Support double-quoted in HttpHeaders::getValuesAsList

This commit introduces support for double-quoted HTTP header values in
HttpHeaders::getValuesAsList, as described in RFC 9110 section 5.5.

Closes gh-29785

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

@@ -1537,8 +1537,11 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	}
 
 	/**
-	 * Return all values of a given header name,
+	 * Return all values of a given header name, even if this header is set
-	 * even if this header is set multiple times.
+	 * multiple times.
+	 * <p>This method supports double-quoted values, as described in
+	 * <a href="https://www.rfc-editor.org/rfc/rfc9110.html#section-5.5-8">RFC
+	 * 9110, section 5.5</a>.
 	 * @param headerName the header name
 	 * @return all associated values
 	 * @since 4.3
@@ -1549,7 +1552,7 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 			List<String> result = new ArrayList<>();
 			for (String value : values) {
 				if (value != null) {
-					Collections.addAll(result, StringUtils.tokenizeToStringArray(value, ","));
+					result.addAll(tokenizeQuoted(value));
 				}
 			}
 			return result;
@@ -1557,6 +1560,53 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 		return Collections.emptyList();
 	}
 
+	private static List<String> tokenizeQuoted(String str) {
+		List<String> tokens = new ArrayList<>();
+		boolean quoted = false;
+		boolean trim = true;
+		StringBuilder builder = new StringBuilder(str.length());
+		for (int i = 0; i < str.length(); ++i) {
+			char ch = str.charAt(i);
+			if (ch == '"') {
+				if (builder.isEmpty()) {
+					quoted = true;
+				}
+				else if (quoted) {
+					quoted = false;
+					trim = false;
+				}
+				else {
+					builder.append(ch);
+				}
+			}
+			else if (ch == '\\' && quoted && i < str.length() - 1) {
+				builder.append(str.charAt(++i));
+			}
+			else if (ch == ',' && !quoted) {
+				addToken(builder, tokens, trim);
+				builder.setLength(0);
+				trim = false;
+			}
+			else if (quoted || (!builder.isEmpty() && trim) || !Character.isWhitespace(ch)) {
+				builder.append(ch);
+			}
+		}
+		if (!builder.isEmpty()) {
+			addToken(builder, tokens, trim);
+		}
+		return tokens;
+	}
+
+	private static void addToken(StringBuilder builder, List<String> tokens, boolean trim) {
+		String token = builder.toString();
+		if (trim) {
+			token = token.trim();
+		}
+		if (!token.isEmpty()) {
+			tokens.add(token);
+		}
+	}
+
 	/**
 	 * Remove the well-known {@code "Content-*"} HTTP headers.
 	 * <p>Such headers should be cleared from the response if the intended

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -713,4 +713,19 @@ public class HttpHeadersTests {
 		assertThat(headers2).isEqualTo(headers1);
 	}
 
+	@Test
+	void getValuesAsList() {
+		HttpHeaders headers = new HttpHeaders();
+		headers.add("Foo", "Bar");
+		headers.add("Foo", "Baz, Qux");
+		headers.add("Quux", "\t\"Corge\", \"Grault\"");
+		headers.add("Garply", " Waldo \"Fred\\!\", \"\tPlugh, Xyzzy! \"");
+		headers.add("Example-Dates", "\"Sat, 04 May 1996\", \"Wed, 14 Sep 2005\"");
+
+		assertThat(headers.getValuesAsList("Foo")).containsExactly("Bar", "Baz", "Qux");
+		assertThat(headers.getValuesAsList("Quux")).containsExactly("Corge", "Grault");
+		assertThat(headers.getValuesAsList("Garply")).containsExactly("Waldo \"Fred\\!\"", "\tPlugh, Xyzzy! ");
+		assertThat(headers.getValuesAsList("Example-Dates")).containsExactly("Sat, 04 May 1996", "Wed, 14 Sep 2005");
+	}
+
 }