watch: indicate which input of tx is spend the watch txo.

If we generate a tx which spends a heap of TXOs (eg. steal
transaction), we'll need this.

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

daemon/chaintopology.c

@@ -148,7 +148,7 @@ static void connect_blocks(struct lightningd_state *dstate, struct block *b)
 
 			txo = txowatch_hash_get(&dstate->txowatches, &out);
 			if (txo)
-				txowatch_fire(dstate, txo, tx);
+				txowatch_fire(dstate, txo, tx, j);
 		}
 
 		/* We do spends first, in case that tells us to watch tx. */

daemon/peer.c

@@ -754,11 +754,18 @@ static void close_depth_cb(struct peer *peer, int depth,
  * invalid transactions! */
 static void anchor_spent(struct peer *peer,
 			 const struct bitcoin_tx *tx,
+			 size_t input_num,
 			 void *unused)
 {
 	struct anchor_watch *w = peer->anchor.watches;
 	union input idata;
 
+	assert(input_num < tx->input_count);
+
+	/* We only ever sign single-input txs. */
+	if (input_num != 0)
+		fatal("Anchor spend by non-single input tx");
+	
 	/* FIXME: change type in idata? */
 	idata.btc = (struct bitcoin_event *)tx;
 	if (is_unrevoked_commit(peer->them.commit, tx))
@@ -867,6 +874,7 @@ static void commit_tx_depth(struct peer *peer, int depth,
 /* We should map back from commit_tx permutation to figure out what happened. */
 static void our_commit_spent(struct peer *peer,
 			     const struct bitcoin_tx *commit_tx,
+			     size_t input_num,
 			     struct commit_info *info)
 {
 	/* FIXME: do something useful here, if HTLCs spent */

daemon/watch.c

@@ -126,6 +126,7 @@ struct txowatch *watch_txo_(const tal_t *ctx,
 			    unsigned int output,
 			    void (*cb)(struct peer *peer,
 				       const struct bitcoin_tx *tx,
+				       size_t input_num,
 				       void *),
 			    void *cbdata)
 {
@@ -162,7 +163,8 @@ void txwatch_fire(struct lightningd_state *dstate,
 
 void txowatch_fire(struct lightningd_state *dstate,
 		   const struct txowatch *txow,
-		   const struct bitcoin_tx *tx)
+		   const struct bitcoin_tx *tx,
+		   size_t input_num)
 {
 	struct sha256_double txid;
 
@@ -177,7 +179,7 @@ void txowatch_fire(struct lightningd_state *dstate,
 		  txid.sha.u.u8[1],
 		  txid.sha.u.u8[2],
 		  txid.sha.u.u8[3]);
-	txow->cb(txow->peer, tx, txow->cbdata);
+	txow->cb(txow->peer, tx, input_num, txow->cbdata);
 }
 
 void watch_topology_changed(struct lightningd_state *dstate)

daemon/watch.h

@@ -27,6 +27,7 @@ struct txowatch {
 	/* A new tx. */
 	void (*cb)(struct peer *peer,
 		   const struct bitcoin_tx *tx,
+		   size_t input_num,
 		   void *cbdata);
 
 	void *cbdata;
@@ -103,6 +104,7 @@ struct txowatch *watch_txo_(const tal_t *ctx,
 			    unsigned int output,
 			    void (*cb)(struct peer *peer,
 				       const struct bitcoin_tx *tx,
+				       size_t input_num,
 				       void *),
 			    void *cbdata);
 
@@ -111,7 +113,8 @@ struct txowatch *watch_txo_(const tal_t *ctx,
 		  typesafe_cb_preargs(void, void *,			\
 				      (cb), (cbdata),			\
 				      struct peer *,			\
-				      const struct bitcoin_tx *),	\
+				      const struct bitcoin_tx *,	\
+				      size_t),				\
 		  (cbdata))
 
 void txwatch_fire(struct lightningd_state *dstate,
@@ -120,7 +123,7 @@ void txwatch_fire(struct lightningd_state *dstate,
 
 void txowatch_fire(struct lightningd_state *dstate,
 		   const struct txowatch *txow,
-		   const struct bitcoin_tx *tx);
+		   const struct bitcoin_tx *tx, size_t input_num);
 
 void watch_topology_changed(struct lightningd_state *dstate);
 #endif /* LIGHTNING_DAEMON_WATCH_H */