Synchronized updates of STOMP header key cache

Issue: SPR-14901

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompEncoder.java

@@ -25,6 +25,7 @@ import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -53,15 +54,26 @@ public class StompEncoder  {
 
 	private static final int HEADER_KEY_CACHE_LIMIT = 32;
 
+
+	private final Map<String, byte[]> headerKeyAccessCache =
+			new ConcurrentHashMap<>(HEADER_KEY_CACHE_LIMIT);
+
 	@SuppressWarnings("serial")
-	private final Map<String, byte[]> headerKeyCache =
+	private final Map<String, byte[]> headerKeyUpdateCache =
 			new LinkedHashMap<String, byte[]>(HEADER_KEY_CACHE_LIMIT, 0.75f, true) {
 				@Override
 				protected boolean removeEldestEntry(Map.Entry<String, byte[]> eldest) {
-					return size() > HEADER_KEY_CACHE_LIMIT;
+					if (size() > HEADER_KEY_CACHE_LIMIT) {
+						headerKeyAccessCache.remove(eldest.getKey());
+						return true;
+					}
+					else {
+						return false;
+					}
 				}
 			};
 
+
 	/**
 	 * Encodes the given STOMP {@code message} into a {@code byte[]}
 	 * @param message the message to encode
@@ -160,21 +172,23 @@ public class StompEncoder  {
 
 	private byte[] encodeHeaderKey(String input, boolean escape) {
 		String inputToUse = (escape ? escape(input) : input);
-		if (headerKeyCache.containsKey(inputToUse)) {
-			return headerKeyCache.get(inputToUse);
+		if (this.headerKeyAccessCache.containsKey(inputToUse)) {
+			return this.headerKeyAccessCache.get(inputToUse);
+		}
+		synchronized (this.headerKeyUpdateCache) {
+			byte[] bytes = this.headerKeyUpdateCache.get(inputToUse);
+			if (bytes == null) {
+				bytes = inputToUse.getBytes(StandardCharsets.UTF_8);
+				this.headerKeyAccessCache.put(inputToUse, bytes);
+				this.headerKeyUpdateCache.put(inputToUse, bytes);
+			}
+			return bytes;
 		}
-		byte[] bytes = encodeHeaderString(inputToUse);
-		headerKeyCache.put(inputToUse, bytes);
-		return bytes;
 	}
 
 	private byte[] encodeHeaderValue(String input, boolean escape) {
 		String inputToUse = (escape ? escape(input) : input);
-		return encodeHeaderString(inputToUse);
-	}
-
-	private byte[] encodeHeaderString(String input) {
-		return input.getBytes(StandardCharsets.UTF_8);
+		return inputToUse.getBytes(StandardCharsets.UTF_8);
 	}
 
 	/**

spring-websocket/src/main/java/org/springframework/web/socket/messaging/StompSubProtocolHandler.java

@@ -88,13 +88,14 @@ public class StompSubProtocolHandler implements SubProtocolHandler, ApplicationE
 
 	private static final byte[] EMPTY_PAYLOAD = new byte[0];
 
+
 	private StompSubProtocolErrorHandler errorHandler;
 
 	private int messageSizeLimit = 64 * 1024;
 
-	private StompEncoder stompEncoder;
+	private StompEncoder stompEncoder = new StompEncoder();
 
-	private StompDecoder stompDecoder;
+	private StompDecoder stompDecoder = new StompDecoder();
 
 	private final Map<String, BufferingStompDecoder> decoders = new ConcurrentHashMap<>();
 
@@ -106,10 +107,6 @@ public class StompSubProtocolHandler implements SubProtocolHandler, ApplicationE
 
 	private final Stats stats = new Stats();
 
-	public StompSubProtocolHandler() {
-		setEncoder(new StompEncoder());
-		setDecoder(new StompDecoder());
-	}
 
 	/**
 	 * Configure a handler for error messages sent to clients which allows
@@ -129,24 +126,6 @@ public class StompSubProtocolHandler implements SubProtocolHandler, ApplicationE
 		return this.errorHandler;
 	}
 
-	/**
-	 * Configure a {@link StompEncoder} for encoding STOMP frames
-	 * @param encoder the encoder
-	 * @since 4.3.5
-	 */
-	public void setEncoder(StompEncoder encoder) {
-		this.stompEncoder = encoder;
-	}
-
-	/**
-	 * Configure a {@link StompDecoder} for decoding STOMP frames
-	 * @param decoder the decoder
-	 * @since 4.3.5
-	 */
-	public void setDecoder(StompDecoder decoder) {
-		this.stompDecoder = decoder;
-	}
-
 	/**
 	 * Configure the maximum size allowed for an incoming STOMP message.
 	 * Since a STOMP message can be received in multiple WebSocket messages,
@@ -167,6 +146,24 @@ public class StompSubProtocolHandler implements SubProtocolHandler, ApplicationE
 		return this.messageSizeLimit;
 	}
 
+	/**
+	 * Configure a {@link StompEncoder} for encoding STOMP frames
+	 * @param encoder the encoder
+	 * @since 4.3.5
+	 */
+	public void setEncoder(StompEncoder encoder) {
+		this.stompEncoder = encoder;
+	}
+
+	/**
+	 * Configure a {@link StompDecoder} for decoding STOMP frames
+	 * @param decoder the decoder
+	 * @since 4.3.5
+	 */
+	public void setDecoder(StompDecoder decoder) {
+		this.stompDecoder = decoder;
+	}
+
 	/**
 	 * Configure a {@link MessageHeaderInitializer} to apply to the headers of all
 	 * messages created from decoded STOMP frames and other messages sent to the