Breakout ResourceHolder from AwsXrayRemoteSamplerProvider

ResourceHolder provides generic utility for other components in the awsxray package, and could be more broadly used. In this commit, we are breaking out the ResourceHolder inner class to it's own class, and exposing the functionality of getResource, so that other classes can rely on it.

Related issue: #789

aws-xray/build.gradle.kts

@@ -16,6 +16,7 @@ dependencies {
   implementation("io.opentelemetry:opentelemetry-semconv")
 
   annotationProcessor("com.google.auto.service:auto-service")
+  testImplementation("com.google.auto.service:auto-service")
   compileOnly("com.google.auto.service:auto-service-annotations")
 
   annotationProcessor("com.google.auto.value:auto-value")

aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/AwsXrayRemoteSamplerProvider.java

@@ -6,25 +6,18 @@
 package io.opentelemetry.contrib.awsxray;
 
 import com.google.auto.service.AutoService;
-import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizer;
-import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizerProvider;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
 import io.opentelemetry.sdk.autoconfigure.spi.traces.ConfigurableSamplerProvider;
 import io.opentelemetry.sdk.resources.Resource;
 import io.opentelemetry.sdk.trace.samplers.Sampler;
 import java.util.Map;
-import javax.annotation.Nullable;
 
 @AutoService(ConfigurableSamplerProvider.class)
 public class AwsXrayRemoteSamplerProvider implements ConfigurableSamplerProvider {
 
   @Override
   public Sampler createSampler(ConfigProperties config) {
-    Resource resource = ResourceHolder.resource;
-    if (resource == null) {
-      // Should never be the case in practice.
-      resource = Resource.getDefault();
-    }
+    Resource resource = ResourceHolder.getResource();
     AwsXrayRemoteSamplerBuilder builder = AwsXrayRemoteSampler.newBuilder(resource);
 
     Map<String, String> params = config.getMap("otel.traces.sampler.arg");
@@ -41,22 +34,4 @@ public Sampler createSampler(ConfigProperties config) {
   public String getName() {
     return "xray";
   }
-
-  // Currently the only way to read the Resource from autoconfiguration. Best would be if the SPI
-  // could return a Function<SamplerFactoryArgs, Sampler> where SamplerFactoryArgs has
-  // SDK-constructed components like Resource and Clock.
-  @AutoService(AutoConfigurationCustomizerProvider.class)
-  public static final class ResourceHolder implements AutoConfigurationCustomizerProvider {
-
-    @Nullable static volatile Resource resource;
-
-    @Override
-    public void customize(AutoConfigurationCustomizer autoConfiguration) {
-      autoConfiguration.addResourceCustomizer(
-          (resource, config) -> {
-            ResourceHolder.resource = resource;
-            return resource;
-          });
-    }
-  }
 }

aws-xray/src/main/java/io/opentelemetry/contrib/awsxray/ResourceHolder.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.awsxray;
+
+import com.google.auto.service.AutoService;
+import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizer;
+import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizerProvider;
+import io.opentelemetry.sdk.resources.Resource;
+import javax.annotation.Nullable;
+
+/**
+ * Currently the only way to read the Resource from autoconfiguration. Best would be if the SPI
+ * could return a {@code Function<SamplerFactoryArgs, Sampler>} where SamplerFactoryArgs has
+ * SDK-constructed components like Resource and Clock.
+ */
+@AutoService(AutoConfigurationCustomizerProvider.class)
+public final class ResourceHolder implements AutoConfigurationCustomizerProvider {
+
+  @Nullable static volatile Resource resource;
+
+  @Override
+  public void customize(AutoConfigurationCustomizer autoConfiguration) {
+    autoConfiguration.addResourceCustomizer(
+        (resource, config) -> {
+          ResourceHolder.resource = resource;
+          return resource;
+        });
+  }
+
+  /**
+   * Returns held resource, unless resource is null, in which case {@link Resource#getDefault()} is
+   * returned. This should not happen in practice, as {@link #customize} should be automatically
+   * run, populating {@link #resource}.
+   */
+  public static Resource getResource() {
+    Resource resourceReference = resource;
+    if (resourceReference == null) {
+      // Should never be the case in practice.
+      resourceReference = Resource.getDefault();
+    }
+    return resourceReference;
+  }
+}

aws-xray/src/test/java/io/opentelemetry/contrib/awsxray/ResourceHolderTest.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.awsxray;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizer;
+import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
+import io.opentelemetry.sdk.resources.Resource;
+import java.util.function.BiFunction;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for {@link ResourceHolder}. Note that there isn't a great way to test the "default"
+ * fallback logic, as when the test suite is run, the customize logic appears to be invoked.
+ */
+public class ResourceHolderTest {
+
+  @Test
+  @SuppressWarnings("unchecked")
+  public void testCustomized() {
+    Resource customizedResource = Resource.create(Attributes.empty());
+    AutoConfigurationCustomizer mockCustomizer = mock(AutoConfigurationCustomizer.class);
+    ResourceHolder resourceHolder = new ResourceHolder();
+    when(mockCustomizer.addResourceCustomizer(any()))
+        .thenAnswer(
+            invocation -> {
+              BiFunction<Resource, ConfigProperties, Resource> biFunction =
+                  (BiFunction<Resource, ConfigProperties, Resource>) invocation.getArguments()[0];
+              assertThat(biFunction.apply(customizedResource, null)).isEqualTo(customizedResource);
+              return mockCustomizer;
+            });
+    resourceHolder.customize(mockCustomizer);
+    assertThat(ResourceHolder.getResource()).isEqualTo(customizedResource);
+  }
+}