Add OnchainTxHandler::get_fully_signed_htlc

In case of channel force-closure, access to local commitment
transactions and its dependent HTLCs is needed. Instead of using
broadcast_by_local_state which registers outpoint to claim and
outputs to watch which are going to be discarded in this case,
we simply ask OnchainTxHandler to build and sign HTLC transactions
through new API.

Author: Antoine Riard

lightning/src/ln/channelmonitor.rs

@@ -1812,10 +1812,17 @@ impl<ChanSigner: ChannelKeys> ChannelMonitor<ChanSigner> {
 	pub fn get_latest_local_commitment_txn(&mut self) -> Vec<Transaction> {
 		log_trace!(self, "Getting signed latest local commitment transaction!");
 		if let Some(commitment_tx) = self.onchain_tx_handler.get_fully_signed_local_tx(self.channel_value_satoshis.unwrap()) {
+			let txid = commitment_tx.txid();
 			let mut res = vec![commitment_tx];
 			if let &Some(ref local_tx) = &self.current_local_signed_commitment_tx {
-				let mut htlc_txn = self.broadcast_by_local_state(res.get(0).unwrap(), local_tx).0;
-				res.append(&mut htlc_txn);
+				for htlc in local_tx.htlc_outputs.iter() {
+					if let Some(htlc_index) = htlc.0.transaction_output_index {
+						let preimage = if let Some(preimage) = self.payment_preimages.get(&htlc.0.payment_hash) { Some(*preimage) } else { None };
+						if let Some(htlc_tx) = self.onchain_tx_handler.get_fully_signed_htlc_tx(txid, htlc_index, preimage) {
+							res.push(htlc_tx);
+						}
+					}
+				}
 				// We throw away the generated waiting_first_conf data as we aren't (yet) confirmed and we don't actually know what the caller wants to do.
 				// The data will be re-generated and tracked in check_spend_local_transaction if we get a confirmation.
 			}

lightning/src/ln/onchaintx.rs

@@ -15,7 +15,7 @@ use secp256k1;
 
 use ln::msgs::DecodeError;
 use ln::channelmonitor::{ANTI_REORG_DELAY, CLTV_SHARED_CLAIM_BUFFER, InputMaterial, ClaimRequest};
-use ln::channelmanager::HTLCSource;
+use ln::channelmanager::{HTLCSource, PaymentPreimage};
 use ln::chan_utils;
 use ln::chan_utils::{HTLCType, LocalCommitmentTransaction, TxCreationKeys, HTLCOutputInCommitment};
 use chain::chaininterface::{FeeEstimator, BroadcasterInterface, ConfirmationTarget, MIN_RELAY_FEE_SAT_PER_1000_WEIGHT};
@@ -874,4 +874,23 @@ impl<ChanSigner: ChannelKeys> OnchainTxHandler<ChanSigner> {
 		}
 		None
 	}
+
+	pub(super) fn get_fully_signed_htlc_tx(&mut self, txid: Sha256dHash, htlc_index: u32, preimage: Option<PaymentPreimage>) -> Option<Transaction> {
+		//TODO: store preimage in OnchainTxHandler
+		if let Some(ref local_commitment) = self.local_commitment {
+			if local_commitment.txid() == txid {
+				if let Some(ref htlc_cache) = self.current_htlc_cache {
+					if let Some(htlc) = htlc_cache.per_htlc.get(&htlc_index) {
+						if !htlc.0.offered && preimage.is_none() { return None; }; // If we don't have preimage for HTLC-Success, don't try to generate
+						let htlc_secret = if !htlc.0.offered { preimage } else { None }; // If we have a preimage for a HTLC-Timeout, don't use it that's likely a duplicate HTLC hash
+						let mut htlc_tx = chan_utils::build_htlc_transaction(&txid, htlc_cache.feerate_per_kw, self.local_csv, &htlc.0, &htlc_cache.local_keys.a_delayed_payment_key, &htlc_cache.local_keys.revocation_key);
+						self.key_storage.sign_htlc_transaction(&mut htlc_tx, htlc.1.as_ref().unwrap(), &htlc_secret, &htlc.0, &htlc_cache.local_keys.a_htlc_key, &htlc_cache.local_keys.b_htlc_key, &htlc_cache.local_keys.revocation_key, &htlc_cache.local_keys.per_commitment_point, &self.secp_ctx);
+						return Some(htlc_tx);
+
+					}
+				}
+			}
+		}
+		None
+	}
 }