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Canonicalization should handle transactions that spend from two conflicting transactions #1917

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Merged
merged 1 commit into from
Apr 23, 2025
Merged

Canonicalization should handle transactions that spend from two conflicting transactions #1917

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71 changes: 57 additions & 14 deletions crates/chain/src/canonical_iter.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,12 +1,16 @@
use crate::collections::{hash_map, HashMap, HashSet, VecDeque};
use crate::collections::{HashMap, HashSet, VecDeque};
use crate::tx_graph::{TxAncestors, TxDescendants};
use crate::{Anchor, ChainOracle, TxGraph};
use alloc::boxed::Box;
use alloc::collections::BTreeSet;
use alloc::sync::Arc;
use alloc::vec::Vec;
use bdk_core::BlockId;
use bitcoin::{Transaction, Txid};

type CanonicalMap<A> = HashMap<Txid, (Arc<Transaction>, CanonicalReason<A>)>;
type NotCanonicalSet = HashSet<Txid>;

/// Iterates over canonical txs.
pub struct CanonicalIter<'g, A, C> {
tx_graph: &'g TxGraph<A>,
Expand All @@ -18,8 +22,8 @@ pub struct CanonicalIter<'g, A, C> {
unprocessed_txs_with_last_seens: Box<dyn Iterator<Item = (Txid, Arc<Transaction>, u64)> + 'g>,
unprocessed_txs_left_over: VecDeque<(Txid, Arc<Transaction>, u32)>,

canonical: HashMap<Txid, (Arc<Transaction>, CanonicalReason<A>)>,
not_canonical: HashSet<Txid>,
canonical: CanonicalMap<A>,
not_canonical: NotCanonicalSet,

queue: VecDeque<Txid>,
}
Expand Down Expand Up @@ -87,27 +91,49 @@ impl<'g, A: Anchor, C: ChainOracle> CanonicalIter<'g, A, C> {
Ok(())
}

/// Marks a transaction and it's ancestors as canonical. Mark all conflicts of these as
/// Marks `tx` and it's ancestors as canonical and mark all conflicts of these as
/// `not_canonical`.
///
/// The exception is when it is discovered that `tx` double spends itself (i.e. two of it's
/// inputs conflict with each other), then no changes will be made.
///
/// The logic works by having two loops where one is nested in another.
/// * The outer loop iterates through ancestors of `tx` (including `tx`). We can transitively
/// assume that all ancestors of `tx` are also canonical.
/// * The inner loop loops through conflicts of ancestors of `tx`. Any descendants of conflicts
/// are also conflicts and are transitively considered non-canonical.
///
/// If the inner loop ends up marking `tx` as non-canonical, then we know that it double spends
/// itself.
fn mark_canonical(&mut self, txid: Txid, tx: Arc<Transaction>, reason: CanonicalReason<A>) {
let starting_txid = txid;
let mut is_root = true;
TxAncestors::new_include_root(
let mut is_starting_tx = true;

// We keep track of changes made so far so that we can undo it later in case we detect that
// `tx` double spends itself.
let mut detected_self_double_spend = false;
let mut undo_not_canonical = Vec::<Txid>::new();

// `staged_queue` doubles as the `undo_canonical` data.
let staged_queue = TxAncestors::new_include_root(
self.tx_graph,
tx,
|_: usize, tx: Arc<Transaction>| -> Option<()> {
|_: usize, tx: Arc<Transaction>| -> Option<Txid> {
let this_txid = tx.compute_txid();
let this_reason = if is_root {
is_root = false;
let this_reason = if is_starting_tx {
is_starting_tx = false;
reason.clone()
} else {
reason.to_transitive(starting_txid)
};

use crate::collections::hash_map::Entry;
let canonical_entry = match self.canonical.entry(this_txid) {
// Already visited tx before, exit early.
hash_map::Entry::Occupied(_) => return None,
hash_map::Entry::Vacant(entry) => entry,
Entry::Occupied(_) => return None,
Entry::Vacant(entry) => entry,
};

// Any conflicts with a canonical tx can be added to `not_canonical`. Descendants
// of `not_canonical` txs can also be added to `not_canonical`.
for (_, conflict_txid) in self.tx_graph.direct_conflicts(&tx) {
Expand All @@ -116,6 +142,7 @@ impl<'g, A: Anchor, C: ChainOracle> CanonicalIter<'g, A, C> {
conflict_txid,
|_: usize, txid: Txid| -> Option<()> {
if self.not_canonical.insert(txid) {
undo_not_canonical.push(txid);
Some(())
} else {
None
Expand All @@ -124,12 +151,28 @@ impl<'g, A: Anchor, C: ChainOracle> CanonicalIter<'g, A, C> {
)
.run_until_finished()
}

if self.not_canonical.contains(&this_txid) {
// Early exit if self-double-spend is detected.
detected_self_double_spend = true;
return None;
}
canonical_entry.insert((tx, this_reason));
self.queue.push_back(this_txid);
Some(())
Some(this_txid)
},
)
.run_until_finished()
.collect::<Vec<Txid>>();

if detected_self_double_spend {
for txid in staged_queue {
self.canonical.remove(&txid);
}
for txid in undo_not_canonical {
self.not_canonical.remove(&txid);
}
} else {
self.queue.extend(staged_queue);
}
}
}

Expand Down
106 changes: 105 additions & 1 deletion crates/chain/tests/test_tx_graph_conflicts.rs
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -686,7 +686,111 @@ fn test_tx_conflict_handling() {
exp_chain_txouts: HashSet::from([("tx", 0)]),
exp_unspents: HashSet::from([("tx", 0)]),
exp_balance: Balance { trusted_pending: Amount::from_sat(9000), ..Default::default() }
}
},
Scenario {
name: "tx spends from 2 conflicting transactions where a conflict spends another",
tx_templates: &[
TxTemplate {
tx_name: "A",
inputs: &[TxInTemplate::Bogus],
outputs: &[TxOutTemplate::new(10_000, None)],
last_seen: Some(1),
..Default::default()
},
TxTemplate {
tx_name: "S1",
inputs: &[TxInTemplate::PrevTx("A", 0)],
outputs: &[TxOutTemplate::new(9_000, None)],
last_seen: Some(2),
..Default::default()
},
TxTemplate {
tx_name: "S2",
inputs: &[TxInTemplate::PrevTx("A", 0), TxInTemplate::PrevTx("S1", 0)],
outputs: &[TxOutTemplate::new(17_000, None)],
last_seen: Some(3),
..Default::default()
},
],
exp_chain_txs: HashSet::from(["A", "S1"]),
exp_chain_txouts: HashSet::from([]),
exp_unspents: HashSet::from([]),
exp_balance: Balance::default(),
},
Scenario {
name: "tx spends from 2 conflicting transactions where the conflict is nested",
tx_templates: &[
TxTemplate {
tx_name: "A",
inputs: &[TxInTemplate::Bogus],
outputs: &[TxOutTemplate::new(10_000, Some(0))],
last_seen: Some(1),
..Default::default()
},
TxTemplate {
tx_name: "S1",
inputs: &[TxInTemplate::PrevTx("A", 0)],
outputs: &[TxOutTemplate::new(9_000, Some(0))],
last_seen: Some(3),
..Default::default()
},
TxTemplate {
tx_name: "B",
inputs: &[TxInTemplate::PrevTx("S1", 0)],
outputs: &[TxOutTemplate::new(8_000, Some(0))],
last_seen: Some(2),
..Default::default()
},
TxTemplate {
tx_name: "S2",
inputs: &[TxInTemplate::PrevTx("B", 0), TxInTemplate::PrevTx("A", 0)],
outputs: &[TxOutTemplate::new(17_000, Some(0))],
last_seen: Some(4),
..Default::default()
},
],
exp_chain_txs: HashSet::from(["A", "S1", "B"]),
exp_chain_txouts: HashSet::from([("A", 0), ("B", 0), ("S1", 0)]),
exp_unspents: HashSet::from([("B", 0)]),
exp_balance: Balance { trusted_pending: Amount::from_sat(8_000), ..Default::default() },
},
Scenario {
name: "tx spends from 2 conflicting transactions where the conflict is nested (different last_seens)",
tx_templates: &[
TxTemplate {
tx_name: "A",
inputs: &[TxInTemplate::Bogus],
outputs: &[TxOutTemplate::new(10_000, Some(0))],
last_seen: Some(1),
..Default::default()
},
TxTemplate {
tx_name: "S1",
inputs: &[TxInTemplate::PrevTx("A", 0)],
outputs: &[TxOutTemplate::new(9_000, Some(0))],
last_seen: Some(4),
..Default::default()
},
TxTemplate {
tx_name: "B",
inputs: &[TxInTemplate::PrevTx("S1", 0)],
outputs: &[TxOutTemplate::new(8_000, Some(0))],
last_seen: Some(2),
..Default::default()
},
TxTemplate {
tx_name: "S2",
inputs: &[TxInTemplate::PrevTx("A", 0), TxInTemplate::PrevTx("B", 0)],
outputs: &[TxOutTemplate::new(17_000, Some(0))],
last_seen: Some(3),
..Default::default()
},
],
exp_chain_txs: HashSet::from(["A", "S1", "B"]),
exp_chain_txouts: HashSet::from([("A", 0), ("B", 0), ("S1", 0)]),
exp_unspents: HashSet::from([("B", 0)]),
exp_balance: Balance { trusted_pending: Amount::from_sat(8_000), ..Default::default() },
},
];

for scenario in scenarios {
Expand Down
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