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);
   }