remove scrape time validation

Signed-off-by: Jay DeLuca <jaydeluca4@gmail.com>

Author: jaydeluca

docs/content/getting-started/metric-types.md

@@ -276,3 +276,6 @@ in the `prometheus-metrics-core` API.
 However, `prometheus-metrics-model` implements the underlying data model for these types.
 To use these types, you need to implement your own `Collector` where the `collect()` method returns
 an `UnknownSnapshot` or a `HistogramSnapshot` with `.gaugeHistogram(true)`.
+If your custom collector does not implement `getMetricType()` and `getLabelNames()`, ensure it does
+not produce the same metric name and label set as another collector, or the exposition may contain
+duplicate time series.

docs/content/getting-started/registry.md

@@ -78,6 +78,17 @@ Counter eventsTotal2 = Counter.builder()
     .register(); // IllegalArgumentException, because a metric with that name is already registered
 ```
 
+## Validation at registration only
+
+Validation of duplicate metric names and label schemas happens at registration time only.
+Built-in metrics (Counter, Gauge, Histogram, etc.) participate in this validation.
+
+Custom collectors that implement the `Collector` or `MultiCollector` interface can optionally
+implement `getMetricType()` and `getLabelNames()` (or the MultiCollector per-name variants) so the
+registry can enforce consistency. If those methods return `null`, the registry does not validate
+that collector. If two such collectors produce the same metric name and same label set at scrape
+time, the exposition output may contain duplicate time series and be invalid for Prometheus.
+
 ## Unregistering a Metric
 
 There is no automatic expiry of unused metrics (yet), once a metric is registered it will remain

docs/content/internals/model.md

@@ -19,7 +19,10 @@ All metric types implement
 the [Collector](/client_java/api/io/prometheus/metrics/model/registry/Collector.html) interface,
 i.e. they provide
 a [collect()](</client_java/api/io/prometheus/metrics/model/registry/Collector.html#collect()>)
-method to produce snapshots.
+method to produce snapshots. Implementers that do not provide metric type or label names (returning
+null from `getMetricType()` and `getLabelNames()`) are not validated at registration; they must
+avoid producing the same metric name and label schema as another collector, or exposition may be
+invalid.
 
 ## prometheus-metrics-model
 

prometheus-metrics-exposition-textformats/src/test/java/io/prometheus/metrics/expositionformats/DuplicateNamesExpositionTest.java

@@ -2,7 +2,6 @@
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 import io.prometheus.metrics.model.registry.Collector;
 import io.prometheus.metrics.model.registry.PrometheusRegistry;
@@ -181,57 +180,4 @@ void testOpenMetricsFormat_withDuplicateNames() throws IOException {
     """;
     assertThat(output).isEqualTo(expected);
   }
-
-  @Test
-  void testDuplicateNames_sameLabels_throwsException() {
-    PrometheusRegistry registry = new PrometheusRegistry();
-
-    registry.register(
-        new Collector() {
-          @Override
-          public MetricSnapshot collect() {
-            return CounterSnapshot.builder()
-                .name("api_responses")
-                .help("API responses")
-                .dataPoint(
-                    CounterSnapshot.CounterDataPointSnapshot.builder()
-                        .labels(Labels.of("uri", "/hello", "outcome", "SUCCESS"))
-                        .value(100)
-                        .build())
-                .build();
-          }
-
-          @Override
-          public String getPrometheusName() {
-            return "api_responses_total";
-          }
-        });
-
-    registry.register(
-        new Collector() {
-          @Override
-          public MetricSnapshot collect() {
-            return CounterSnapshot.builder()
-                .name("api_responses")
-                .help("API responses")
-                .dataPoint(
-                    CounterSnapshot.CounterDataPointSnapshot.builder()
-                        .labels(Labels.of("uri", "/hello", "outcome", "SUCCESS"))
-                        .value(50)
-                        .build())
-                .build();
-          }
-
-          @Override
-          public String getPrometheusName() {
-            return "api_responses_total";
-          }
-        });
-
-    // Scrape should throw exception due to duplicate time series (same name + same labels)
-    assertThatThrownBy(registry::scrape)
-        .isInstanceOf(IllegalStateException.class)
-        .hasMessageContaining("duplicate metric name with identical label schema [uri, outcome]")
-        .hasMessageContaining("api_responses");
-  }
 }

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

@@ -86,6 +86,10 @@ default String getPrometheusName() {
    * <p>This is used to prevent different metric types (e.g., Counter and Gauge) from sharing the
    * same name. Returning {@code null} means type validation is skipped for this collector.
    *
+   * <p>Validation is performed only at registration time. If this method returns {@code null}, no
+   * type validation is performed for this collector, and duplicate or conflicting metrics may
+   * result in invalid exposition output.
+   *
    * @return the metric type, or {@code null} to skip validation
    */
   @Nullable
@@ -106,6 +110,11 @@ default MetricType getMetricType() {
    *
    * <p>Returning {@code null} means label schema validation is skipped for this collector.
    *
+   * <p>Validation is performed only at registration time. If this method returns {@code null}, no
+   * label-schema validation is performed for this collector. If such a collector produces the same
+   * metric name and label schema as another at scrape time, the exposition may contain duplicate
+   * time series, which is invalid in Prometheus.
+   *
    * @return the set of all label names, or {@code null} to skip validation
    */
   @Nullable

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

@@ -78,6 +78,10 @@ default List<String> getPrometheusNames() {
    * <p>This is used for per-name type validation during registration. Returning {@code null} means
    * type validation is skipped for that specific metric name.
    *
+   * <p>Validation is performed only at registration time. If this method returns {@code null}, no
+   * type validation is performed for that name, and duplicate or conflicting metrics may result in
+   * invalid exposition output.
+   *
    * @param prometheusName the Prometheus metric name
    * @return the metric type for the given name, or {@code null} to skip validation
    */
@@ -98,6 +102,11 @@ default MetricType getMetricType(String prometheusName) {
    * <p>Returning {@code null} means label schema validation is skipped for that specific metric
    * name.
    *
+   * <p>Validation is performed only at registration time. If this method returns {@code null}, no
+   * label-schema validation is performed for that name. If such a collector produces the same
+   * metric name and label schema as another at scrape time, the exposition may contain duplicate
+   * time series, which is invalid in Prometheus.
+   *
    * @param prometheusName the Prometheus metric name
    * @return the set of all label names for the given name, or {@code null} to skip validation
    */

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

@@ -1,14 +1,11 @@
 package io.prometheus.metrics.model.registry;
 
-import io.prometheus.metrics.model.snapshots.DataPointSnapshot;
 import io.prometheus.metrics.model.snapshots.MetricSnapshot;
 import io.prometheus.metrics.model.snapshots.MetricSnapshots;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
-import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.function.Predicate;
@@ -254,8 +251,6 @@ public MetricSnapshots scrape(@Nullable PrometheusScrapeRequest scrapeRequest) {
       }
     }
 
-    validateNoDuplicateLabelSchemas(allSnapshots);
-
     MetricSnapshots.Builder result = MetricSnapshots.builder();
     for (MetricSnapshot snapshot : allSnapshots) {
       result.metricSnapshot(snapshot);
@@ -316,78 +311,10 @@ public MetricSnapshots scrape(
       }
     }
 
-    validateNoDuplicateLabelSchemas(allSnapshots);
-
     MetricSnapshots.Builder result = MetricSnapshots.builder();
     for (MetricSnapshot snapshot : allSnapshots) {
       result.metricSnapshot(snapshot);
     }
     return result.build();
   }
-
-  /**
-   * Validates that snapshots with the same metric name don't have identical label schemas. This
-   * prevents duplicate time series which would occur if two snapshots produce data points with
-   * identical label sets.
-   */
-  private void validateNoDuplicateLabelSchemas(List<MetricSnapshot> snapshots) {
-    Map<String, List<MetricSnapshot>> snapshotsByName = new HashMap<>();
-    for (MetricSnapshot snapshot : snapshots) {
-      String name = snapshot.getMetadata().getPrometheusName();
-      snapshotsByName.computeIfAbsent(name, k -> new ArrayList<>()).add(snapshot);
-    }
-
-    // For each group with the same name, check for duplicate label schemas
-    for (Map.Entry<String, List<MetricSnapshot>> entry : snapshotsByName.entrySet()) {
-      List<MetricSnapshot> group = entry.getValue();
-      if (group.size() <= 1) {
-        continue;
-      }
-
-      List<Set<String>> labelSchemas = new ArrayList<>();
-      for (MetricSnapshot snapshot : group) {
-        Set<String> labelSchema = extractLabelSchema(snapshot);
-        if (labelSchema != null) {
-          if (labelSchemas.contains(labelSchema)) {
-            throw new IllegalStateException(
-                snapshot.getMetadata().getPrometheusName()
-                    + ": duplicate metric name with identical label schema "
-                    + labelSchema);
-          }
-          labelSchemas.add(labelSchema);
-        }
-      }
-    }
-  }
-
-  /**
-   * Extracts the label schema (set of label names) from a snapshot's data points. Returns null if
-   * the snapshot has no data points or if data points have inconsistent label schemas.
-   */
-  @Nullable
-  private Set<String> extractLabelSchema(MetricSnapshot snapshot) {
-    if (snapshot.getDataPoints().isEmpty()) {
-      return null;
-    }
-
-    DataPointSnapshot firstDataPoint = snapshot.getDataPoints().get(0);
-    Set<String> labelNames = new HashSet<>();
-    for (int i = 0; i < firstDataPoint.getLabels().size(); i++) {
-      labelNames.add(firstDataPoint.getLabels().getName(i));
-    }
-
-    for (DataPointSnapshot dataPoint : snapshot.getDataPoints()) {
-      Set<String> currentLabelNames = new HashSet<>();
-      for (int i = 0; i < dataPoint.getLabels().size(); i++) {
-        currentLabelNames.add(dataPoint.getLabels().getName(i));
-      }
-      if (!currentLabelNames.equals(labelNames)) {
-        // Data points have inconsistent label schemas - this is unusual but valid
-        // We can't determine a single label schema, so return null
-        return null;
-      }
-    }
-
-    return labelNames;
-  }
 }

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

@@ -9,7 +9,6 @@
 import io.prometheus.metrics.model.snapshots.GaugeSnapshot;
 import io.prometheus.metrics.model.snapshots.MetricSnapshot;
 import io.prometheus.metrics.model.snapshots.MetricSnapshots;
-
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
@@ -439,7 +438,7 @@ public MetricType getMetricType() {
 
           @Override
           public Set<String> getLabelNames() {
-            return new HashSet<>(List.of("region"));
+            return new HashSet<>(asList("region"));
           }
         };
 
@@ -474,66 +473,6 @@ public Set<String> getLabelNames() {
     assertThatCode(() -> registry.register(counterWithPathLabelAgain)).doesNotThrowAnyException();
   }
 
-  @Test
-  public void scrape_withFilter_shouldValidateDuplicateLabelSchemas() {
-    PrometheusRegistry registry = new PrometheusRegistry();
-
-    Collector collector1 =
-        new Collector() {
-          @Override
-          public MetricSnapshot collect() {
-            return GaugeSnapshot.builder()
-                .name("requests")
-                .dataPoint(
-                    GaugeSnapshot.GaugeDataPointSnapshot.builder()
-                        .value(100)
-                        .labels(io.prometheus.metrics.model.snapshots.Labels.of("path", "/api"))
-                        .build())
-                .build();
-          }
-
-          @Override
-          public String getPrometheusName() {
-            return "requests";
-          }
-          // No getMetricType() or getLabelNames() - returns null by default
-        };
-
-    Collector collector2 =
-        new Collector() {
-          @Override
-          public MetricSnapshot collect() {
-            return GaugeSnapshot.builder()
-                .name("requests")
-                .dataPoint(
-                    GaugeSnapshot.GaugeDataPointSnapshot.builder()
-                        .value(200)
-                        .labels(io.prometheus.metrics.model.snapshots.Labels.of("path", "/home"))
-                        .build())
-                .build();
-          }
-
-          @Override
-          public String getPrometheusName() {
-            return "requests";
-          }
-          // No getMetricType() or getLabelNames() - returns null by default
-        };
-
-    // Both collectors can register because they don't provide type/label info
-    registry.register(collector1);
-    registry.register(collector2);
-
-    assertThatThrownBy(registry::scrape)
-        .isInstanceOf(IllegalStateException.class)
-        .hasMessageContaining("duplicate metric name with identical label schema");
-
-    // Filtered scrape should also detect duplicate label schemas
-    assertThatThrownBy(() -> registry.scrape(name -> name.equals("requests")))
-        .isInstanceOf(IllegalStateException.class)
-        .hasMessageContaining("duplicate metric name with identical label schema");
-  }
-
   @Test
   public void register_withEmptyLabelSets_shouldDetectDuplicates() {
     PrometheusRegistry registry = new PrometheusRegistry();