valgrind-fix: patch valgrind error on log statement in pay plugin

The htlc_budget only exists iff the hint is a 'local' one; we were
failing to write to the htlc_budget field for non-local cases.

To avoid this, we make `local` into a struct that contains the fields
that pertain to local-only payments (in this case, `htlc_budget`).

Valgrind error file: valgrind-errors.1813487
==1813487== Conditional jump or move depends on uninitialised value(s)
==1813487==    at 0x4A9C958: __vfprintf_internal (vfprintf-internal.c:1687)
==1813487==    by 0x4AB0F99: __vsnprintf_internal (vsnprintf.c:114)
==1813487==    by 0x1D2EF9: do_vfmt (str.c:66)
==1813487==    by 0x1D3006: tal_vfmt_ (str.c:92)
==1813487==    by 0x11A60A: paymod_log (libplugin-pay.c:167)
==1813487==    by 0x11B749: payment_chanhints_apply_route (libplugin-pay.c:534)
==1813487==    by 0x11EB36: payment_compute_onion_payloads (libplugin-pay.c:1707)
==1813487==    by 0x12000F: payment_continue (libplugin-pay.c:2135)
==1813487==    by 0x1245B9: adaptive_splitter_cb (libplugin-pay.c:3800)
==1813487==    by 0x11FFB6: payment_continue (libplugin-pay.c:2123)
==1813487==    by 0x1206BC: retry_step_cb (libplugin-pay.c:2301)
==1813487==    by 0x11FFB6: payment_continue (libplugin-pay.c:2123)
==1813487==
{
   <insert_a_suppression_name_here>
   Memcheck:Cond
   fun:__vfprintf_internal
   fun:__vsnprintf_internal
   fun:do_vfmt
   fun:tal_vfmt_
   fun:paymod_log
   fun:payment_chanhints_apply_route
   fun:payment_compute_onion_payloads
   fun:payment_continue
   fun:adaptive_splitter_cb
   fun:payment_continue
   fun:retry_step_cb
[sesh] 0:[tmux]*Z

Suggested-By: @nothingmuch

plugins/libplugin-pay.c

@@ -351,8 +351,9 @@ static void channel_hints_update(struct payment *p,
 				hint->estimated_capacity = *estimated_capacity;
 				modified = true;
 			}
-			if (htlc_budget != NULL && *htlc_budget < hint->htlc_budget) {
+			if (htlc_budget != NULL) {
-				hint->htlc_budget = *htlc_budget;
+				assert(hint->local);
+				hint->local->htlc_budget = *htlc_budget;
 				modified = true;
 			}
 
@@ -376,17 +377,15 @@ static void channel_hints_update(struct payment *p,
 	newhint.enabled = enabled;
 	newhint.scid.scid = scid;
 	newhint.scid.dir = direction;
-	newhint.local = local;
+	if (local) {
+		newhint.local = tal(root->channel_hints, struct local_hint);
+		assert(htlc_budget);
+		newhint.local->htlc_budget = *htlc_budget;
+	} else
+		newhint.local = NULL;
 	if (estimated_capacity != NULL)
 		newhint.estimated_capacity = *estimated_capacity;
 
-	/* This happens if we get a temporary channel failure: we don't know
-	 * htlc capacity here, so assume it's not a problem. */
-	if (htlc_budget != NULL)
-		newhint.htlc_budget = *htlc_budget;
-	else
-		newhint.htlc_budget = 20;
-
 	tal_arr_expand(&root->channel_hints, newhint);
 
 	paymod_log(
@@ -515,7 +514,8 @@ static bool payment_chanhints_apply_route(struct payment *p, bool remove)
 
 		/* For local channels we check that we don't overwhelm
 		 * them with too many HTLCs. */
-		apply = (!curhint->local) || curhint->htlc_budget > 0;
+		apply = (!curhint->local) ||
+			(curhint->local->htlc_budget > 0);
 
 		/* For all channels we check that they have a
 		 * sufficiently large estimated capacity to have some
@@ -538,12 +538,15 @@ static bool payment_chanhints_apply_route(struct payment *p, bool remove)
 			paymod_log(
 			    p, LOG_DBG,
 			    "Capacity: estimated_capacity=%s, hop_amount=%s. "
-			    "HTLC Budget: htlc_budget=%d, local=%d",
+			    "local=%s%s",
 			    type_to_string(tmpctx, struct amount_msat,
 					   &curhint->estimated_capacity),
 			    type_to_string(tmpctx, struct amount_msat,
 					   &curhop->amount),
-			    curhint->htlc_budget, curhint->local);
+			    curhint->local ? "Y" : "N",
+			    curhint->local ?
+			    tal_fmt(tmpctx, " HTLC Budget: htlc_budget=%d",
+				    curhint->local->htlc_budget) : "");
 			return false;
 		}
 	}
@@ -558,10 +561,12 @@ apply_changes:
 
 		/* Update the number of htlcs for any local
 		 * channel in the route */
-		if (curhint->local && remove)
+		if (curhint->local) {
-			curhint->htlc_budget++;
+			if (remove)
-		else if (curhint->local)
+				curhint->local->htlc_budget++;
-			curhint->htlc_budget--;
+			else
+				curhint->local->htlc_budget--;
+		}
 
 		if (remove && !amount_msat_add(
 			    &curhint->estimated_capacity,
@@ -602,7 +607,7 @@ payment_get_excluded_channels(const tal_t *ctx, struct payment *p)
 					     hint->estimated_capacity))
 			tal_arr_expand(&res, hint->scid);
 
-		else if (hint->local && hint->htlc_budget == 0)
+		else if (hint->local && hint->local->htlc_budget == 0)
 			/* If we cannot add any HTLCs to the channel we
 			 * shouldn't look for a route through that channel */
 			tal_arr_expand(&res, hint->scid);
@@ -679,7 +684,7 @@ static bool payment_route_check(const struct gossmap *gossmap,
 		 * estimate to the smallest failed attempt. */
 		return false;
 
-	if (hint->local && hint->htlc_budget == 0)
+	if (hint->local && hint->local->htlc_budget == 0)
 		/* If we cannot add any HTLCs to the channel we
 		 * shouldn't look for a route through that channel */
 		return false;
@@ -3471,7 +3476,7 @@ static u32 payment_max_htlcs(const struct payment *p)
 	for (size_t i = 0; i < tal_count(p->channel_hints); i++) {
 		h = &p->channel_hints[i];
 		if (h->local && h->enabled)
-			res += h->htlc_budget;
+			res += h->local->htlc_budget;
 	}
 	root = p;
 	while (root->parent)

plugins/libplugin-pay.h

@@ -53,6 +53,13 @@ struct payment_result {
 	int *erring_direction;
 };
 
+struct local_hint {
+	/* How many more htlcs can we send over this channel? Only set if this
+	 * is a local channel, because those are the channels we have exact
+	 * numbers on, and they are the bottleneck onto the network. */
+	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
@@ -73,13 +80,9 @@ struct channel_hint {
 	/* Is the channel enabled? */
 	bool enabled;
 
-	/* True if we are one endpoint of this channel */
+	/* Non-null if we are one endpoint of this channel */
-	bool local;
+	struct local_hint *local;
 
-	/* How many more htlcs can we send over this channel? Only set if this
-	 * is a local channel, because those are the channels we have exact
-	 * numbers on, and they are the bottleneck onto the network. */
-	u16 htlc_budget;
 };
 
 /* Each payment goes through a number of steps that are always processed in