From 57b8100a063e87886eaf67d5910f3ad94da63ac6 Mon Sep 17 00:00:00 2001
From: Arjen Poutsma <arjen.poutsma@broadcom.com>
Date: Mon, 11 Dec 2023 12:57:09 +0100
Subject: [PATCH] Copy headers map in RestClientResponseException to ensure
 serializability

This commit ensures that the HttpHeaders used are serializable by making
 a copy.

Closes gh-31787
---
 .../client/RestClientResponseException.java   | 20 ++++++++++++++++++-
 .../DefaultResponseErrorHandlerTests.java     |  2 +-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/spring-web/src/main/java/org/springframework/web/client/RestClientResponseException.java b/spring-web/src/main/java/org/springframework/web/client/RestClientResponseException.java
index 20974f96b039..e1a8a76333f8 100644
--- a/spring-web/src/main/java/org/springframework/web/client/RestClientResponseException.java
+++ b/spring-web/src/main/java/org/springframework/web/client/RestClientResponseException.java
@@ -27,6 +27,8 @@
 import org.springframework.http.HttpStatusCode;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
 
 /**
  * Common base class for exceptions that contain actual HTTP response data.
@@ -88,11 +90,27 @@ public RestClientResponseException(
 		super(message);
 		this.statusCode = statusCode;
 		this.statusText = statusText;
-		this.responseHeaders = headers;
+		this.responseHeaders = copyHeaders(headers);
 		this.responseBody = (responseBody != null ? responseBody : new byte[0]);
 		this.responseCharset = (responseCharset != null ? responseCharset.name() : null);
 	}
 
+	/**
+	 * Copies the given headers, because the backing map might not be
+	 * serializable.
+	 */
+	@Nullable
+	private static HttpHeaders copyHeaders(@Nullable HttpHeaders headers) {
+		if (headers != null) {
+			MultiValueMap<String, String> result = new LinkedMultiValueMap<>(headers.size());
+			headers.forEach((name, values) -> values.forEach(value -> result.add(name, value)));
+			return HttpHeaders.readOnlyHttpHeaders(result);
+		}
+		else {
+			return null;
+		}
+	}
+
 
 	/**
 	 * Return the HTTP status code.
diff --git a/spring-web/src/test/java/org/springframework/web/client/DefaultResponseErrorHandlerTests.java b/spring-web/src/test/java/org/springframework/web/client/DefaultResponseErrorHandlerTests.java
index 43c9dfc2c783..1e713b4ab230 100644
--- a/spring-web/src/test/java/org/springframework/web/client/DefaultResponseErrorHandlerTests.java
+++ b/spring-web/src/test/java/org/springframework/web/client/DefaultResponseErrorHandlerTests.java
@@ -74,7 +74,7 @@ public void handleError() throws Exception {
 		assertThatExceptionOfType(HttpClientErrorException.class)
 				.isThrownBy(() -> handler.handleError(response))
 				.withMessage("404 Not Found: \"Hello World\"")
-				.satisfies(ex -> assertThat(ex.getResponseHeaders()).isSameAs(headers));
+				.satisfies(ex -> assertThat(ex.getResponseHeaders()).isEqualTo(headers));
 	}
 
 	@Test