HttpHeaders#equals handles wrapping correctly

Closes gh-25034

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -1677,8 +1677,14 @@ public boolean equals(Object other) {
 		if (!(other instanceof HttpHeaders)) {
 			return false;
 		}
-		HttpHeaders otherHeaders = (HttpHeaders) other;
-		return this.headers.equals(otherHeaders.headers);
+		return unwrap(this).equals(unwrap((HttpHeaders) other));
+	}
+
+	private static MultiValueMap<String, String> unwrap(HttpHeaders headers) {
+		while (headers.headers instanceof HttpHeaders) {
+			headers = (HttpHeaders) headers.headers;
+		}
+		return headers.headers;
 	}
 
 	@Override
@@ -1693,33 +1699,25 @@ public String toString() {
 
 
 	/**
-	 * Return an {@code HttpHeaders} object that can only be read, not written to.
+	 * Apply a read-only {@code HttpHeaders} wrapper around the given headers.
 	 */
-	public static HttpHeaders readOnlyHttpHeaders(HttpHeaders headers) {
+	public static HttpHeaders readOnlyHttpHeaders(MultiValueMap<String, String> headers) {
 		Assert.notNull(headers, "HttpHeaders must not be null");
-		if (headers instanceof ReadOnlyHttpHeaders) {
-			return headers;
-		}
-		else {
-			return new ReadOnlyHttpHeaders(headers);
-		}
+		return (headers instanceof ReadOnlyHttpHeaders ?
+				(HttpHeaders) headers : new ReadOnlyHttpHeaders(headers));
 	}
 
 	/**
-	 * Return an {@code HttpHeaders} object that can be read and written to.
+	 * Remove any read-only wrapper that may have been previously applied around
+	 * the given headers via {@link #readOnlyHttpHeaders(MultiValueMap)}.
 	 * @since 5.1.1
 	 */
 	public static HttpHeaders writableHttpHeaders(HttpHeaders headers) {
 		Assert.notNull(headers, "HttpHeaders must not be null");
 		if (headers == EMPTY) {
 			return new HttpHeaders();
 		}
-		else if (headers instanceof ReadOnlyHttpHeaders) {
-			return new HttpHeaders(headers.headers);
-		}
-		else {
-			return headers;
-		}
+		return (headers instanceof ReadOnlyHttpHeaders ? new HttpHeaders(headers.headers) : headers);
 	}
 
 	/**

spring-web/src/main/java/org/springframework/http/ReadOnlyHttpHeaders.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -46,8 +46,8 @@ class ReadOnlyHttpHeaders extends HttpHeaders {
 	private List<MediaType> cachedAccept;
 
 
-	ReadOnlyHttpHeaders(HttpHeaders headers) {
-		super(headers.headers);
+	ReadOnlyHttpHeaders(MultiValueMap<String, String> headers) {
+		super(headers);
 	}
 
 

spring-web/src/test/java/org/springframework/http/HttpHeadersTests.java

@@ -678,4 +678,12 @@ public void readOnlyHttpHeadersRetainEntrySetOrder() {
 		assertArrayEquals(expectedKeys, readOnlyHttpHeaders.entrySet().stream().map(Entry::getKey).toArray());
 	}
 
+	@Test // gh-25034
+	public void equalsUnwrapsHttpHeaders() {
+		HttpHeaders headers1 = new HttpHeaders();
+		HttpHeaders headers2 = new HttpHeaders(new HttpHeaders(headers1));
+
+		assertEquals(headers1, headers2);
+		assertEquals(headers2, headers1);
+	}
 }