askrene: reservation implementation.

They tell us what paths they're using, so we can adjust capacity estimates
accordingly.

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


Header from folded patch 'reserve-fixup.patch':

fixup! askrene: reservation implementation.

plugins/askrene/Makefile

@@ -1,5 +1,5 @@
-PLUGIN_ASKRENE_SRC := plugins/askrene/askrene.c plugins/askrene/layer.c
-PLUGIN_ASKRENE_HEADER := plugins/askrene/askrene.h plugins/askrene/layer.h
+PLUGIN_ASKRENE_SRC := plugins/askrene/askrene.c plugins/askrene/layer.c plugins/askrene/reserve.c
+PLUGIN_ASKRENE_HEADER := plugins/askrene/askrene.h plugins/askrene/layer.h plugins/askrene/reserve.h
 PLUGIN_ASKRENE_OBJS := $(PLUGIN_ASKRENE_SRC:.c=.o)
 
 $(PLUGIN_ASKRENE_OBJS): $(PLUGIN_ASKRENE_HEADER)

plugins/askrene/askrene.c

@@ -16,6 +16,7 @@
 #include <errno.h>
 #include <plugins/askrene/askrene.h>
 #include <plugins/askrene/layer.h>
+#include <plugins/askrene/reserve.h>
 #include <plugins/libplugin.h>
 
 static struct askrene *get_askrene(struct plugin *plugin)
@@ -209,12 +210,26 @@ static struct command_result *json_askrene_reserve(struct command *cmd,
 {
 	struct reserve_path *path;
 	struct json_stream *response;
+	size_t num;
+	struct askrene *askrene = get_askrene(cmd->plugin);
 
 	if (!param(cmd, buffer, params,
 		   p_req("path", param_reserve_path, &path),
 		   NULL))
 		return command_param_failed();
 
+	num = reserves_add(askrene->reserved, path->scidds, path->amounts,
+			   tal_count(path->scidds));
+	if (num != tal_count(path->scidds)) {
+		const struct reserve *r = find_reserve(askrene->reserved, &path->scidds[num]);
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+				    "Overflow reserving %zu: %s amount %s (%s reserved already)",
+				    num,
+				    fmt_short_channel_id_dir(tmpctx, &path->scidds[num]),
+				    fmt_amount_msat(tmpctx, path->amounts[num]),
+				    r ? fmt_amount_msat(tmpctx, r->amount) : "none");
+	}
+
 	response = jsonrpc_stream_success(cmd);
 	return command_finished(cmd, response);
 }
@@ -225,12 +240,27 @@ static struct command_result *json_askrene_unreserve(struct command *cmd,
 {
 	struct reserve_path *path;
 	struct json_stream *response;
+	size_t num;
+	struct askrene *askrene = get_askrene(cmd->plugin);
 
 	if (!param(cmd, buffer, params,
 		   p_req("path", param_reserve_path, &path),
 		   NULL))
 		return command_param_failed();
 
+	num = reserves_remove(askrene->reserved, path->scidds, path->amounts,
+			      tal_count(path->scidds));
+	if (num != tal_count(path->scidds)) {
+		const struct reserve *r = find_reserve(askrene->reserved, &path->scidds[num]);
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+				    "Underflow unreserving %zu: %s amount %s (%zu reserved, amount %s)",
+				    num,
+				    fmt_short_channel_id_dir(tmpctx, &path->scidds[num]),
+				    fmt_amount_msat(tmpctx, path->amounts[num]),
+				    r ? r->num_htlcs : 0,
+				    r ? fmt_amount_msat(tmpctx, r->amount) : "none");
+	}
+
 	response = jsonrpc_stream_success(cmd);
 	return command_finished(cmd, response);
 }
@@ -456,6 +486,7 @@ static const char *init(struct plugin *plugin,
 	struct askrene *askrene = tal(plugin, struct askrene);
 	askrene->plugin = plugin;
 	list_head_init(&askrene->layers);
+	askrene->reserved = new_reserve_hash(askrene);
 	askrene->gossmap = gossmap_load(askrene, GOSSIP_STORE_FILENAME, NULL);
 
 	if (!askrene->gossmap)

plugins/askrene/askrene.h

@@ -5,13 +5,6 @@
 #include <ccan/list/list.h>
 #include <common/amount.h>
 
-/* We reserve a path being used.  This records how many and how much */
-struct reserve {
-	size_t num_htlcs;
-	struct short_channel_id_dir sciddir;
-	struct amount_msat amount;
-};
-
 /* A single route. */
 struct route {
 	/* Actual path to take */
@@ -26,6 +19,8 @@ struct askrene {
 	struct gossmap *gossmap;
 	/* List of layers */
 	struct list_head layers;
+	/* In-flight payment attempts */
+	struct reserve_hash *reserved;
 };
 
 #endif /* LIGHTNING_PLUGINS_ASKRENE_ASKRENE_H */

plugins/askrene/reserve.c

@@ -0,0 +1,119 @@
+#include "config.h"
+#include <assert.h>
+#include <ccan/htable/htable_type.h>
+#include <plugins/askrene/reserve.h>
+
+/* Hash table for reservations */
+static const struct short_channel_id_dir *
+reserve_scidd(const struct reserve *r)
+{
+	return &r->scidd;
+}
+
+static size_t hash_scidd(const struct short_channel_id_dir *scidd)
+{
+	/* scids cost money to generate, so simple hash works here */
+	return (scidd->scid.u64 >> 32) ^ (scidd->scid.u64 >> 16) ^ (scidd->scid.u64 << 1) ^ scidd->dir;
+}
+
+static bool reserve_eq_scidd(const struct reserve *r,
+			     const struct short_channel_id_dir *scidd)
+{
+	return short_channel_id_dir_eq(scidd, &r->scidd);
+}
+
+HTABLE_DEFINE_TYPE(struct reserve, reserve_scidd, hash_scidd,
+		   reserve_eq_scidd, reserve_hash);
+
+struct reserve_hash *new_reserve_hash(const tal_t *ctx)
+{
+	struct reserve_hash *reserved = tal(ctx, struct reserve_hash);
+	reserve_hash_init(reserved);
+	return reserved;
+}
+
+/* Find a reservation for this scidd (if any!) */
+const struct reserve *find_reserve(const struct reserve_hash *reserved,
+				   const struct short_channel_id_dir *scidd)
+{
+	return reserve_hash_get(reserved, scidd);
+}
+
+/* Create a new (empty) reservation */
+static struct reserve *new_reserve(struct reserve_hash *reserved,
+				   const struct short_channel_id_dir *scidd)
+{
+	struct reserve *r = tal(reserved, struct reserve);
+
+	r->num_htlcs = 0;
+	r->amount = AMOUNT_MSAT(0);
+	r->scidd = *scidd;
+
+	reserve_hash_add(reserved, r);
+	return r;
+}
+
+static void del_reserve(struct reserve_hash *reserved, struct reserve *r)
+{
+	assert(r->num_htlcs == 0);
+
+	reserve_hash_del(reserved, r);
+	tal_free(r);
+}
+
+/* Add to existing reservation (false if would overflow). */
+static bool add(struct reserve *r, struct amount_msat amount)
+{
+	if (!amount_msat_add(&r->amount, r->amount, amount))
+		return false;
+	r->num_htlcs++;
+	return true;
+}
+
+static bool remove(struct reserve *r, struct amount_msat amount)
+{
+	if (r->num_htlcs == 0)
+		return false;
+	if (!amount_msat_sub(&r->amount, r->amount, amount))
+		return false;
+	r->num_htlcs--;
+	return true;
+}
+
+/* Atomically add to reserves, or fail.
+ * Returns offset of failure, or num on success */
+size_t reserves_add(struct reserve_hash *reserved,
+		    const struct short_channel_id_dir *scidds,
+		    const struct amount_msat *amounts,
+		    size_t num)
+{
+	for (size_t i = 0; i < num; i++) {
+		struct reserve *r = reserve_hash_get(reserved, &scidds[i]);
+		if (!r)
+			r = new_reserve(reserved, &scidds[i]);
+		if (!add(r, amounts[i])) {
+			reserves_remove(reserved, scidds, amounts, i);
+			return i;
+		}
+	}
+	return num;
+}
+
+/* Atomically remove from reserves, to fail.
+ * Returns offset of failure or tal_count(scidds) */
+size_t reserves_remove(struct reserve_hash *reserved,
+		       const struct short_channel_id_dir *scidds,
+		       const struct amount_msat *amounts,
+		       size_t num)
+{
+	for (size_t i = 0; i < num; i++) {
+		struct reserve *r = reserve_hash_get(reserved, &scidds[i]);
+		if (!r || !remove(r, amounts[i])) {
+			reserves_add(reserved, scidds, amounts, i);
+			return i;
+		}
+		if (r->num_htlcs == 0)
+			del_reserve(reserved, r);
+	}
+	return num;
+}

plugins/askrene/reserve.h

@@ -0,0 +1,38 @@
+#ifndef LIGHTNING_PLUGINS_ASKRENE_RESERVE_H
+#define LIGHTNING_PLUGINS_ASKRENE_RESERVE_H
+/* We have to know what payments are in progress, so we can take into
+ * account the reduced capacity of channels.  We do this by telling
+ * everyone to reserve / unreserve paths as they use them. */
+#include "config.h"
+#include <bitcoin/short_channel_id.h>
+#include <common/amount.h>
+
+/* We reserve a path being used.  This records how many and how much */
+struct reserve {
+	size_t num_htlcs;
+	struct short_channel_id_dir scidd;
+	struct amount_msat amount;
+};
+
+/* Initialize hash table for reservations */
+struct reserve_hash *new_reserve_hash(const tal_t *ctx);
+
+/* Find a reservation for this scidd (if any!) */
+const struct reserve *find_reserve(const struct reserve_hash *reserved,
+				   const struct short_channel_id_dir *scidd);
+
+/* Atomically add to reserves, or fail.
+ * Returns offset of failure, or num on success */
+size_t reserves_add(struct reserve_hash *reserved,
+		    const struct short_channel_id_dir *scidds,
+		    const struct amount_msat *amounts,
+		    size_t num);
+
+/* Atomically remove from reserves, to fail.
+ * Returns offset of failure or tal_count(scidds) */
+size_t reserves_remove(struct reserve_hash *reserved,
+		       const struct short_channel_id_dir *scidds,
+		       const struct amount_msat *amounts,
+		       size_t num);
+
+#endif /* LIGHTNING_PLUGINS_ASKRENE_RESERVE_H */