pay: Share channel_hints across payments and plugins

common/json_parse.c

@@ -5,7 +5,6 @@
 #include <bitcoin/privkey.h>
 #include <bitcoin/psbt.h>
 #include <bitcoin/pubkey.h>
-#include <bitcoin/short_channel_id.h>
 #include <bitcoin/tx.h>
 #include <ccan/json_escape/json_escape.h>
 #include <ccan/mem/mem.h>
@@ -574,6 +573,25 @@ bool json_to_short_channel_id(const char *buffer, const jsmntok_t *tok,
 					  tok->end - tok->start, scid));
 }
 
+bool json_to_short_channel_id_dir(const char *buffer, const jsmntok_t *tok,
+				  struct short_channel_id_dir *scidd)
+{
+	jsmntok_t scidtok, numtok;
+	u32 dir;
+
+	if (!split_tok(buffer, tok, '/', &scidtok, &numtok))
+		return false;
+
+	if (!json_to_short_channel_id(buffer, &scidtok, &scidd->scid))
+		return false;
+
+	if (!json_to_u32(buffer, &numtok, &dir) || (dir > 1))
+		return false;
+
+	scidd->dir = dir;
+	return true;
+}
+
 bool json_to_txid(const char *buffer, const jsmntok_t *tok,
 		  struct bitcoin_txid *txid)
 {

common/json_parse.h

@@ -1,6 +1,7 @@
 #ifndef LIGHTNING_COMMON_JSON_PARSE_H
 #define LIGHTNING_COMMON_JSON_PARSE_H
 #include "config.h"
+#include <bitcoin/short_channel_id.h>
 #include <ccan/crypto/sha256/sha256.h>
 #include <common/coin_mvt.h>
 #include <common/errcode.h>
@@ -110,6 +111,10 @@ bool json_to_outpoint(const char *buffer, const jsmntok_t *tok,
 bool json_to_channel_id(const char *buffer, const jsmntok_t *tok,
 			struct channel_id *cid);
 
+/* Extract a channel id + dir from this */
+bool json_to_short_channel_id_dir(const char *buffer, const jsmntok_t *tok,
+				  struct short_channel_id_dir *scidd);
+
 /* Extract a coin movement 'tag' from this */
 bool json_to_coin_mvt_tag(const char *buffer, const jsmntok_t *tok,
 			  enum mvt_tag *tag);

common/json_stream.c

@@ -3,7 +3,6 @@
 #include <bitcoin/preimage.h>
 #include <bitcoin/privkey.h>
 #include <bitcoin/psbt.h>
-#include <bitcoin/short_channel_id.h>
 #include <bitcoin/signature.h>
 #include <bitcoin/tx.h>
 #include <ccan/io/io.h>
@@ -485,6 +484,16 @@ void json_add_short_channel_id(struct json_stream *response,
 			 short_channel_id_outnum(scid));
 }
 
+void json_add_short_channel_id_dir(struct json_stream *response,
+			       const char *fieldname,
+			       struct short_channel_id_dir scidd)
+{
+	json_add_str_fmt(response, fieldname, "%dx%dx%d/%d",
+			 short_channel_id_blocknum(scidd.scid),
+			 short_channel_id_txnum(scidd.scid),
+			 short_channel_id_outnum(scidd.scid), scidd.dir);
+}
+
 static void json_add_address_fields(struct json_stream *response,
 				    const struct wireaddr *addr,
 				    const char *typefield)

common/json_stream.h

@@ -5,6 +5,7 @@
 #define LIGHTNING_COMMON_JSON_STREAM_H
 #include "config.h"
 
+#include <bitcoin/short_channel_id.h>
 #define JSMN_STRICT 1
 # include <external/jsmn/jsmn.h>
 
@@ -313,6 +314,11 @@ void json_add_short_channel_id(struct json_stream *response,
 			       const char *fieldname,
 			       struct short_channel_id id);
 
+/* '"fieldname" : "1234:5:6/1"' */
+void json_add_short_channel_id_dir(struct json_stream *response,
+				   const char *fieldname,
+				   struct short_channel_id_dir idd);
+
 /* JSON serialize a network address for a node */
 void json_add_address(struct json_stream *response, const char *fieldname,
 		      const struct wireaddr *addr);

plugins/libplugin-pay.c

@@ -386,6 +386,58 @@ void payment_start(struct payment *p)
 	payment_start_at_blockheight(p, INVALID_BLOCKHEIGHT);
 }
 
+static void channel_hint_to_json(const char *name, const struct channel_hint *hint, struct json_stream *dest)
+{
+	json_object_start(dest, name);
+	json_add_u32(dest, "timestamp", hint->timestamp);
+	json_add_short_channel_id_dir(dest, "scid", hint->scid);
+	json_add_amount_msat(dest, "capacity_msat", hint->estimated_capacity);
+	json_add_bool(dest, "enabled", hint->enabled);
+	json_object_end(dest);
+}
+
+/**
+ * Load a channel_hint from its JSON representation.
+ *
+ * @return The initialized `channel_hint` or `NULL` if we encountered a parsing
+ *         error.
+ */
+/*
+static struct channel_hint *channel_hint_from_json(const tal_t *ctx,
+						   const char *buffer,
+						   const jsmntok_t *toks)
+{
+	const char *ret;
+	struct channel_hint *hint = tal(ctx, struct channel_hint);
+	ret = json_scan(ctx, buffer, toks,
+			"{timestamp:%,scid:%,capacity_msat:%,enabled:%}",
+			JSON_SCAN(json_to_u32, &hint->timestamp),
+			JSON_SCAN(json_to_short_channel_id_dir, &hint->scid),
+			JSON_SCAN(json_to_msat, &hint->estimated_capacity),
+			JSON_SCAN(json_to_bool, &hint->enabled));
+
+	if (ret != NULL)
+		hint = tal_free(hint);
+	return hint;
+}
+*/
+    /**
+     * Notify subscribers of the `channel_hint` topic about a changed hint
+     *
+     * We share the channel_hints across payments, and across plugins, in order
+     * to maximize the context they have when performing payments.
+     */
+static void channel_hint_notify(struct plugin *plugin,
+				const struct channel_hint *hint)
+{
+	struct json_stream *js =
+	    plugin_notification_start(plugin, "channel_hint_update");
+
+	/* The timestamp used to decay the observation over time. */
+	channel_hint_to_json("channel_hint", hint, js);
+	plugin_notification_end(plugin, js);
+}
+
 static void channel_hints_update(struct payment *p,
 				 const struct short_channel_id scid,
 				 int direction, bool enabled, bool local,
@@ -394,6 +446,7 @@ static void channel_hints_update(struct payment *p,
 {
 	struct payment *root = payment_root(p);
 	struct channel_hint newhint;
+	u32 timestamp = time_now().ts.tv_sec;
 
 	/* If the channel is marked as enabled it must have an estimate. */
 	assert(!enabled || estimated_capacity != NULL);
@@ -423,7 +476,8 @@ static void channel_hints_update(struct payment *p,
 				modified = true;
 			}
 
-			if (modified)
+			if (modified) {
+				hint->timestamp = timestamp;
 				paymod_log(p, LOG_DBG,
 					   "Updated a channel hint for %s: "
 					   "enabled %s, "
@@ -433,12 +487,15 @@ static void channel_hints_update(struct payment *p,
 					   hint->enabled ? "true" : "false",
 					   fmt_amount_msat(tmpctx,
 						hint->estimated_capacity));
+				channel_hint_notify(p->plugin, hint);
+			}
 			return;
 		}
 	}
 
 	/* No hint found, create one. */
 	newhint.enabled = enabled;
+	newhint.timestamp = timestamp;
 	newhint.scid.scid = scid;
 	newhint.scid.dir = direction;
 	if (local) {
@@ -458,6 +515,7 @@ static void channel_hints_update(struct payment *p,
 	    fmt_short_channel_id_dir(tmpctx, &newhint.scid),
 	    newhint.enabled ? "true" : "false",
 	    fmt_amount_msat(tmpctx, newhint.estimated_capacity));
+	channel_hint_notify(p->plugin, &newhint);
 }
 
 static void payment_exclude_most_expensive(struct payment *p)

plugins/libplugin-pay.h

@@ -68,6 +68,13 @@ struct local_hint {
  * get remove on failure. Success keeps the capacities, since the capacities
  * changed due to the successful HTLCs. */
 struct channel_hint {
+	/* The timestamp this observation was made. Used to let the
+	 * constraint expressed by this hint decay over time, until it
+	 * is fully relaxed, at which point we can forget about it
+	 * (the structural information is the best we can do in that
+	 * case).
+	 */
+	u32 timestamp;
 	/* The short_channel_id we're going to use when referring to
 	 * this channel. This can either be the real scid, or the
 	 * local alias. The `pay` algorithm doesn't really care which

plugins/offers_offer.c

@@ -352,25 +352,6 @@ static struct command_result *currency_done(struct command *cmd,
 	return maybe_add_path(cmd, offinfo);
 }
 
-static bool json_to_short_channel_id_dir(const char *buffer, const jsmntok_t *tok,
-					 struct short_channel_id_dir *scidd)
-{
-	jsmntok_t scidtok, numtok;
-	u32 dir;
-
-	if (!split_tok(buffer, tok, '/', &scidtok, &numtok))
-		return false;
-
-	if (!json_to_short_channel_id(buffer, &scidtok, &scidd->scid))
-		return false;
-
-	if (!json_to_u32(buffer, &numtok, &dir) || (dir > 1))
-		return false;
-
-	scidd->dir = dir;
-	return true;
-}
-
 static bool json_to_sciddir_or_pubkey(const char *buffer, const jsmntok_t *tok,
 				      struct sciddir_or_pubkey *sciddir_or_pubkey)
 {

plugins/pay.c

@@ -1531,6 +1531,7 @@ static const struct plugin_command commands[] = {
 static const char *notification_topics[] = {
 	"pay_success",
 	"pay_failure",
+	"channel_hint_update",
 };
 
 int main(int argc, char *argv[])

plugins/test/run-route-calc.c

@@ -81,6 +81,10 @@ void json_add_amount_msat(struct json_stream *result UNNEEDED,
 			  struct amount_msat msat)
 
 { fprintf(stderr, "json_add_amount_msat called!\n"); abort(); }
+/* Generated stub for json_add_bool */
+void json_add_bool(struct json_stream *result UNNEEDED, const char *fieldname UNNEEDED,
+		   bool value UNNEEDED)
+{ fprintf(stderr, "json_add_bool called!\n"); abort(); }
 /* Generated stub for json_add_hex_talarr */
 void json_add_hex_talarr(struct json_stream *result UNNEEDED,
 			 const char *fieldname UNNEEDED,
@@ -116,6 +120,11 @@ void json_add_short_channel_id(struct json_stream *response UNNEEDED,
 			       const char *fieldname UNNEEDED,
 			       struct short_channel_id id UNNEEDED)
 { fprintf(stderr, "json_add_short_channel_id called!\n"); abort(); }
+/* Generated stub for json_add_short_channel_id_dir */
+void json_add_short_channel_id_dir(struct json_stream *response UNNEEDED,
+				   const char *fieldname UNNEEDED,
+				   struct short_channel_id_dir idd UNNEEDED)
+{ fprintf(stderr, "json_add_short_channel_id_dir called!\n"); abort(); }
 /* Generated stub for json_add_string */
 void json_add_string(struct json_stream *js UNNEEDED,
 		     const char *fieldname UNNEEDED,

plugins/test/run-route-overlong.c

@@ -78,6 +78,10 @@ void json_add_amount_msat(struct json_stream *result UNNEEDED,
 			  struct amount_msat msat)
 
 { fprintf(stderr, "json_add_amount_msat called!\n"); abort(); }
+/* Generated stub for json_add_bool */
+void json_add_bool(struct json_stream *result UNNEEDED, const char *fieldname UNNEEDED,
+		   bool value UNNEEDED)
+{ fprintf(stderr, "json_add_bool called!\n"); abort(); }
 /* Generated stub for json_add_hex_talarr */
 void json_add_hex_talarr(struct json_stream *result UNNEEDED,
 			 const char *fieldname UNNEEDED,
@@ -113,6 +117,11 @@ void json_add_short_channel_id(struct json_stream *response UNNEEDED,
 			       const char *fieldname UNNEEDED,
 			       struct short_channel_id id UNNEEDED)
 { fprintf(stderr, "json_add_short_channel_id called!\n"); abort(); }
+/* Generated stub for json_add_short_channel_id_dir */
+void json_add_short_channel_id_dir(struct json_stream *response UNNEEDED,
+				   const char *fieldname UNNEEDED,
+				   struct short_channel_id_dir idd UNNEEDED)
+{ fprintf(stderr, "json_add_short_channel_id_dir called!\n"); abort(); }
 /* Generated stub for json_add_string */
 void json_add_string(struct json_stream *js UNNEEDED,
 		     const char *fieldname UNNEEDED,