Add rescan logic to ChainMonitor::block_connected

Electrum clients will only provide transaction data for outputs that
have been explicitly registered. Hence, upon registering new outputs,
recursively register any outputs to watch contained within dependent
transactions from the same block.

Author: jkczyz

lightning/src/chain/chainmonitor.rs

@@ -82,23 +82,40 @@ where C::Target: chain::Filter,
 	/// descendants of such transactions. It is not necessary to re-fetch the block to obtain
 	/// updated `txdata`.
 	pub fn block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
+		let mut dependent_txdata = Vec::new();
 		let monitors = self.monitors.read().unwrap();
 		for monitor in monitors.values() {
 			let mut txn_outputs = monitor.block_connected(header, txdata, height, &*self.broadcaster, &*self.fee_estimator, &*self.logger);
 
+			// Register any new outputs with the chain source for filtering, storing any dependent
+			// transactions from within the block that previously had not been included in txdata.
 			if let Some(ref chain_source) = self.chain_source {
 				let block_hash = header.block_hash();
 				for (txid, outputs) in txn_outputs.drain(..) {
 					for (idx, output) in outputs.iter() {
-						chain_source.register_output(WatchedOutput {
+						// Register any new outputs with the chain source for filtering and recurse
+						// if it indicates that there are dependent transactions within the block
+						// that had not been previously included in txdata.
+						let output = WatchedOutput {
 							block_hash: Some(block_hash),
 							outpoint: OutPoint { txid, index: *idx as u16 },
 							script_pubkey: output.script_pubkey.clone(),
-						});
+						};
+						if let Some(tx) = chain_source.register_output(output) {
+							dependent_txdata.push(tx);
+						}
 					}
 				}
 			}
 		}
+
+		// Recursively call for any dependent transactions that were identified by the chain source.
+		if !dependent_txdata.is_empty() {
+			dependent_txdata.sort_unstable_by_key(|(index, _tx)| *index);
+			dependent_txdata.dedup_by_key(|(index, _tx)| *index);
+			let txdata: Vec<_> = dependent_txdata.iter().map(|(index, tx)| (*index, tx)).collect();
+			self.block_connected(header, &txdata, height);
+		}
 	}
 
 	/// Dispatches to per-channel monitors, which are responsible for updating their on-chain view