feat(chain): Signed txs should displace unsigned txs in TxGraph.

Author: evanlinjin

crates/chain/src/tx_graph.rs

@@ -624,11 +624,20 @@ impl<A: Anchor> TxGraph<A> {
         let tx_node = self.txs.entry(txid).or_default();
         match tx_node {
             TxNodeInternal::Whole(existing_tx) => {
-                debug_assert_eq!(
-                    existing_tx.as_ref(),
-                    tx.as_ref(),
-                    "tx of same txid should never change"
-                );
+                // We want to be able to replace an unsigned tx with a signed tx.
+                // The tx with more weight has precedence (and tiebreak with the actual tx data).
+                // We can also check whether the witness is valid and also prioritize signatures
+                // with less weight, but that is more work and this solution is good enough.
+                if existing_tx.as_ref() != tx.as_ref() {
+                    let (_, tx_with_precedence) = Ord::max(
+                        (existing_tx.weight(), existing_tx.as_ref()),
+                        (tx.weight(), tx.as_ref()),
+                    );
+                    if tx_with_precedence == tx.as_ref() {
+                        *existing_tx = tx.clone();
+                        changeset.txs.insert(tx);
+                    }
+                }
             }
             partial_tx => {
                 for txin in &tx.input {

crates/chain/tests/test_tx_graph.rs

@@ -10,6 +10,8 @@ use bdk_chain::{
     Anchor, ChainOracle, ChainPosition, Merge,
 };
 use bdk_testenv::{block_id, hash, utils::new_tx};
+use bitcoin::hex::FromHex;
+use bitcoin::Witness;
 use bitcoin::{
     absolute, hashes::Hash, transaction, Amount, BlockHash, OutPoint, ScriptBuf, SignedAmount,
     Transaction, TxIn, TxOut, Txid,
@@ -284,6 +286,74 @@ fn insert_tx_displaces_txouts() {
     assert_eq!(tx_graph.get_txout(outpoint), Some(txout));
 }
 
+#[test]
+fn insert_signed_tx_displaces_unsigned() {
+    let previous_output = OutPoint::new(hash!("prev"), 2);
+    let unsigned_tx = Transaction {
+        version: transaction::Version::ONE,
+        lock_time: absolute::LockTime::ZERO,
+        input: vec![TxIn {
+            previous_output,
+            script_sig: ScriptBuf::default(),
+            sequence: transaction::Sequence::ENABLE_RBF_NO_LOCKTIME,
+            witness: Witness::default(),
+        }],
+        output: vec![TxOut {
+            value: Amount::from_sat(24_000),
+            script_pubkey: ScriptBuf::default(),
+        }],
+    };
+    let signed_tx = Transaction {
+        input: vec![TxIn {
+            previous_output,
+            script_sig: ScriptBuf::default(),
+            sequence: transaction::Sequence::ENABLE_RBF_NO_LOCKTIME,
+            witness: Witness::from_slice(&[
+                // Random witness from mempool.space
+                Vec::from_hex("d59118058bf9e8604cec5c0b4a13430b07286482784da313594e932faad074dc4bd27db7cbfff9ad32450db097342d0148ec21c3033b0c27888fd2fd0de2e9b5")
+                    .unwrap(),
+            ]),
+        }],
+        ..unsigned_tx.clone()
+    };
+
+    // Signed tx must displace unsigned.
+    {
+        let mut tx_graph = TxGraph::<ConfirmationBlockTime>::default();
+        let changeset_insert_unsigned = tx_graph.insert_tx(unsigned_tx.clone());
+        let changeset_insert_signed = tx_graph.insert_tx(signed_tx.clone());
+        assert_eq!(
+            changeset_insert_unsigned,
+            ChangeSet {
+                txs: [Arc::new(unsigned_tx.clone())].into(),
+                ..Default::default()
+            }
+        );
+        assert_eq!(
+            changeset_insert_signed,
+            ChangeSet {
+                txs: [Arc::new(signed_tx.clone())].into(),
+                ..Default::default()
+            }
+        );
+    }
+
+    // Unsigned tx must not displace signed.
+    {
+        let mut tx_graph = TxGraph::<ConfirmationBlockTime>::default();
+        let changeset_insert_signed = tx_graph.insert_tx(signed_tx.clone());
+        let changeset_insert_unsigned = tx_graph.insert_tx(unsigned_tx.clone());
+        assert_eq!(
+            changeset_insert_signed,
+            ChangeSet {
+                txs: [Arc::new(signed_tx)].into(),
+                ..Default::default()
+            }
+        );
+        assert!(changeset_insert_unsigned.is_empty());
+    }
+}
+
 #[test]
 fn insert_txout_does_not_displace_tx() {
     let mut tx_graph = TxGraph::<ConfirmationBlockTime>::default();