WIP

Author: evanlinjin

src/coin_control.rs

@@ -0,0 +1,229 @@
+use core::{convert::Infallible, fmt::Display};
+
+use crate::{
+    collections::{BTreeMap, HashMap, HashSet},
+    Input, InputCandidates, InputGroup, InputStatus,
+};
+use alloc::vec::Vec;
+use bdk_chain::{BlockId, ChainOracle, ConfirmationBlockTime, TxGraph};
+use bitcoin::{absolute, OutPoint, Txid};
+use miniscript::{bitcoin, plan::Plan};
+
+/// Coin control.
+///
+/// Builds the set of input candidates.
+/// Tries to ensure that all candidates are part of a consistent view of history.
+///
+/// Does not check ownership of coins before placing them in candidate set.
+#[must_use]
+pub struct CoinControl<'g, C> {
+    /// Chain Oracle.
+    chain: &'g C,
+    /// Consistent chain tip.
+    chain_tip: BlockId,
+
+    /// Tx graph.
+    tx_graph: &'g TxGraph<ConfirmationBlockTime>,
+    /// Stops the caller from adding inputs (local or foreign) that are definitely not canonical.
+    ///
+    /// This is not a perfect check for callers that add foreign inputs, or if the caller's
+    /// `TxGraph` has incomplete information. However, this will stop most unintended double-spends
+    /// and/or money-printing-txs.
+    canonical: HashSet<Txid>,
+
+    /// All candidates.
+    candidate_inputs: HashMap<OutPoint, Input>,
+    ///// Maintains candidate order.
+    //pub order: VecDeque<OutPoint>,
+    /// Excluded stuff goes here.
+    excluded_inputs: HashMap<OutPoint, ExcludeInputReason>,
+}
+
+/// ExcludedReason.
+#[derive(Debug, Clone)]
+pub enum ExcludeInputReason {
+    /// Cannot find outpoint in the graph.
+    DoesNotExist,
+    /// Input already spent.
+    AlreadySpent,
+    /// Input spends from an output that is not canonical.
+    NotCanonical,
+}
+
+impl Display for ExcludeInputReason {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            ExcludeInputReason::DoesNotExist => {
+                write!(f, "outpoint does not exist")
+            }
+            ExcludeInputReason::AlreadySpent => {
+                write!(f, "including this input is a double spend")
+            }
+            ExcludeInputReason::NotCanonical => {
+                write!(f, "outpoint is in tx that is not canonical")
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for ExcludeInputReason {}
+
+impl<'g, C: ChainOracle<Error = Infallible>> CoinControl<'g, C> {
+    /// New
+    ///
+    /// TODO: Replace `to_exclude` with `CanonicalizationParams` when that is available.
+    pub fn new(
+        tx_graph: &'g TxGraph<ConfirmationBlockTime>,
+        chain: &'g C,
+        chain_tip: BlockId,
+        replace: impl IntoIterator<Item = Txid>,
+    ) -> Self {
+        let mut canonical = tx_graph
+            .canonical_iter(chain, chain_tip)
+            .map(|r| r.expect("infallible"))
+            .map(|(txid, _, _)| txid)
+            .collect::<HashSet<Txid>>();
+        let exclude = replace
+            .into_iter()
+            .filter_map(|txid| tx_graph.get_tx(txid))
+            .flat_map(|tx| {
+                tx_graph
+                    .walk_conflicts(&tx, move |_, txid| Some(txid))
+                    .collect::<Vec<_>>()
+            });
+        for txid in exclude {
+            canonical.remove(&txid);
+        }
+        Self {
+            tx_graph,
+            chain,
+            canonical,
+            chain_tip,
+            candidate_inputs: HashMap::new(),
+            excluded_inputs: HashMap::new(),
+        }
+    }
+
+    /// Try include the given input.
+    pub fn try_include_input(&mut self, outpoint: OutPoint, plan: Plan) -> &mut Self {
+        match self._try_include_input(outpoint, plan) {
+            Ok(_) => self.excluded_inputs.remove(&outpoint),
+            Err(err) => self.excluded_inputs.insert(outpoint, err),
+        };
+        self
+    }
+
+    /// Try include the given inputs.
+    pub fn try_include_inputs<I>(&mut self, inputs: I) -> &mut Self
+    where
+        I: IntoIterator<Item = (OutPoint, Plan)>,
+    {
+        for (outpoint, plan) in inputs {
+            self.try_include_input(outpoint, plan);
+        }
+        self
+    }
+
+    fn _try_include_input(
+        &mut self,
+        outpoint: OutPoint,
+        plan: Plan,
+    ) -> Result<(), ExcludeInputReason> {
+        let tx_node = self
+            .tx_graph
+            .get_tx_node(outpoint.txid)
+            .ok_or(ExcludeInputReason::DoesNotExist)?;
+        if self.canonical.contains(&tx_node.txid) {
+            return Err(ExcludeInputReason::NotCanonical);
+        }
+        if self.is_spent(outpoint) {
+            return Err(ExcludeInputReason::AlreadySpent);
+        }
+
+        let status = tx_node
+            .anchors
+            .iter()
+            .find(|anchor| {
+                self.chain
+                    .is_block_in_chain(anchor.block_id, self.chain_tip)
+                    .expect("infallible")
+                    .unwrap_or(false)
+            })
+            .map(|anchor| InputStatus {
+                height: absolute::Height::from_consensus(anchor.block_id.height)
+                    .expect("height must not overflow"),
+                time: absolute::Time::from_consensus(anchor.confirmation_time as u32)
+                    .expect("time must not overflow"),
+            });
+
+        let input = Input::from_prev_tx(
+            plan,
+            tx_node.tx,
+            outpoint.vout.try_into().expect("u32 must fit into usize"),
+            status,
+        )
+        .map_err(|_| ExcludeInputReason::DoesNotExist)?;
+
+        self.candidate_inputs.insert(outpoint, input);
+        Ok(())
+    }
+
+    /// Whether the outpoint is spent already.
+    ///
+    /// Spent outputs cannot be candidates for coin selection.
+    fn is_spent(&self, outpoint: OutPoint) -> bool {
+        self.tx_graph
+            .outspends(outpoint)
+            .iter()
+            .any(|txid| self.canonical.contains(txid))
+    }
+
+    /// Map of excluded inputs and their exclusion reasons.
+    pub fn excluded(&self) -> &HashMap<OutPoint, ExcludeInputReason> {
+        &self.excluded_inputs
+    }
+
+    /// Into candidates.
+    pub fn into_candidates<G: Ord>(
+        self,
+        group_policy: impl Fn(&Input) -> G,
+        filter_policy: impl Fn(&InputGroup) -> bool,
+    ) -> InputCandidates {
+        let mut group_map = BTreeMap::<G, InputGroup>::new();
+        for input in self.candidate_inputs.into_values() {
+            let group_key = group_policy(&input);
+            use std::collections::btree_map::Entry;
+            match group_map.entry(group_key) {
+                Entry::Vacant(entry) => {
+                    entry.insert(InputGroup::from_input(input));
+                }
+                Entry::Occupied(mut entry) => entry.get_mut().push(input),
+            };
+        }
+        InputCandidates::new(None, group_map.into_values().filter(filter_policy))
+    }
+}
+
+/// Default group policy.
+pub fn group_by_spk() -> impl Fn(&Input) -> bitcoin::ScriptBuf {
+    |input| input.prev_txout().script_pubkey.clone()
+}
+
+/// No grouping.
+pub fn no_grouping() -> impl Fn(&Input) -> OutPoint {
+    |input| input.prev_outpoint()
+}
+
+/// Filter out inputs that cannot be spent now.
+pub fn filter_unspendable_now(
+    tip_height: absolute::Height,
+    tip_time: absolute::Time,
+) -> impl Fn(&InputGroup) -> bool {
+    move |group| group.is_spendable_now(tip_height, tip_time)
+}
+
+/// No filtering.
+pub fn no_filtering() -> impl Fn(&InputGroup) -> bool {
+    |_| true
+}