lib/connections: Skip and warn on malformed URLs (fixes #6697) (#6699)

lib/connections/service.go

@@ -601,14 +601,25 @@ func (s *service) CommitConfiguration(from, to config.Configuration) bool {
 			continue
 		}
 
-		if _, ok := s.listeners[addr]; ok {
-			seen[addr] = struct{}{}
+		uri, err := url.Parse(addr)
+		if err != nil {
+			l.Warnf("Skipping malformed listener URL %q: %v", addr, err)
 			continue
 		}
 
-		uri, err := url.Parse(addr)
-		if err != nil {
-			l.Infof("Parsing listener address %s: %v", addr, err)
+		// Make sure we always have the canonical representation of the URL.
+		// This is for consistency as we use it as a map key, but also to
+		// avoid misunderstandings. We do not just use the canonicalized
+		// version, because an URL that looks very similar to a human might
+		// mean something entirely different to the computer (e.g.,
+		// tcp:/127.0.0.1:22000 in fact being equivalent to tcp://:22000).
+		if canonical := uri.String(); canonical != addr {
+			l.Warnf("Skipping malformed listener URL %q (not canonical)", addr)
+			continue
+		}
+
+		if _, ok := s.listeners[addr]; ok {
+			seen[addr] = struct{}{}
 			continue
 		}