From ec42b9acd05fc29f8b908e836eadb27a11b8b716 Mon Sep 17 00:00:00 2001
From: MPins <mpinsdorf@gmail.com>
Date: Mon, 3 Mar 2025 07:07:14 -0300
Subject: [PATCH] routing: add logging for routes discarded due to low success
 probability

Create the ChanIDString function to return a string representation
of the route's channel IDs, formatting them in the order they appear
in the route (e.g., "chanID1 -> chanID2").

Discarded routes with a success probability lower than the minimum
threshold are now logged accordingly when finding a blinded path.
---
 routing/route/route.go | 16 ++++++++++++++++
 routing/router.go      | 24 ++++++++++++++++--------
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/routing/route/route.go b/routing/route/route.go
index 2d62af465..b3e91a6f4 100644
--- a/routing/route/route.go
+++ b/routing/route/route.go
@@ -773,3 +773,19 @@ func (r *Route) String() string {
 		b.String(), r.TotalTimeLock,
 	)
 }
+
+// ChanIDString returns the route's channel IDs as a formatted string.
+func ChanIDString(r *Route) string {
+	var b strings.Builder
+
+	for i, hop := range r.Hops {
+		b.WriteString(fmt.Sprintf("%v",
+			strconv.FormatUint(hop.ChannelID, 10),
+		))
+		if i != len(r.Hops)-1 {
+			b.WriteString(" -> ")
+		}
+	}
+
+	return b.String()
+}
diff --git a/routing/router.go b/routing/router.go
index 8c9e145be..0ce9a1ca8 100644
--- a/routing/router.go
+++ b/routing/router.go
@@ -684,19 +684,27 @@ func (r *ChannelRouter) FindBlindedPaths(destination route.Vertex,
 			prevNode = path[j].vertex
 		}
 
-		// Don't bother adding a route if its success probability less
-		// minimum that can be assigned to any single pair.
-		if totalRouteProbability <= DefaultMinRouteProbability {
-			continue
-		}
-
-		routes = append(routes, &routeWithProbability{
+		routeWithProbability := &routeWithProbability{
 			route: &route.Route{
 				SourcePubKey: introNode,
 				Hops:         hops,
 			},
 			probability: totalRouteProbability,
-		})
+		}
+
+		// Don't bother adding a route if its success probability less
+		// minimum that can be assigned to any single pair.
+		if totalRouteProbability <= DefaultMinRouteProbability {
+			log.Debugf("Not using route (%v) as a blinded "+
+				"path since it resulted in an low "+
+				"probability path(%.3f)",
+				route.ChanIDString(routeWithProbability.route),
+				routeWithProbability.probability,
+			)
+			continue
+		}
+
+		routes = append(routes, routeWithProbability)
 	}
 
 	// Sort the routes based on probability.