Improve batch handling (#316)

* restrict batch size to ~25kb

* add batch size check to node

* rate limit batches to 1 per serai block

* add support for multiple batches for block

* fix review comments

* Misc fixes

Doesn't yet update tests/processor until data flow is inspected.

* Move the block from SignId to ProcessorMessage::BatchPreprocesses

* Misc clean up

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

Cargo.lock

@@ -8075,6 +8075,7 @@ dependencies = [
  "serai-tokens-pallet",
  "serai-validator-sets-pallet",
  "sp-application-crypto",
+ "sp-core",
  "sp-runtime",
  "thiserror",
 ]

coordinator/src/main.rs

@@ -535,7 +535,7 @@ pub async fn handle_processors<D: Db, Pro: Processors, P: P2p>(
 
           Some(Transaction::SubstrateBlock(block))
         }
-        coordinator::ProcessorMessage::BatchPreprocess { id, preprocess } => {
+        coordinator::ProcessorMessage::BatchPreprocess { id, block, preprocess } => {
           // If this is the first attempt instance, synchronize around the block first
           if id.attempt == 0 {
             // Save the preprocess to disk so we can publish it later
@@ -545,7 +545,9 @@ pub async fn handle_processors<D: Db, Pro: Processors, P: P2p>(
             MainDb::<D>::save_first_preprocess(&mut txn, id.id, preprocess);
             txn.commit();
 
-            Some(Transaction::ExternalBlock(id.id))
+            // TODO: This will publish one ExternalBlock per Batch. We should only publish one per
+            // all batches within a block
+            Some(Transaction::ExternalBlock(block.0))
           } else {
             Some(Transaction::BatchPreprocess(SignData {
               plan: id.id,

coordinator/src/substrate/mod.rs

@@ -8,7 +8,7 @@ use frost::ThresholdParams;
 
 use serai_client::{
   SeraiError, Block, Serai,
-  primitives::BlockHash,
+  primitives::{BlockHash, NetworkId},
   validator_sets::{
     primitives::{Session, ValidatorSet, KeyPair},
     ValidatorSetsEvent,
@@ -157,21 +157,23 @@ async fn handle_batch_and_burns<Pro: Processors>(
   // While that shouldn't be needed, ensuring order never hurts, and may enable design choices
   // with regards to Processor <-> Coordinator message passing
   let mut networks_with_event = vec![];
-  let mut network_had_event = |burns: &mut HashMap<_, _>, network| {
+  let mut network_had_event = |burns: &mut HashMap<_, _>, batches: &mut HashMap<_, _>, network| {
     // Don't insert this network multiple times
     // A Vec is still used in order to maintain the insertion order
     if !networks_with_event.contains(&network) {
       networks_with_event.push(network);
       burns.insert(network, vec![]);
+      batches.insert(network, vec![]);
     }
   };
 
   let mut batch_block = HashMap::new();
+  let mut batches = HashMap::<NetworkId, Vec<u32>>::new();
   let mut burns = HashMap::new();
 
   for batch in serai.get_batch_events(hash).await? {
-    if let InInstructionsEvent::Batch { network, id: _, block: network_block } = batch {
+    if let InInstructionsEvent::Batch { network, id, block: network_block } = batch {
-      network_had_event(&mut burns, network);
+      network_had_event(&mut burns, &mut batches, network);
 
       // Track what Serai acknowledges as the latest block for this network
       // If this Substrate block has multiple batches, the last batch's block will overwrite the
@@ -180,6 +182,9 @@ async fn handle_batch_and_burns<Pro: Processors>(
       // the last batch will be the latest batch, so its block will be the latest block
       // This is just a mild optimization to prevent needing an additional RPC call to grab this
       batch_block.insert(network, network_block);
+
+      // Add the batch included by this block
+      batches.get_mut(&network).unwrap().push(id);
     } else {
       panic!("Batch event wasn't Batch: {batch:?}");
     }
@@ -188,12 +193,10 @@ async fn handle_batch_and_burns<Pro: Processors>(
   for burn in serai.get_burn_events(hash).await? {
     if let TokensEvent::Burn { address: _, balance, instruction } = burn {
       let network = balance.coin.network();
-      network_had_event(&mut burns, network);
+      network_had_event(&mut burns, &mut batches, network);
 
       // network_had_event should register an entry in burns
-      let mut burns_so_far = burns.remove(&network).unwrap();
+      burns.get_mut(&network).unwrap().push(OutInstructionWithBalance { balance, instruction });
-      burns_so_far.push(OutInstructionWithBalance { balance, instruction });
-      burns.insert(network, burns_so_far);
     } else {
       panic!("Burn event wasn't Burn: {burn:?}");
     }
@@ -230,6 +233,7 @@ async fn handle_batch_and_burns<Pro: Processors>(
               .map(|keys| keys.1.into_inner())
               .expect("batch/burn for network which never set keys"),
             burns: burns.remove(&network).unwrap(),
+            batches: batches.remove(&network).unwrap(),
           },
         ),
       )

processor/messages/src/lib.rs

@@ -115,12 +115,16 @@ pub mod coordinator {
   }
 
   impl CoordinatorMessage {
+    // The Coordinator will only send Batch messages once the Batch ID has been recognized
+    // The ID will only be recognized when the block is acknowledged by a super-majority of the
+    // network *and the local node*
+    // This synchrony obtained lets us ignore the synchrony requirement offered here
     pub fn required_block(&self) -> Option<BlockHash> {
-      Some(match self {
+      match self {
-        CoordinatorMessage::BatchPreprocesses { id, .. } => BlockHash(id.id),
+        CoordinatorMessage::BatchPreprocesses { .. } => None,
-        CoordinatorMessage::BatchShares { id, .. } => BlockHash(id.id),
+        CoordinatorMessage::BatchShares { .. } => None,
-        CoordinatorMessage::BatchReattempt { id } => BlockHash(id.id),
+        CoordinatorMessage::BatchReattempt { .. } => None,
-      })
+      }
     }
 
     pub fn key(&self) -> &[u8] {
@@ -135,7 +139,7 @@ pub mod coordinator {
   #[derive(Clone, PartialEq, Eq, Debug, Zeroize, Serialize, Deserialize)]
   pub enum ProcessorMessage {
     SubstrateBlockAck { network: NetworkId, block: u64, plans: Vec<[u8; 32]> },
-    BatchPreprocess { id: SignId, preprocess: Vec<u8> },
+    BatchPreprocess { id: SignId, block: BlockHash, preprocess: Vec<u8> },
     BatchShare { id: SignId, share: [u8; 32] },
   }
 }
@@ -156,6 +160,7 @@ pub mod substrate {
       block: u64,
       key: Vec<u8>,
       burns: Vec<OutInstructionWithBalance>,
+      batches: Vec<u32>,
     },
   }
 

processor/src/main.rs

@@ -12,13 +12,13 @@ use frost::{curve::Ciphersuite, ThresholdKeys};
 use log::{info, warn, error};
 use tokio::time::sleep;
 
-use scale::Decode;
+use scale::{Encode, Decode};
 
 use serai_client::{
   primitives::{MAX_DATA_LEN, BlockHash, NetworkId},
   tokens::primitives::{OutInstruction, OutInstructionWithBalance},
   in_instructions::primitives::{
-    Shorthand, RefundableInInstruction, InInstructionWithBalance, Batch,
+    Shorthand, RefundableInInstruction, InInstructionWithBalance, Batch, MAX_BATCH_SIZE,
   },
 };
 
@@ -396,6 +396,7 @@ async fn handle_coordinator_msg<D: Db, N: Network, Co: Coordinator>(
           block,
           key: key_vec,
           burns,
+          batches,
         } => {
           assert_eq!(network_id, N::NETWORK, "coordinator sent us data for another network");
 
@@ -405,12 +406,11 @@ async fn handle_coordinator_msg<D: Db, N: Network, Co: Coordinator>(
           let key = <N::Curve as Ciphersuite>::read_G::<&[u8]>(&mut key_vec.as_ref()).unwrap();
 
           // We now have to acknowledge every block for this key up to the acknowledged block
-          let (blocks, outputs) =
+          let outputs = substrate_mutable.scanner.ack_up_to_block(txn, key, block_id).await;
-            substrate_mutable.scanner.ack_up_to_block(txn, key, block_id).await;
           // Since this block was acknowledged, we no longer have to sign the batch for it
-          for block in blocks {
+          for batch_id in batches {
             for (_, signer) in tributary_mutable.substrate_signers.iter_mut() {
-              signer.batch_signed(txn, block);
+              signer.batch_signed(txn, batch_id);
             }
           }
 
@@ -665,51 +665,84 @@ async fn run<N: Network, D: Db, Co: Coordinator>(mut raw_db: D, network: N, mut
         let mut txn = raw_db.txn();
 
         match msg.unwrap() {
-          ScannerEvent::Block { key, block, batch, outputs } => {
+          ScannerEvent::Block { key, block, outputs } => {
             let mut block_hash = [0; 32];
             block_hash.copy_from_slice(block.as_ref());
+            // TODO: Move this out from Scanner now that the Scanner no longer handles batches
+            let mut batch_id = substrate_mutable.scanner.next_batch_id(&txn);
 
-            let batch = Batch {
+            // start with empty batch
+            let mut batches = vec![Batch {
               network: N::NETWORK,
-              id: batch,
+              id: batch_id,
               block: BlockHash(block_hash),
-              instructions: outputs.iter().filter_map(|output| {
+              instructions: vec![],
-                // If these aren't externally received funds, don't handle it as an instruction
+            }];
-                if output.kind() != OutputType::External {
+            for output in outputs {
-                  return None;
+              // If these aren't externally received funds, don't handle it as an instruction
-                }
+              if output.kind() != OutputType::External {
+                continue;
+              }
 
-                let mut data = output.data();
+              let mut data = output.data();
-                let max_data_len = MAX_DATA_LEN.try_into().unwrap();
+              let max_data_len = usize::try_from(MAX_DATA_LEN).unwrap();
-                if data.len() > max_data_len {
+              // TODO: Should we drop this, instead of truncating?
-                  error!(
+              // A truncating message likely doesn't have value yet has increased data load and is
-                    "data in output {} exceeded MAX_DATA_LEN ({MAX_DATA_LEN}): {}",
+              // corrupt vs a NOP. The former seems more likely to cause problems
-                    hex::encode(output.id()),
+              if data.len() > max_data_len {
-                    data.len(),
+                error!(
-                  );
+                  "data in output {} exceeded MAX_DATA_LEN ({MAX_DATA_LEN}): {}. truncating",
-                  data = &data[.. max_data_len];
+                  hex::encode(output.id()),
-                }
+                  data.len(),
+                );
+                data = &data[.. max_data_len];
+              }
 
-                let shorthand = Shorthand::decode(&mut data).ok()?;
+              let Ok(shorthand) = Shorthand::decode(&mut data) else { continue };
-                let instruction = RefundableInInstruction::try_from(shorthand).ok()?;
+              let Ok(instruction) = RefundableInInstruction::try_from(shorthand) else { continue };
-                // TODO2: Set instruction.origin if not set (and handle refunds in general)
-                Some(InInstructionWithBalance {
-                  instruction: instruction.instruction,
-                  balance: output.balance(),
-                })
-              }).collect()
-            };
 
-            info!("created batch {} ({} instructions)", batch.id, batch.instructions.len());
+              // TODO2: Set instruction.origin if not set (and handle refunds in general)
+              let instruction = InInstructionWithBalance {
+                instruction: instruction.instruction,
+                balance: output.balance(),
+              };
+
+              let batch = batches.last_mut().unwrap();
+              batch.instructions.push(instruction);
+
+              // check if batch is over-size
+              if batch.encode().len() > MAX_BATCH_SIZE {
+                // pop the last instruction so it's back in size
+                let instruction = batch.instructions.pop().unwrap();
+
+                // bump the id for the new batch
+                batch_id += 1;
+
+                // make a new batch with this instruction included
+                batches.push(Batch {
+                  network: N::NETWORK,
+                  id: batch_id,
+                  block: BlockHash(block_hash),
+                  instructions: vec![instruction],
+                });
+              }
+            }
+
+            // Save the next batch ID
+            substrate_mutable.scanner.set_next_batch_id(&mut txn, batch_id + 1);
 
             // Start signing this batch
-            // TODO: Don't reload both sets of keys in full just to get the Substrate public key
+            for batch in batches {
-            tributary_mutable
+              info!("created batch {} ({} instructions)", batch.id, batch.instructions.len());
-              .substrate_signers
+
-              .get_mut(tributary_mutable.key_gen.keys(&key).0.group_key().to_bytes().as_slice())
+              // TODO: Don't reload both sets of keys in full just to get the Substrate public key
-              .unwrap()
+              tributary_mutable
-              .sign(&mut txn, batch)
+                .substrate_signers
-              .await;
+                .get_mut(tributary_mutable.key_gen.keys(&key).0.group_key().to_bytes().as_slice())
+                .unwrap()
+                .sign(&mut txn, batch)
+                .await;
+            }
           },
 
           ScannerEvent::Completed(id, tx) => {

processor/src/scanner.rs

@@ -14,8 +14,6 @@ use tokio::{
   time::sleep,
 };
 
-use serai_client::primitives::BlockHash;
-
 use crate::{
   Get, DbTxn, Db,
   networks::{Output, Transaction, EventualitiesTracker, Block, Network},
@@ -27,7 +25,6 @@ pub enum ScannerEvent<N: Network> {
   Block {
     key: <N::Curve as Ciphersuite>::G,
     block: <N::Block as Block<N>>::Id,
-    batch: u32,
     outputs: Vec<N::Output>,
   },
   // Eventuality completion found on-chain
@@ -115,9 +112,6 @@ impl<N: Network, D: Db> ScannerDb<N, D> {
   fn next_batch_key() -> Vec<u8> {
     Self::scanner_key(b"next_batch", [])
   }
-  fn batch_key(key: &<N::Curve as Ciphersuite>::G, block: &<N::Block as Block<N>>::Id) -> Vec<u8> {
-    Self::scanner_key(b"batch", [key.to_bytes().as_ref(), block.as_ref()].concat())
-  }
   fn outputs_key(
     key: &<N::Curve as Ciphersuite>::G,
     block: &<N::Block as Block<N>>::Id,
@@ -129,12 +123,7 @@ impl<N: Network, D: Db> ScannerDb<N, D> {
     key: &<N::Curve as Ciphersuite>::G,
     block: &<N::Block as Block<N>>::Id,
     outputs: &[N::Output],
-  ) -> u32 {
+  ) {
-    let batch_key = Self::batch_key(key, block);
-    if let Some(batch) = txn.get(batch_key) {
-      return u32::from_le_bytes(batch.try_into().unwrap());
-    }
-
     let mut bytes = Vec::with_capacity(outputs.len() * 64);
     for output in outputs {
       output.write(&mut bytes).unwrap();
@@ -150,13 +139,6 @@ impl<N: Network, D: Db> ScannerDb<N, D> {
     // 0a, 1a, 2a, 3a, 4a, 5a, 4b, 5b
     // when it should be
     // 0a, 1a, 2a, 3a, 4a, 4b, 5a, 5b
-
-    // Because it's a new set of outputs, allocate a batch ID for it
-    let next_bytes = txn.get(Self::next_batch_key()).unwrap_or(vec![0; 4]).try_into().unwrap();
-    let next = u32::from_le_bytes(next_bytes);
-    txn.put(Self::next_batch_key(), (next + 1).to_le_bytes());
-    txn.put(Self::batch_key(key, block), next_bytes);
-    next
   }
   fn outputs(
     txn: &D::Transaction<'_>,
@@ -182,7 +164,7 @@ impl<N: Network, D: Db> ScannerDb<N, D> {
     txn: &mut D::Transaction<'_>,
     key: &<N::Curve as Ciphersuite>::G,
     block: usize,
-  ) -> (Option<<N::Block as Block<N>>::Id>, Vec<N::Output>) {
+  ) -> Vec<N::Output> {
     let id = Self::block(txn, block); // It may be None for the first key rotated to
     let outputs = if let Some(id) = id.as_ref() {
       Self::outputs(txn, key, id).unwrap_or(vec![])
@@ -198,7 +180,7 @@ impl<N: Network, D: Db> ScannerDb<N, D> {
     txn.put(Self::scanned_block_key(key), u64::try_from(block).unwrap().to_le_bytes());
 
     // Return this block's outputs so they can be pruned from the RAM cache
-    (id, outputs)
+    outputs
   }
   fn latest_scanned_block<G: Get>(getter: &G, key: <N::Curve as Ciphersuite>::G) -> usize {
     let bytes = getter
@@ -280,7 +262,7 @@ impl<N: Network, D: Db> ScannerHandle<N, D> {
 
     info!("Rotating scanner to key {} at {activation_number}", hex::encode(key.to_bytes()));
 
-    let (_, outputs) = ScannerDb::<N, D>::save_scanned_block(txn, &key, activation_number);
+    let outputs = ScannerDb::<N, D>::save_scanned_block(txn, &key, activation_number);
     scanner.ram_scanned.insert(key.to_bytes().as_ref().to_vec(), activation_number);
     assert!(outputs.is_empty());
 
@@ -295,13 +277,25 @@ impl<N: Network, D: Db> ScannerHandle<N, D> {
     ScannerDb::<N, D>::block_number(&self.scanner.read().await.db, id)
   }
 
+  // Set the next batch ID to use
+  pub fn set_next_batch_id(&self, txn: &mut D::Transaction<'_>, batch: u32) {
+    txn.put(ScannerDb::<N, D>::next_batch_key(), batch.to_le_bytes());
+  }
+
+  // Get the next batch ID
+  pub fn next_batch_id(&self, txn: &D::Transaction<'_>) -> u32 {
+    txn
+      .get(ScannerDb::<N, D>::next_batch_key())
+      .map_or(0, |v| u32::from_le_bytes(v.try_into().unwrap()))
+  }
+
   /// Acknowledge having handled a block for a key.
   pub async fn ack_up_to_block(
     &mut self,
     txn: &mut D::Transaction<'_>,
     key: <N::Curve as Ciphersuite>::G,
     id: <N::Block as Block<N>>::Id,
-  ) -> (Vec<BlockHash>, Vec<N::Output>) {
+  ) -> Vec<N::Output> {
     let mut scanner = self.scanner.write().await;
     debug!("Block {} acknowledged", hex::encode(&id));
 
@@ -311,21 +305,16 @@ impl<N: Network, D: Db> ScannerHandle<N, D> {
     // Get the number of the last block we acknowledged
     let prior = ScannerDb::<N, D>::latest_scanned_block(txn, key);
 
-    let mut blocks = vec![];
     let mut outputs = vec![];
     for number in (prior + 1) ..= number {
-      let (block, these_outputs) = ScannerDb::<N, D>::save_scanned_block(txn, &key, number);
+      outputs.extend(ScannerDb::<N, D>::save_scanned_block(txn, &key, number));
-      let block = BlockHash(block.unwrap().as_ref().try_into().unwrap());
-      blocks.push(block);
-      outputs.extend(these_outputs);
     }
-    assert_eq!(blocks.last().unwrap().as_ref(), id.as_ref());
 
     for output in &outputs {
       assert!(scanner.ram_outputs.remove(output.id().as_ref()));
     }
 
-    (blocks, outputs)
+    outputs
   }
 }
 
@@ -514,11 +503,11 @@ impl<N: Network, D: Db> Scanner<N, D> {
 
             // Save the outputs to disk
             let mut txn = scanner.db.txn();
-            let batch = ScannerDb::<N, D>::save_outputs(&mut txn, &key, &block_id, &outputs);
+            ScannerDb::<N, D>::save_outputs(&mut txn, &key, &block_id, &outputs);
             txn.commit();
 
             // Send all outputs
-            if !scanner.emit(ScannerEvent::Block { key, block: block_id, batch, outputs }) {
+            if !scanner.emit(ScannerEvent::Block { key, block: block_id, outputs }) {
               return;
             }
             // Write this number as scanned so we won't re-fire these outputs

processor/src/substrate_signer.rs

@@ -18,10 +18,7 @@ use frost_schnorrkel::Schnorrkel;
 
 use log::{info, debug, warn};
 
-use serai_client::{
+use serai_client::in_instructions::primitives::{Batch, SignedBatch, batch_message};
-  primitives::BlockHash,
-  in_instructions::primitives::{Batch, SignedBatch, batch_message},
-};
 
 use messages::{sign::SignId, coordinator::*};
 use crate::{Get, DbTxn, Db};
@@ -149,7 +146,9 @@ impl<D: Db> SubstrateSigner<D> {
     }
 
     // Start this attempt
-    if !self.signable.contains_key(&id) {
+    let block = if let Some(batch) = self.signable.get(&id) {
+      batch.block
+    } else {
       warn!("told to attempt signing a batch we aren't currently signing for");
       return;
     };
@@ -162,7 +161,7 @@ impl<D: Db> SubstrateSigner<D> {
     self.attempt.insert(id, attempt);
 
     let id = SignId { key: self.keys.group_key().to_bytes().to_vec(), id, attempt };
-    info!("signing batch {}, attempt #{}", hex::encode(id.id), id.attempt);
+    info!("signing batch {} #{}", hex::encode(id.id), id.attempt);
 
     // If we reboot mid-sign, the current design has us abort all signs and wait for latter
     // attempts/new signing protocols
@@ -199,19 +198,21 @@ impl<D: Db> SubstrateSigner<D> {
 
     // Broadcast our preprocess
     self.events.push_back(SubstrateSignerEvent::ProcessorMessage(
-      ProcessorMessage::BatchPreprocess { id, preprocess: preprocess.serialize() },
+      ProcessorMessage::BatchPreprocess { id, block, preprocess: preprocess.serialize() },
     ));
   }
 
   pub async fn sign(&mut self, txn: &mut D::Transaction<'_>, batch: Batch) {
-    if SubstrateSignerDb::<D>::completed(txn, batch.block.0) {
+    // Use the batch id as the ID
+    let mut id = [0u8; 32];
+    id[.. 4].copy_from_slice(&batch.id.to_le_bytes());
+
+    if SubstrateSignerDb::<D>::completed(txn, id) {
       debug!("Sign batch order for ID we've already completed signing");
       // See batch_signed for commentary on why this simply returns
       return;
     }
 
-    // Use the block hash as the ID
-    let id = batch.block.0;
     self.signable.insert(id, batch);
     self.attempt(txn, id, 0).await;
   }
@@ -335,14 +336,19 @@ impl<D: Db> SubstrateSigner<D> {
     }
   }
 
-  pub fn batch_signed(&mut self, txn: &mut D::Transaction<'_>, block: BlockHash) {
+  pub fn batch_signed(&mut self, txn: &mut D::Transaction<'_>, batch_id: u32) {
-    // Stop trying to sign for this batch
+    // Convert into 32-byte ID
-    SubstrateSignerDb::<D>::complete(txn, block.0);
+    // TODO: Add a BatchSignId so we don't have this inefficiency
+    let mut id = [0u8; 32];
+    id[.. 4].copy_from_slice(&batch_id.to_le_bytes());
 
-    self.signable.remove(&block.0);
+    // Stop trying to sign for this batch
-    self.attempt.remove(&block.0);
+    SubstrateSignerDb::<D>::complete(txn, id);
-    self.preprocessing.remove(&block.0);
+
-    self.signing.remove(&block.0);
+    self.signable.remove(&id);
+    self.attempt.remove(&id);
+    self.preprocessing.remove(&id);
+    self.signing.remove(&id);
 
     // This doesn't emit SignedBatch because it doesn't have access to the SignedBatch
     // This function is expected to only be called once Substrate acknowledges this block,

processor/src/tests/addresses.rs

@@ -20,7 +20,6 @@ async fn spend<N: Network, D: Db>(
   network: &N,
   keys: &HashMap<Participant, ThresholdKeys<N::Curve>>,
   scanner: &mut ScannerHandle<N, D>,
-  batch: u32,
   outputs: Vec<N::Output>,
 ) -> Vec<N::Output> {
   let key = keys[&Participant::new(1).unwrap()].group_key();
@@ -52,9 +51,8 @@ async fn spend<N: Network, D: Db>(
     network.mine_block().await;
   }
   match timeout(Duration::from_secs(30), scanner.events.recv()).await.unwrap().unwrap() {
-    ScannerEvent::Block { key: this_key, block: _, batch: this_batch, outputs } => {
+    ScannerEvent::Block { key: this_key, block: _, outputs } => {
       assert_eq!(this_key, key);
-      assert_eq!(this_batch, batch);
       assert_eq!(outputs.len(), 1);
       // Make sure this is actually a change output
       assert_eq!(outputs[0].kind(), OutputType::Change);
@@ -91,10 +89,9 @@ pub async fn test_addresses<N: Network>(network: N) {
   // Verify the Scanner picked them up
   let outputs =
     match timeout(Duration::from_secs(30), scanner.events.recv()).await.unwrap().unwrap() {
-      ScannerEvent::Block { key: this_key, block, batch, outputs } => {
+      ScannerEvent::Block { key: this_key, block, outputs } => {
         assert_eq!(this_key, key);
         assert_eq!(block, block_id);
-        assert_eq!(batch, 0);
         assert_eq!(outputs.len(), 1);
         assert_eq!(outputs[0].kind(), OutputType::Branch);
         outputs
@@ -105,7 +102,7 @@ pub async fn test_addresses<N: Network>(network: N) {
     };
 
   // Spend the branch output, creating a change output and ensuring we actually get change
-  let outputs = spend(&network, &keys, &mut scanner, 1, outputs).await;
+  let outputs = spend(&network, &keys, &mut scanner, outputs).await;
   // Also test spending the change output
-  spend(&network, &keys, &mut scanner, 2, outputs).await;
+  spend(&network, &keys, &mut scanner, outputs).await;
 }

processor/src/tests/scanner.rs

@@ -55,10 +55,9 @@ pub async fn test_scanner<N: Network>(network: N) {
   let verify_event = |mut scanner: ScannerHandle<N, MemDb>| async {
     let outputs =
       match timeout(Duration::from_secs(30), scanner.events.recv()).await.unwrap().unwrap() {
-        ScannerEvent::Block { key, block, batch, outputs } => {
+        ScannerEvent::Block { key, block, outputs } => {
           assert_eq!(key, keys.group_key());
           assert_eq!(block, block_id);
-          assert_eq!(batch, 0);
           assert_eq!(outputs.len(), 1);
           assert_eq!(outputs[0].kind(), OutputType::External);
           outputs
@@ -90,10 +89,7 @@ pub async fn test_scanner<N: Network>(network: N) {
 
   let mut cloned_db = db.clone();
   let mut txn = cloned_db.txn();
-  assert_eq!(
+  assert_eq!(scanner.ack_up_to_block(&mut txn, keys.group_key(), block_id).await, outputs);
-    scanner.ack_up_to_block(&mut txn, keys.group_key(), block_id).await,
-    (blocks, outputs)
-  );
   txn.commit();
 
   // There should be no more events

processor/src/tests/substrate_signer.rs

@@ -24,13 +24,16 @@ async fn test_substrate_signer() {
 
   let participant_one = Participant::new(1).unwrap();
 
+  let id: u32 = 5;
+  let mut id_arr = [0u8; 32];
+  id_arr[.. 4].copy_from_slice(&id.to_le_bytes());
   let block = BlockHash([0xaa; 32]);
   let actual_id =
-    SignId { key: keys[&participant_one].group_key().to_bytes().to_vec(), id: block.0, attempt: 0 };
+    SignId { key: keys[&participant_one].group_key().to_bytes().to_vec(), id: id_arr, attempt: 0 };
 
   let batch = Batch {
     network: NetworkId::Monero,
-    id: 5,
+    id,
     block,
     instructions: vec![
       InInstructionWithBalance {
@@ -81,10 +84,12 @@ async fn test_substrate_signer() {
     let i = Participant::new(u16::try_from(i).unwrap()).unwrap();
     if let SubstrateSignerEvent::ProcessorMessage(ProcessorMessage::BatchPreprocess {
       id,
+      block: batch_block,
       preprocess,
     }) = signers.get_mut(&i).unwrap().events.pop_front().unwrap()
     {
       assert_eq!(id, actual_id);
+      assert_eq!(batch_block, block);
       if signing_set.contains(&i) {
         preprocesses.insert(i, preprocess);
       }

processor/src/tests/wallet.rs

@@ -36,10 +36,9 @@ pub async fn test_wallet<N: Network>(network: N) {
     let block_id = block.id();
 
     match timeout(Duration::from_secs(30), scanner.events.recv()).await.unwrap().unwrap() {
-      ScannerEvent::Block { key: this_key, block, batch, outputs } => {
+      ScannerEvent::Block { key: this_key, block, outputs } => {
         assert_eq!(this_key, key);
         assert_eq!(block, block_id);
-        assert_eq!(batch, 0);
         assert_eq!(outputs.len(), 1);
         (block_id, outputs)
       }
@@ -110,10 +109,9 @@ pub async fn test_wallet<N: Network>(network: N) {
   }
 
   match timeout(Duration::from_secs(30), scanner.events.recv()).await.unwrap().unwrap() {
-    ScannerEvent::Block { key: this_key, block: block_id, batch, outputs: these_outputs } => {
+    ScannerEvent::Block { key: this_key, block: block_id, outputs: these_outputs } => {
       assert_eq!(this_key, key);
       assert_eq!(block_id, block.id());
-      assert_eq!(batch, 1);
       assert_eq!(these_outputs, outputs);
     }
     ScannerEvent::Completed(_, _) => {
@@ -124,7 +122,7 @@ pub async fn test_wallet<N: Network>(network: N) {
   // Check the Scanner DB can reload the outputs
   let mut txn = db.txn();
   assert_eq!(
-    scanner.ack_up_to_block(&mut txn, key, block.id()).await.1,
+    scanner.ack_up_to_block(&mut txn, key, block.id()).await,
     [first_outputs, outputs].concat().to_vec()
   );
   txn.commit();

substrate/client/src/serai/in_instructions.rs

@@ -19,7 +19,7 @@ impl Serai {
     hash: [u8; 32],
     network: NetworkId,
   ) -> Result<Option<BlockHash>, SeraiError> {
-    self.storage(PALLET, "LatestBlock", Some(vec![scale_value(network)]), hash).await
+    self.storage(PALLET, "LatestNetworkBlock", Some(vec![scale_value(network)]), hash).await
   }
 
   pub async fn get_batch_events(

substrate/in-instructions/pallet/Cargo.toml

@@ -19,6 +19,7 @@ scale-info = { version = "2", default-features = false, features = ["derive"] }
 
 sp-application-crypto = { git = "https://github.com/serai-dex/substrate", default-features = false }
 sp-runtime = { git = "https://github.com/serai-dex/substrate", default-features = false }
+sp-core = { git = "https://github.com/serai-dex/substrate", default-features = false }
 
 frame-system = { git = "https://github.com/serai-dex/substrate", default-features = false }
 frame-support = { git = "https://github.com/serai-dex/substrate", default-features = false }

substrate/in-instructions/pallet/src/lib.rs

@@ -23,6 +23,8 @@ pub enum PalletError {
 #[frame_support::pallet]
 pub mod pallet {
   use sp_application_crypto::RuntimePublic;
+  use sp_runtime::traits::Zero;
+  use sp_core::sr25519::Public;
 
   use frame_support::pallet_prelude::*;
   use frame_system::pallet_prelude::*;
@@ -55,10 +57,16 @@ pub mod pallet {
   #[pallet::getter(fn batches)]
   pub(crate) type Batches<T: Config> = StorageMap<_, Blake2_256, NetworkId, u32, OptionQuery>;
 
+  // The last Serai block in which this validator set included a batch
+  #[pallet::storage]
+  #[pallet::getter(fn last_batch_block)]
+  pub(crate) type LastBatchBlock<T: Config> =
+    StorageMap<_, Blake2_256, NetworkId, BlockNumberFor<T>, OptionQuery>;
+
   // The latest block a network has acknowledged as finalized
   #[pallet::storage]
-  #[pallet::getter(fn last_block)]
+  #[pallet::getter(fn latest_network_block)]
-  pub(crate) type LatestBlock<T: Config> =
+  pub(crate) type LatestNetworkBlock<T: Config> =
     StorageMap<_, Blake2_256, NetworkId, BlockHash, OptionQuery>;
 
   impl<T: Config> Pallet<T> {
@@ -71,6 +79,31 @@ pub mod pallet {
     }
   }
 
+  fn key_for_network<T: Config>(network: NetworkId) -> Result<Public, InvalidTransaction> {
+    // TODO: Get the latest session
+    let session = Session(0);
+
+    let mut set = ValidatorSet { session, network };
+    // TODO: If this session just set their keys, it'll invalidate any batches in the mempool
+    // Should there be a transitory period/future-set cut off?
+    if let Some(keys) = ValidatorSets::<T>::keys(set) {
+      Ok(keys.0)
+    } else {
+      // If this set hasn't set their keys yet, use the previous set's
+      if set.session.0 == 0 {
+        // Since there haven't been any keys set, no signature can legitimately exist
+        Err(InvalidTransaction::BadProof)?;
+      }
+      set.session.0 -= 1;
+
+      if let Some(keys) = ValidatorSets::<T>::keys(set) {
+        Ok(keys.0)
+      } else {
+        Err(InvalidTransaction::BadProof)?
+      }
+    }
+  }
+
   #[pallet::call]
   impl<T: Config> Pallet<T> {
     #[pallet::call_index(0)]
@@ -78,16 +111,20 @@ pub mod pallet {
     pub fn execute_batch(origin: OriginFor<T>, batch: SignedBatch) -> DispatchResult {
       ensure_none(origin)?;
 
-      let mut batch = batch.batch;
+      let batch = batch.batch;
+
+      // TODO: Test validate_unsigned is actually called prior to execution, which is required for
+      // this to be safe
+      LastBatchBlock::<T>::insert(batch.network, frame_system::Pallet::<T>::block_number());
 
       Batches::<T>::insert(batch.network, batch.id);
-      LatestBlock::<T>::insert(batch.network, batch.block);
+      LatestNetworkBlock::<T>::insert(batch.network, batch.block);
       Self::deposit_event(Event::Batch {
         network: batch.network,
         id: batch.id,
         block: batch.block,
       });
-      for (i, instruction) in batch.instructions.drain(..).enumerate() {
+      for (i, instruction) in batch.instructions.into_iter().enumerate() {
         // TODO: Check this balance's coin belongs to this network
         // If they don't, the validator set should be completely slashed, without question
 
@@ -116,37 +153,30 @@ pub mod pallet {
       };
 
       let network = batch.batch.network;
+      let key = key_for_network::<T>(network)?;
 
-      // TODO: Get the latest session
+      // verify the batch size
-      let session = Session(0);
+      // TODO: Merge this encode with the one done by batch_message
-
+      if batch.batch.encode().len() > MAX_BATCH_SIZE {
-      let mut set = ValidatorSet { session, network };
+        Err(InvalidTransaction::ExhaustsResources)?;
-      // TODO: If this session just set their keys, it'll invalidate anything in the mempool
+      }
-      // Should there be a transitory period/future-set cut off?
-      let key = if let Some(keys) = ValidatorSets::<T>::keys(set) {
-        keys.0
-      } else {
-        // If this set hasn't set their keys yet, use the previous set's
-        if set.session.0 == 0 {
-          Err(InvalidTransaction::BadProof)?;
-        }
-        set.session.0 -= 1;
-
-        if let Some(keys) = ValidatorSets::<T>::keys(set) {
-          keys.0
-        } else {
-          Err(InvalidTransaction::BadProof)?
-        }
-      };
 
+      // verify the signature
       if !key.verify(&batch_message(&batch.batch), &batch.signature) {
         Err(InvalidTransaction::BadProof)?;
       }
 
+      // check that this validator set isn't publishing a batch more than once per block
+      let current_block = <frame_system::Pallet<T>>::block_number();
+      let last_block = LastBatchBlock::<T>::get(network).unwrap_or(Zero::zero());
+      if last_block >= current_block {
+        Err(InvalidTransaction::Future)?;
+      }
+
       // Verify the batch is sequential
       // Batches has the last ID set. The next ID should be it + 1
       // If there's no ID, the next ID should be 0
-      let expected = Batches::<T>::get(network).map(|prev| prev + 1).unwrap_or(0);
+      let expected = Batches::<T>::get(network).map_or(0, |prev| prev + 1);
       if batch.batch.id < expected {
         Err(InvalidTransaction::Stale)?;
       }

substrate/in-instructions/primitives/src/lib.rs

@@ -21,6 +21,8 @@ use serai_primitives::{BlockHash, Balance, NetworkId, SeraiAddress, ExternalAddr
 mod shorthand;
 pub use shorthand::*;
 
+pub const MAX_BATCH_SIZE: usize = 25_000; // ~25kb
+
 #[derive(
   Clone, PartialEq, Eq, Debug, Serialize, Deserialize, Encode, Decode, MaxEncodedLen, TypeInfo,
 )]

tests/processor/src/tests/batch.rs

@@ -22,6 +22,7 @@ pub(crate) async fn recv_batch_preprocesses(
   attempt: u32,
 ) -> (SignId, HashMap<Participant, Vec<u8>>) {
   let mut id = None;
+  let mut block = None;
   let mut preprocesses = HashMap::new();
   for (i, coordinator) in coordinators.iter_mut().enumerate() {
     let i = Participant::new(u16::try_from(i).unwrap() + 1).unwrap();
@@ -29,14 +30,20 @@ pub(crate) async fn recv_batch_preprocesses(
     let msg = coordinator.recv_message().await;
     match msg {
       messages::ProcessorMessage::Coordinator(
-        messages::coordinator::ProcessorMessage::BatchPreprocess { id: this_id, preprocess },
+        messages::coordinator::ProcessorMessage::BatchPreprocess {
+          id: this_id,
+          block: this_block,
+          preprocess,
+        },
       ) => {
         if id.is_none() {
           assert_eq!(&this_id.key, &key);
           assert_eq!(this_id.attempt, attempt);
           id = Some(this_id.clone());
+          block = Some(this_block);
         }
         assert_eq!(&this_id, id.as_ref().unwrap());
+        assert_eq!(&this_block, block.as_ref().unwrap());
 
         preprocesses.insert(i, preprocess);
       }
@@ -147,6 +154,7 @@ pub(crate) async fn substrate_block(
       block: sent_block,
       key: _,
       burns: _,
+      batches: _,
     } => {
       coordinator.send_message(block).await;
       match coordinator.recv_message().await {
@@ -280,6 +288,7 @@ fn batch_test() {
               // TODO: Should we use the network key here? Or should we only use the Ristretto key?
               key: key_pair.1.to_vec(),
               burns: vec![],
+              batches: vec![batch.batch.id],
             },
           )
           .await

tests/processor/src/tests/send.rs

@@ -219,6 +219,7 @@ fn send_test() {
               instruction: OutInstruction { address: wallet.address(), data: None },
               balance: balance_sent,
             }],
+            batches: vec![batch.batch.id],
           },
         )
         .await;