Efficient ETag parsing

Closes gh-33372

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

@@ -0,0 +1,161 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.http;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.util.StringUtils;
+
+/**
+ * Represents an ETag for HTTP conditional requests.
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.3.38
+ * @see <a href="https://datatracker.ietf.org/doc/html/rfc7232">RFC 7232</a>
+ */
+public class ETag {
+
+	private static final Log logger = LogFactory.getLog(ETag.class);
+
+	private static final ETag WILDCARD = new ETag("*", false);
+
+
+	private final String tag;
+
+	private final boolean weak;
+
+
+	public ETag(String tag, boolean weak) {
+		this.tag = tag;
+		this.weak = weak;
+	}
+
+
+	public String tag() {
+		return this.tag;
+	}
+
+	public boolean weak() {
+		return this.weak;
+	}
+
+	/**
+	 * Whether this a wildcard tag matching to any entity tag value.
+	 */
+	public boolean isWildcard() {
+		return (this == WILDCARD);
+	}
+
+	/**
+	 * Return the fully formatted tag including "W/" prefix and quotes.
+	 */
+	public String formattedTag() {
+		if (this == WILDCARD) {
+			return "*";
+		}
+		return (this.weak ? "W/" : "") + "\"" + this.tag + "\"";
+	}
+
+	@Override
+	public String toString() {
+		return formattedTag();
+	}
+
+
+	/**
+	 * Parse entity tags from an "If-Match" or "If-None-Match" header.
+	 * @param source the source string to parse
+	 * @return the parsed ETags
+	 */
+	public static List<ETag> parse(String source) {
+
+		List<ETag> result = new ArrayList<>();
+		State state = State.BEFORE_QUOTES;
+		int startIndex = -1;
+		boolean weak = false;
+
+		for (int i = 0; i < source.length(); i++) {
+			char c = source.charAt(i);
+
+			if (state == State.IN_QUOTES) {
+				if (c == '"') {
+					String tag = source.substring(startIndex, i);
+					if (StringUtils.hasText(tag)) {
+						result.add(new ETag(tag, weak));
+					}
+					state = State.AFTER_QUOTES;
+					startIndex = -1;
+					weak = false;
+				}
+				continue;
+			}
+
+			if (Character.isWhitespace(c)) {
+				continue;
+			}
+
+			if (c == ',') {
+				state = State.BEFORE_QUOTES;
+				continue;
+			}
+
+			if (state == State.BEFORE_QUOTES) {
+				if (c == '*') {
+					result.add(WILDCARD);
+					state = State.AFTER_QUOTES;
+					continue;
+				}
+				if (c == '"') {
+					state = State.IN_QUOTES;
+					startIndex = i + 1;
+					continue;
+				}
+				if (c == 'W' && source.length() > i + 2) {
+					if (source.charAt(i + 1) == '/' && source.charAt(i + 2) == '"') {
+						state = State.IN_QUOTES;
+						i = i + 2;
+						startIndex = i + 1;
+						weak = true;
+						continue;
+					}
+				}
+			}
+
+			if (logger.isDebugEnabled()) {
+				logger.debug("Unexpected char at index " + i);
+			}
+		}
+
+		if (state != State.IN_QUOTES && logger.isDebugEnabled()) {
+			logger.debug("Expected closing '\"'");
+		}
+
+		return result;
+	}
+
+
+	private enum State {
+
+		BEFORE_QUOTES, IN_QUOTES, AFTER_QUOTES
+
+	}
+
+}

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

@@ -40,8 +40,6 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.StringJoiner;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
 import org.springframework.lang.Nullable;
@@ -393,12 +391,6 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	 */
 	public static final HttpHeaders EMPTY = new ReadOnlyHttpHeaders(new LinkedMultiValueMap<>());
 
-	/**
-	 * Pattern matching ETag multiple field values in headers such as "If-Match", "If-None-Match".
-	 * @see <a href="https://tools.ietf.org/html/rfc7232#section-2.3">Section 2.3 of RFC 7232</a>
-	 */
-	private static final Pattern ETAG_HEADER_VALUE_PATTERN = Pattern.compile("\\*|\\s*((W\\/)?(\"[^\"]*\"))\\s*,?");
-
 	private static final DecimalFormatSymbols DECIMAL_FORMAT_SYMBOLS = new DecimalFormatSymbols(Locale.ENGLISH);
 
 	private static final ZoneId GMT = ZoneId.of("GMT");
@@ -1568,35 +1560,27 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 
 	/**
 	 * Retrieve a combined result from the field values of the ETag header.
-	 * @param headerName the header name
+	 * @param name the header name
 	 * @return the combined result
 	 * @throws IllegalArgumentException if parsing fails
 	 * @since 4.3
 	 */
-	protected List<String> getETagValuesAsList(String headerName) {
-		List<String> values = get(headerName);
-		if (values != null) {
-			List<String> result = new ArrayList<>();
-			for (String value : values) {
-				if (value != null) {
-					Matcher matcher = ETAG_HEADER_VALUE_PATTERN.matcher(value);
-					while (matcher.find()) {
-						if ("*".equals(matcher.group())) {
-							result.add(matcher.group());
-						}
-						else {
-							result.add(matcher.group(1));
-						}
-					}
-					if (result.isEmpty()) {
-						throw new IllegalArgumentException(
-								"Could not parse header '" + headerName + "' with value '" + value + "'");
-					}
+	protected List<String> getETagValuesAsList(String name) {
+		List<String> values = get(name);
+		if (values == null) {
+			return Collections.emptyList();
+		}
+		List<String> result = new ArrayList<>();
+		for (String value : values) {
+			if (value != null) {
+				List<ETag> tags = ETag.parse(value);
+				Assert.notEmpty(tags, "Could not parse header '" + name + "' with value '" + value + "'");
+				for (ETag tag : tags) {
+					result.add(tag.formattedTag());
 				}
 			}
-			return result;
 		}
-		return Collections.emptyList();
+		return result;
 	}
 
 	/**

spring-web/src/main/java/org/springframework/web/context/request/ServletWebRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 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.
@@ -26,13 +26,12 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.TimeZone;
-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
 
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 
+import org.springframework.http.ETag;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
@@ -54,12 +53,6 @@ public class ServletWebRequest extends ServletRequestAttributes implements Nativ
 
 	private static final List<String> SAFE_METHODS = Arrays.asList("GET", "HEAD");
 
-	/**
-	 * Pattern matching ETag multiple field values in headers such as "If-Match", "If-None-Match".
-	 * @see <a href="https://tools.ietf.org/html/rfc7232#section-2.3">Section 2.3 of RFC 7232</a>
-	 */
-	private static final Pattern ETAG_HEADER_VALUE_PATTERN = Pattern.compile("\\*|\\s*((W\\/)?(\"[^\"]*\"))\\s*,?");
-
 	/**
 	 * Date formats as specified in the HTTP RFC.
 	 * @see <a href="https://tools.ietf.org/html/rfc7231#section-7.1.1.1">Section 7.1.1.1 of RFC 7231</a>
@@ -289,11 +282,10 @@ public class ServletWebRequest extends ServletRequestAttributes implements Nativ
 			etag = etag.substring(2);
 		}
 		while (ifNoneMatch.hasMoreElements()) {
-			String clientETags = ifNoneMatch.nextElement();
-			Matcher etagMatcher = ETAG_HEADER_VALUE_PATTERN.matcher(clientETags);
 			// Compare weak/strong ETags as per https://tools.ietf.org/html/rfc7232#section-2.3
-			while (etagMatcher.find()) {
-				if (StringUtils.hasLength(etagMatcher.group()) && etag.equals(etagMatcher.group(3))) {
+			for (ETag requestedETag : ETag.parse(ifNoneMatch.nextElement())) {
+				String tag = requestedETag.tag();
+				if (StringUtils.hasLength(tag) && etag.equals(padEtagIfNecessary(tag))) {
 					this.notModified = true;
 					break;
 				}