peer: cache txid for commitment_tx.

Minor efficiency and simplification.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

daemon/packets.c

@@ -315,12 +315,14 @@ void queue_pkt_commit(struct peer *peer)
 	ci->cstate = copy_cstate(ci, peer->remote.staging_cstate);
 	ci->tx = create_commit_tx(ci, peer, &ci->revocation_hash,
 				  ci->cstate, REMOTE, &ci->map);
+	bitcoin_txid(ci->tx, &ci->txid);
 
 	log_debug(peer->log, "Signing tx for %u/%u msatoshis, %zu/%zu htlcs",
 		  ci->cstate->side[OURS].pay_msat,
 		  ci->cstate->side[THEIRS].pay_msat,
 		  tal_count(ci->cstate->side[OURS].htlcs),
 		  tal_count(ci->cstate->side[THEIRS].htlcs));
+	log_add_struct(peer->log, " (txid %s)", struct sha256_double, &ci->txid);
 
 	/* BOLT #2:
 	 *
@@ -819,6 +821,7 @@ Pkt *accept_pkt_commit(struct peer *peer, const Pkt *pkt)
 	ci->cstate = copy_cstate(ci, peer->local.staging_cstate);
 	ci->tx = create_commit_tx(ci, peer, &ci->revocation_hash,
 				  ci->cstate, LOCAL, &ci->map);
+	bitcoin_txid(ci->tx, &ci->txid);
 
 	/* BOLT #2:
 	 *

daemon/peer.c

@@ -585,7 +585,7 @@ static const struct bitcoin_tx *htlc_fulfill_tx(const struct peer *peer,
 				   REMOTE);
 
 	tx->input[0].index = ci->map[i];
-	bitcoin_txid(ci->tx, &tx->input[0].txid);
+	tx->input[0].txid = ci->txid;
 	satoshis = htlc->msatoshis / 1000;
 	tx->input[0].amount = tal_dup(tx->input, u64, &satoshis);
 	tx->input[0].sequence_number = bitcoin_nsequence(&peer->remote.locktime);
@@ -1349,22 +1349,13 @@ static enum watch_result anchor_depthchange(struct peer *peer,
 	return KEEP_WATCHING;
 }
 
-/* Yay, segwit!  We can just compare txids, even though we don't have both
- * signatures. */
-static bool txidmatch(const struct bitcoin_tx *tx,
-		      const struct sha256_double *txid)
-{
-	struct sha256_double tx_txid;
-
-	bitcoin_txid(tx, &tx_txid);
-	return structeq(txid, &tx_txid);
-}
-
 static struct commit_info *find_commit(struct commit_info *ci,
 				       const struct sha256_double *txid)
 {
 	while (ci) {
-		if (txidmatch(ci->tx, txid))
+		/* Yay, segwit!  We can just compare txids, even
+		 * though we don't have both signatures. */
+		if (structeq(txid, &ci->txid))
 			return ci;
 		ci = ci->prev;
 	}
@@ -1426,7 +1417,7 @@ static const struct bitcoin_tx *htlc_timeout_tx(const struct peer *peer,
 	/* We must set locktime so HTLC expiry can OP_CHECKLOCKTIMEVERIFY */
 	tx->lock_time = htlc->expiry.locktime;
 	tx->input[0].index = 0;
-	bitcoin_txid(ci->tx, &tx->input[0].txid);
+	tx->input[0].txid = ci->txid;
 	satoshis = htlc->msatoshis / 1000;
 	tx->input[0].amount = tal_dup(tx->input, u64, &satoshis);
 	tx->input[0].sequence_number = bitcoin_nsequence(&peer->remote.locktime);
@@ -2163,7 +2154,7 @@ static enum watch_result anchor_spent(struct peer *peer,
 			err = pkt_err(peer, "Unilateral close tx seen");
 			resolve_their_unilateral(peer);
 		}
-	} else if (txidmatch(peer->local.commit->tx, &txid)) {
+	} else if (structeq(&peer->local.commit->txid, &txid)) {
 		newstate = STATE_CLOSE_ONCHAIN_OUR_UNILATERAL;
 		/* We're almost certainly closed to them by now. */
 		err = pkt_err(peer, "Our own unilateral close tx seen");
@@ -2425,7 +2416,7 @@ const struct bitcoin_tx *bitcoin_spend_ours(struct peer *peer)
 
 	/* Now, create transaction to spend it. */
 	tx = bitcoin_tx(peer, 1, 1);
-	bitcoin_txid(commit, &tx->input[0].txid);
+	tx->input[0].txid = peer->local.commit->txid;
 	p2wsh_out = find_p2wsh_out(commit, witnessscript);
 	tx->input[0].index = p2wsh_out;
 	tx->input[0].sequence_number = bitcoin_nsequence(&peer->remote.locktime);
@@ -2817,6 +2808,7 @@ bool setup_first_commit(struct peer *peer)
 						  peer->local.commit->cstate,
 						  LOCAL,
 						  &peer->local.commit->map);
+	bitcoin_txid(peer->local.commit->tx, &peer->local.commit->txid);
 
 	peer->remote.commit->tx = create_commit_tx(peer->remote.commit,
 						   peer,
@@ -2824,6 +2816,7 @@ bool setup_first_commit(struct peer *peer)
 						   peer->remote.commit->cstate,
 						   REMOTE,
 						   &peer->remote.commit->map);
+	bitcoin_txid(peer->remote.commit->tx, &peer->remote.commit->txid);
 
 	peer->local.staging_cstate = copy_cstate(peer, peer->local.commit->cstate);
 	peer->remote.staging_cstate = copy_cstate(peer, peer->remote.commit->cstate);

daemon/peer.h

@@ -62,8 +62,9 @@ struct commit_info {
 	u64 commit_num;
 	/* Revocation hash. */
 	struct sha256 revocation_hash;
-	/* Commit tx. */
+	/* Commit tx & txid */
 	struct bitcoin_tx *tx;
+	struct sha256_double txid;
 	/* Channel state for this tx. */
 	struct channel_state *cstate;
 	/* Other side's signature for last commit tx (if known) */