plugin: Split out the struct channel_hint handling

We're getting serious about how we manage the channel_hints, so let's
give them a proper home.

plugins/Makefile

@@ -27,8 +27,14 @@ PLUGIN_LIB_SRC := plugins/libplugin.c
 PLUGIN_LIB_HEADER := plugins/libplugin.h
 PLUGIN_LIB_OBJS := $(PLUGIN_LIB_SRC:.c=.o)
 
-PLUGIN_PAY_LIB_SRC := plugins/libplugin-pay.c
-PLUGIN_PAY_LIB_HEADER := plugins/libplugin-pay.h
+PLUGIN_PAY_LIB_SRC := \
+	plugins/channel_hint.c \
+	plugins/libplugin-pay.c
+
+PLUGIN_PAY_LIB_HEADER := \
+	plugins/channel_hint.h \
+	plugins/libplugin-pay.h
+
 PLUGIN_PAY_LIB_OBJS := $(PLUGIN_PAY_LIB_SRC:.c=.o)
 
 PLUGIN_OFFERS_SRC := plugins/offers.c plugins/offers_offer.c plugins/offers_invreq_hook.c plugins/offers_inv_hook.c plugins/establish_onion_path.c plugins/fetchinvoice.c

plugins/channel_hint.c

@@ -0,0 +1,96 @@
+#include "config.h"
+#include <plugins/channel_hint.h>
+
+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, "estimated_capacity_msat",
+			     hint->estimated_capacity);
+	json_add_amount_msat(dest, "overall_capacity_msat",
+			     hint->overall_capacity);
+	json_add_bool(dest, "enabled", hint->enabled);
+	json_object_end(dest);
+}
+
+#define PAY_REFILL_TIME 7200
+
+/**
+ * Update the `channel_hint` in place, return whether it should be kept.
+ *
+ * This computes the refill-rate based on the overall capacity, and
+ * the time elapsed since the last update and relaxes the upper bound
+ * on the capacity, and resets the enabled flag if appropriate. If the
+ * hint is no longer useful, i.e., it does not provide any additional
+ * information on top of the structural information we've learned from
+ * the gossip, then we return `false` to signal that the
+ * `channel_hint` may be removed.
+ */
+bool channel_hint_update(const struct timeabs now, struct channel_hint *hint)
+{
+	/* Precision is not required here, so integer division is good
+	 * enough. But keep the order such that we do not round down
+	 * too much. We do so by first multiplying, before
+	 * dividing. The formula is `current = last + delta_t *
+	 * overall / refill_rate`.
+	 */
+	struct amount_msat refill;
+	u64 seconds = now.ts.tv_sec - hint->timestamp;
+	if (!amount_msat_mul(&refill, hint->overall_capacity, seconds))
+		abort();
+
+	refill = amount_msat_div(refill, PAY_REFILL_TIME);
+	if (!amount_msat_add(&hint->estimated_capacity,
+			     hint->estimated_capacity, refill))
+		abort();
+
+	/* Clamp the value to the `overall_capacity` */
+	if (amount_msat_greater(hint->estimated_capacity,
+				hint->overall_capacity))
+		hint->estimated_capacity = hint->overall_capacity;
+
+	/* TODO This is rather coarse. We could map the disabled flag
+	to having 0msat capacity, and then relax from there. But it'd
+	likely be too slow of a relaxation.*/
+	if (seconds > 60)
+		hint->enabled = true;
+
+	/* Since we update in-place we should make sure that we can
+	 * just call update again and the result is stable, if no time
+	 * has passed. */
+	hint->timestamp = now.ts.tv_sec;
+
+	/* We report this hint as useless, if the hint does not
+	 * restrict the channel, i.e., if it is enabled and the
+	 * estimate is the same as the overall capacity. */
+	return !hint->enabled || amount_msat_greater(hint->overall_capacity,
+						     hint->estimated_capacity);
+}
+
+/**
+ * Load a channel_hint from its JSON representation.
+ *
+ * @return The initialized `channel_hint` or `NULL` if we encountered a parsing
+ *         error.
+ */
+/*
+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:%,estimated_capacity_msat:%,overall_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;
+}
+*/

plugins/channel_hint.h

@@ -0,0 +1,61 @@
+#ifndef LIGHTNING_PLUGINS_CHANNEL_HINT_H
+#define LIGHTNING_PLUGINS_CHANNEL_HINT_H
+
+#include "config.h"
+#include <bitcoin/short_channel_id.h>
+#include <ccan/short_types/short_types.h>
+#include <ccan/time/time.h>
+#include <common/amount.h>
+#include <common/json_stream.h>
+#include <plugins/libplugin-pay.h>
+#include <plugins/libplugin.h>
+
+/* Information about channels we inferred from a) looking at our channels, and
+ * b) from failures encountered during attempts to perform a payment. These
+ * are attached to the root payment, since that information is
+ * global. Attempts update the estimated channel capacities when starting, and
+ * 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
+	 * one it is, but we'll prefer the scid as that's likely more
+	 * readable than the alias. */
+	struct short_channel_id_dir scid;
+
+	/* Upper bound on remove channels inferred from payment failures. */
+	struct amount_msat estimated_capacity;
+
+	/* Is the channel enabled? */
+	bool enabled;
+
+	/* Non-null if we are one endpoint of this channel */
+	struct local_hint *local;
+
+	/* The total `amount_msat` that were used to fund the
+	 * channel. This is always smaller gte the
+	 * estimated_capacity */
+	struct amount_msat overall_capacity;
+};
+
+/* A collection of channel_hint instances, allowing us to handle and
+ * update them more easily. */
+struct channel_hint_set {
+	/* tal_arr of channel_hints. */
+	struct channel_hint *hints;
+};
+
+bool channel_hint_update(const struct timeabs now,
+				struct channel_hint *hint);
+
+void channel_hint_to_json(const char *name, const struct channel_hint *hint, struct json_stream *dest);
+
+#endif /* LIGHTNING_PLUGINS_CHANNEL_HINT_H */

plugins/libplugin-pay.c

@@ -387,87 +387,6 @@ 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, "estimated_capacity_msat", hint->estimated_capacity);
-	json_add_amount_msat(dest, "overall_capacity_msat", hint->overall_capacity);
-	json_add_bool(dest, "enabled", hint->enabled);
-	json_object_end(dest);
-}
-
-#define PAY_REFILL_TIME 7200
-
-/**
- * Update the `channel_hint` in place, return whether it should be kept.
- *
- * This computes the refill-rate based on the overall capacity, and
- * the time elapsed since the last update and relaxes the upper bound
- * on the capacity, and resets the enabled flag if appropriate. If the
- * hint is no longer useful, i.e., it does not provide any additional
- * information on top of the structural information we've learned from
- * the gossip, then we return `false` to signal that the
- * `channel_hint` may be removed.
- */
-static bool channel_hint_update(const struct timeabs now,
-				struct channel_hint *hint)
-{
-	/* Precision is not required here, so integer division is good enough.
-	 */
-	u64 refill_rate = hint->overall_capacity.millisatoshis / PAY_REFILL_TIME; /* Raw: just simpler */
-	u64 seconds = now.ts.tv_sec - hint->timestamp;
-	hint->estimated_capacity.millisatoshis += refill_rate * seconds; /* Raw: simpler */
-
-	/* Clamp the value to the `overall_capacity` */
-	if (amount_msat_greater(hint->estimated_capacity,
-				hint->overall_capacity))
-		hint->estimated_capacity = hint->overall_capacity;
-
-	/* TODO This is rather coarse. We could map the disabled flag
-	to having 0msat capacity, and then relax from there. But it'd
-	likely be too slow of a relaxation.*/
-	if (seconds > 60)
-		hint->enabled = true;
-
-	/* Since we update in-place we should make sure that we can
-	 * just call update again and the result is stable, if no time
-	 * has passed. */
-	hint->timestamp = now.ts.tv_sec;
-
-	/* We report this hint as useless, if the hint does not
-	 * restrict the channel, i.e., if it is enabled and the
-	 * estimate is the same as the overall capacity. */
-	return !hint->enabled || amount_msat_greater(hint->overall_capacity,
-						     hint->estimated_capacity);
-}
-
-/**
- * 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:%,estimated_capacity_msat:%,overall_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
      *

plugins/libplugin-pay.h

@@ -5,6 +5,7 @@
 #include <ccan/io/io.h>
 #include <common/bolt11.h>
 #include <common/route.h>
+#include <plugins/channel_hint.h>
 #include <plugins/libplugin.h>
 #include <wire/onion_wire.h>
 
@@ -61,42 +62,6 @@ struct local_hint {
 	u16 htlc_budget;
 };
 
-/* Information about channels we inferred from a) looking at our channels, and
- * b) from failures encountered during attempts to perform a payment. These
- * are attached to the root payment, since that information is
- * global. Attempts update the estimated channel capacities when starting, and
- * 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
-	 * one it is, but we'll prefer the scid as that's likely more
-	 * readable than the alias. */
-	struct short_channel_id_dir scid;
-
-	/* Upper bound on remove channels inferred from payment failures. */
-	struct amount_msat estimated_capacity;
-
-	/* Is the channel enabled? */
-	bool enabled;
-
-	/* Non-null if we are one endpoint of this channel */
-	struct local_hint *local;
-
-	/* The total `amount_msat` that were used to fund the
-	 * channel. This is always smaller gte the
-	 * estimated_capacity */
-	struct amount_msat overall_capacity;
-};
-
 /* Each payment goes through a number of steps that are always processed in
  * the same order, and some modifiers are called with the payment, and the
  * modifier's data before and after certain steps, allowing customization. The

plugins/test/Makefile

@@ -20,14 +20,16 @@ plugins/test/run-route-overlong:		\
 	common/gossmap.o			\
 	common/node_id.o			\
 	common/route.o				\
-        gossipd/gossip_store_wiregen.o
+        gossipd/gossip_store_wiregen.o		\
+	plugins/channel_hint.o
 
 plugins/test/run-route-calc:			\
 	common/fp16.o				\
 	common/gossmap.o			\
 	common/node_id.o			\
 	common/route.o				\
-	gossipd/gossip_store_wiregen.o
+	gossipd/gossip_store_wiregen.o		\
+	plugins/channel_hint.o
 
 $(PLUGIN_TEST_PROGRAMS): $(BITCOIN_OBJS) $(WIRE_OBJS) $(PLUGIN_TEST_COMMON_OBJS)