Explicitly track the set of spendable transactions which confirm

In `ChannelMonitor`s, when a transaction containing a spend of a
revoked remote output reaches 6 confs, we may have no other
tracking of that txid remaining. Thus, if we see that transaction
again (because a user duplicatively confirms it), we'll generate a
redundant spendable output event for it.

Here we simply explicitly track all txids of transactions which
confirm with a spendable output, allowing us to check this
condition in the next commit.

diff --git a/lightning/src/chain/channelmonitor.rs b/lightning/src/chain/channelmonitor.rs
index c0d0affcce5d2fad616ab1ae48e49feaea2a76d7..1cbc85350302ab27d86758609b4632fa8b67722c 100644 (file)
--- a/lightning/src/chain/channelmonitor.rs
+++ b/lightning/src/chain/channelmonitor.rs
@@ -826,6 +826,13 @@ pub(crate) struct ChannelMonitorImpl<Signer: Sign> {
        /// spending CSV for revocable outputs).
        htlcs_resolved_on_chain: Vec<IrrevocablyResolvedHTLC>,
 
+       /// The set of `SpendableOutput` events which we have already passed upstream to be claimed.
+       /// These are tracked explicitly to ensure that we don't generate the same events redundantly
+       /// if users duplicatively confirm old transactions. Specifically for transactions claiming a
+       /// revoked remote outpoint we otherwise have no tracking at all once they've reached
+       /// [`ANTI_REORG_DELAY`], so we have to track them here.
+       spendable_txids_confirmed: Vec<Txid>,
+
        // We simply modify best_block in Channel's block_connected so that serialization is
        // consistent but hopefully the users' copy handles block_connected in a consistent way.
        // (we do *not*, however, update them in update_monitor to ensure any local user copies keep
@@ -1071,6 +1078,7 @@ impl<Signer: Sign> Writeable for ChannelMonitorImpl<Signer> {
                        (7, self.funding_spend_seen, required),
                        (9, self.counterparty_node_id, option),
                        (11, self.confirmed_commitment_tx_counterparty_output, option),
+                       (13, self.spendable_txids_confirmed, vec_type),
                });
 
                Ok(())
@@ -1179,6 +1187,7 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
                        funding_spend_confirmed: None,
                        confirmed_commitment_tx_counterparty_output: None,
                        htlcs_resolved_on_chain: Vec::new(),
+                       spendable_txids_confirmed: Vec::new(),
 
                        best_block,
                        counterparty_node_id: Some(counterparty_node_id),
@@ -3042,6 +3051,7 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
                                        self.pending_events.push(Event::SpendableOutputs {
                                                outputs: vec![descriptor]
                                        });
+                                       self.spendable_txids_confirmed.push(entry.txid);
                                },
                                OnchainEvent::HTLCSpendConfirmation { commitment_tx_output_idx, preimage, .. } => {
                                        self.htlcs_resolved_on_chain.push(IrrevocablyResolvedHTLC {
@@ -3763,6 +3773,7 @@ impl<'a, K: KeysInterface> ReadableArgs<&'a K>
                let mut funding_spend_seen = Some(false);
                let mut counterparty_node_id = None;
                let mut confirmed_commitment_tx_counterparty_output = None;
+               let mut spendable_txids_confirmed = Some(Vec::new());
                read_tlv_fields!(reader, {
                        (1, funding_spend_confirmed, option),
                        (3, htlcs_resolved_on_chain, vec_type),
@@ -3770,6 +3781,7 @@ impl<'a, K: KeysInterface> ReadableArgs<&'a K>
                        (7, funding_spend_seen, option),
                        (9, counterparty_node_id, option),
                        (11, confirmed_commitment_tx_counterparty_output, option),
+                       (13, spendable_txids_confirmed, vec_type),
                });
 
                let mut secp_ctx = Secp256k1::new();
@@ -3822,6 +3834,7 @@ impl<'a, K: KeysInterface> ReadableArgs<&'a K>
                        funding_spend_confirmed,
                        confirmed_commitment_tx_counterparty_output,
                        htlcs_resolved_on_chain: htlcs_resolved_on_chain.unwrap(),
+                       spendable_txids_confirmed: spendable_txids_confirmed.unwrap(),
 
                        best_block,
                        counterparty_node_id,