Merge branch '5.2.x'

# Conflicts:
#	build.gradle
#	spring-test/src/main/java/org/springframework/mock/http/server/reactive/MockServerHttpRequest.java
#	spring-web/src/main/java/org/springframework/http/HttpHeaders.java
#	spring-web/src/testFixtures/java/org/springframework/web/testfixture/http/server/reactive/MockServerHttpRequest.java

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

@@ -385,7 +385,7 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	 * An empty {@code HttpHeaders} instance (immutable).
 	 * @since 5.0
 	 */
-	public static final HttpHeaders EMPTY = new ReadOnlyHttpHeaders(new HttpHeaders(new LinkedMultiValueMap<>(0)));
+	public static final HttpHeaders EMPTY = new ReadOnlyHttpHeaders(new LinkedMultiValueMap<>());
 
 	/**
 	 * Pattern matching ETag multiple field values in headers such as "If-Match", "If-None-Match".
@@ -1769,19 +1769,21 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 
 
 	/**
-	 * Apply a read-only {@code HttpHeaders} wrapper around the given headers
-	 * that also caches the parsed representations of the "Accept" and
-	 * "Content-Type" headers.
+	 * Apply a read-only {@code HttpHeaders} wrapper around the given headers, if necessary.
+	 * <p>Also caches the parsed representations of the "Accept" and "Content-Type" headers.
+	 * @param headers the headers to expose
+	 * @return a read-only variant of the headers, or the original headers as-is
 	 */
-	public static HttpHeaders readOnlyHttpHeaders(MultiValueMap<String, String> headers) {
+	public static HttpHeaders readOnlyHttpHeaders(HttpHeaders headers) {
 		Assert.notNull(headers, "HttpHeaders must not be null");
-		return (headers instanceof ReadOnlyHttpHeaders ?
-				(HttpHeaders) headers : new ReadOnlyHttpHeaders(headers));
+		return (headers instanceof ReadOnlyHttpHeaders ? headers : new ReadOnlyHttpHeaders(headers.headers));
 	}
 
 	/**
 	 * Remove any read-only wrapper that may have been previously applied around
-	 * the given headers via {@link #readOnlyHttpHeaders(MultiValueMap)}.
+	 * the given headers via {@link #readOnlyHttpHeaders(HttpHeaders)}.
+	 * @param headers the headers to expose
+	 * @return a writable variant of the headers, or the original headers as-is
 	 * @since 5.1.1
 	 */
 	public static HttpHeaders writableHttpHeaders(HttpHeaders headers) {

spring-web/src/main/java/org/springframework/http/server/reactive/DefaultServerHttpRequestBuilder.java

@@ -195,20 +195,20 @@ class DefaultServerHttpRequestBuilder implements ServerHttpRequest.Builder {
 			return this.originalRequest.getCookies();
 		}
 
-		@Nullable
 		@Override
-		public InetSocketAddress getRemoteAddress() {
-			return this.originalRequest.getRemoteAddress();
-		}
-
 		@Nullable
-		@Override
 		public InetSocketAddress getLocalAddress() {
 			return this.originalRequest.getLocalAddress();
 		}
 
-		@Nullable
 		@Override
+		@Nullable
+		public InetSocketAddress getRemoteAddress() {
+			return this.originalRequest.getRemoteAddress();
+		}
+
+		@Override
+		@Nullable
 		protected SslInfo initSslInfo() {
 			return this.sslInfo;
 		}

spring-web/src/main/java/org/springframework/http/server/reactive/ReactorServerHttpRequest.java

@@ -95,6 +95,7 @@ class ReactorServerHttpRequest extends AbstractServerHttpRequest {
 		}
 		else {
 			InetSocketAddress localAddress = request.hostAddress();
+			Assert.state(localAddress != null, "No host address available");
 			return new URI(scheme, null, localAddress.getHostString(),
 					localAddress.getPort(), null, null, null);
 		}
@@ -145,13 +146,15 @@ class ReactorServerHttpRequest extends AbstractServerHttpRequest {
 	}
 
 	@Override
-	public InetSocketAddress getRemoteAddress() {
-		return this.request.remoteAddress();
+	@Nullable
+	public InetSocketAddress getLocalAddress() {
+		return this.request.hostAddress();
 	}
 
 	@Override
-	public InetSocketAddress getLocalAddress() {
-		return this.request.hostAddress();
+	@Nullable
+	public InetSocketAddress getRemoteAddress() {
+		return this.request.remoteAddress();
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/server/reactive/ServerHttpRequest.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.
@@ -65,19 +65,19 @@ public interface ServerHttpRequest extends HttpRequest, ReactiveHttpInputMessage
 	MultiValueMap<String, HttpCookie> getCookies();
 
 	/**
-	 * Return the remote address where this request is connected to, if available.
+	 * Return the local address the request was accepted on, if available.
+	 * @since 5.2.3
 	 */
 	@Nullable
-	default InetSocketAddress getRemoteAddress() {
+	default InetSocketAddress getLocalAddress() {
 		return null;
 	}
 
 	/**
-	 * Return the local address the request was accepted on, if available.
-	 * 5.2.3
+	 * Return the remote address where this request is connected to, if available.
 	 */
 	@Nullable
-	default InetSocketAddress getLocalAddress() {
+	default InetSocketAddress getRemoteAddress() {
 		return null;
 	}
 

spring-web/src/main/java/org/springframework/http/server/reactive/ServerHttpRequestDecorator.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.
@@ -97,17 +97,19 @@ public class ServerHttpRequestDecorator implements ServerHttpRequest {
 	}
 
 	@Override
+	@Nullable
+	public InetSocketAddress getLocalAddress() {
+		return getDelegate().getLocalAddress();
+	}
+
+	@Override
+	@Nullable
 	public InetSocketAddress getRemoteAddress() {
 		return getDelegate().getRemoteAddress();
 	}
 
 	@Override
-	public InetSocketAddress getLocalAddress() {
-		return getDelegate().getLocalAddress();
-	}
-
 	@Nullable
-	@Override
 	public SslInfo getSslInfo() {
 		return getDelegate().getSslInfo();
 	}

spring-web/src/main/java/org/springframework/http/server/reactive/ServletServerHttpRequest.java

@@ -43,6 +43,7 @@ import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.http.HttpCookie;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
+import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
@@ -179,13 +180,15 @@ class ServletServerHttpRequest extends AbstractServerHttpRequest {
 	}
 
 	@Override
-	public InetSocketAddress getRemoteAddress() {
-		return new InetSocketAddress(this.request.getRemoteHost(), this.request.getRemotePort());
+	@NonNull
+	public InetSocketAddress getLocalAddress() {
+		return new InetSocketAddress(this.request.getLocalAddr(), this.request.getLocalPort());
 	}
 
 	@Override
-	public InetSocketAddress getLocalAddress() {
-		return new InetSocketAddress(this.request.getLocalAddr(), this.request.getLocalPort());
+	@NonNull
+	public InetSocketAddress getRemoteAddress() {
+		return new InetSocketAddress(this.request.getRemoteHost(), this.request.getRemotePort());
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/server/reactive/UndertowServerHttpRequest.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.
@@ -93,13 +93,15 @@ class UndertowServerHttpRequest extends AbstractServerHttpRequest {
 	}
 
 	@Override
-	public InetSocketAddress getRemoteAddress() {
-		return this.exchange.getSourceAddress();
+	@Nullable
+	public InetSocketAddress getLocalAddress() {
+		return this.exchange.getDestinationAddress();
 	}
 
 	@Override
-	public InetSocketAddress getLocalAddress() {
-		return this.exchange.getDestinationAddress();
+	@Nullable
+	public InetSocketAddress getRemoteAddress() {
+		return this.exchange.getSourceAddress();
 	}
 
 	@Nullable