feat: adds channel_state_changed notification

This notification will be raised whenever a channel state changes.
The payload includes the channel and peer identifiers and the
old and the new state.

Example payload:

```
{
    "channel_state_changed": {
        "peer_id": "03bc9337c7a28bb784d67742ebedd30a93bacdf7e4ca16436ef3798000242b2251",
        "channel_id": "a2d0851832f0e30a0cf778a826d72f077ca86b69f72677e0267f23f63a0599b4",
        "short_channel_id" : "561820x1020x1",
        "old_state": "CHANNELD_NORMAL",
        "new_state": "AWAITING_UNILATERAL"
    }
}
```

Changelog-Added: Plugins: channel_state_changed notification

lightningd/channel.c

@@ -18,6 +18,7 @@
 #include <lightningd/jsonrpc.h>
 #include <lightningd/lightningd.h>
 #include <lightningd/log.h>
+#include <lightningd/notification.h>
 #include <lightningd/opening_control.h>
 #include <lightningd/peer_control.h>
 #include <lightningd/subd.h>
@@ -384,6 +385,8 @@ void channel_set_state(struct channel *channel,
 		       enum channel_state old_state,
 		       enum channel_state state)
 {
+	struct channel_id cid;
+
 	log_info(channel->log, "State changed from %s to %s",
 		 channel_state_name(channel), channel_state_str(state));
 	if (channel->state != old_state)
@@ -394,6 +397,15 @@ void channel_set_state(struct channel *channel,
 
 	/* TODO(cdecker) Selectively save updated fields to DB */
 	wallet_channel_save(channel->peer->ld->wallet, channel);
+
+	/* plugin notification channel_state_changed */
+	derive_channel_id(&cid, &channel->funding_txid, channel->funding_outnum);
+	notify_channel_state_changed(channel->peer->ld,
+				     &channel->peer->id,
+				     &cid,
+				     channel->scid,
+				     old_state,
+				     state);
 }
 
 void channel_fail_permanent(struct channel *channel, const char *fmt, ...)

lightningd/notification.c

@@ -210,6 +210,51 @@ void notify_channel_opened(struct lightningd *ld, struct node_id *node_id,
 	plugins_notify(ld->plugins, take(n));
 }
 
+static void channel_state_changed_notification_serialize(struct json_stream *stream,
+							 struct node_id *peer_id,
+							 struct channel_id *cid,
+							 struct short_channel_id *scid,
+							 enum channel_state old_state,
+							 enum channel_state new_state)
+{
+	json_object_start(stream, "channel_state_changed");
+	json_add_node_id(stream, "peer_id", peer_id);
+	json_add_string(stream, "channel_id",
+			type_to_string(tmpctx, struct channel_id, cid));
+	if (scid)
+		json_add_short_channel_id(stream, "short_channel_id", scid);
+	else
+		json_add_null(stream, "short_channel_id");
+	json_add_string(stream, "old_state", channel_state_str(old_state));
+	json_add_string(stream, "new_state", channel_state_str(new_state));
+	json_object_end(stream);
+}
+
+
+REGISTER_NOTIFICATION(channel_state_changed,
+		      channel_state_changed_notification_serialize)
+
+void notify_channel_state_changed(struct lightningd *ld,
+				  struct node_id *peer_id,
+				  struct channel_id *cid,
+				  struct short_channel_id *scid,
+				  enum channel_state old_state,
+				  enum channel_state new_state)
+{
+	void (*serialize)(struct json_stream *,
+			  struct node_id *,
+			  struct channel_id *,
+			  struct short_channel_id *,
+			  enum channel_state,
+			  enum channel_state) = channel_state_changed_notification_gen.serialize;
+
+	struct jsonrpc_notification *n
+		= jsonrpc_notification_start(NULL, channel_state_changed_notification_gen.topic);
+	serialize(n->stream, peer_id, cid, scid, old_state, new_state);
+	jsonrpc_notification_end(n);
+	plugins_notify(ld->plugins, take(n));
+}
+
 static void forward_event_notification_serialize(struct json_stream *stream,
 						 const struct htlc_in *in,
 						 const struct short_channel_id *scid_out,

lightningd/notification.h

@@ -7,9 +7,11 @@
 #include <ccan/json_escape/json_escape.h>
 #include <ccan/time/time.h>
 #include <common/amount.h>
+#include <common/channel_id.h>
 #include <common/coin_mvt.h>
 #include <common/errcode.h>
 #include <common/node_id.h>
+#include <lightningd/channel_state.h>
 #include <lightningd/htlc_end.h>
 #include <lightningd/jsonrpc.h>
 #include <lightningd/lightningd.h>
@@ -55,6 +57,13 @@ void notify_channel_opened(struct lightningd *ld, struct node_id *node_id,
 			   struct amount_sat *funding_sat, struct bitcoin_txid *funding_txid,
 			   bool *funding_locked);
 
+void notify_channel_state_changed(struct lightningd *ld,
+				  struct node_id *peer_id,
+				  struct channel_id *cid,
+				  struct short_channel_id *scid,
+				  enum channel_state old_state,
+				  enum channel_state new_state);
+
 void notify_forward_event(struct lightningd *ld,
 			  const struct htlc_in *in,
 			  /* May be NULL if we don't know. */

wallet/db_postgres_sqlgen.c

@@ -1648,4 +1648,4 @@ struct db_query db_postgres_queries[] = {
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_POSTGRES */
 
-// SHA256STAMP:e55a8febb74330a9167e8498b26e556609d95b7ca6ef984da1fa200e53e36a7e
+// SHA256STAMP:4c9787464f33fe9bfd209efbd84daebeb5584d52daa1d83f4c34f9a0a6108b46

wallet/db_sqlite3_sqlgen.c

@@ -1648,4 +1648,4 @@ struct db_query db_sqlite3_queries[] = {
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_SQLITE3 */
 
-// SHA256STAMP:e55a8febb74330a9167e8498b26e556609d95b7ca6ef984da1fa200e53e36a7e
+// SHA256STAMP:4c9787464f33fe9bfd209efbd84daebeb5584d52daa1d83f4c34f9a0a6108b46

wallet/statements_gettextgen.po

@@ -1082,7 +1082,7 @@ msgstr ""
 msgid "not a valid SQL statement"
 msgstr ""
 
-#: wallet/test/run-wallet.c:1351
+#: wallet/test/run-wallet.c:1359
 msgid "INSERT INTO channels (id) VALUES (1);"
 msgstr ""
-#  SHA256STAMP:de15ae770286fe050f7b2d712bcc2a3311a8737e920353bb8c7d8dbf0188db69
+#  SHA256STAMP:108fcc46e6fa6e190b27773161a9c6bf9a83cb25e9d3164fa40e9de9e6f98644

wallet/test/run-wallet.c

@@ -428,6 +428,14 @@ void notify_chain_mvt(struct lightningd *ld UNNEEDED, const struct chain_coin_mv
 /* Generated stub for notify_channel_mvt */
 void notify_channel_mvt(struct lightningd *ld UNNEEDED, const struct channel_coin_mvt *mvt UNNEEDED)
 { fprintf(stderr, "notify_channel_mvt called!\n"); abort(); }
+/* Generated stub for notify_channel_state_changed */
+void notify_channel_state_changed(struct lightningd *ld UNNEEDED,
+				  struct node_id *peer_id UNNEEDED,
+				  struct channel_id *cid UNNEEDED,
+				  struct short_channel_id *scid UNNEEDED,
+				  enum channel_state old_state UNNEEDED,
+				  enum channel_state new_state UNNEEDED)
+{ fprintf(stderr, "notify_channel_state_changed called!\n"); abort(); }
 /* Generated stub for notify_connect */
 void notify_connect(struct lightningd *ld UNNEEDED, struct node_id *nodeid UNNEEDED,
 		    struct wireaddr_internal *addr UNNEEDED)