fix: legacy label endpoint route (#14933)

pkg/lokifrontend/frontend/v1/frontend_test.go

@@ -42,7 +42,7 @@ import (
 const (
 	query        = "/loki/api/v1/query_range?end=1536716898&query=sum%28container_memory_rss%29+by+%28namespace%29&start=1536673680&step=120"
 	responseBody = `{"status":"success","data":{"resultType":"Matrix","result":[{"metric":{"foo":"bar"},"values":[[1536673680,"137"],[1536673780,"137"]]}]}}`
-	labelQuery   = `/prom/label/foo/values`
+	labelQuery   = `/api/prom/label/foo/values`
 )
 
 func TestFrontend(t *testing.T) {

pkg/querier/queryrange/roundtrip.go

@@ -523,7 +523,7 @@ func getOperation(path string) string {
 	case path == "/loki/api/v1/detected_fields":
 		return DetectedFieldsOp
 	case strings.HasSuffix(path, "/values"):
-		if strings.HasPrefix(path, "/loki/api/v1/label") || strings.HasPrefix(path, "/prom/label") {
+		if strings.HasPrefix(path, "/loki/api/v1/label") || strings.HasPrefix(path, "/api/prom/label") {
 			return LabelNamesOp
 		}
 

pkg/querier/queryrange/roundtrip_test.go

@@ -1213,7 +1213,7 @@ func Test_getOperation(t *testing.T) {
 		},
 		{
 			name:       "range_query_prom",
-			path:       "/prom/query",
+			path:       "/api/prom/query",
 			expectedOp: QueryRangeOp,
 		},
 		{
@@ -1228,7 +1228,7 @@ func Test_getOperation(t *testing.T) {
 		},
 		{
 			name:       "series_query_prom",
-			path:       "/prom/series",
+			path:       "/api/prom/series",
 			expectedOp: SeriesOp,
 		},
 		{
@@ -1238,7 +1238,7 @@ func Test_getOperation(t *testing.T) {
 		},
 		{
 			name:       "labels_query_prom",
-			path:       "/prom/labels",
+			path:       "/api/prom/labels",
 			expectedOp: LabelNamesOp,
 		},
 		{
@@ -1248,7 +1248,7 @@ func Test_getOperation(t *testing.T) {
 		},
 		{
 			name:       "labels_query_prom",
-			path:       "/prom/label",
+			path:       "/api/prom/label",
 			expectedOp: LabelNamesOp,
 		},
 		{
@@ -1258,7 +1258,7 @@ func Test_getOperation(t *testing.T) {
 		},
 		{
 			name:       "label_values_query_prom",
-			path:       "/prom/label/__name__/values",
+			path:       "/api/prom/label/__name__/values",
 			expectedOp: LabelNamesOp,
 		},
 		{