renepay: change the groupid selection

Searches the first unused groupid and uses that number for the current
payment attempt.
We previously used the highest value of used groupid + 1, which breaks
in a few corner cases.

Changelog-None

Signed-off-by: Lagrang3 <[email protected]>

Author: Lagrang3

plugins/renepay/mods.c

@@ -1,4 +1,5 @@
 #include "config.h"
+#include <ccan/asort/asort.h>
 #include <ccan/bitmap/bitmap.h>
 #include <common/amount.h>
 #include <common/bolt11.h>
@@ -14,8 +15,6 @@
 #include <plugins/renepay/routetracker.h>
 #include <unistd.h>
 
-#define INVALID_ID UINT64_MAX
-
 #define OP_NULL NULL
 #define OP_CALL (void *)1
 #define OP_IF (void *)2
@@ -918,6 +917,15 @@ REGISTER_PAYMENT_MODIFIER(checktimeout, checktimeout_cb);
  * we should return payment_success inmediately.
  */
 
+static int cmp_u64(const u64 *a, const u64 *b, void *unused)
+{
+	if (*a < *b)
+		return -1;
+	if (*a > *b)
+		return 1;
+	return 0;
+}
+
 static struct command_result *pendingsendpays_done(struct command *cmd,
 						   const char *method UNUSED,
 						   const char *buf,
@@ -927,11 +935,12 @@ static struct command_result *pendingsendpays_done(struct command *cmd,
 	size_t i;
 	const char *err;
 	const jsmntok_t *t, *arr;
-	u64 max_group_id = 0;
 
 	/* Data for pending payments, this will be the one
 	 * who's result gets replayed if we end up suspending. */
-	u64 pending_group_id = INVALID_ID;
+	bool has_pending = false;
+	u64 unused_groupid;
+	u64 pending_group_id;
 	u64 max_pending_partid = 0;
 	struct amount_msat pending_sent = AMOUNT_MSAT(0),
 			   pending_msat = AMOUNT_MSAT(0);
@@ -961,6 +970,8 @@ static struct command_result *pendingsendpays_done(struct command *cmd,
 		return payment_success(payment, &success.preimage);
 	}
 
+	u64 *groupid_arr = tal_arr(tmpctx, u64, 0);
+
 	// find if there is one pending group
 	json_for_each_arr(i, t, arr)
 	{
@@ -980,10 +991,13 @@ static struct command_result *pendingsendpays_done(struct command *cmd,
 				   __func__, err);
 
 		if (streq(status, "pending")) {
+			has_pending = true;
 			pending_group_id = groupid;
 			break;
 		}
+		tal_arr_expand(&groupid_arr, groupid);
 	}
+	assert(tal_count(groupid_arr) == arr->size);
 
 	/* We need two loops to get the highest partid for a groupid that has
 	 * pending sendpays. */
@@ -1014,12 +1028,8 @@ static struct command_result *pendingsendpays_done(struct command *cmd,
 				   "following error: %s",
 				   __func__, err);
 
-		/* If we decide to create a new group, we base it on
-		 * max_group_id */
-		if (groupid > max_group_id)
-			max_group_id = groupid;
-
-		if (groupid == pending_group_id && partid > max_pending_partid)
+		if (has_pending && groupid == pending_group_id &&
+		    partid > max_pending_partid)
 			max_pending_partid = partid;
 
 		/* status could be completed, pending or failed */
@@ -1043,7 +1053,17 @@ static struct command_result *pendingsendpays_done(struct command *cmd,
 		assert(!streq(status, "complete"));
 	}
 
-	if (pending_group_id != INVALID_ID) {
+	/* find the first unused groupid */
+	unused_groupid = 0;
+	asort(groupid_arr, tal_count(groupid_arr), cmp_u64, NULL);
+	for (i = 0; i < tal_count(groupid_arr); i++) {
+		if (unused_groupid < groupid_arr[i])
+			break;
+		if (unused_groupid == groupid_arr[i])
+			unused_groupid++;
+	}
+
+	if (has_pending) {
 		/* Continue where we left off? */
 		payment->groupid = pending_group_id;
 		payment->next_partid = max_pending_partid + 1;
@@ -1061,7 +1081,7 @@ static struct command_result *pendingsendpays_done(struct command *cmd,
 	} else {
 		/* There are no pending nor completed sendpays, get me the last
 		 * sendpay group. */
-		payment->groupid = max_group_id + 1;
+		payment->groupid = unused_groupid;
 		payment->next_partid = 1;
 		payment->total_sent = AMOUNT_MSAT(0);
 		payment->total_delivering = AMOUNT_MSAT(0);