Add a database of all Monero outs into the processor

Enables synchronous transaction creation (which requires synchronous decoy
selection).

Cargo.lock

@@ -8515,6 +8515,7 @@ version = "0.1.0"
 dependencies = [
  "borsh",
  "ciphersuite",
+ "curve25519-dalek",
  "dalek-ff-group",
  "dkg",
  "flexible-transcript",

networks/monero/rpc/src/lib.rs

@@ -249,7 +249,7 @@ fn rpc_point(point: &str) -> Result<EdwardsPoint, RpcError> {
 /// While no implementors are directly provided, [monero-simple-request-rpc](
 ///   https://github.com/serai-dex/serai/tree/develop/networks/monero/rpc/simple-request
 /// ) is recommended.
-pub trait Rpc: Sync + Clone + Debug {
+pub trait Rpc: Sync + Clone {
   /// Perform a POST request to the specified route with the specified body.
   ///
   /// The implementor is left to handle anything such as authentication.
@@ -1003,10 +1003,10 @@ pub trait Rpc: Sync + Clone + Debug {
 /// An implementation is provided for any satisfier of `Rpc`. It is not recommended to use an `Rpc`
 /// object to satisfy this. This should be satisfied by a local store of the output distribution,
 /// both for performance and to prevent potential attacks a remote node can perform.
-pub trait DecoyRpc: Sync + Clone + Debug {
+pub trait DecoyRpc: Sync {
   /// Get the height the output distribution ends at.
   ///
-  /// This is equivalent to the hight of the blockchain it's for. This is intended to be cheaper
+  /// This is equivalent to the height of the blockchain it's for. This is intended to be cheaper
   /// than fetching the entire output distribution.
   fn get_output_distribution_end_height(
     &self,

processor/monero/Cargo.toml

@@ -25,6 +25,7 @@ scale = { package = "parity-scale-codec", version = "3", default-features = fals
 borsh = { version = "1", default-features = false, features = ["std", "derive", "de_strict_order"] }
 
 transcript = { package = "flexible-transcript", path = "../../crypto/transcript", default-features = false, features = ["std", "recommended"] }
+curve25519-dalek = { version = "4", default-features = false, features = ["alloc", "zeroize"] }
 dalek-ff-group = { path = "../../crypto/dalek-ff-group", default-features = false, features = ["std"] }
 ciphersuite = { path = "../../crypto/ciphersuite", default-features = false, features = ["std", "ed25519"] }
 dkg = { path = "../../crypto/dkg", default-features = false, features = ["std", "evrf-ed25519"] }

processor/monero/src/decoys.rs

@@ -0,0 +1,294 @@
+use core::{
+  future::Future,
+  ops::{Bound, RangeBounds},
+};
+
+use curve25519_dalek::{
+  scalar::Scalar,
+  edwards::{CompressedEdwardsY, EdwardsPoint},
+};
+use monero_wallet::{
+  DEFAULT_LOCK_WINDOW,
+  primitives::Commitment,
+  transaction::{Timelock, Input, Pruned, Transaction},
+  rpc::{OutputInformation, RpcError, Rpc as MRpcTrait, DecoyRpc},
+};
+
+use borsh::{BorshSerialize, BorshDeserialize};
+use serai_db::{Get, DbTxn, Db, create_db};
+
+use primitives::task::ContinuallyRan;
+use scanner::ScannerFeed;
+
+use crate::Rpc;
+
+#[derive(BorshSerialize, BorshDeserialize)]
+struct EncodableOutputInformation {
+  height: u64,
+  timelocked: bool,
+  key: [u8; 32],
+  commitment: [u8; 32],
+}
+
+create_db! {
+  MoneroProcessorDecoys {
+    NextToIndexBlock: () -> u64,
+    PriorIndexedBlock: () -> [u8; 32],
+    DistributionStartBlock: () -> u64,
+    Distribution: () -> Vec<u64>,
+    Out: (index: u64) -> EncodableOutputInformation,
+  }
+}
+
+/*
+  We want to be able to select decoys when planning transactions, but planning transactions is a
+  synchronous process. We store the decoys to a local database and have our database implement
+  `DecoyRpc` to achieve synchronous decoy selection.
+
+  This is only needed as the transactions we sign must have decoys decided and agreed upon. With
+  FCMP++s, we'll be able to sign transactions without the membership proof, letting any signer
+  prove for membership after the fact (with their local views). Until then, this task remains.
+*/
+pub(crate) struct DecoysTask<D: Db> {
+  pub(crate) rpc: Rpc<D>,
+  pub(crate) current_distribution: Vec<u64>,
+}
+
+impl<D: Db> ContinuallyRan for DecoysTask<D> {
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+    async move {
+      let finalized_block_number = self
+        .rpc
+        .rpc
+        .get_height()
+        .await
+        .map_err(|e| format!("couldn't fetch latest block number: {e:?}"))?
+        .checked_sub(Rpc::<D>::CONFIRMATIONS.try_into().unwrap())
+        .ok_or(format!(
+          "blockchain only just started and doesn't have {} blocks yet",
+          Rpc::<D>::CONFIRMATIONS
+        ))?;
+
+      if NextToIndexBlock::get(&self.rpc.db).is_none() {
+        let distribution = self
+          .rpc
+          .rpc
+          .get_output_distribution(..= finalized_block_number)
+          .await
+          .map_err(|e| format!("failed to get output distribution: {e:?}"))?;
+        if distribution.is_empty() {
+          Err("distribution was empty".to_string())?;
+        }
+
+        let distribution_start_block = finalized_block_number - (distribution.len() - 1);
+        // There may have been a reorg between the time of getting the distribution and the time of
+        // getting this block. This is an invariant and assumed not to have happened in the split
+        // second it's possible.
+        let block = self
+          .rpc
+          .rpc
+          .get_block_by_number(distribution_start_block)
+          .await
+          .map_err(|e| format!("failed to get the start block for the distribution: {e:?}"))?;
+
+        let mut txn = self.rpc.db.txn();
+        NextToIndexBlock::set(&mut txn, &distribution_start_block.try_into().unwrap());
+        PriorIndexedBlock::set(&mut txn, &block.header.previous);
+        DistributionStartBlock::set(&mut txn, &u64::try_from(distribution_start_block).unwrap());
+        txn.commit();
+      }
+
+      let next_to_index_block =
+        usize::try_from(NextToIndexBlock::get(&self.rpc.db).unwrap()).unwrap();
+      if next_to_index_block >= finalized_block_number {
+        return Ok(false);
+      }
+
+      for b in next_to_index_block ..= finalized_block_number {
+        // Fetch the block
+        let block = self
+          .rpc
+          .rpc
+          .get_block_by_number(b)
+          .await
+          .map_err(|e| format!("decoys task failed to fetch block: {e:?}"))?;
+        let prior = PriorIndexedBlock::get(&self.rpc.db).unwrap();
+        if block.header.previous != prior {
+          panic!(
+            "decoys task detected reorg: expected {}, found {}",
+            hex::encode(prior),
+            hex::encode(block.header.previous)
+          );
+        }
+
+        // Fetch the transactions in the block
+        let transactions = self
+          .rpc
+          .rpc
+          .get_pruned_transactions(&block.transactions)
+          .await
+          .map_err(|e| format!("failed to get the pruned transactions within a block: {e:?}"))?;
+
+        fn outputs(
+          list: &mut Vec<EncodableOutputInformation>,
+          block_number: u64,
+          tx: Transaction<Pruned>,
+        ) {
+          match tx {
+            Transaction::V1 { .. } => {}
+            Transaction::V2 { prefix, proofs } => {
+              for (i, output) in prefix.outputs.into_iter().enumerate() {
+                list.push(EncodableOutputInformation {
+                  // This is correct per the documentation on OutputInformation, which this maps to
+                  height: block_number,
+                  timelocked: prefix.additional_timelock != Timelock::None,
+                  key: output.key.to_bytes(),
+                  commitment: if matches!(
+                    prefix.inputs.first().expect("Monero transaction had no inputs"),
+                    Input::Gen(_)
+                  ) {
+                    Commitment::new(
+                      Scalar::ONE,
+                      output.amount.expect("miner transaction outputs didn't have amounts set"),
+                    )
+                    .calculate()
+                    .compress()
+                    .to_bytes()
+                  } else {
+                    proofs
+                      .as_ref()
+                      .expect("non-miner V2 transaction didn't have proofs")
+                      .base
+                      .commitments
+                      .get(i)
+                      .expect("amount of commitments didn't match amount of outputs")
+                      .compress()
+                      .to_bytes()
+                  },
+                });
+              }
+            }
+          }
+        }
+
+        let block_hash = block.hash();
+
+        let b = u64::try_from(b).unwrap();
+        let mut encodable = Vec::with_capacity(2 * (1 + block.transactions.len()));
+        outputs(&mut encodable, b, block.miner_transaction.into());
+        for transaction in transactions {
+          outputs(&mut encodable, b, transaction);
+        }
+
+        let existing_outputs = self.current_distribution.last().copied().unwrap_or(0);
+        let now_outputs = existing_outputs + u64::try_from(encodable.len()).unwrap();
+        self.current_distribution.push(now_outputs);
+
+        let mut txn = self.rpc.db.txn();
+        NextToIndexBlock::set(&mut txn, &(b + 1));
+        PriorIndexedBlock::set(&mut txn, &block_hash);
+        // TODO: Don't write the entire 10 MB distribution to the DB every two minutes
+        Distribution::set(&mut txn, &self.current_distribution);
+        for (b, out) in (existing_outputs .. now_outputs).zip(encodable) {
+          Out::set(&mut txn, b, &out);
+        }
+        txn.commit();
+      }
+      Ok(true)
+    }
+  }
+}
+
+// TODO: Cache the distribution in a static
+pub(crate) struct Decoys<'a, G: Get>(&'a G);
+impl<'a, G: Sync + Get> DecoyRpc for Decoys<'a, G> {
+  #[rustfmt::skip]
+  fn get_output_distribution_end_height(
+    &self,
+  ) -> impl Send + Future<Output = Result<usize, RpcError>> {
+    async move {
+      Ok(NextToIndexBlock::get(self.0).map_or(0, |b| usize::try_from(b).unwrap() + 1))
+    }
+  }
+  fn get_output_distribution(
+    &self,
+    range: impl Send + RangeBounds<usize>,
+  ) -> impl Send + Future<Output = Result<Vec<u64>, RpcError>> {
+    async move {
+      let from = match range.start_bound() {
+        Bound::Included(from) => *from,
+        Bound::Excluded(from) => from.checked_add(1).ok_or_else(|| {
+          RpcError::InternalError("range's from wasn't representable".to_string())
+        })?,
+        Bound::Unbounded => 0,
+      };
+      let to = match range.end_bound() {
+        Bound::Included(to) => *to,
+        Bound::Excluded(to) => to
+          .checked_sub(1)
+          .ok_or_else(|| RpcError::InternalError("range's to wasn't representable".to_string()))?,
+        Bound::Unbounded => {
+          panic!("requested distribution till latest block, which is non-deterministic")
+        }
+      };
+      if from > to {
+        Err(RpcError::InternalError(format!(
+          "malformed range: inclusive start {from}, inclusive end {to}"
+        )))?;
+      }
+
+      let distribution_start_block = usize::try_from(
+        DistributionStartBlock::get(self.0).expect("never populated the distribution start block"),
+      )
+      .unwrap();
+      let len_of_distribution_until_to =
+        to.checked_sub(distribution_start_block).ok_or_else(|| {
+          RpcError::InternalError(
+            "requested distribution until a block when the distribution had yet to start"
+              .to_string(),
+          )
+        })? +
+          1;
+      let distribution = Distribution::get(self.0).expect("never populated the distribution");
+      assert!(
+        distribution.len() >= len_of_distribution_until_to,
+        "requested distribution until block we have yet to index"
+      );
+      Ok(
+        distribution[from.saturating_sub(distribution_start_block) .. len_of_distribution_until_to]
+          .to_vec(),
+      )
+    }
+  }
+  fn get_outs(
+    &self,
+    _indexes: &[u64],
+  ) -> impl Send + Future<Output = Result<Vec<OutputInformation>, RpcError>> {
+    async move { unimplemented!("get_outs is unused") }
+  }
+  fn get_unlocked_outputs(
+    &self,
+    indexes: &[u64],
+    height: usize,
+    fingerprintable_deterministic: bool,
+  ) -> impl Send + Future<Output = Result<Vec<Option<[EdwardsPoint; 2]>>, RpcError>> {
+    assert!(fingerprintable_deterministic, "processor wasn't using deterministic output selection");
+    async move {
+      let mut res = vec![];
+      for index in indexes {
+        let out = Out::get(self.0, *index).expect("requested output we didn't index");
+        let unlocked = (!out.timelocked) &&
+          ((usize::try_from(out.height).unwrap() + DEFAULT_LOCK_WINDOW) <= height);
+        res.push(unlocked.then(|| CompressedEdwardsY(out.key).decompress()).flatten().map(|key| {
+          [
+            key,
+            CompressedEdwardsY(out.commitment)
+              .decompress()
+              .expect("output with invalid commitment"),
+          ]
+        }));
+      }
+      Ok(res)
+    }
+  }
+}

processor/monero/src/lib.rs

@@ -107,146 +107,6 @@ impl Monero {
     Ok(FeeRate::new(fee.max(MINIMUM_FEE), 10000).unwrap())
   }
 
-  async fn make_signable_transaction(
-    &self,
-    block_number: usize,
-    plan_id: &[u8; 32],
-    inputs: &[Output],
-    payments: &[Payment<Self>],
-    change: &Option<Address>,
-    calculating_fee: bool,
-  ) -> Result<Option<MakeSignableTransactionResult>, NetworkError> {
-    for payment in payments {
-      assert_eq!(payment.balance.coin, Coin::Monero);
-    }
-
-    // TODO2: Use an fee representative of several blocks, cached inside Self
-    let block_for_fee = self.get_block(block_number).await?;
-    let fee_rate = self.median_fee(&block_for_fee).await?;
-
-    // Determine the RCT proofs to make based off the hard fork
-    // TODO: Make a fn for this block which is duplicated with tests
-    let rct_type = match block_for_fee.header.hardfork_version {
-      14 => RctType::ClsagBulletproof,
-      15 | 16 => RctType::ClsagBulletproofPlus,
-      _ => panic!("Monero hard forked and the processor wasn't updated for it"),
-    };
-
-    let mut transcript =
-      RecommendedTranscript::new(b"Serai Processor Monero Transaction Transcript");
-    transcript.append_message(b"plan", plan_id);
-
-    // All signers need to select the same decoys
-    // All signers use the same height and a seeded RNG to make sure they do so.
-    let mut inputs_actual = Vec::with_capacity(inputs.len());
-    for input in inputs {
-      inputs_actual.push(
-        OutputWithDecoys::fingerprintable_deterministic_new(
-          &mut ChaCha20Rng::from_seed(transcript.rng_seed(b"decoys")),
-          &self.rpc,
-          // TODO: Have Decoys take RctType
-          match rct_type {
-            RctType::ClsagBulletproof => 11,
-            RctType::ClsagBulletproofPlus => 16,
-            _ => panic!("selecting decoys for an unsupported RctType"),
-          },
-          block_number + 1,
-          input.0.clone(),
-        )
-        .await
-        .map_err(map_rpc_err)?,
-      );
-    }
-
-    // Monero requires at least two outputs
-    // If we only have one output planned, add a dummy payment
-    let mut payments = payments.to_vec();
-    let outputs = payments.len() + usize::from(u8::from(change.is_some()));
-    if outputs == 0 {
-      return Ok(None);
-    } else if outputs == 1 {
-      payments.push(Payment {
-        address: Address::new(
-          ViewPair::new(EdwardsPoint::generator().0, Zeroizing::new(Scalar::ONE.0))
-            .unwrap()
-            .legacy_address(MoneroNetwork::Mainnet),
-        )
-        .unwrap(),
-        balance: Balance { coin: Coin::Monero, amount: Amount(0) },
-        data: None,
-      });
-    }
-
-    let payments = payments
-      .into_iter()
-      .map(|payment| (payment.address.into(), payment.balance.amount.0))
-      .collect::<Vec<_>>();
-
-    match MSignableTransaction::new(
-      rct_type,
-      // Use the plan ID as the outgoing view key
-      Zeroizing::new(*plan_id),
-      inputs_actual,
-      payments,
-      Change::fingerprintable(change.as_ref().map(|change| change.clone().into())),
-      vec![],
-      fee_rate,
-    ) {
-      Ok(signable) => Ok(Some({
-        if calculating_fee {
-          MakeSignableTransactionResult::Fee(signable.necessary_fee())
-        } else {
-          MakeSignableTransactionResult::SignableTransaction(signable)
-        }
-      })),
-      Err(e) => match e {
-        SendError::UnsupportedRctType => {
-          panic!("trying to use an RctType unsupported by monero-wallet")
-        }
-        SendError::NoInputs |
-        SendError::InvalidDecoyQuantity |
-        SendError::NoOutputs |
-        SendError::TooManyOutputs |
-        SendError::NoChange |
-        SendError::TooMuchArbitraryData |
-        SendError::TooLargeTransaction |
-        SendError::WrongPrivateKey => {
-          panic!("created an invalid Monero transaction: {e}");
-        }
-        SendError::MultiplePaymentIds => {
-          panic!("multiple payment IDs despite not supporting integrated addresses");
-        }
-        SendError::NotEnoughFunds { inputs, outputs, necessary_fee } => {
-          log::debug!(
-            "Monero NotEnoughFunds. inputs: {:?}, outputs: {:?}, necessary_fee: {necessary_fee:?}",
-            inputs,
-            outputs
-          );
-          match necessary_fee {
-            Some(necessary_fee) => {
-              // If we're solely calculating the fee, return the fee this TX will cost
-              if calculating_fee {
-                Ok(Some(MakeSignableTransactionResult::Fee(necessary_fee)))
-              } else {
-                // If we're actually trying to make the TX, return None
-                Ok(None)
-              }
-            }
-            // We didn't have enough funds to even cover the outputs
-            None => {
-              // Ensure we're not misinterpreting this
-              assert!(outputs > inputs);
-              Ok(None)
-            }
-          }
-        }
-        SendError::MaliciousSerialization | SendError::ClsagError(_) | SendError::FrostError(_) => {
-          panic!("supposedly unreachable (at this time) Monero error: {e}");
-        }
-      },
-    }
-  }
-
   #[cfg(test)]
   fn test_view_pair() -> ViewPair {
     ViewPair::new(*EdwardsPoint::generator(), Zeroizing::new(Scalar::ONE.0)).unwrap()

processor/monero/src/main.rs

@@ -15,6 +15,8 @@ mod key_gen;
 use crate::key_gen::KeyGenParams;
 mod rpc;
 use rpc::Rpc;
+
+mod decoys;
 /*
 mod scheduler;
 use scheduler::Scheduler;

processor/monero/src/rpc.rs

@@ -5,6 +5,7 @@ use monero_simple_request_rpc::SimpleRequestRpc;
 
 use serai_client::primitives::{NetworkId, Coin, Amount};
 
+use serai_db::Db;
 use scanner::ScannerFeed;
 use signers::TransactionPublisher;
 
@@ -14,11 +15,12 @@ use crate::{
 };
 
 #[derive(Clone)]
-pub(crate) struct Rpc {
+pub(crate) struct Rpc<D: Db> {
+  pub(crate) db: D,
   pub(crate) rpc: SimpleRequestRpc,
 }
 
-impl ScannerFeed for Rpc {
+impl<D: Db> ScannerFeed for Rpc<D> {
   const NETWORK: NetworkId = NetworkId::Monero;
   // Outputs aren't spendable until 10 blocks later due to the 10-block lock
   // Since we assumed scanned outputs are spendable, that sets a minimum confirmation depth of 10
@@ -37,16 +39,15 @@ impl ScannerFeed for Rpc {
     &self,
   ) -> impl Send + Future<Output = Result<u64, Self::EphemeralError>> {
     async move {
-      Ok(
+      // The decoys task only indexes finalized blocks
-        self
+      crate::decoys::NextToIndexBlock::get(&self.db)
-          .rpc
+        .ok_or_else(|| {
-          .get_height()
+          RpcError::InternalError("decoys task hasn't indexed any blocks yet".to_string())
-          .await?
+        })?
         .checked_sub(1)
-          .expect("connected to an invalid Monero RPC")
+        .ok_or_else(|| {
-          .try_into()
+          RpcError::InternalError("only the genesis block has been indexed".to_string())
-          .unwrap(),
+        })
-      )
     }
   }
 
@@ -127,7 +128,7 @@ impl ScannerFeed for Rpc {
   }
 }
 
-impl TransactionPublisher<Transaction> for Rpc {
+impl<D: Db> TransactionPublisher<Transaction> for Rpc<D> {
   type EphemeralError = RpcError;
 
   fn publish(

processor/monero/src/scheduler.rs

@@ -1,3 +1,144 @@
+async fn make_signable_transaction(
+block_number: usize,
+plan_id: &[u8; 32],
+inputs: &[Output],
+payments: &[Payment<Self>],
+change: &Option<Address>,
+calculating_fee: bool,
+) -> Result<Option<MakeSignableTransactionResult>, NetworkError> {
+for payment in payments {
+  assert_eq!(payment.balance.coin, Coin::Monero);
+}
+
+// TODO2: Use an fee representative of several blocks, cached inside Self
+let block_for_fee = self.get_block(block_number).await?;
+let fee_rate = self.median_fee(&block_for_fee).await?;
+
+// Determine the RCT proofs to make based off the hard fork
+// TODO: Make a fn for this block which is duplicated with tests
+let rct_type = match block_for_fee.header.hardfork_version {
+  14 => RctType::ClsagBulletproof,
+  15 | 16 => RctType::ClsagBulletproofPlus,
+  _ => panic!("Monero hard forked and the processor wasn't updated for it"),
+};
+
+let mut transcript =
+  RecommendedTranscript::new(b"Serai Processor Monero Transaction Transcript");
+transcript.append_message(b"plan", plan_id);
+
+// All signers need to select the same decoys
+// All signers use the same height and a seeded RNG to make sure they do so.
+let mut inputs_actual = Vec::with_capacity(inputs.len());
+for input in inputs {
+  inputs_actual.push(
+    OutputWithDecoys::fingerprintable_deterministic_new(
+      &mut ChaCha20Rng::from_seed(transcript.rng_seed(b"decoys")),
+      &self.rpc,
+      // TODO: Have Decoys take RctType
+      match rct_type {
+        RctType::ClsagBulletproof => 11,
+        RctType::ClsagBulletproofPlus => 16,
+        _ => panic!("selecting decoys for an unsupported RctType"),
+      },
+      block_number + 1,
+      input.0.clone(),
+    )
+    .await
+    .map_err(map_rpc_err)?,
+  );
+}
+
+// Monero requires at least two outputs
+// If we only have one output planned, add a dummy payment
+let mut payments = payments.to_vec();
+let outputs = payments.len() + usize::from(u8::from(change.is_some()));
+if outputs == 0 {
+  return Ok(None);
+} else if outputs == 1 {
+  payments.push(Payment {
+    address: Address::new(
+      ViewPair::new(EdwardsPoint::generator().0, Zeroizing::new(Scalar::ONE.0))
+        .unwrap()
+        .legacy_address(MoneroNetwork::Mainnet),
+    )
+    .unwrap(),
+    balance: Balance { coin: Coin::Monero, amount: Amount(0) },
+    data: None,
+  });
+}
+
+let payments = payments
+  .into_iter()
+  .map(|payment| (payment.address.into(), payment.balance.amount.0))
+  .collect::<Vec<_>>();
+
+match MSignableTransaction::new(
+  rct_type,
+  // Use the plan ID as the outgoing view key
+  Zeroizing::new(*plan_id),
+  inputs_actual,
+  payments,
+  Change::fingerprintable(change.as_ref().map(|change| change.clone().into())),
+  vec![],
+  fee_rate,
+) {
+  Ok(signable) => Ok(Some({
+    if calculating_fee {
+      MakeSignableTransactionResult::Fee(signable.necessary_fee())
+    } else {
+      MakeSignableTransactionResult::SignableTransaction(signable)
+    }
+  })),
+  Err(e) => match e {
+    SendError::UnsupportedRctType => {
+      panic!("trying to use an RctType unsupported by monero-wallet")
+    }
+    SendError::NoInputs |
+    SendError::InvalidDecoyQuantity |
+    SendError::NoOutputs |
+    SendError::TooManyOutputs |
+    SendError::NoChange |
+    SendError::TooMuchArbitraryData |
+    SendError::TooLargeTransaction |
+    SendError::WrongPrivateKey => {
+      panic!("created an invalid Monero transaction: {e}");
+    }
+    SendError::MultiplePaymentIds => {
+      panic!("multiple payment IDs despite not supporting integrated addresses");
+    }
+    SendError::NotEnoughFunds { inputs, outputs, necessary_fee } => {
+      log::debug!(
+        "Monero NotEnoughFunds. inputs: {:?}, outputs: {:?}, necessary_fee: {necessary_fee:?}",
+        inputs,
+        outputs
+      );
+      match necessary_fee {
+        Some(necessary_fee) => {
+          // If we're solely calculating the fee, return the fee this TX will cost
+          if calculating_fee {
+            Ok(Some(MakeSignableTransactionResult::Fee(necessary_fee)))
+          } else {
+            // If we're actually trying to make the TX, return None
+            Ok(None)
+          }
+        }
+        // We didn't have enough funds to even cover the outputs
+        None => {
+          // Ensure we're not misinterpreting this
+          assert!(outputs > inputs);
+          Ok(None)
+        }
+      }
+    }
+    SendError::MaliciousSerialization | SendError::ClsagError(_) | SendError::FrostError(_) => {
+      panic!("supposedly unreachable (at this time) Monero error: {e}");
+    }
+  },
+}
+}
+
+
+/*
 use ciphersuite::{Ciphersuite, Secp256k1};
 
 use bitcoin_serai::{
@@ -186,3 +327,4 @@ impl TransactionPlanner<Rpc, ()> for Planner {
 }
 
 pub(crate) type Scheduler = utxo_standard_scheduler::Scheduler<Rpc, Planner>;
+*/