Add non-transaction-chaining scheduler

.github/workflows/tests.yml

@@ -45,6 +45,7 @@ jobs:
             -p serai-processor-scanner \
             -p serai-processor-scheduler-primitives \
             -p serai-processor-utxo-scheduler-primitives \
+            -p serai-processor-utxo-scheduler \
             -p serai-processor-transaction-chaining-scheduler \
             -p serai-processor \
             -p tendermint-machine \

Cargo.lock

@@ -8733,11 +8733,27 @@ dependencies = [
  "serai-processor-utxo-scheduler-primitives",
 ]
 
+[[package]]
+name = "serai-processor-utxo-scheduler"
+version = "0.1.0"
+dependencies = [
+ "borsh",
+ "group",
+ "parity-scale-codec",
+ "serai-db",
+ "serai-primitives",
+ "serai-processor-primitives",
+ "serai-processor-scanner",
+ "serai-processor-scheduler-primitives",
+ "serai-processor-utxo-scheduler-primitives",
+]
+
 [[package]]
 name = "serai-processor-utxo-scheduler-primitives"
 version = "0.1.0"
 dependencies = [
  "async-trait",
+ "borsh",
  "serai-primitives",
  "serai-processor-primitives",
  "serai-processor-scanner",

Cargo.toml

@@ -77,6 +77,7 @@ members = [
   "processor/scanner",
   "processor/scheduler/primitives",
   "processor/scheduler/utxo/primitives",
+  "processor/scheduler/utxo/standard",
   "processor/scheduler/utxo/transaction-chaining",
   "processor",
 

deny.toml

@@ -52,6 +52,7 @@ exceptions = [
   { allow = ["AGPL-3.0"], name = "serai-processor-scanner" },
   { allow = ["AGPL-3.0"], name = "serai-processor-scheduler-primitives" },
   { allow = ["AGPL-3.0"], name = "serai-processor-utxo-scheduler-primitives" },
+  { allow = ["AGPL-3.0"], name = "serai-processor-standard-scheduler" },
   { allow = ["AGPL-3.0"], name = "serai-processor-transaction-chaining-scheduler" },
   { allow = ["AGPL-3.0"], name = "serai-processor" },
 

processor/primitives/src/output.rs

@@ -3,12 +3,22 @@ use std::io;
 
 use group::GroupEncoding;
 
+use borsh::{BorshSerialize, BorshDeserialize};
+
 use serai_primitives::{ExternalAddress, Balance};
 
 use crate::Id;
 
 /// An address on the external network.
-pub trait Address: Send + Sync + Clone + Into<ExternalAddress> + TryFrom<ExternalAddress> {
+pub trait Address:
+  Send
+  + Sync
+  + Clone
+  + Into<ExternalAddress>
+  + TryFrom<ExternalAddress>
+  + BorshSerialize
+  + BorshDeserialize
+{
   /// Write this address.
   fn write(&self, writer: &mut impl io::Write) -> io::Result<()>;
   /// Read an address.

processor/primitives/src/payment.rs

@@ -1,6 +1,7 @@
 use std::io;
 
 use scale::{Encode, Decode, IoReader};
+use borsh::{BorshSerialize, BorshDeserialize};
 
 use serai_primitives::{Balance, Data};
 use serai_coins_primitives::OutInstructionWithBalance;
@@ -8,7 +9,7 @@ use serai_coins_primitives::OutInstructionWithBalance;
 use crate::Address;
 
 /// A payment to fulfill.
-#[derive(Clone)]
+#[derive(Clone, BorshSerialize, BorshDeserialize)]
 pub struct Payment<A: Address> {
   address: A,
   balance: Balance,

processor/scheduler/primitives/Cargo.toml

@@ -13,6 +13,9 @@ publish = false
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
 
+[package.metadata.cargo-machete]
+ignored = ["scale", "borsh"]
+
 [lints]
 workspace = true
 

processor/scheduler/utxo/primitives/Cargo.toml

@@ -19,6 +19,8 @@ workspace = true
 [dependencies]
 async-trait = { version = "0.1", default-features = false }
 
+borsh = { version = "1", default-features = false, features = ["std", "derive", "de_strict_order"] }
+
 serai-primitives = { path = "../../../../substrate/primitives", default-features = false, features = ["std"] }
 
 primitives = { package = "serai-processor-primitives", path = "../../../primitives" }

processor/scheduler/utxo/primitives/src/lib.rs

@@ -8,6 +8,9 @@ use primitives::{ReceivedOutput, Payment};
 use scanner::{ScannerFeed, KeyFor, AddressFor, OutputFor, EventualityFor, BlockFor};
 use scheduler_primitives::*;
 
+mod tree;
+pub use tree::*;
+
 /// A planned transaction.
 pub struct PlannedTransaction<S: ScannerFeed, ST: SignableTransaction, A> {
   /// The signable transaction.
@@ -18,6 +21,23 @@ pub struct PlannedTransaction<S: ScannerFeed, ST: SignableTransaction, A> {
   pub auxilliary: A,
 }
 
+/// A planned transaction which was created via amortizing the fee.
+pub struct AmortizePlannedTransaction<S: ScannerFeed, ST: SignableTransaction, A> {
+  /// The amounts the included payments were worth.
+  ///
+  /// If the payments passed as an argument are sorted from highest to lowest valued, these `n`
+  /// amounts will be for the first `n` payments.
+  pub effected_payments: Vec<Amount>,
+  /// Whether or not the planned transaction had a change output.
+  pub has_change: bool,
+  /// The signable transaction.
+  pub signable: ST,
+  /// The Eventuality to watch for.
+  pub eventuality: EventualityFor<S>,
+  /// The auxilliary data for this transaction.
+  pub auxilliary: A,
+}
+
 /// An object able to plan a transaction.
 #[async_trait::async_trait]
 pub trait TransactionPlanner<S: ScannerFeed, A>: 'static + Send + Sync {
@@ -60,7 +80,8 @@ pub trait TransactionPlanner<S: ScannerFeed, A>: 'static + Send + Sync {
   /// This must only require the same fee as would be returned by `calculate_fee`. The caller is
   /// trusted to maintain `sum(inputs) - sum(payments) >= if change.is_some() { DUST } else { 0 }`.
   ///
-  /// `change` will always be an address belonging to the Serai network.
+  /// `change` will always be an address belonging to the Serai network. If it is `Some`, a change
+  /// output must be created.
   fn plan(
     fee_rate: Self::FeeRate,
     inputs: Vec<OutputFor<S>>,
@@ -82,7 +103,7 @@ pub trait TransactionPlanner<S: ScannerFeed, A>: 'static + Send + Sync {
     inputs: Vec<OutputFor<S>>,
     mut payments: Vec<Payment<AddressFor<S>>>,
     mut change: Option<KeyFor<S>>,
-  ) -> Option<PlannedTransaction<S, Self::SignableTransaction, A>> {
+  ) -> Option<AmortizePlannedTransaction<S, Self::SignableTransaction, A>> {
     // If there's no change output, we can't recoup any operating costs we would amortize
     // We also don't have any losses if the inputs are written off/the change output is reduced
     let mut operating_costs_if_no_change = 0;
@@ -192,6 +213,48 @@ pub trait TransactionPlanner<S: ScannerFeed, A>: 'static + Send + Sync {
     }
 
     // Because we amortized, or accrued as operating costs, the fee, make the transaction
-    Some(Self::plan(fee_rate, inputs, payments, change))
+    let effected_payments = payments.iter().map(|payment| payment.balance().amount).collect();
+    let has_change = change.is_some();
+    let PlannedTransaction { signable, eventuality, auxilliary } =
+      Self::plan(fee_rate, inputs, payments, change);
+    Some(AmortizePlannedTransaction {
+      effected_payments,
+      has_change,
+      signable,
+      eventuality,
+      auxilliary,
+    })
+  }
+
+  /// Create a tree to fulfill a set of payments.
+  ///
+  /// Returns a `TreeTransaction` whose children (and arbitrary children of children) fulfill all
+  /// these payments. This tree root will be able to be made with a change output.
+  fn tree(payments: &[Payment<AddressFor<S>>]) -> TreeTransaction<AddressFor<S>> {
+    // This variable is for the current layer of the tree being built
+    let mut tree = Vec::with_capacity(payments.len().div_ceil(Self::MAX_OUTPUTS));
+
+    // Push the branches for the leaves (the payments out)
+    for payments in payments.chunks(Self::MAX_OUTPUTS) {
+      let value = payments.iter().map(|payment| payment.balance().amount.0).sum::<u64>();
+      tree.push(TreeTransaction::<AddressFor<S>>::Leaves { payments: payments.to_vec(), value });
+    }
+
+    // While we haven't calculated a tree root, or the tree root doesn't support a change output,
+    // keep working
+    while (tree.len() != 1) || (tree[0].children() == Self::MAX_OUTPUTS) {
+      let mut branch_layer = vec![];
+      for children in tree.chunks(Self::MAX_OUTPUTS) {
+        branch_layer.push(TreeTransaction::<AddressFor<S>>::Branch {
+          children: children.to_vec(),
+          value: children.iter().map(TreeTransaction::value).sum(),
+        });
+      }
+      tree = branch_layer;
+    }
+    assert_eq!(tree.len(), 1);
+    let tree_root = tree.remove(0);
+    assert!((tree_root.children() + 1) <= Self::MAX_OUTPUTS);
+    tree_root
   }
 }

processor/scheduler/utxo/primitives/src/tree.rs

@@ -0,0 +1,146 @@
+use borsh::{BorshSerialize, BorshDeserialize};
+
+use serai_primitives::{Coin, Amount, Balance};
+
+use primitives::{Address, Payment};
+use scanner::ScannerFeed;
+
+/// A transaction within a tree to fulfill payments.
+#[derive(Clone, BorshSerialize, BorshDeserialize)]
+pub enum TreeTransaction<A: Address> {
+  /// A transaction for the leaves (payments) of the tree.
+  Leaves {
+    /// The payments within this transaction.
+    payments: Vec<Payment<A>>,
+    /// The sum value of the payments.
+    value: u64,
+  },
+  /// A transaction for the branches of the tree.
+  Branch {
+    /// The child transactions.
+    children: Vec<Self>,
+    /// The sum value of the child transactions.
+    value: u64,
+  },
+}
+impl<A: Address> TreeTransaction<A> {
+  /// How many children this transaction has.
+  ///
+  /// A child is defined as any dependent, whether payment or transaction.
+  pub fn children(&self) -> usize {
+    match self {
+      Self::Leaves { payments, .. } => payments.len(),
+      Self::Branch { children, .. } => children.len(),
+    }
+  }
+
+  /// The value this transaction wants to spend.
+  pub fn value(&self) -> u64 {
+    match self {
+      Self::Leaves { value, .. } | Self::Branch { value, .. } => *value,
+    }
+  }
+
+  /// The payments to make to enable this transaction's children.
+  ///
+  /// A child is defined as any dependent, whether payment or transaction.
+  ///
+  /// The input value given to this transaction MUST be less than or equal to the desired value.
+  /// The difference will be amortized over all dependents.
+  ///
+  /// Returns None if no payments should be made. Returns Some containing a non-empty Vec if any
+  /// payments should be made.
+  pub fn payments<S: ScannerFeed>(
+    &self,
+    coin: Coin,
+    branch_address: &A,
+    input_value: u64,
+  ) -> Option<Vec<Payment<A>>> {
+    // Fetch the amounts for the payments we'll make
+    let mut amounts: Vec<_> = match self {
+      Self::Leaves { payments, .. } => payments
+        .iter()
+        .map(|payment| {
+          assert_eq!(payment.balance().coin, coin);
+          Some(payment.balance().amount.0)
+        })
+        .collect(),
+      Self::Branch { children, .. } => children.iter().map(|child| Some(child.value())).collect(),
+    };
+
+    // We need to reduce them so their sum is our input value
+    assert!(input_value <= self.value());
+    let amount_to_amortize = self.value() - input_value;
+
+    // If any payments won't survive the reduction, set them to None
+    let mut amortized = 0;
+    'outer: while amounts.iter().any(Option::is_some) && (amortized < amount_to_amortize) {
+      let adjusted_fee = amount_to_amortize - amortized;
+      let amounts_len =
+        u64::try_from(amounts.iter().filter(|amount| amount.is_some()).count()).unwrap();
+      let per_payment_fee_check = adjusted_fee.div_ceil(amounts_len);
+
+      // Check each amount to see if it's not viable
+      let mut i = 0;
+      while i < amounts.len() {
+        if let Some(amount) = amounts[i] {
+          if amount.saturating_sub(per_payment_fee_check) < S::dust(coin).0 {
+            amounts[i] = None;
+            amortized += amount;
+            // If this amount wasn't viable, re-run with the new fee/amortization amounts
+            continue 'outer;
+          }
+        }
+        i += 1;
+      }
+
+      // Now that we have the payments which will survive, reduce them
+      for (i, amount) in amounts.iter_mut().enumerate() {
+        if let Some(amount) = amount {
+          *amount -= adjusted_fee / amounts_len;
+          if i < usize::try_from(adjusted_fee % amounts_len).unwrap() {
+            *amount -= 1;
+          }
+        }
+      }
+      break;
+    }
+
+    // Now that we have the reduced amounts, create the payments
+    let payments: Vec<_> = match self {
+      Self::Leaves { payments, .. } => {
+        payments
+          .iter()
+          .zip(amounts)
+          .filter_map(|(payment, amount)| {
+            amount.map(|amount| {
+              // The existing payment, with the new amount
+              Payment::new(
+                payment.address().clone(),
+                Balance { coin, amount: Amount(amount) },
+                payment.data().clone(),
+              )
+            })
+          })
+          .collect()
+      }
+      Self::Branch { .. } => {
+        amounts
+          .into_iter()
+          .filter_map(|amount| {
+            amount.map(|amount| {
+              // A branch output with the new amount
+              Payment::new(branch_address.clone(), Balance { coin, amount: Amount(amount) }, None)
+            })
+          })
+          .collect()
+      }
+    };
+
+    // Use None for vec![] so we never actually use vec![]
+    if payments.is_empty() {
+      None?;
+    }
+    Some(payments)
+  }
+}

processor/scheduler/utxo/standard/Cargo.toml

@@ -0,0 +1,35 @@
+[package]
+name = "serai-processor-utxo-scheduler"
+version = "0.1.0"
+description = "Scheduler for UTXO networks for the Serai processor"
+license = "AGPL-3.0-only"
+repository = "https://github.com/serai-dex/serai/tree/develop/processor/scheduler/utxo/standard"
+authors = ["Luke Parker <lukeparker5132@gmail.com>"]
+keywords = []
+edition = "2021"
+publish = false
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[package.metadata.cargo-machete]
+ignored = ["scale", "borsh"]
+
+[lints]
+workspace = true
+
+[dependencies]
+group = { version = "0.13", default-features = false }
+
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["std"] }
+borsh = { version = "1", default-features = false, features = ["std", "derive", "de_strict_order"] }
+
+serai-primitives = { path = "../../../../substrate/primitives", default-features = false, features = ["std"] }
+
+serai-db = { path = "../../../../common/db" }
+
+primitives = { package = "serai-processor-primitives", path = "../../../primitives" }
+scanner = { package = "serai-processor-scanner", path = "../../../scanner" }
+scheduler-primitives = { package = "serai-processor-scheduler-primitives", path = "../../primitives" }
+utxo-scheduler-primitives = { package = "serai-processor-utxo-scheduler-primitives", path = "../primitives" }

processor/scheduler/utxo/standard/LICENSE

@@ -0,0 +1,15 @@
+AGPL-3.0-only license
+
+Copyright (c) 2024 Luke Parker
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License Version 3 as
+published by the Free Software Foundation.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.

processor/scheduler/utxo/standard/README.md

@@ -0,0 +1,17 @@
+# UTXO Scheduler
+
+A scheduler of transactions for networks premised on the UTXO model.
+
+### Design
+
+The scheduler is designed to achieve fulfillment of all expected payments with
+an `O(1)` delay (regardless of prior scheduler state), `O(log n)` time, and
+`O(log(n) + n)` computational complexity.
+
+For the time/computational complexity, we use a tree to fulfill payments.
+This quickly gives us the ability to make as many outputs as necessary
+(regardless of per-transaction output limits) and only has the latency of
+including a chain of `O(log n)` transactions on-chain. The only computational
+overhead is in creating the transactions which are branches in the tree.
+Since we split off the root of the tree from a master output, the delay to start
+fulfillment is the delay for the master output to re-appear on-chain.

processor/scheduler/utxo/standard/src/db.rs

@@ -0,0 +1,113 @@
+use core::marker::PhantomData;
+
+use group::GroupEncoding;
+
+use serai_primitives::{Coin, Amount, Balance};
+
+use borsh::BorshDeserialize;
+use serai_db::{Get, DbTxn, create_db, db_channel};
+
+use primitives::{Payment, ReceivedOutput};
+use utxo_scheduler_primitives::TreeTransaction;
+use scanner::{ScannerFeed, KeyFor, AddressFor, OutputFor};
+
+create_db! {
+  UtxoScheduler {
+    OperatingCosts: (coin: Coin) -> Amount,
+    SerializedOutputs: (key: &[u8], coin: Coin) -> Vec<u8>,
+    SerializedQueuedPayments: (key: &[u8], coin: Coin) -> Vec<u8>,
+  }
+}
+
+db_channel! {
+  UtxoScheduler {
+    PendingBranch: (key: &[u8], balance: Balance) -> Vec<u8>,
+  }
+}
+
+pub(crate) struct Db<S: ScannerFeed>(PhantomData<S>);
+impl<S: ScannerFeed> Db<S> {
+  pub(crate) fn operating_costs(getter: &impl Get, coin: Coin) -> Amount {
+    OperatingCosts::get(getter, coin).unwrap_or(Amount(0))
+  }
+  pub(crate) fn set_operating_costs(txn: &mut impl DbTxn, coin: Coin, amount: Amount) {
+    OperatingCosts::set(txn, coin, &amount)
+  }
+
+  pub(crate) fn outputs(
+    getter: &impl Get,
+    key: KeyFor<S>,
+    coin: Coin,
+  ) -> Option<Vec<OutputFor<S>>> {
+    let buf = SerializedOutputs::get(getter, key.to_bytes().as_ref(), coin)?;
+    let mut buf = buf.as_slice();
+
+    let mut res = Vec::with_capacity(buf.len() / 128);
+    while !buf.is_empty() {
+      res.push(OutputFor::<S>::read(&mut buf).unwrap());
+    }
+    Some(res)
+  }
+  pub(crate) fn set_outputs(
+    txn: &mut impl DbTxn,
+    key: KeyFor<S>,
+    coin: Coin,
+    outputs: &[OutputFor<S>],
+  ) {
+    let mut buf = Vec::with_capacity(outputs.len() * 128);
+    for output in outputs {
+      output.write(&mut buf).unwrap();
+    }
+    SerializedOutputs::set(txn, key.to_bytes().as_ref(), coin, &buf);
+  }
+  pub(crate) fn del_outputs(txn: &mut impl DbTxn, key: KeyFor<S>, coin: Coin) {
+    SerializedOutputs::del(txn, key.to_bytes().as_ref(), coin);
+  }
+
+  pub(crate) fn queued_payments(
+    getter: &impl Get,
+    key: KeyFor<S>,
+    coin: Coin,
+  ) -> Option<Vec<Payment<AddressFor<S>>>> {
+    let buf = SerializedQueuedPayments::get(getter, key.to_bytes().as_ref(), coin)?;
+    let mut buf = buf.as_slice();
+
+    let mut res = Vec::with_capacity(buf.len() / 128);
+    while !buf.is_empty() {
+      res.push(Payment::read(&mut buf).unwrap());
+    }
+    Some(res)
+  }
+  pub(crate) fn set_queued_payments(
+    txn: &mut impl DbTxn,
+    key: KeyFor<S>,
+    coin: Coin,
+    queued: &[Payment<AddressFor<S>>],
+  ) {
+    let mut buf = Vec::with_capacity(queued.len() * 128);
+    for queued in queued {
+      queued.write(&mut buf).unwrap();
+    }
+    SerializedQueuedPayments::set(txn, key.to_bytes().as_ref(), coin, &buf);
+  }
+  pub(crate) fn del_queued_payments(txn: &mut impl DbTxn, key: KeyFor<S>, coin: Coin) {
+    SerializedQueuedPayments::del(txn, key.to_bytes().as_ref(), coin);
+  }
+
+  pub(crate) fn queue_pending_branch(
+    txn: &mut impl DbTxn,
+    key: KeyFor<S>,
+    balance: Balance,
+    child: &TreeTransaction<AddressFor<S>>,
+  ) {
+    PendingBranch::send(txn, key.to_bytes().as_ref(), balance, &borsh::to_vec(child).unwrap())
+  }
+  pub(crate) fn take_pending_branch(
+    txn: &mut impl DbTxn,
+    key: KeyFor<S>,
+    balance: Balance,
+  ) -> Option<TreeTransaction<AddressFor<S>>> {
+    PendingBranch::try_recv(txn, key.to_bytes().as_ref(), balance)
+      .map(|bytes| TreeTransaction::<AddressFor<S>>::deserialize(&mut bytes.as_slice()).unwrap())
+  }
+}

processor/scheduler/utxo/standard/src/lib.rs

@@ -0,0 +1,508 @@
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![doc = include_str!("../README.md")]
+#![deny(missing_docs)]
+
+use core::marker::PhantomData;
+use std::collections::HashMap;
+
+use group::GroupEncoding;
+
+use serai_primitives::{Coin, Amount, Balance};
+
+use serai_db::DbTxn;
+
+use primitives::{ReceivedOutput, Payment};
+use scanner::{
+  LifetimeStage, ScannerFeed, KeyFor, AddressFor, OutputFor, EventualityFor, BlockFor,
+  SchedulerUpdate, Scheduler as SchedulerTrait,
+};
+use scheduler_primitives::*;
+use utxo_scheduler_primitives::*;
+
+mod db;
+use db::Db;
+
+/// A scheduler of transactions for networks premised on the UTXO model.
+pub struct Scheduler<S: ScannerFeed, P: TransactionPlanner<S, ()>>(PhantomData<S>, PhantomData<P>);
+
+impl<S: ScannerFeed, P: TransactionPlanner<S, ()>> Scheduler<S, P> {
+  fn aggregate_inputs(
+    txn: &mut impl DbTxn,
+    block: &BlockFor<S>,
+    key_for_change: KeyFor<S>,
+    key: KeyFor<S>,
+    coin: Coin,
+  ) -> Vec<EventualityFor<S>> {
+    let mut eventualities = vec![];
+
+    let mut operating_costs = Db::<S>::operating_costs(txn, coin).0;
+    let mut outputs = Db::<S>::outputs(txn, key, coin).unwrap();
+    outputs.sort_by_key(|output| output.balance().amount.0);
+    while outputs.len() > P::MAX_INPUTS {
+      let to_aggregate = outputs.drain(.. P::MAX_INPUTS).collect::<Vec<_>>();
+
+      let Some(planned) = P::plan_transaction_with_fee_amortization(
+        &mut operating_costs,
+        P::fee_rate(block, coin),
+        to_aggregate,
+        vec![],
+        Some(key_for_change),
+      ) else {
+        continue;
+      };
+
+      TransactionsToSign::<P::SignableTransaction>::send(txn, &key, &planned.signable);
+      eventualities.push(planned.eventuality);
+    }
+
+    Db::<S>::set_outputs(txn, key, coin, &outputs);
+    Db::<S>::set_operating_costs(txn, coin, Amount(operating_costs));
+    eventualities
+  }
+
+  fn fulfillable_payments(
+    txn: &mut impl DbTxn,
+    operating_costs: &mut u64,
+    key: KeyFor<S>,
+    coin: Coin,
+    value_of_outputs: u64,
+  ) -> Vec<Payment<AddressFor<S>>> {
+    // Fetch all payments for this key
+    let mut payments = Db::<S>::queued_payments(txn, key, coin).unwrap();
+    if payments.is_empty() {
+      return vec![];
+    }
+
+    loop {
+      // inputs must be >= (payments - operating costs)
+      // Accordingly, (inputs + operating costs) must be >= payments
+      let value_fulfillable = value_of_outputs + *operating_costs;
+
+      // Drop to just the payments we can currently fulfill
+      {
+        let mut can_handle = 0;
+        let mut value_used = 0;
+        for payment in &payments {
+          value_used += payment.balance().amount.0;
+          if value_fulfillable < value_used {
+            break;
+          }
+          can_handle += 1;
+        }
+
+        let remaining_payments = payments.drain(can_handle ..).collect::<Vec<_>>();
+        // Restore the rest to the database
+        Db::<S>::set_queued_payments(txn, key, coin, &remaining_payments);
+      }
+
+      // If these payments are worth less than the operating costs, immediately drop them
+      let payments_value = payments.iter().map(|payment| payment.balance().amount.0).sum::<u64>();
+      if payments_value <= *operating_costs {
+        *operating_costs -= payments_value;
+        Db::<S>::set_operating_costs(txn, coin, Amount(*operating_costs));
+
+        // Reset payments to the queued payments
+        payments = Db::<S>::queued_payments(txn, key, coin).unwrap();
+        // If there's no more payments, stop looking for which payments we should fulfill
+        if payments.is_empty() {
+          return vec![];
+        }
+        // Find which of these we should handle
+        continue;
+      }
+
+      return payments;
+    }
+  }
+
+  fn queue_branches(
+    txn: &mut impl DbTxn,
+    key: KeyFor<S>,
+    coin: Coin,
+    effected_payments: Vec<Amount>,
+    tx: TreeTransaction<AddressFor<S>>,
+  ) {
+    match tx {
+      TreeTransaction::Leaves { .. } => {}
+      TreeTransaction::Branch { mut children, .. } => {
+        children.sort_by_key(TreeTransaction::value);
+        children.reverse();
+
+        /*
+          This may only be a subset of payments but it'll be the originally-highest-valued
+          payments. `zip` will truncate to the first children which will be the highest-valued
+          children thanks to our sort.
+        */
+        for (amount, child) in effected_payments.into_iter().zip(children) {
+          Db::<S>::queue_pending_branch(txn, key, Balance { coin, amount }, &child);
+        }
+      }
+    }
+  }
+
+  fn handle_branch(
+    txn: &mut impl DbTxn,
+    block: &BlockFor<S>,
+    eventualities: &mut Vec<EventualityFor<S>>,
+    output: OutputFor<S>,
+    tx: TreeTransaction<AddressFor<S>>,
+  ) -> bool {
+    let key = output.key();
+    let coin = output.balance().coin;
+    let Some(payments) = tx.payments::<S>(coin, &P::branch_address(key), output.balance().amount.0)
+    else {
+      // If this output has become too small to satisfy this branch, drop it
+      return false;
+    };
+
+    let Some(planned) = P::plan_transaction_with_fee_amortization(
+      // Uses 0 as there's no operating costs to incur/amortize here
+      &mut 0,
+      P::fee_rate(block, coin),
+      vec![output],
+      payments,
+      None,
+    ) else {
+      // This Branch isn't viable, so drop it (and its children)
+      return false;
+    };
+
+    TransactionsToSign::<P::SignableTransaction>::send(txn, &key, &planned.signable);
+    eventualities.push(planned.eventuality);
+
+    Self::queue_branches(txn, key, coin, planned.effected_payments, tx);
+
+    true
+  }
+
+  fn step(
+    txn: &mut impl DbTxn,
+    active_keys: &[(KeyFor<S>, LifetimeStage)],
+    block: &BlockFor<S>,
+    key: KeyFor<S>,
+  ) -> Vec<EventualityFor<S>> {
+    let mut eventualities = vec![];
+
+    let key_for_change = match active_keys[0].1 {
+      LifetimeStage::ActiveYetNotReporting => {
+        panic!("expected to fulfill payments despite not reporting for the oldest key")
+      }
+      LifetimeStage::Active => active_keys[0].0,
+      LifetimeStage::UsingNewForChange | LifetimeStage::Forwarding | LifetimeStage::Finishing => {
+        active_keys[1].0
+      }
+    };
+    let branch_address = P::branch_address(key);
+
+    'coin: for coin in S::NETWORK.coins() {
+      let coin = *coin;
+
+      // Perform any input aggregation we should
+      eventualities.append(&mut Self::aggregate_inputs(txn, block, key_for_change, key, coin));
+
+      // Fetch the operating costs/outputs
+      let mut operating_costs = Db::<S>::operating_costs(txn, coin).0;
+      let outputs = Db::<S>::outputs(txn, key, coin).unwrap();
+
+      // Fetch the fulfillable payments
+      let payments = Self::fulfillable_payments(
+        txn,
+        &mut operating_costs,
+        key,
+        coin,
+        outputs.iter().map(|output| output.balance().amount.0).sum(),
+      );
+      if payments.is_empty() {
+        continue;
+      }
+
+      // Create a tree to fulfill the payments
+      let mut tree = vec![P::tree(&payments)];
+
+      // Create the transaction for the root of the tree
+      // Try creating this transaction twice, once with a change output and once with increased
+      // operating costs to ensure a change output (as necessary to meet the requirements of the
+      // scanner API)
+      let mut planned_outer = None;
+      for i in 0 .. 2 {
+        let Some(planned) = P::plan_transaction_with_fee_amortization(
+          &mut operating_costs,
+          P::fee_rate(block, coin),
+          outputs.clone(),
+          tree[0]
+            .payments::<S>(coin, &branch_address, tree[0].value())
+            .expect("payments were dropped despite providing an input of the needed value"),
+          Some(key_for_change),
+        ) else {
+          // This should trip on the first iteration or not at all
+          assert_eq!(i, 0);
+          // This doesn't have inputs even worth aggregating so drop the entire tree
+          Db::<S>::set_operating_costs(txn, coin, Amount(operating_costs));
+          continue 'coin;
+        };
+
+        // If this doesn't have a change output, increase operating costs and try again
+        if !planned.has_change {
+          /*
+            Since we'll create a change output if it's worth at least dust, amortizing dust from
+            the payments should solve this. If the new transaction can't afford those operating
+            costs, then the payments should be amortized out, causing there to be a change or no
+            transaction at all.
+          */
+          operating_costs += S::dust(coin).0;
+          continue;
+        }
+
+        // Since this had a change output, move forward with it
+        planned_outer = Some(planned);
+        break;
+      }
+      let Some(planned) = planned_outer else {
+        panic!("couldn't create a tree root with a change output")
+      };
+      Db::<S>::set_operating_costs(txn, coin, Amount(operating_costs));
+      TransactionsToSign::<P::SignableTransaction>::send(txn, &key, &planned.signable);
+      eventualities.push(planned.eventuality);
+
+      // Now save the next layer of the tree to the database
+      // We'll execute it when it appears
+      Self::queue_branches(txn, key, coin, planned.effected_payments, tree.remove(0));
+    }
+
+    eventualities
+  }
+
+  fn flush_outputs(
+    txn: &mut impl DbTxn,
+    eventualities: &mut HashMap<Vec<u8>, Vec<EventualityFor<S>>>,
+    block: &BlockFor<S>,
+    from: KeyFor<S>,
+    to: KeyFor<S>,
+    coin: Coin,
+  ) {
+    let from_bytes = from.to_bytes().as_ref().to_vec();
+    // Ensure our inputs are aggregated
+    eventualities
+      .entry(from_bytes.clone())
+      .or_insert(vec![])
+      .append(&mut Self::aggregate_inputs(txn, block, to, from, coin));
+
+    // Now that our inputs are aggregated, transfer all of them to the new key
+    let mut operating_costs = Db::<S>::operating_costs(txn, coin).0;
+    let outputs = Db::<S>::outputs(txn, from, coin).unwrap();
+    if outputs.is_empty() {
+      return;
+    }
+    let planned = P::plan_transaction_with_fee_amortization(
+      &mut operating_costs,
+      P::fee_rate(block, coin),
+      outputs,
+      vec![],
+      Some(to),
+    );
+    Db::<S>::set_operating_costs(txn, coin, Amount(operating_costs));
+    let Some(planned) = planned else { return };
+
+    TransactionsToSign::<P::SignableTransaction>::send(txn, &from, &planned.signable);
+    eventualities.get_mut(&from_bytes).unwrap().push(planned.eventuality);
+  }
+}
+
+impl<S: ScannerFeed, P: TransactionPlanner<S, ()>> SchedulerTrait<S> for Scheduler<S, P> {
+  fn activate_key(txn: &mut impl DbTxn, key: KeyFor<S>) {
+    for coin in S::NETWORK.coins() {
+      assert!(Db::<S>::outputs(txn, key, *coin).is_none());
+      Db::<S>::set_outputs(txn, key, *coin, &[]);
+      assert!(Db::<S>::queued_payments(txn, key, *coin).is_none());
+      Db::<S>::set_queued_payments(txn, key, *coin, &[]);
+    }
+  }
+
+  fn flush_key(
+    txn: &mut impl DbTxn,
+    block: &BlockFor<S>,
+    retiring_key: KeyFor<S>,
+    new_key: KeyFor<S>,
+  ) -> HashMap<Vec<u8>, Vec<EventualityFor<S>>> {
+    let mut eventualities = HashMap::new();
+    for coin in S::NETWORK.coins() {
+      // Move the payments to the new key
+      {
+        let still_queued = Db::<S>::queued_payments(txn, retiring_key, *coin).unwrap();
+        let mut new_queued = Db::<S>::queued_payments(txn, new_key, *coin).unwrap();
+
+        let mut queued = still_queued;
+        queued.append(&mut new_queued);
+
+        Db::<S>::set_queued_payments(txn, retiring_key, *coin, &[]);
+        Db::<S>::set_queued_payments(txn, new_key, *coin, &queued);
+      }
+
+      // Move the outputs to the new key
+      Self::flush_outputs(txn, &mut eventualities, block, retiring_key, new_key, *coin);
+    }
+    eventualities
+  }
+
+  fn retire_key(txn: &mut impl DbTxn, key: KeyFor<S>) {
+    for coin in S::NETWORK.coins() {
+      assert!(Db::<S>::outputs(txn, key, *coin).unwrap().is_empty());
+      Db::<S>::del_outputs(txn, key, *coin);
+      assert!(Db::<S>::queued_payments(txn, key, *coin).unwrap().is_empty());
+      Db::<S>::del_queued_payments(txn, key, *coin);
+    }
+  }
+
+  fn update(
+    txn: &mut impl DbTxn,
+    block: &BlockFor<S>,
+    active_keys: &[(KeyFor<S>, LifetimeStage)],
+    update: SchedulerUpdate<S>,
+  ) -> HashMap<Vec<u8>, Vec<EventualityFor<S>>> {
+    let mut eventualities = HashMap::new();
+
+    // Accumulate the new outputs
+    {
+      let mut outputs_by_key = HashMap::new();
+      for output in update.outputs() {
+        // If this aligns for a branch, handle it
+        if let Some(branch) = Db::<S>::take_pending_branch(txn, output.key(), output.balance()) {
+          if Self::handle_branch(
+            txn,
+            block,
+            eventualities.entry(output.key().to_bytes().as_ref().to_vec()).or_insert(vec![]),
+            output.clone(),
+            branch,
+          ) {
+            // If we could use it for a branch, we do and move on
+            // Else, we let it be accumulated by the standard accumulation code
+            continue;
+          }
+        }
+
+        let coin = output.balance().coin;
+        outputs_by_key
+          // Index by key and coin
+          .entry((output.key().to_bytes().as_ref().to_vec(), coin))
+          // If we haven't accumulated here prior, read the outputs from the database
+          .or_insert_with(|| (output.key(), Db::<S>::outputs(txn, output.key(), coin).unwrap()))
+          .1
+          .push(output.clone());
+      }
+      // Write the outputs back to the database
+      for ((_key_vec, coin), (key, outputs)) in outputs_by_key {
+        Db::<S>::set_outputs(txn, key, coin, &outputs);
+      }
+    }
+
+    // Fulfill the payments we prior couldn't
+    for (key, _stage) in active_keys {
+      eventualities
+        .entry(key.to_bytes().as_ref().to_vec())
+        .or_insert(vec![])
+        .append(&mut Self::step(txn, active_keys, block, *key));
+    }
+
+    // If this key has been flushed, forward all outputs
+    match active_keys[0].1 {
+      LifetimeStage::ActiveYetNotReporting |
+      LifetimeStage::Active |
+      LifetimeStage::UsingNewForChange => {}
+      LifetimeStage::Forwarding | LifetimeStage::Finishing => {
+        for coin in S::NETWORK.coins() {
+          Self::flush_outputs(
+            txn,
+            &mut eventualities,
+            block,
+            active_keys[0].0,
+            active_keys[1].0,
+            *coin,
+          );
+        }
+      }
+    }
+
+    // Create the transactions for the forwards/burns
+    {
+      let mut planned_txs = vec![];
+      for forward in update.forwards() {
+        let key = forward.key();
+
+        assert_eq!(active_keys.len(), 2);
+        assert_eq!(active_keys[0].1, LifetimeStage::Forwarding);
+        assert_eq!(active_keys[1].1, LifetimeStage::Active);
+        let forward_to_key = active_keys[1].0;
+
+        let Some(plan) = P::plan_transaction_with_fee_amortization(
+          // This uses 0 for the operating costs as we don't incur any here
+          // If the output can't pay for itself to be forwarded, we simply drop it
+          &mut 0,
+          P::fee_rate(block, forward.balance().coin),
+          vec![forward.clone()],
+          vec![Payment::new(P::forwarding_address(forward_to_key), forward.balance(), None)],
+          None,
+        ) else {
+          continue;
+        };
+        planned_txs.push((key, plan));
+      }
+      for to_return in update.returns() {
+        let key = to_return.output().key();
+        let out_instruction =
+          Payment::new(to_return.address().clone(), to_return.output().balance(), None);
+        let Some(plan) = P::plan_transaction_with_fee_amortization(
+          // This uses 0 for the operating costs as we don't incur any here
+          // If the output can't pay for itself to be returned, we simply drop it
+          &mut 0,
+          P::fee_rate(block, out_instruction.balance().coin),
+          vec![to_return.output().clone()],
+          vec![out_instruction],
+          None,
+        ) else {
+          continue;
+        };
+        planned_txs.push((key, plan));
+      }
+
+      for (key, planned_tx) in planned_txs {
+        // Send the transactions off for signing
+        TransactionsToSign::<P::SignableTransaction>::send(txn, &key, &planned_tx.signable);
+
+        // Insert the Eventualities into the result
+        eventualities.get_mut(key.to_bytes().as_ref()).unwrap().push(planned_tx.eventuality);
+      }
+
+      eventualities
+    }
+  }
+
+  fn fulfill(
+    txn: &mut impl DbTxn,
+    block: &BlockFor<S>,
+    active_keys: &[(KeyFor<S>, LifetimeStage)],
+    payments: Vec<Payment<AddressFor<S>>>,
+  ) -> HashMap<Vec<u8>, Vec<EventualityFor<S>>> {
+    // Find the key to filfill these payments with
+    let fulfillment_key = match active_keys[0].1 {
+      LifetimeStage::ActiveYetNotReporting => {
+        panic!("expected to fulfill payments despite not reporting for the oldest key")
+      }
+      LifetimeStage::Active | LifetimeStage::UsingNewForChange => active_keys[0].0,
+      LifetimeStage::Forwarding | LifetimeStage::Finishing => active_keys[1].0,
+    };
+
+    // Queue the payments for this key
+    for coin in S::NETWORK.coins() {
+      let mut queued_payments = Db::<S>::queued_payments(txn, fulfillment_key, *coin).unwrap();
+      queued_payments
+        .extend(payments.iter().filter(|payment| payment.balance().coin == *coin).cloned());
+      Db::<S>::set_queued_payments(txn, fulfillment_key, *coin, &queued_payments);
+    }
+
+    // Handle the queued payments
+    HashMap::from([(
+      fulfillment_key.to_bytes().as_ref().to_vec(),
+      Self::step(txn, active_keys, block, fulfillment_key),
+    )])
+  }
+}

processor/scheduler/utxo/transaction-chaining/README.md

@@ -9,7 +9,7 @@ to build and sign a transaction spending it.
 
 The scheduler is designed to achieve fulfillment of all expected payments with
 an `O(1)` delay (regardless of prior scheduler state), `O(log n)` time, and
-`O(n)` computational complexity.
+`O(log(n) + n)` computational complexity.
 
 Due to the ability to chain transactions, we can immediately plan/sign dependent
 transactions. For the time/computational complexity, we use a tree to fulfill

processor/scheduler/utxo/transaction-chaining/src/lib.rs

@@ -7,7 +7,7 @@ use std::collections::HashMap;
 
 use group::GroupEncoding;
 
-use serai_primitives::{Coin, Amount, Balance};
+use serai_primitives::{Coin, Amount};
 
 use serai_db::DbTxn;
 
@@ -22,114 +22,6 @@ use utxo_scheduler_primitives::*;
 mod db;
 use db::Db;
 
-#[derive(Clone)]
-enum TreeTransaction<S: ScannerFeed> {
-  Leaves { payments: Vec<Payment<AddressFor<S>>>, value: u64 },
-  Branch { children: Vec<Self>, value: u64 },
-}
-impl<S: ScannerFeed> TreeTransaction<S> {
-  fn children(&self) -> usize {
-    match self {
-      Self::Leaves { payments, .. } => payments.len(),
-      Self::Branch { children, .. } => children.len(),
-    }
-  }
-  fn value(&self) -> u64 {
-    match self {
-      Self::Leaves { value, .. } | Self::Branch { value, .. } => *value,
-    }
-  }
-  fn payments(
-    &self,
-    coin: Coin,
-    branch_address: &AddressFor<S>,
-    input_value: u64,
-  ) -> Option<Vec<Payment<AddressFor<S>>>> {
-    // Fetch the amounts for the payments we'll make
-    let mut amounts: Vec<_> = match self {
-      Self::Leaves { payments, .. } => {
-        payments.iter().map(|payment| Some(payment.balance().amount.0)).collect()
-      }
-      Self::Branch { children, .. } => children.iter().map(|child| Some(child.value())).collect(),
-    };
-
-    // We need to reduce them so their sum is our input value
-    assert!(input_value <= self.value());
-    let amount_to_amortize = self.value() - input_value;
-
-    // If any payments won't survive the reduction, set them to None
-    let mut amortized = 0;
-    'outer: while amounts.iter().any(Option::is_some) && (amortized < amount_to_amortize) {
-      let adjusted_fee = amount_to_amortize - amortized;
-      let amounts_len =
-        u64::try_from(amounts.iter().filter(|amount| amount.is_some()).count()).unwrap();
-      let per_payment_fee_check = adjusted_fee.div_ceil(amounts_len);
-
-      // Check each amount to see if it's not viable
-      let mut i = 0;
-      while i < amounts.len() {
-        if let Some(amount) = amounts[i] {
-          if amount.saturating_sub(per_payment_fee_check) < S::dust(coin).0 {
-            amounts[i] = None;
-            amortized += amount;
-            // If this amount wasn't viable, re-run with the new fee/amortization amounts
-            continue 'outer;
-          }
-        }
-        i += 1;
-      }
-
-      // Now that we have the payments which will survive, reduce them
-      for (i, amount) in amounts.iter_mut().enumerate() {
-        if let Some(amount) = amount {
-          *amount -= adjusted_fee / amounts_len;
-          if i < usize::try_from(adjusted_fee % amounts_len).unwrap() {
-            *amount -= 1;
-          }
-        }
-      }
-      break;
-    }
-
-    // Now that we have the reduced amounts, create the payments
-    let payments: Vec<_> = match self {
-      Self::Leaves { payments, .. } => {
-        payments
-          .iter()
-          .zip(amounts)
-          .filter_map(|(payment, amount)| {
-            amount.map(|amount| {
-              // The existing payment, with the new amount
-              Payment::new(
-                payment.address().clone(),
-                Balance { coin, amount: Amount(amount) },
-                payment.data().clone(),
-              )
-            })
-          })
-          .collect()
-      }
-      Self::Branch { .. } => {
-        amounts
-          .into_iter()
-          .filter_map(|amount| {
-            amount.map(|amount| {
-              // A branch output with the new amount
-              Payment::new(branch_address.clone(), Balance { coin, amount: Amount(amount) }, None)
-            })
-          })
-          .collect()
-      }
-    };
-
-    // Use None for vec![] so we never actually use vec![]
-    if payments.is_empty() {
-      None?;
-    }
-    Some(payments)
-  }
-}
-
 /// The outputs which will be effected by a PlannedTransaction and received by Serai.
 pub struct EffectedReceivedOutputs<S: ScannerFeed>(Vec<OutputFor<S>>);
 
@@ -306,30 +198,8 @@ impl<S: ScannerFeed, P: TransactionPlanner<S, EffectedReceivedOutputs<S>>> Sched
         assert!(Db::<S>::queued_payments(txn, key, coin).unwrap().is_empty());
       }
 
-      // Create a tree to fulfillthe payments
+      // Create a tree to fulfill the payments
-      // This variable is for the current layer of the tree being built
+      let mut tree = vec![P::tree(&payments)];
-      let mut tree = Vec::with_capacity(payments.len().div_ceil(P::MAX_OUTPUTS));
-
-      // Push the branches for the leaves (the payments out)
-      for payments in payments.chunks(P::MAX_OUTPUTS) {
-        let value = payments.iter().map(|payment| payment.balance().amount.0).sum::<u64>();
-        tree.push(TreeTransaction::<S>::Leaves { payments: payments.to_vec(), value });
-      }
-
-      // While we haven't calculated a tree root, or the tree root doesn't support a change output,
-      // keep working
-      while (tree.len() != 1) || (tree[0].children() == P::MAX_OUTPUTS) {
-        let mut branch_layer = vec![];
-        for children in tree.chunks(P::MAX_OUTPUTS) {
-          branch_layer.push(TreeTransaction::<S>::Branch {
-            children: children.to_vec(),
-            value: children.iter().map(TreeTransaction::value).sum(),
-          });
-        }
-        tree = branch_layer;
-      }
-      assert_eq!(tree.len(), 1);
-      assert!((tree[0].children() + 1) <= P::MAX_OUTPUTS);
 
       // Create the transaction for the root of the tree
       let mut branch_outputs = {
@@ -343,7 +213,7 @@ impl<S: ScannerFeed, P: TransactionPlanner<S, EffectedReceivedOutputs<S>>> Sched
             P::fee_rate(block, coin),
             outputs.clone(),
             tree[0]
-              .payments(coin, &branch_address, tree[0].value())
+              .payments::<S>(coin, &branch_address, tree[0].value())
               .expect("payments were dropped despite providing an input of the needed value"),
             Some(key_for_change),
           ) else {
@@ -355,7 +225,7 @@ impl<S: ScannerFeed, P: TransactionPlanner<S, EffectedReceivedOutputs<S>>> Sched
           };
 
           // If this doesn't have a change output, increase operating costs and try again
-          if !planned.auxilliary.0.iter().any(|output| output.kind() == OutputType::Change) {
+          if !planned.has_change {
             /*
               Since we'll create a change output if it's worth at least dust, amortizing dust from
               the payments should solve this. If the new transaction can't afford those operating
@@ -399,11 +269,13 @@ impl<S: ScannerFeed, P: TransactionPlanner<S, EffectedReceivedOutputs<S>>> Sched
         TreeTransaction::Branch { children, .. } => children,
       };
       while !tree.is_empty() {
-        // Sort the branch outputs by their value
+        // Sort the branch outputs by their value (high to low)
         branch_outputs.sort_by_key(|a| a.balance().amount.0);
+        branch_outputs.reverse();
         // Sort the transactions we should create by their value so they share an order with the
         // branch outputs
         tree.sort_by_key(TreeTransaction::value);
+        tree.reverse();
 
         // If we dropped any Branch outputs, drop the associated children
         tree.truncate(branch_outputs.len());
@@ -417,7 +289,8 @@ impl<S: ScannerFeed, P: TransactionPlanner<S, EffectedReceivedOutputs<S>>> Sched
         for (branch_output, tx) in branch_outputs_for_this_layer.into_iter().zip(this_layer) {
           assert_eq!(branch_output.kind(), OutputType::Branch);
 
-          let Some(payments) = tx.payments(coin, &branch_address, branch_output.balance().amount.0)
+          let Some(payments) =
+            tx.payments::<S>(coin, &branch_address, branch_output.balance().amount.0)
           else {
             // If this output has become too small to satisfy this branch, drop it
             continue;
@@ -550,8 +423,9 @@ impl<S: ScannerFeed, P: TransactionPlanner<S, EffectedReceivedOutputs<S>>> Sched
     // Fulfill the payments we prior couldn't
     let mut eventualities = HashMap::new();
     for (key, _stage) in active_keys {
-      eventualities
+      assert!(eventualities
-        .insert(key.to_bytes().as_ref().to_vec(), Self::step(txn, active_keys, block, *key));
+        .insert(key.to_bytes().as_ref().to_vec(), Self::step(txn, active_keys, block, *key))
+        .is_none());
     }
 
     // If this key has been flushed, forward all outputs