reject empty labels

Signed-off-by: Gregor Zeitlinger <[email protected]>

Author: zeitlinger

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/snapshots/PrometheusNaming.java

@@ -121,7 +121,7 @@ public static String validateMetricName(String name) {
       case LEGACY_VALIDATION:
         return validateLegacyMetricName(name);
       case UTF_8_VALIDATION:
-        if (name.isEmpty() || !StandardCharsets.UTF_8.newEncoder().canEncode(name)) {
+        if (!isValidUtf8(name)) {
           return "The metric name contains unsupported characters";
         }
         return null;
@@ -165,13 +165,17 @@ public static boolean isValidLabelName(String name) {
       case LEGACY_VALIDATION:
         return isValidLegacyLabelName(name);
       case UTF_8_VALIDATION:
-        return StandardCharsets.UTF_8.newEncoder().canEncode(name);
+        return isValidUtf8(name);
       default:
         throw new RuntimeException(
             "Invalid name validation scheme requested: " + getValidationScheme());
     }
   }
 
+  private static boolean isValidUtf8(String name) {
+    return !name.isEmpty() && StandardCharsets.UTF_8.newEncoder().canEncode(name);
+  }
+
   public static boolean isValidLegacyLabelName(String name) {
     return LEGACY_LABEL_NAME_PATTERN.matcher(name).matches()
         && !(name.startsWith("__")

prometheus-metrics-model/src/test/java/io/prometheus/metrics/model/snapshots/PrometheusNamingTest.java

@@ -126,8 +126,7 @@ public void testLabelNameIsValidUtf8(
       String labelName, boolean legacyValid, boolean utf8Valid, boolean legacyCharsetValid) {
     PrometheusNaming.resetForTest();
     assertMetricName(labelName, utf8Valid);
-    // for some reason, an empty label name is considered valid in UTF-8 validation
-    assertLabelName(labelName, utf8Valid || labelName.isEmpty());
+    assertLabelName(labelName, utf8Valid);
   }
 
   @SuppressWarnings("unused")