Avoid claiming remote received HTLCs with preimage

In case of duplicate HTLCs with same hash going in opposite
directions we may learn preimage of offered one, but we shouldn't
claim received one to avoid invalidation of combined claim.
The received HTLC is going to be claimed by a timeout tx at
timelock expiration.

Fix #337

Author: Antoine Riard

src/ln/channelmonitor.rs

@@ -1643,46 +1643,48 @@ impl ChannelMonitor {
 								return (txn_to_broadcast, (commitment_txid, watch_outputs), spendable_outputs); // Corrupted per_commitment_data, fuck this user
 							}
 							if let Some(payment_preimage) = self.payment_preimages.get(&htlc.payment_hash) {
-								let input = TxIn {
-									previous_output: BitcoinOutPoint {
-										txid: commitment_txid,
-										vout: transaction_output_index,
-									},
-									script_sig: Script::new(),
-									sequence: idx as u32, // reset to 0xfffffffd in sign_input
-									witness: Vec::new(),
-								};
-								if htlc.cltv_expiry > height + CLTV_SHARED_CLAIM_BUFFER {
-									inputs.push(input);
-									inputs_desc.push(if htlc.offered { InputDescriptors::OfferedHTLC } else { InputDescriptors::ReceivedHTLC });
-									inputs_info.push((payment_preimage, tx.output[transaction_output_index as usize].value, htlc.cltv_expiry));
-									total_value += tx.output[transaction_output_index as usize].value;
-								} else {
-									let mut single_htlc_tx = Transaction {
-										version: 2,
-										lock_time: 0,
-										input: vec![input],
-										output: vec!(TxOut {
-											script_pubkey: self.destination_script.clone(),
-											value: htlc.amount_msat / 1000,
-										}),
+								if htlc.offered {
+									let input = TxIn {
+										previous_output: BitcoinOutPoint {
+											txid: commitment_txid,
+											vout: transaction_output_index,
+										},
+										script_sig: Script::new(),
+										sequence: idx as u32, // reset to 0xfffffffd in sign_input
+										witness: Vec::new(),
 									};
-									let predicted_weight = single_htlc_tx.get_weight() + Self::get_witnesses_weight(&[if htlc.offered { InputDescriptors::OfferedHTLC } else { InputDescriptors::ReceivedHTLC }]);
-									let height_timer = Self::get_height_timer(height, htlc.cltv_expiry);
-									let mut used_feerate;
-									if subtract_high_prio_fee!(self, fee_estimator, single_htlc_tx.output[0].value, predicted_weight, tx.txid(), used_feerate) {
-										let sighash_parts = bip143::SighashComponents::new(&single_htlc_tx);
-										let (redeemscript, htlc_key) = sign_input!(sighash_parts, single_htlc_tx.input[0], htlc.amount_msat / 1000, payment_preimage.0.to_vec());
-										assert!(predicted_weight >= single_htlc_tx.get_weight());
-										spendable_outputs.push(SpendableOutputDescriptor::StaticOutput {
-											outpoint: BitcoinOutPoint { txid: single_htlc_tx.txid(), vout: 0 },
-											output: single_htlc_tx.output[0].clone(),
-										});
-										match self.our_claim_txn_waiting_first_conf.entry(single_htlc_tx.input[0].previous_output.clone()) {
-											hash_map::Entry::Occupied(_) => {},
-											hash_map::Entry::Vacant(entry) => { entry.insert((height_timer, TxMaterial::RemoteHTLC { script: redeemscript, key: htlc_key, preimage: Some(*payment_preimage), amount: htlc.amount_msat / 1000 }, used_feerate, htlc.cltv_expiry, height)); }
+									if htlc.cltv_expiry > height + CLTV_SHARED_CLAIM_BUFFER {
+										inputs.push(input);
+										inputs_desc.push(if htlc.offered { InputDescriptors::OfferedHTLC } else { InputDescriptors::ReceivedHTLC });
+										inputs_info.push((payment_preimage, tx.output[transaction_output_index as usize].value, htlc.cltv_expiry));
+										total_value += tx.output[transaction_output_index as usize].value;
+									} else {
+										let mut single_htlc_tx = Transaction {
+											version: 2,
+											lock_time: 0,
+											input: vec![input],
+											output: vec!(TxOut {
+												script_pubkey: self.destination_script.clone(),
+												value: htlc.amount_msat / 1000,
+											}),
+										};
+										let predicted_weight = single_htlc_tx.get_weight() + Self::get_witnesses_weight(&[if htlc.offered { InputDescriptors::OfferedHTLC } else { InputDescriptors::ReceivedHTLC }]);
+										let height_timer = Self::get_height_timer(height, htlc.cltv_expiry);
+										let mut used_feerate;
+										if subtract_high_prio_fee!(self, fee_estimator, single_htlc_tx.output[0].value, predicted_weight, tx.txid(), used_feerate) {
+											let sighash_parts = bip143::SighashComponents::new(&single_htlc_tx);
+											let (redeemscript, htlc_key) = sign_input!(sighash_parts, single_htlc_tx.input[0], htlc.amount_msat / 1000, payment_preimage.0.to_vec());
+											assert!(predicted_weight >= single_htlc_tx.get_weight());
+											spendable_outputs.push(SpendableOutputDescriptor::StaticOutput {
+												outpoint: BitcoinOutPoint { txid: single_htlc_tx.txid(), vout: 0 },
+												output: single_htlc_tx.output[0].clone(),
+											});
+											match self.our_claim_txn_waiting_first_conf.entry(single_htlc_tx.input[0].previous_output.clone()) {
+												hash_map::Entry::Occupied(_) => {},
+												hash_map::Entry::Vacant(entry) => { entry.insert((height_timer, TxMaterial::RemoteHTLC { script: redeemscript, key: htlc_key, preimage: Some(*payment_preimage), amount: htlc.amount_msat / 1000 }, used_feerate, htlc.cltv_expiry, height)); }
+											}
+											txn_to_broadcast.push(single_htlc_tx);
 										}
-										txn_to_broadcast.push(single_htlc_tx);
 									}
 								}
 							}