revert

Author: trask

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/semconv/messaging/CapturedMessageHeadersUtil.java

@@ -5,21 +5,31 @@
 
 package io.opentelemetry.instrumentation.api.incubator.semconv.messaging;
 
+import static java.util.Collections.unmodifiableList;
+
 import io.opentelemetry.api.common.AttributeKey;
 import java.util.List;
+import java.util.Locale;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
+import java.util.stream.Collectors;
 
 final class CapturedMessageHeadersUtil {
 
   private static final ConcurrentMap<String, AttributeKey<List<String>>> attributeKeysCache =
       new ConcurrentHashMap<>();
 
+  static List<String> lowercase(List<String> names) {
+    return unmodifiableList(
+        names.stream().map(s -> s.toLowerCase(Locale.ROOT)).collect(Collectors.toList()));
+  }
+
   static AttributeKey<List<String>> attributeKey(String headerName) {
     return attributeKeysCache.computeIfAbsent(headerName, n -> createKey(n));
   }
 
   private static AttributeKey<List<String>> createKey(String headerName) {
+    // headerName is always lowercase, see MessagingAttributesExtractor
     String key = "messaging.header." + headerName.replace('-', '_');
     return AttributeKey.stringArrayKey(key);
   }

instrumentation-api-incubator/src/main/java/io/opentelemetry/instrumentation/api/incubator/semconv/messaging/MessagingAttributesExtractor.java

@@ -13,7 +13,6 @@
 import io.opentelemetry.instrumentation.api.instrumenter.AttributesExtractor;
 import io.opentelemetry.instrumentation.api.internal.SpanKey;
 import io.opentelemetry.instrumentation.api.internal.SpanKeyProvider;
-import java.util.ArrayList;
 import java.util.List;
 import javax.annotation.Nullable;
 
@@ -86,7 +85,7 @@ public static <REQUEST, RESPONSE> MessagingAttributesExtractorBuilder<REQUEST, R
       List<String> capturedHeaders) {
     this.getter = getter;
     this.operation = operation;
-    this.capturedHeaders = new ArrayList<>(capturedHeaders);
+    this.capturedHeaders = CapturedMessageHeadersUtil.lowercase(capturedHeaders);
   }
 
   @Override