Allow colon in Prometheus meter name; add test (helidon-io#9689)

Author: tjquinno

metrics/providers/micrometer/src/main/java/io/helidon/metrics/providers/micrometer/MicrometerPrometheusFormatter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2024 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2025 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -92,7 +92,7 @@ public static String normalizeNameToPrometheus(String name) {
         }
 
         // Replace non-identifier characters.
-        result = result.replaceAll("[^A-Za-z0-9_]", "_");
+        result = result.replaceAll("[^A-Za-z0-9_:]", "_");
 
         return result;
     }

metrics/providers/micrometer/src/test/java/io/helidon/metrics/providers/micrometer/TestPrometheusFormatting.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2025 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -202,6 +202,42 @@ void testRetrievingByScope() {
                          endsWith(OPENMETRICS_EOF)));
     }
 
+    @Test
+    void testMeterNameWithColon() {
+        Counter withColon = meterRegistry.getOrCreate(Counter.builder("c:withColon"));
+        withColon.increment();
+
+        Counter withoutColon = meterRegistry.getOrCreate(Counter.builder("cWithoutColon"));
+        withoutColon.increment(2L);
+
+        Counter withQuestionMark = meterRegistry.getOrCreate(Counter.builder("c?withQuestionMark"));
+        withQuestionMark.increment();
+
+        MicrometerPrometheusFormatter formatter = MicrometerPrometheusFormatter.builder(meterRegistry)
+                .resultMediaType(MediaTypes.APPLICATION_OPENMETRICS_TEXT)
+                .scopeTagName(SCOPE_TAG_NAME)
+                .scopeSelection(Set.of("app"))
+                .build();
+
+        Optional<Object> outputOpt = formatter.format();
+
+        assertThat("Formatted output",
+                   checkAndCast(outputOpt),
+                   allOf(containsString(scopeExpr("c:withColon_total",
+                                                  "this_scope",
+                                                  "app",
+                                                  "1.0")),
+                         containsString(scopeExpr("cWithoutColon_total",
+                                                  "this_scope",
+                                                  "app",
+                                                  "2.0")),
+                         containsString(scopeExpr("c_withQuestionMark_total",
+                                                  "this_scope",
+                                                  "app",
+                                                  "1.0")),
+                         endsWith(OPENMETRICS_EOF)));
+    }
+
     private static String scopeExpr(String meterName, String key, String value, String suffix) {
         return meterName + "{" + key + "=\"" + value + "\"} " + suffix;
     }