if Burns queued prior to this block's acknowledgement caused any Eventualities
-        let prior_block = b - 1;
+          (which may resolve this block), we have them. If it wasn't for that, it'd be so if this
-        if ScannerGlobalDb::<S>::is_block_notable(&self.db, prior_block) &&
+          block's acknowledgement caused any Eventualities, we have them, though those would only
-          (prior_block > highest_acknowledged)
+          potentially resolve in the next block (letting us scan this block without delay).
-        {
+        */
+        if b > highest_acknowledged {
           break;
         }
+
+        // Since this block is notable, ensure we've intaked all the Burns preceding it
+        // We can know with certainty that the channel is fully populated at this time since we've
+        // acknowledged a newer block (so we've handled the state up to this point and new state
+        // will be for the newer block)
+        #[allow(unused_assignments)]
+        {
+          made_progress |= self.intake_burns();
+        }
       }
 
-      iterated = true;
+      // Since we're handling this block, we are making progress
+      made_progress = true;
 
       let block = self.feed.block_by_number(&self.db, b).await?;
 
@@ -186,6 +253,7 @@ impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> ContinuallyRan for EventualityTas
         let mut non_external_outputs = block.scan_for_outputs(key.key);
         non_external_outputs.retain(|output| output.kind() != OutputType::External);
         // Drop any outputs less than the dust limit
+        // TODO: Either further filter to outputs we made or also check cost_to_aggregate
         non_external_outputs.retain(|output| {
           let balance = output.balance();
           balance.amount.0 >= self.feed.dust(balance.coin).0
@@ -288,10 +356,16 @@ impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> ContinuallyRan for EventualityTas
 
       // Update the next-to-check block
       EventualityDb::<S>::set_next_to_check_for_eventualities_block(&mut txn, next_to_check);
+
+      // If this block was notable, update the latest-handled notable block
+      if is_block_notable {
+        EventualityDb::<S>::set_latest_handled_notable_block(&mut txn, b);
+      }
+
       txn.commit();
     }
 
     // Run dependents if we successfully checked any blocks
-    Ok(iterated)
+    Ok(made_progress)
   }
 }

processor/scanner/src/lib.rs

@@ -7,6 +7,7 @@ use serai_db::{Get, DbTxn, Db};
 
 use serai_primitives::{NetworkId, Coin, Amount};
 use serai_in_instructions_primitives::Batch;
+use serai_coins_primitives::OutInstructionWithBalance;
 
 use primitives::{task::*, Address, ReceivedOutput, Block};
 
@@ -15,7 +16,7 @@ mod lifetime;
 
 // Database schema definition and associated functions.
 mod db;
-use db::ScannerGlobalDb;
+use db::{ScannerGlobalDb, SubstrateToEventualityDb};
 // Task to index the blockchain, ensuring we don't reorganize finalized blocks.
 mod index;
 // Scans blocks for received coins.
@@ -147,7 +148,7 @@ pub trait ScannerFeed: 'static + Send + Sync + Clone {
 
   /// The dust threshold for the specified coin.
   ///
-  /// This MUST be constant. Serai MJUST NOT create internal outputs worth less than this. This
+  /// This MUST be constant. Serai MUST NOT create internal outputs worth less than this. This
   /// SHOULD be a value worth handling at a human level.
   fn dust(&self, coin: Coin) -> Amount;
 }
@@ -195,6 +196,40 @@ pub trait Scheduler<S: ScannerFeed>: 'static + Send {
     txn: &mut impl DbTxn,
     update: SchedulerUpdate<S>,
   ) -> HashMap<Vec<u8>, Vec<EventualityFor<S>>>;
+
+  /// Fulfill a series of payments, yielding the Eventualities now to be scanned for.
+  ///
+  /// Any Eventualities returned by this function must include an output-to-self (such as a Branch
+  /// or Change), unless they descend from a transaction returned by this function which satisfies
+  /// that requirement.
+  ///
+  /// The `Vec<u8>` used as the key in the returned HashMap should be the encoded key the
+  /// Eventualities are for.
+  /*
+    We need an output-to-self so we can detect a block with an Eventuality completion with regards
+    to Burns, forcing us to ensure we have accumulated all the Burns we should by the time we
+    handle that block. We explicitly don't require children have this requirement as by detecting
+    the first resolution, we ensure we'll accumulate the Burns (therefore becoming aware of the
+    childrens' Eventualities, enabling recognizing their resolutions).
+
+    This carve out enables the following:
+
+      ------------------  Fulfillment TX  ----------------------
+      | Primary Output | ---------------> | New Primary Output |
+      ------------------         |        ----------------------
+                                 |
+                                 |        ------------------------------
+                                 |------> | Branching Output for Burns |
+                                          ------------------------------
+
+    Without wasting pointless Change outputs on every transaction (as there's a single parent which
+    has an output-to-self).
+  */
+  fn fulfill(
+    &mut self,
+    txn: &mut impl DbTxn,
+    payments: Vec<OutInstructionWithBalance>,
+  ) -> HashMap<Vec<u8>, Vec<EventualityFor<S>>>;
 }
 
 /// A representation of a scanner.
@@ -242,6 +277,8 @@ impl<S: ScannerFeed> Scanner<S> {
   ///
   /// This means this block was ordered on Serai in relation to `Burn` events, and all validators
   /// have achieved synchrony on it.
+  ///
+  /// The calls to this function must be ordered with regards to `queue_burns`.
   pub fn acknowledge_block(
     &mut self,
     mut txn: impl DbTxn,
@@ -249,10 +286,23 @@ impl<S: ScannerFeed> Scanner<S> {
     key_to_activate: Option<KeyFor<S>>,
   ) {
     log::info!("acknowledging block {block_number}");
+
     assert!(
       ScannerGlobalDb::<S>::is_block_notable(&txn, block_number),
       "acknowledging a block which wasn't notable"
     );
+    if let Some(prior_highest_acknowledged_block) =
+      ScannerGlobalDb::<S>::highest_acknowledged_block(&txn)
+    {
+      assert!(block_number > prior_highest_acknowledged_block, "acknowledging blocks out-of-order");
+      for b in (prior_highest_acknowledged_block + 1) .. (block_number - 1) {
+        assert!(
+          !ScannerGlobalDb::<S>::is_block_notable(&txn, b),
+          "skipped acknowledging a block which was notable"
+        );
+      }
+    }
+
     ScannerGlobalDb::<S>::set_highest_acknowledged_block(&mut txn, block_number);
     if let Some(key_to_activate) = key_to_activate {
       ScannerGlobalDb::<S>::queue_key(&mut txn, block_number + S::WINDOW_LENGTH, key_to_activate);
@@ -268,13 +318,38 @@ impl<S: ScannerFeed> Scanner<S> {
 
   /// Queue Burns.
   ///
-  /// The scanner only updates the scheduler with new outputs upon acknowledging a block. We can
+  /// The scanner only updates the scheduler with new outputs upon acknowledging a block. The
-  /// safely queue Burns so long as they're only actually added once we've handled the outputs from
+  /// ability to fulfill Burns, and therefore their order, is dependent on the current output
-  /// the block acknowledged prior to their queueing.
+  /// state. This immediately sets a bound that this function is ordered with regards to
-  pub fn queue_burns(&mut self, txn: &mut impl DbTxn, burns: Vec<()>) {
+  /// `acknowledge_block`.
+  /*
+    The fact Burns can be queued during any Substrate block is problematic. The scanner is allowed
+    to scan anything within the window set by the Eventuality task. The Eventuality task is allowed
+    to handle all blocks until it reaches a block needing acknowledgement.
+
+    This means we may queue Burns when the latest acknowledged block is 1, yet we've already
+    scanned 101. Such Burns may complete back in block 2, and we simply wouldn't have noticed due
+    to not having yet generated the Eventualities.
+
+    We solve this by mandating all transactions made as the result of an Eventuality include a
+    output-to-self worth at least `N::DUST`. If that occurs, the scanner will force a consensus
+    protocol on block 2. Accordingly, we won't scan all the way to block 101 (missing the
+    resolution of the Eventuality) as we'll obtain synchrony on block 2 and all Burns queued prior
+    to it.
+
+    Another option would be to re-check historical blocks, yet this would potentially redo an
+    unbounded amount of work. It would also not allow us to safely detect if received outputs were
+    in fact the result of Eventualities or not.
+
+    Another option would be to schedule Burns after the next-acknowledged block, yet this would add
+    latency and likely practically require we add regularly scheduled notable blocks (which may be
+    unnecessary).
+  */
+  pub fn queue_burns(&mut self, txn: &mut impl DbTxn, burns: &Vec<OutInstructionWithBalance>) {
     let queue_as_of = ScannerGlobalDb::<S>::highest_acknowledged_block(txn)
       .expect("queueing Burns yet never acknowledged a block");
-    todo!("TODO")
+
+    SubstrateToEventualityDb::send_burns(txn, queue_as_of, burns)
   }
 }