Add ChannelMonitor::transaction_unconfirmed

Define an Electrum-friendly interface for ChannelMonitor where
transactions are unconfirmed independently from updating the latest
block.

Author: jkczyz

lightning/src/chain/channelmonitor.rs

@@ -1331,6 +1331,29 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 			header, txdata, height, broadcaster, fee_estimator, logger)
 	}
 
+	/// Processes a transaction that was reorganized out of the chain.
+	///
+	/// Used instead of [`block_disconnected`] by clients that are notified of transactions rather
+	/// than blocks. May be called before or after [`update_best_block`] for transactions in the
+	/// corresponding block. See [`update_best_block`] for further calling expectations.
+	///
+	/// [`block_disconnected`]: Self::block_disconnected
+	/// [`update_best_block`]: Self::update_best_block
+	pub fn transaction_unconfirmed<B: Deref, F: Deref, L: Deref>(
+		&self,
+		txid: &Txid,
+		broadcaster: B,
+		fee_estimator: F,
+		logger: L,
+	) where
+		B::Target: BroadcasterInterface,
+		F::Target: FeeEstimator,
+		L::Target: Logger,
+	{
+		self.inner.lock().unwrap().transaction_unconfirmed(
+			txid, broadcaster, fee_estimator, logger);
+	}
+
 	/// Updates the monitor with the current best chain tip, returning new outputs to watch. See
 	/// [`block_connected`] for details.
 	///
@@ -1339,10 +1362,14 @@ impl<Signer: Sign> ChannelMonitor<Signer> {
 	/// block.
 	///
 	/// Must be called after new blocks become available for the most recent block. Intermediary
-	/// blocks, however, may be safely skipped.
+	/// blocks, however, may be safely skipped. For a chain reorganization, must either be:
+	/// * called at at the fork point and then again for the most recent block -- intermediary
+	///   blocks may be skipped as before -- or
+	/// * not called in favor of calling [`transaction_unconfirmed`] for any affected transactions.
 	///
 	/// [`block_connected`]: Self::block_connected
 	/// [`transactions_confirmed`]: Self::transactions_confirmed
+	/// [`transaction_unconfirmed`]: Self::transaction_unconfirmed
 	pub fn update_best_block<B: Deref, F: Deref, L: Deref>(
 		&self,
 		header: &BlockHeader,
@@ -2293,6 +2320,21 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
 		self.best_block = BestBlock::new(header.prev_blockhash, height - 1);
 	}
 
+	fn transaction_unconfirmed<B: Deref, F: Deref, L: Deref>(
+		&mut self,
+		txid: &Txid,
+		broadcaster: B,
+		fee_estimator: F,
+		logger: L,
+	) where
+		B::Target: BroadcasterInterface,
+		F::Target: FeeEstimator,
+		L::Target: Logger,
+	{
+		self.onchain_events_waiting_threshold_conf.retain(|ref entry| entry.txid != *txid);
+		self.onchain_tx_handler.transaction_unconfirmed(txid, broadcaster, fee_estimator, logger);
+	}
+
 	/// Filters a block's `txdata` for transactions spending watched outputs or for any child
 	/// transactions thereof.
 	fn filter_block<'a>(&self, txdata: &TransactionData<'a>) -> Vec<&'a Transaction> {

lightning/src/ln/onchaintx.rs

@@ -869,6 +869,30 @@ impl<ChannelSigner: Sign> OnchainTxHandler<ChannelSigner> {
 		}
 	}
 
+	pub(crate) fn transaction_unconfirmed<B: Deref, F: Deref, L: Deref>(
+		&mut self,
+		txid: &Txid,
+		broadcaster: B,
+		fee_estimator: F,
+		logger: L,
+	) where
+		B::Target: BroadcasterInterface,
+		F::Target: FeeEstimator,
+		L::Target: Logger,
+	{
+		let mut height = None;
+		for entry in self.onchain_events_waiting_threshold_conf.iter() {
+			if entry.txid == *txid {
+				height = Some(entry.height);
+				break;
+			}
+		}
+
+		if let Some(height) = height {
+			self.block_disconnected(height, broadcaster, fee_estimator, logger);
+		}
+	}
+
 	pub(crate) fn block_disconnected<B: Deref, F: Deref, L: Deref>(&mut self, height: u32, broadcaster: B, fee_estimator: F, logger: L)
 		where B::Target: BroadcasterInterface,
 		      F::Target: FeeEstimator,