lightningd: add generic scriptpubkey watches.

diff --git a/lightningd/chaintopology.c b/lightningd/chaintopology.c
index 17880818..9e9ea0fc 100644
--- a/lightningd/chaintopology.c
+++ b/lightningd/chaintopology.c
@@ -40,19 +40,17 @@ static bool we_broadcast(const struct chain_topology *topo,
 
 static void filter_block_txs(struct chain_topology *topo, struct block *b)
 {
-	size_t i;
-
 	/* Now we see if any of those txs are interesting. */
 	const size_t num_txs = tal_count(b->full_txs);
-	for (i = 0; i < num_txs; i++) {
+	for (size_t i = 0; i < num_txs; i++) {
 		struct bitcoin_tx *tx = b->full_txs[i];
 		struct bitcoin_txid txid;
-		size_t j;
+		const struct txlocator loc = { b->height, i };
 		bool is_coinbase = i == 0;
 		size_t *our_outnums;
 
 		/* Tell them if it spends a txo we care about. */
-		for (j = 0; j < tx->wtx->num_inputs; j++) {
+		for (size_t j = 0; j < tx->wtx->num_inputs; j++) {
 			struct bitcoin_outpoint out;
 			struct txowatch_hash_iter it;
 
@@ -89,7 +87,11 @@ static void filter_block_txs(struct chain_topology *topo, struct block *b)
 		}
 
 		/* We did spends first, in case that tells us to watch tx. */
-		if (watching_txid(topo, &txid) || we_broadcast(topo, &txid)) {
+
+		/* Make sure we preserve any transaction we are interested in */
+		if (watch_check_tx_outputs(topo, &loc, tx, &txid)
+		    || watching_txid(topo, &txid)
+		    || we_broadcast(topo, &txid)) {
 			wallet_transaction_add(topo->ld->wallet,
 					       tx->wtx, b->height, i);
 		}
@@ -1233,6 +1235,7 @@ struct chain_topology *new_topology(struct lightningd *ld, struct logger *log)
 	topo->outgoing_txs = new_htable(topo, outgoing_tx_map);
 	topo->txwatches = new_htable(topo, txwatch_hash);
 	topo->txowatches = new_htable(topo, txowatch_hash);
+	topo->scriptpubkeywatches = new_htable(topo, scriptpubkeywatch_hash);
 	topo->log = log;
 	topo->bitcoind = new_bitcoind(topo, ld, log);
 	topo->poll_seconds = 30;
diff --git a/lightningd/chaintopology.h b/lightningd/chaintopology.h
index 8515cb5b..e9721775 100644
--- a/lightningd/chaintopology.h
+++ b/lightningd/chaintopology.h
@@ -9,6 +9,7 @@ struct command;
 struct lightningd;
 struct peer;
 struct txwatch;
+struct scriptpubkeywatch;
 struct wallet;
 
 /* We keep the last three in case there are outliers (for min/max) */
@@ -139,6 +140,7 @@ struct chain_topology {
 	/* Transactions/txos we are watching. */
 	struct txwatch_hash *txwatches;
 	struct txowatch_hash *txowatches;
+	struct scriptpubkeywatch_hash *scriptpubkeywatches;
 
 	/* The number of headers known to the bitcoin backend at startup. Not
 	 * updated after the initial check. */
diff --git a/lightningd/channel.c b/lightningd/channel.c
index 2d4167d7..fa22c40a 100644
--- a/lightningd/channel.c
+++ b/lightningd/channel.c
@@ -92,6 +92,7 @@ void delete_channel(struct channel *channel STEALS,
 	struct peer *peer = channel->peer;
 	struct lightningd *ld = peer->ld;
 
+	
 	if (channel->dbid != 0) {
 		wallet_channel_close(ld->wallet, channel);
 		/* Never open at all, not ours. */
diff --git a/lightningd/watch.c b/lightningd/watch.c
index 0731f711..93712fcf 100644
--- a/lightningd/watch.c
+++ b/lightningd/watch.c
@@ -31,6 +31,8 @@
  */
 #include "config.h"
 #include <bitcoin/psbt.h>
+#include <ccan/tal/str/str.h>
+#include <common/addr.h>
 #include <lightningd/chaintopology.h>
 #include <lightningd/channel.h>
 #include <lightningd/lightningd.h>
@@ -316,3 +318,154 @@ void txwatch_inform(const struct chain_topology *topo,
 	if (taken(tx))
 		tal_free(tx);
 }
+
+struct scriptpubkeywatch {
+	struct script_with_len swl;
+	struct bitcoin_outpoint expected_outpoint;
+	struct amount_sat expected_amount;
+	void (*cb)(struct lightningd *ld,
+		   const struct bitcoin_tx *tx,
+		   u32 outnum,
+		   const struct txlocator *loc,
+		   void *);
+	void *arg;
+};
+
+const struct script_with_len *scriptpubkeywatch_keyof(const struct scriptpubkeywatch *w)
+{
+	return &w->swl;
+}
+
+bool scriptpubkeywatch_eq(const struct scriptpubkeywatch *w, const struct script_with_len *swl)
+{
+	return script_with_len_eq(&w->swl, swl);
+}
+
+static void destroy_scriptpubkeywatch(struct scriptpubkeywatch *w, struct chain_topology *topo)
+{
+	scriptpubkeywatch_hash_del(topo->scriptpubkeywatches, w);
+}
+
+void watch_scriptpubkey_(const tal_t *ctx,
+			 struct chain_topology *topo,
+			 const u8 *scriptpubkey TAKES,
+			 const struct bitcoin_outpoint *expected_outpoint,
+			 struct amount_sat expected_amount,
+			 void (*cb)(struct lightningd *ld,
+				    const struct bitcoin_tx *tx,
+				    u32 outnum,
+				    const struct txlocator *loc,
+				    void *),
+			 void *arg)
+{
+	struct scriptpubkeywatch *w = tal(ctx, struct scriptpubkeywatch);
+	w->swl.script = tal_dup_talarr(w, u8, scriptpubkey);
+	w->swl.len = tal_bytelen(w->swl.script);
+	w->expected_outpoint = *expected_outpoint;
+	w->expected_amount = expected_amount;
+	w->cb = cb;
+	w->arg = arg;
+	scriptpubkeywatch_hash_add(topo->scriptpubkeywatches, w);
+	tal_add_destructor2(w, destroy_scriptpubkeywatch, topo);
+}
+
+bool unwatch_scriptpubkey_(const tal_t *ctx,
+			   struct chain_topology *topo,
+			   const u8 *scriptpubkey TAKES,
+			   const struct bitcoin_outpoint *expected_outpoint,
+			   struct amount_sat expected_amount,
+			   void (*cb)(struct lightningd *ld,
+				      const struct bitcoin_tx *tx,
+				      u32 outnum,
+				      const struct txlocator *loc,
+				      void *),
+			   void *arg)
+{
+	struct scriptpubkeywatch_hash_iter it;
+	const struct script_with_len swl = { scriptpubkey, tal_bytelen(scriptpubkey) };
+
+	for (struct scriptpubkeywatch *w = scriptpubkeywatch_hash_getfirst(topo->scriptpubkeywatches, &swl, &it);
+	     w;
+	     w = scriptpubkeywatch_hash_getnext(topo->scriptpubkeywatches, &swl, &it)) {
+		if (!bitcoin_outpoint_eq(&w->expected_outpoint, expected_outpoint)
+		    || !amount_sat_eq(w->expected_amount, expected_amount)
+		    || w->cb != cb
+		    || w->arg != arg) {
+			continue;
+		}
+		tal_free(w);
+		return true;
+	}
+	return false;
+}
+
+bool watch_check_tx_outputs(const struct chain_topology *topo,
+			    const struct txlocator *loc,
+			    const struct bitcoin_tx *tx,
+			    const struct bitcoin_txid *txid)
+{
+	bool tx_interesting = false;
+
+	for (size_t outnum = 0; outnum < tx->wtx->num_outputs; outnum++) {
+		const struct wally_tx_output *txout = &tx->wtx->outputs[outnum];
+		const struct script_with_len swl = { txout->script, txout->script_len };
+		struct scriptpubkeywatch_hash_iter it;
+		bool output_matched = false, bad_txid = false, bad_amount = false, bad_outnum = false;
+		struct amount_asset outasset = bitcoin_tx_output_get_amount(tx, outnum);
+
+		/* Ensure callbacks don't do an insert during iteration! */
+		scriptpubkeywatch_hash_lock(topo->scriptpubkeywatches);
+		for (struct scriptpubkeywatch *w = scriptpubkeywatch_hash_getfirst(topo->scriptpubkeywatches, &swl, &it);
+		     w;
+		     w = scriptpubkeywatch_hash_getnext(topo->scriptpubkeywatches, &swl, &it)) {
+			if (!bitcoin_txid_eq(&w->expected_outpoint.txid, txid)) {
+				bad_txid = true;
+				continue;
+			}
+			if (outnum != w->expected_outpoint.n) {
+				bad_outnum = true;
+				continue;
+			}
+			if (!amount_asset_is_main(&outasset)
+			    || !amount_sat_eq(amount_asset_to_sat(&outasset), w->expected_amount)) {
+				bad_amount = true;
+				continue;
+			}
+
+			w->cb(topo->ld, tx, outnum, loc, w->arg);
+			output_matched = true;
+			tx_interesting = true;
+		}
+		scriptpubkeywatch_hash_unlock(topo->scriptpubkeywatches);
+
+		/* Only complain about mismatch if we missed all of them.
+		 * This helps diagnose mistakes like wrong txid, see
+		 * https://github.com/ElementsProject/lightning/issues/8892 */
+		if (!output_matched && (bad_txid || bad_amount || bad_outnum)) {
+			const char *addr = encode_scriptpubkey_to_addr(tmpctx, chainparams,
+								       txout->script, txout->script_len);
+			if (!addr)
+				addr = tal_fmt(tmpctx, "Scriptpubkey %s", tal_hexstr(tmpctx, txout->script, txout->script_len));
+			if (bad_txid) {
+				log_unusual(topo->ld->log,
+					    "Unexpected spend to %s by unexpected txid %s:%zu",
+					    addr, fmt_bitcoin_txid(tmpctx, txid), outnum);
+			}
+			if (bad_amount) {
+				log_unusual(topo->ld->log,
+					    "Unexpected amount %s to %s by txid %s:%zu",
+					    amount_asset_is_main(&outasset)
+					    ? fmt_amount_sat(tmpctx, amount_asset_to_sat(&outasset))
+					    : "fee output",
+					    addr, fmt_bitcoin_txid(tmpctx, txid), outnum);
+			}
+			if (bad_outnum) {
+				log_unusual(topo->ld->log,
+					    "Unexpected output number %zu paying to %s in txid %s",
+					    outnum, addr, fmt_bitcoin_txid(tmpctx, txid));
+			}
+		}
+	}
+
+	return tx_interesting;
+}
diff --git a/lightningd/watch.h b/lightningd/watch.h
index 596da3a3..57ceb149 100644
--- a/lightningd/watch.h
+++ b/lightningd/watch.h
@@ -1,6 +1,7 @@
 #ifndef LIGHTNING_LIGHTNINGD_WATCH_H
 #define LIGHTNING_LIGHTNINGD_WATCH_H
 #include "config.h"
+#include <bitcoin/script.h>
 #include <bitcoin/tx.h>
 #include <ccan/htable/htable_type.h>
 
@@ -8,8 +9,10 @@ struct block;
 struct channel;
 struct chain_topology;
 struct lightningd;
+struct txlocator;
 struct txowatch;
 struct txwatch;
+struct scriptpubkeywatch;
 
 enum watch_result {
 	DELETE_WATCH = -1,
@@ -29,6 +32,10 @@ bool txwatch_eq(const struct txwatch *w, const struct bitcoin_txid *txid);
 HTABLE_DEFINE_DUPS_TYPE(struct txwatch, txwatch_keyof, txid_hash, txwatch_eq,
 			txwatch_hash);
 
+const struct script_with_len *scriptpubkeywatch_keyof(const struct scriptpubkeywatch *w);
+bool scriptpubkeywatch_eq(const struct scriptpubkeywatch *w, const struct script_with_len *swl);
+HTABLE_DEFINE_DUPS_TYPE(struct scriptpubkeywatch, scriptpubkeywatch_keyof, script_with_len_hash, scriptpubkeywatch_eq,
+			scriptpubkeywatch_hash);
 
 struct txwatch *watch_txid_(const tal_t *ctx,
 			    struct chain_topology *topo,
@@ -93,5 +100,58 @@ void txwatch_inform(const struct chain_topology *topo,
 		    const struct bitcoin_txid *txid,
 		    struct bitcoin_tx *tx TAKES);
 
+/* Watch for specific spends to this scriptpubkey */
+void watch_scriptpubkey_(const tal_t *ctx,
+			 struct chain_topology *topo,
+			 const u8 *scriptpubkey TAKES,
+			 const struct bitcoin_outpoint *expected_outpoint,
+			 struct amount_sat expected_amount,
+			 void (*cb)(struct lightningd *ld,
+				    const struct bitcoin_tx *tx,
+				    u32 outnum,
+				    const struct txlocator *loc,
+				    void *),
+			 void *arg);
+
+#define watch_scriptpubkey(ctx, topo, scriptpubkey, expected_outpoint, expected_amount, cb, arg) \
+	watch_scriptpubkey_((ctx), (topo), (scriptpubkey),		\
+			    (expected_outpoint), (expected_amount), \
+			    typesafe_cb_preargs(void, void *,		\
+						(cb), (arg),		\
+						struct lightningd *,	\
+						const struct bitcoin_tx *, \
+						u32 outnum,		\
+						const struct txlocator *), \
+			    (arg))
+
+bool unwatch_scriptpubkey_(const tal_t *ctx,
+			   struct chain_topology *topo,
+			   const u8 *scriptpubkey TAKES,
+			   const struct bitcoin_outpoint *expected_outpoint,
+			   struct amount_sat expected_amount,
+			   void (*cb)(struct lightningd *ld,
+				      const struct bitcoin_tx *tx,
+				      u32 outnum,
+				      const struct txlocator *loc,
+				      void *),
+			   void *arg);
+
+#define unwatch_scriptpubkey(ctx, topo, scriptpubkey, expected_outpoint, expected_amount, cb, arg) \
+	unwatch_scriptpubkey_((ctx), (topo), (scriptpubkey),		\
+			      (expected_outpoint), (expected_amount),	\
+			      typesafe_cb_preargs(void, void *,		\
+						  (cb), (arg),		\
+						  struct lightningd *,	\
+						  const struct bitcoin_tx *, \
+						  u32 outnum,		\
+						  const struct txlocator *), \
+			      (arg))
+
+/* Call any scriptpubkey callbacks for this tx */
+bool watch_check_tx_outputs(const struct chain_topology *topo,
+			    const struct txlocator *loc,
+			    const struct bitcoin_tx *tx,
+			    const struct bitcoin_txid *txid);
+
 void watch_topology_changed(struct chain_topology *topo);
 #endif /* LIGHTNING_LIGHTNINGD_WATCH_H */