From 9533fbfed0d8b51d066e0e79fab05c68ba1c87e9 Mon Sep 17 00:00:00 2001
From: Marcin Grzejszczak <marcin@grzejszczak.pl>
Date: Fri, 3 May 2019 22:08:09 +0400
Subject: [PATCH] Making a copy of "nativeHeaders" and working on a copy

otherwise we got ConcurrentModificationExceptions

fixes gh-1345
---
 .../instrument/messaging/MessageHeaderPropagation.java   | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/messaging/MessageHeaderPropagation.java b/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/messaging/MessageHeaderPropagation.java
index 13ec0e0f8..4d0fffa9c 100644
--- a/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/messaging/MessageHeaderPropagation.java
+++ b/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/messaging/MessageHeaderPropagation.java
@@ -151,11 +151,18 @@ enum MessageHeaderPropagation
 						nativeHeaders);
 			}
 			if (nativeHeaders instanceof Map<?, ?>) {
-				((Map) nativeHeaders).put(key, Collections.singletonList(value));
+				Map<String, List<String>> copy = toNativeHeaderMap(
+						(Map<String, List<String>>) nativeHeaders);
+				copy.put(key, Collections.singletonList(value));
+				accessor.setHeader(NativeMessageHeaderAccessor.NATIVE_HEADERS, copy);
 			}
 		}
 	}
 
+	private Map<String, List<String>> toNativeHeaderMap(Map<String, List<String>> map) {
+		return (map != null ? new LinkedMultiValueMap<>(map) : Collections.emptyMap());
+	}
+
 	@Override
 	public String get(MessageHeaderAccessor accessor, String key) {
 		try {