Polishing and minor refactoring

Update checks whether quoting is needed to be more complete
than what we've used so far, making sure the there is both
opening and closing quotes independent of each other.

See gh-33412

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

@@ -134,16 +134,27 @@ public record ETag(String tag, boolean weak) {
 		return result;
 	}
 
-	public static String format(String etag) {
-		if (!etag.startsWith("\"") && !etag.startsWith("W/\"")) {
-			etag = "\"" + etag;
+	/**
+	 * Add quotes around the ETag value if not present already.
+	 * @param tag the ETag value
+	 * @return the resulting, quoted value
+	 * @since 6.2
+	 */
+	public static String quoteETagIfNecessary(String tag) {
+		if (tag.startsWith("W/\"")) {
+			if (tag.length() > 3 && tag.endsWith("\"")) {
+				return tag;
+			}
 		}
-		if (!etag.endsWith("\"")) {
-			etag = etag + "\"";
+		else if (tag.startsWith("\"")) {
+			if (tag.length() > 1 && tag.endsWith("\"")) {
+				return tag;
+			}
 		}
-		return etag;
+		return ("\"" + tag + "\"");
 	}
 
+
 	private enum State {
 
 		BEFORE_QUOTES, IN_QUOTES, AFTER_QUOTES

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -568,11 +568,9 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 		}
 
 		@Override
-		public BodyBuilder eTag(@Nullable String etag) {
-			if (etag != null) {
-				etag = ETag.format(etag);
-			}
-			this.headers.setETag(etag);
+		public BodyBuilder eTag(@Nullable String eTag) {
+			eTag = (eTag != null ? ETag.quoteETagIfNecessary(eTag) : eTag);
+			this.headers.setETag(eTag);
 			return this;
 		}
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultEntityResponseBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -28,10 +28,17 @@ import java.util.Optional;
 import java.util.Set;
 import java.util.function.Consumer;
 
-import org.springframework.http.*;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.codec.Hints;
+import org.springframework.http.CacheControl;
+import org.springframework.http.ETag;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseCookie;
 import org.springframework.http.codec.HttpMessageWriter;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
@@ -141,9 +148,9 @@ class DefaultEntityResponseBuilder<T> implements EntityResponse.Builder<T> {
 	}
 
 	@Override
-	public EntityResponse.Builder<T> eTag(String etag) {
-		etag = ETag.format(etag);
-		this.headers.setETag(etag);
+	public EntityResponse.Builder<T> eTag(String eTag) {
+		eTag = ETag.quoteETagIfNecessary(eTag);
+		this.headers.setETag(eTag);
 		return this;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerResponseBuilder.java

@@ -32,11 +32,18 @@ import java.util.function.Consumer;
 import java.util.function.Function;
 
 import org.reactivestreams.Publisher;
-import org.springframework.http.*;
 import reactor.core.publisher.Mono;
 
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.codec.Hints;
+import org.springframework.http.CacheControl;
+import org.springframework.http.ETag;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.MediaType;
+import org.springframework.http.ReactiveHttpOutputMessage;
+import org.springframework.http.ResponseCookie;
 import org.springframework.http.codec.HttpMessageWriter;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
@@ -140,10 +147,10 @@ class DefaultServerResponseBuilder implements ServerResponse.BodyBuilder {
 	}
 
 	@Override
-	public ServerResponse.BodyBuilder eTag(String etag) {
-		Assert.notNull(etag, "etag must not be null");
-		etag = ETag.format(etag);
-		this.headers.setETag(etag);
+	public ServerResponse.BodyBuilder eTag(String eTag) {
+		Assert.notNull(eTag, "etag must not be null");
+		eTag = ETag.quoteETagIfNecessary(eTag);
+		this.headers.setETag(eTag);
 		return this;
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultEntityResponseBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -45,7 +45,15 @@ import org.springframework.core.ResolvableType;
 import org.springframework.core.io.InputStreamResource;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.support.ResourceRegion;
-import org.springframework.http.*;
+import org.springframework.http.CacheControl;
+import org.springframework.http.ETag;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpRange;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.InvalidMediaTypeException;
+import org.springframework.http.MediaType;
 import org.springframework.http.converter.GenericHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.SmartHttpMessageConverter;
@@ -158,9 +166,9 @@ final class DefaultEntityResponseBuilder<T> implements EntityResponse.Builder<T>
 	}
 
 	@Override
-	public EntityResponse.Builder<T> eTag(String etag) {
-		etag = ETag.format(etag);
-		this.headers.setETag(etag);
+	public EntityResponse.Builder<T> eTag(String eTag) {
+		eTag = ETag.quoteETagIfNecessary(eTag);
+		this.headers.setETag(eTag);
 		return this;
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerResponseBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -30,7 +30,12 @@ import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
 
 import org.springframework.core.ParameterizedTypeReference;
-import org.springframework.http.*;
+import org.springframework.http.CacheControl;
+import org.springframework.http.ETag;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.MediaType;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.LinkedMultiValueMap;
@@ -122,10 +127,10 @@ class DefaultServerResponseBuilder implements ServerResponse.BodyBuilder {
 	}
 
 	@Override
-	public ServerResponse.BodyBuilder eTag(String etag) {
-		Assert.notNull(etag, "etag must not be null");
-		etag = ETag.format(etag);
-		this.headers.setETag(etag);
+	public ServerResponse.BodyBuilder eTag(String eTag) {
+		Assert.notNull(eTag, "etag must not be null");
+		eTag = ETag.quoteETagIfNecessary(eTag);
+		this.headers.setETag(eTag);
 		return this;
 	}