Remove scrape() from getPrometheusName() default implementation

Signed-off-by: Fabian Stäber <fabian@fstab.de>

integration-tests/it-exporter/it-exporter-httpserver-sample/src/main/java/io/prometheus/metrics/it/exporter/httpserver/HTTPServerSample.java

@@ -53,17 +53,8 @@ public static void main(String[] args) throws IOException, InterruptedException
         gauge.labelValues("outside").set(27.0);
 
         if (mode == Mode.error) {
-            Collector failingCollector = new Collector() {
-
-                @Override
-                public String getPrometheusName() {
-                    return null;
-                }
-
-                @Override
-                public MetricSnapshot collect() {
-                    throw new RuntimeException("Simulating an error.");
-                }
+            Collector failingCollector = () -> {
+                throw new RuntimeException("Simulating an error.");
             };
 
             PrometheusRegistry.defaultRegistry.register(failingCollector);

integration-tests/it-exporter/it-exporter-servlet-jetty-sample/src/main/java/io/prometheus/metrics/it/exporter/servlet/jetty/ExporterServletJettySample.java

@@ -57,17 +57,8 @@ public static void main(String[] args) throws Exception {
         gauge.labelValues("outside").set(27.0);
 
         if (mode == Mode.error) {
-            Collector failingCollector = new Collector() {
-
-                @Override
-                public String getPrometheusName() {
-                    return null;
-                }
-
-                @Override
-                public MetricSnapshot collect() {
-                    throw new RuntimeException("Simulating an error.");
-                }
+            Collector failingCollector = () -> {
+                throw new RuntimeException("Simulating an error.");
             };
 
             PrometheusRegistry.defaultRegistry.register(failingCollector);

integration-tests/it-exporter/it-exporter-servlet-tomcat-sample/src/main/java/io/prometheus/metrics/it/exporter/servlet/tomcat/ExporterServletTomcatSample.java

@@ -61,17 +61,8 @@ public static void main(String[] args) throws LifecycleException, IOException {
         gauge.labelValues("outside").set(27.0);
 
         if (mode == Mode.error) {
-            Collector failingCollector = new Collector() {
-
-                @Override
-                public String getPrometheusName() {
-                    return null;
-                }
-
-                @Override
-                public MetricSnapshot collect() {
-                    throw new RuntimeException("Simulating an error.");
-                }
+            Collector failingCollector = () -> {
+                throw new RuntimeException("Simulating an error.");
             };
 
             PrometheusRegistry.defaultRegistry.register(failingCollector);

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/Collector.java

@@ -34,10 +34,20 @@ default MetricSnapshot collect(Predicate<String> includedNames) {
     }
 
     /**
-     * Override this and return {@code null} if a collector does not have a constant name,
-     * or if you don't want this library to call {@link #collect()} during registration of this collector.
+     * This is called in two places:
+     * <ol>
+     * <li>During registration to check if a metric with that name already exists.</li>
+     * <li>During scrape to check if this collector can be skipped because a name filter is present and the metric name is excluded.</li>
+     * </ol>
+     * Returning {@code null} means checks are omitted (registration the metric always succeeds),
+     * and the collector is always scraped (the result is dropped after scraping if a name filter is present and
+     * the metric name is excluded).
+     * <p>
+     * If your metric has a name that does not change at runtime it is a good idea to overwrite this and return the name.
+     * <p>
+     * All metrics in {@code prometheus-metrics-core} override this.
      */
     default String getPrometheusName() {
-        return collect().getMetadata().getPrometheusName();
+        return null;
     }
 }

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/MultiCollector.java

@@ -3,9 +3,9 @@
 import io.prometheus.metrics.model.snapshots.MetricSnapshot;
 import io.prometheus.metrics.model.snapshots.MetricSnapshots;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 
 /**
  * Like {@link Collector}, but collecting multiple Snapshots at once.
@@ -35,10 +35,18 @@ default MetricSnapshots collect(Predicate<String> includedNames) {
     }
 
     /**
-     * Override this and return an empty list if the MultiCollector does not return a constant list of names
-     * (names may be added / removed between scrapes).
+     * This is called in two places:
+     * <ol>
+     * <li>During registration to check if a metric with that name already exists.</li>
+     * <li>During scrape to check if the collector can be skipped because a name filter is present and all names are excluded.</li>
+     * </ol>
+     * Returning an empty list means checks are omitted (registration metric always succeeds),
+     * and the collector is always scraped (if a name filter is present and all names are excluded the result is dropped).
+     * <p>
+     * If your collector returns a constant list of metrics that have names that do not change at runtime
+     * it is a good idea to overwrite this and return the names.
      */
     default List<String> getPrometheusNames() {
-        return collect().stream().map(snapshot -> snapshot.getMetadata().getPrometheusName()).collect(Collectors.toList());
+        return Collections.emptyList();
     }
 }

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/PrometheusRegistry.java

@@ -40,7 +40,10 @@ public void register(MultiCollector collector) {
 
     public void unregister(Collector collector) {
         collectors.remove(collector);
-        prometheusNames.remove(collector.getPrometheusName());
+        String prometheusName = collector.getPrometheusName();
+        if (prometheusName != null) {
+            prometheusNames.remove(collector.getPrometheusName());
+        }
     }
 
     public void unregister(MultiCollector collector) {
@@ -88,7 +91,7 @@ public MetricSnapshots scrape(Predicate<String> includedNames) {
         }
         for (MultiCollector collector : multiCollectors) {
             List<String> prometheusNames = collector.getPrometheusNames();
-            boolean excluded = true; // the multi-collector is excluded unless at least one name matches
+            boolean excluded = prometheusNames.size() > 0; // the multi-collector is excluded unless at least one name matches
             for (String prometheusName : prometheusNames) {
                 if (includedNames.test(prometheusName)) {
                     excluded = false;

prometheus-metrics-model/src/test/java/io/prometheus/metrics/model/registry/PrometheusRegistryTest.java

@@ -9,35 +9,57 @@
 
 public class PrometheusRegistryTest {
 
-    Collector noName = new Collector() {
+    Collector noName = () -> GaugeSnapshot.builder()
+            .name("no_name_gauge")
+            .build();
+
+    Collector counterA1 = new Collector() {
         @Override
         public MetricSnapshot collect() {
-            return GaugeSnapshot.builder()
-                    .name("no_name_gauge")
-                    .build();
+            return CounterSnapshot.builder().name("counter_a").build();
         }
 
         @Override
         public String getPrometheusName() {
-            return null;
+            return "counter_a";
         }
     };
 
-    Collector counterA1 = () -> CounterSnapshot.builder()
-            .name("counter_a")
-            .build();
+    Collector counterA2 = new Collector() {
+        @Override
+        public MetricSnapshot collect() {
+            return CounterSnapshot.builder().name("counter.a").build();
+        }
 
-    Collector counterA2 = () -> CounterSnapshot.builder()
-            .name("counter.a")
-            .build();
+        @Override
+        public String getPrometheusName() {
+            return "counter_a";
+        }
+    };
 
-    Collector counterB = () -> CounterSnapshot.builder()
-            .name("counter_b")
-            .build();
+    Collector counterB = new Collector() {
+        @Override
+        public MetricSnapshot collect() {
+            return CounterSnapshot.builder().name("counter_b").build();
+        }
 
-    Collector gaugeA = () -> GaugeSnapshot.builder()
-            .name("gauge_a")
-            .build();
+        @Override
+        public String getPrometheusName() {
+            return "counter_b";
+        }
+    };
+
+    Collector gaugeA = new Collector() {
+        @Override
+        public MetricSnapshot collect() {
+            return GaugeSnapshot.builder().name("gauge_a").build();
+        }
+
+        @Override
+        public String getPrometheusName() {
+            return "gauge_a";
+        }
+    };
 
     @Test
     public void registerNoName() {

prometheus-metrics-simpleclient-bridge/src/main/java/io/prometheus/metrics/simpleclient/bridge/SimpleclientCollector.java

@@ -61,16 +61,6 @@ public MetricSnapshots collect() {
         return convert(simpleclientRegistry.metricFamilySamples());
     }
 
-    @Override
-    public MetricSnapshots collect(Predicate<String> includedNames) {
-        return MultiCollector.super.collect(includedNames);
-    }
-
-    @Override
-    public List<String> getPrometheusNames() {
-        return MultiCollector.super.getPrometheusNames();
-    }
-
     private MetricSnapshots convert(Enumeration<Collector.MetricFamilySamples> samples) {
         MetricSnapshots.Builder result = MetricSnapshots.builder();
         while (samples.hasMoreElements()) {