Add a SpanProcessor for applying tags from baggage. (#33)

Author: jkwatson

spring-cloud-sleuth-otel-autoconfigure/src/main/java/org/springframework/cloud/sleuth/autoconfig/otel/OtelPropagationConfiguration.java

@@ -33,6 +33,7 @@
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.cloud.sleuth.BaggageManager;
 import org.springframework.cloud.sleuth.autoconfig.SleuthBaggageProperties;
+import org.springframework.cloud.sleuth.otel.bridge.BaggageTaggingSpanProcessor;
 import org.springframework.cloud.sleuth.otel.propagation.BaggageTextMapPropagator;
 import org.springframework.cloud.sleuth.otel.propagation.CompositeTextMapPropagator;
 import org.springframework.cloud.sleuth.otel.propagation.PropagationType;
@@ -109,6 +110,17 @@ TextMapPropagator baggageTextMapPropagator(SleuthBaggageProperties properties, B
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnProperty(name = "spring.sleuth.baggage.tag-fields")
+	static class BaggageTaggingConfiguration {
+
+		@Bean
+		BaggageTaggingSpanProcessor baggageTaggingSpanProcessor(SleuthBaggageProperties properties) {
+			return new BaggageTaggingSpanProcessor(properties.getTagFields());
+		}
+
+	}
+
 	static class B3PresentOrPropertyEnabledCondition implements Condition {
 
 		@Override

spring-cloud-sleuth-otel/src/main/java/org/springframework/cloud/sleuth/otel/bridge/BaggageTaggingSpanProcessor.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2013-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth.otel.bridge;
+
+import java.util.List;
+import java.util.Map;
+
+import io.opentelemetry.api.baggage.Baggage;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+
+import static io.opentelemetry.api.common.AttributeKey.stringKey;
+import static java.util.stream.Collectors.toMap;
+
+public class BaggageTaggingSpanProcessor implements SpanProcessor {
+
+	private final Map<String, AttributeKey<String>> tagsToApply;
+
+	public BaggageTaggingSpanProcessor(List<String> tagsToApply) {
+		this.tagsToApply = tagsToApply.stream().map(tag -> stringKey(tag))
+				.collect(toMap(AttributeKey::getKey, key -> key));
+	}
+
+	@Override
+	public void onStart(Context context, ReadWriteSpan readWriteSpan) {
+		Baggage baggage = Baggage.fromContext(context);
+
+		baggage.forEach((key, baggageEntry) -> {
+			AttributeKey<String> attributeKey = tagsToApply.get(key);
+			if (attributeKey != null) {
+				readWriteSpan.setAttribute(attributeKey, baggageEntry.getValue());
+			}
+		});
+	}
+
+	@Override
+	public boolean isStartRequired() {
+		return true;
+	}
+
+	@Override
+	public void onEnd(ReadableSpan readableSpan) {
+		// no-op
+	}
+
+	@Override
+	public boolean isEndRequired() {
+		return false;
+	}
+
+}

spring-cloud-sleuth-otel/src/test/java/org/springframework/cloud/sleuth/otel/bridge/BaggageTaggingSpanProcessorTest.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2013-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth.otel.bridge;
+
+import java.util.Arrays;
+import java.util.Collections;
+
+import io.opentelemetry.api.baggage.Baggage;
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import org.junit.jupiter.api.Test;
+
+import static io.opentelemetry.api.common.AttributeKey.stringKey;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoInteractions;
+import static org.mockito.Mockito.verifyNoMoreInteractions;
+
+class BaggageTaggingSpanProcessorTest {
+
+	@Test
+	void interfaceMethods() {
+		BaggageTaggingSpanProcessor spanProcessor = new BaggageTaggingSpanProcessor(Collections.emptyList());
+		assertThat(spanProcessor.isEndRequired()).isFalse();
+		assertThat(spanProcessor.isStartRequired()).isTrue();
+	}
+
+	@Test
+	void onStart_emptyBaggage() {
+		BaggageTaggingSpanProcessor spanProcessor = new BaggageTaggingSpanProcessor(Arrays.asList("tagOne", "tagTwo"));
+
+		Baggage baggage = Baggage.builder().build();
+		ReadWriteSpan span = mock(ReadWriteSpan.class);
+
+		spanProcessor.onStart(Context.root().with(baggage), span);
+		verifyNoInteractions(span);
+	}
+
+	@Test
+	void onStart_withBaggage() {
+		BaggageTaggingSpanProcessor spanProcessor = new BaggageTaggingSpanProcessor(Arrays.asList("tagOne", "tagTwo"));
+
+		Baggage baggage = Baggage.builder().put("tagOne", "valueOne").put("tagTwo", "valueTwo")
+				.put("otherTag", "otherValue").build();
+		ReadWriteSpan span = mock(ReadWriteSpan.class);
+
+		spanProcessor.onStart(Context.root().with(baggage), span);
+		verify(span).setAttribute(stringKey("tagOne"), "valueOne");
+		verify(span).setAttribute(stringKey("tagTwo"), "valueTwo");
+
+		verifyNoMoreInteractions(span);
+	}
+
+}