Quote ETag if not quoted in HttpHeaders#setETag

This aligns HttpHeaders with other places like ServletWebRequest and
DefaultWebExchange where an ETag is accepted as input.

It also allows us to remove quoting from places that delegate to
HttpHeaders#setETag since it now does that internally.

Closes gh-33412

Author: rstoyanchev

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

@@ -1063,11 +1063,9 @@ public long getDate() {
 	/**
 	 * Set the (new) entity tag of the body, as specified by the {@code ETag} header.
 	 */
-	public void setETag(@Nullable String eTag) {
-		if (eTag != null) {
-			Assert.isTrue(eTag.startsWith("\"") || eTag.startsWith("W/\""), "ETag does not start with W/\" or \"");
-			Assert.isTrue(eTag.endsWith("\""), "ETag does not end with \"");
-			set(ETAG, eTag);
+	public void setETag(@Nullable String tag) {
+		if (tag != null) {
+			set(ETAG, ETag.quoteETagIfNecessary(tag));
 		}
 		else {
 			remove(ETAG);

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

@@ -568,9 +568,8 @@ public BodyBuilder contentType(MediaType contentType) {
 		}
 
 		@Override
-		public BodyBuilder eTag(@Nullable String eTag) {
-			eTag = (eTag != null ? ETag.quoteETagIfNecessary(eTag) : eTag);
-			this.headers.setETag(eTag);
+		public BodyBuilder eTag(@Nullable String tag) {
+			this.headers.setETag(tag);
 			return this;
 		}
 

spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java

@@ -417,13 +417,13 @@ private void updateResponseIdempotent(@Nullable String eTag, Instant lastModifie
 		addCachingResponseHeaders(eTag, lastModified);
 	}
 
-	private void addCachingResponseHeaders(@Nullable String eTag, Instant lastModified) {
+	private void addCachingResponseHeaders(@Nullable String tag, Instant lastModified) {
 		if (SAFE_METHODS.contains(getRequest().getMethod())) {
 			if (lastModified.isAfter(Instant.EPOCH) && getResponseHeaders().getLastModified() == -1) {
 				getResponseHeaders().setLastModified(lastModified.toEpochMilli());
 			}
-			if (StringUtils.hasLength(eTag) && getResponseHeaders().getETag() == null) {
-				getResponseHeaders().setETag(ETag.quoteETagIfNecessary(eTag));
+			if (StringUtils.hasLength(tag) && getResponseHeaders().getETag() == null) {
+				getResponseHeaders().setETag(tag);
 			}
 		}
 	}

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

@@ -214,15 +214,15 @@ void ipv6Host() {
 	}
 
 	@Test
-	void illegalETagWithoutQuotes() {
-		String eTag = "v2.6";
-		assertThatIllegalArgumentException().isThrownBy(() -> headers.setETag(eTag));
+	void eTagWithoutQuotes() {
+		headers.setETag("v2.6");
+		assertThat(headers.getETag()).isEqualTo("\"v2.6\"");
 	}
 
 	@Test
-	void illegalWeakETagWithoutLeadingQuote() {
-		String etag = "W/v2.6\"";
-		assertThatIllegalArgumentException().isThrownBy(() -> headers.setETag(etag));
+	void weakETagWithoutLeadingQuote() {
+		headers.setETag("W/v2.6\"");
+		assertThat(headers.getETag()).isEqualTo("\"W/v2.6\"\"");
 	}
 
 	@Test

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

@@ -148,9 +148,8 @@ public EntityResponse.Builder<T> contentType(MediaType contentType) {
 	}
 
 	@Override
-	public EntityResponse.Builder<T> eTag(String eTag) {
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public EntityResponse.Builder<T> eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}
 

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

@@ -147,10 +147,8 @@ public ServerResponse.BodyBuilder contentType(MediaType contentType) {
 	}
 
 	@Override
-	public ServerResponse.BodyBuilder eTag(String eTag) {
-		Assert.notNull(eTag, "etag must not be null");
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public ServerResponse.BodyBuilder eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.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.
@@ -332,8 +332,7 @@ public String getDescription() {
 
 		@Override
 		public HttpHeaders getResponseHeaders() {
-			HttpHeaders headers = (this.original instanceof HttpResource httpResource ?
-					httpResource.getResponseHeaders() : new HttpHeaders());
+			HttpHeaders headers = (this.original instanceof HttpResource hr ? hr.getResponseHeaders() : new HttpHeaders());
 			headers.setETag("W/\"" + this.version + "\"");
 			return headers;
 		}

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

@@ -166,9 +166,8 @@ public EntityResponse.Builder<T> contentType(MediaType contentType) {
 	}
 
 	@Override
-	public EntityResponse.Builder<T> eTag(String eTag) {
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public EntityResponse.Builder<T> eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}
 

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

@@ -127,10 +127,8 @@ public ServerResponse.BodyBuilder contentType(MediaType contentType) {
 	}
 
 	@Override
-	public ServerResponse.BodyBuilder eTag(String eTag) {
-		Assert.notNull(eTag, "etag must not be null");
-		eTag = ETag.quoteETagIfNecessary(eTag);
-		this.headers.setETag(eTag);
+	public ServerResponse.BodyBuilder eTag(String tag) {
+		this.headers.setETag(tag);
 		return this;
 	}