Add MeterFilter.forMeters utility method (#6594)

* Add MeterFilter.forPrefix(..) utility method

I have noticed that I often want to configure MeterFilters only for a selection of meters that start with a given prefix. For example, I might want to ignore tags for a selection of metrics, but not for all of them. The "normal" approach would be to write a custom MeterFilter that checks the name before filtering. The new utility method helps with this task.

Signed-off-by: Peter Jeschke <[email protected]>

* Add MeterFilter.forMeters utility method

---------

Signed-off-by: Peter Jeschke <[email protected]>
Co-authored-by: Jonatan Ivanov <[email protected]>

Author: peterjeschke

docs/modules/ROOT/pages/concepts/meter-filters.adoc

@@ -148,3 +148,22 @@ Generally, you should create a new `DistributionStatisticConfig` with only the p
 * `minExpected(Duration/long)`: Governs the lower bound of percentile histogram buckets shipped from a timer or summary.
 
 Spring Boot offers property-based filters for configuring SLOs, percentiles, and percentile histograms by name prefix.
+
+== Apply MeterFilters conditionally
+
+It is a common use-case to apply MeterFilters only for a selection of Meters (for example for ones that has a certain name or starts with a given prefix).
+In order to do this, Micrometer provides a convenience method `forMeters(Predicate<Meter.Id> predicate, MeterFilter delegate)` that enables the provided (delegate) filter for the Meters selected by the predicate.
+
+See the following example:
+
+====
+[source, java]
+----
+registry.config()
+    .meterFilter(MeterFilter.forMeters(startsWith("prefix"), MeterFilter.ignoreTags("extra")));
+
+Predicate<Meter.Id> startsWith(String prefix) {
+    return id -> id.getName().startsWith(prefix);
+}
+----
+====

micrometer-core/src/main/java/io/micrometer/core/instrument/config/MeterFilter.java

@@ -412,6 +412,35 @@ public DistributionStatisticConfig configure(Meter.Id id, DistributionStatisticC
         };
     }
 
+    /**
+     * Enables the provided filter for the Meters selected by the predicate.
+     * <code>registry.config().meterFilter(MeterFilter.forMeters(id -> id.getName().startsWith("test"), MeterFilter.ignoreTags("ignored")))</code>
+     * @param predicate Apply the provided filter only to Meters selected by this
+     * predicate
+     * @param delegate A filter to apply if the provided predicate returns true
+     * @return A filter that delegates calls to the delegate filter conditionally (based
+     * on the predicate)
+     * @since 1.16.0
+     */
+    static MeterFilter forMeters(Predicate<Meter.Id> predicate, MeterFilter delegate) {
+        return new MeterFilter() {
+            @Override
+            public MeterFilterReply accept(Meter.Id id) {
+                return predicate.test(id) ? delegate.accept(id) : MeterFilter.super.accept(id);
+            }
+
+            @Override
+            public Meter.Id map(Meter.Id id) {
+                return predicate.test(id) ? delegate.map(id) : MeterFilter.super.map(id);
+            }
+
+            @Override
+            public @Nullable DistributionStatisticConfig configure(Meter.Id id, DistributionStatisticConfig config) {
+                return predicate.test(id) ? delegate.configure(id, config) : MeterFilter.super.configure(id, config);
+            }
+        };
+    }
+
     /**
      * @param id Id with {@link MeterFilter#map} transformations applied.
      * @return After all transformations, should a real meter be registered for this id,

micrometer-core/src/test/java/io/micrometer/core/instrument/MeterFilterTest.java

@@ -26,6 +26,7 @@
 
 import java.time.Duration;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Predicate;
 
 import static java.util.stream.StreamSupport.stream;
 import static org.assertj.core.api.Assertions.assertThat;
@@ -266,4 +267,36 @@ public Meter.Id map(Meter.Id id) {
         assertThat(registry.getMeters()).isNotEmpty();
     }
 
+    @Test
+    void forPrefix() {
+        Meter.Id primary = new Meter.Id("primary.gauge", Tags.of("ignored", "true", "other", "value"), null, null,
+                Meter.Type.GAUGE);
+        Meter.Id secondary = new Meter.Id("secondary.gauge", Tags.of("ignored", "false"), null, null, Meter.Type.GAUGE);
+
+        MeterFilter denyPrimaryGauges = MeterFilter.forMeters(startsWith("primary."),
+                MeterFilter.deny(id -> id.getType() == Meter.Type.GAUGE));
+        assertThat(denyPrimaryGauges.accept(primary)).isEqualTo(MeterFilterReply.DENY);
+        assertThat(denyPrimaryGauges.accept(secondary)).isEqualTo(MeterFilterReply.NEUTRAL);
+
+        MeterFilter ignoreTagsOnPrimaryMeters = MeterFilter.forMeters(startsWith("primary."),
+                MeterFilter.ignoreTags("ignored"));
+        assertThat(ignoreTagsOnPrimaryMeters.map(primary).getTags()).containsExactly(Tag.of("other", "value"));
+        assertThat(ignoreTagsOnPrimaryMeters.map(secondary).getTags()).containsExactly(Tag.of("ignored", "false"));
+
+        MeterFilter configurePrimaryMeters = MeterFilter.forMeters(startsWith("primary."), new MeterFilter() {
+            @Override
+            public DistributionStatisticConfig configure(Meter.Id id, DistributionStatisticConfig config) {
+                return DistributionStatisticConfig.DEFAULT;
+            }
+        });
+
+        DistributionStatisticConfig config = new DistributionStatisticConfig();
+        assertThat(configurePrimaryMeters.configure(primary, config)).isEqualTo(DistributionStatisticConfig.DEFAULT);
+        assertThat(configurePrimaryMeters.configure(secondary, config)).isEqualTo(config);
+    }
+
+    private Predicate<Meter.Id> startsWith(String prefix) {
+        return id -> id.getName().startsWith(prefix);
+    }
+
 }