allow skipping ping param in static provider

app/discovery/provider/static.go

@@ -24,11 +24,17 @@ func (s *Static) Events(_ context.Context) <-chan discovery.ProviderID {
 // List all src dst pairs
 func (s *Static) List() (res []discovery.URLMapper, err error) {
 
+	// inp is 4 elements string server,source_url,destination,ping
+	// the last one can be omitted if no ping required
 	parse := func(inp string) (discovery.URLMapper, error) {
 		elems := strings.Split(inp, ",")
-		if len(elems) != 4 {
+		if len(elems) < 3 {
 			return discovery.URLMapper{}, fmt.Errorf("invalid rule %q", inp)
 		}
+		pingURL := ""
+		if len(elems) == 4 {
+			pingURL = strings.TrimSpace(elems[3])
+		}
 		rx, err := regexp.Compile(strings.TrimSpace(elems[1]))
 		if err != nil {
 			return discovery.URLMapper{}, fmt.Errorf("can't parse regex %s: %w", elems[1], err)
@@ -45,7 +51,7 @@ func (s *Static) List() (res []discovery.URLMapper, err error) {
 			Server:     strings.TrimSpace(elems[0]),
 			SrcMatch:   *rx,
 			Dst:        dst,
-			PingURL:    strings.TrimSpace(elems[3]),
+			PingURL:    pingURL,
 			ProviderID: discovery.PIStatic,
 			MatchType:  discovery.MTProxy,
 		}

app/discovery/provider/static_test.go

@@ -24,6 +24,7 @@ func TestStatic_List(t *testing.T) {
 		{"123", "", "", "", "", false, true},
 		{"example.com , 123, 456 ,ping", "example.com", "123", "456", "ping", false, false},
 		{"example.com,123, assets:456, ping ", "example.com", "123", "456", "ping", true, false},
+		{"example.com,123, assets:456 ", "example.com", "123", "456", "", true, false},
 	}
 
 	for i, tt := range tbl {