ElectrumSyncClient: Skip unconfirmed get_history entries

Electrum's `blockchain.scripthash.get_history` will return the
*confirmed* history for any scripthash, but will then also append any
matching entries from the mempool, with respective `height` fields set
to 0 or -1 (depending on whether all inputs are confirmed or not).

Unfortunately we previously only included a filter for confirmed
`get_history` entries in the watched output case, and forgot to add such
a check also when checking for watched transactions. This would have us
treat the entry as confirmed, then failing on the `get_merkle` step
which of course couldn't prove block inclusion. Here we simply fix this
omission and skip entries that are still unconfirmed (e.g., unconfirmed
funding transactions from 0conf channels).

Signed-off-by: Elias Rohrer <dev@tnull.de>

Author: tnull

lightning-transaction-sync/src/electrum.rs

@@ -336,17 +336,29 @@ where
 						script_history.iter().filter(|h| h.tx_hash == **txid);
 					if let Some(history) = filtered_history.next() {
 						let prob_conf_height = history.height as u32;
+						if prob_conf_height <= 0 {
+							// Skip if it's a an unconfirmed entry.
+							continue;
+						}
 						let confirmed_tx = self.get_confirmed_tx(tx, prob_conf_height)?;
 						confirmed_txs.push(confirmed_tx);
 					}
-					debug_assert!(filtered_history.next().is_none());
+					if filtered_history.next().is_some() {
+						log_error!(
+							self.logger,
+							"Failed due to server returning multiple history entries for Tx {}.",
+							txid
+						);
+						return Err(InternalError::Failed);
+					}
 				}
 
 				for (watched_output, script_history) in
 					sync_state.watched_outputs.values().zip(output_results)
 				{
 					for possible_output_spend in script_history {
 						if possible_output_spend.height <= 0 {
+							// Skip if it's a an unconfirmed entry.
 							continue;
 						}