SPR-14901 Allow customization of STOMP message header encoding

Fixes SPR-14901

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

@@ -21,6 +21,7 @@ import java.io.DataOutputStream;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -50,6 +51,16 @@ public class StompEncoder  {
 
 	private static final Log logger = LogFactory.getLog(StompEncoder.class);
 
+	private static final int HEADER_KEY_CACHE_LIMIT = 32;
+
+	@SuppressWarnings("serial")
+	private final Map<String, byte[]> headerKeyCache =
+			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;
+				}
+			};
 
 	/**
 	 * Encodes the given STOMP {@code message} into a {@code byte[]}
@@ -130,11 +141,11 @@ public class StompEncoder  {
 				values = Collections.singletonList(StompHeaderAccessor.getPasscode(headers));
 			}
 
-			byte[] encodedKey = encodeHeaderString(entry.getKey(), shouldEscape);
+			byte[] encodedKey = encodeHeaderKey(entry.getKey(), shouldEscape);
 			for (String value : values) {
 				output.write(encodedKey);
 				output.write(COLON);
-				output.write(encodeHeaderString(value, shouldEscape));
+				output.write(encodeHeaderValue(value, shouldEscape));
 				output.write(LF);
 			}
 		}
@@ -147,9 +158,23 @@ public class StompEncoder  {
 		}
 	}
 
-	private byte[] encodeHeaderString(String input, boolean escape) {
+	private byte[] encodeHeaderKey(String input, boolean escape) {
 		String inputToUse = (escape ? escape(input) : input);
-		return inputToUse.getBytes(StandardCharsets.UTF_8);
+		if (headerKeyCache.containsKey(inputToUse)) {
+			return headerKeyCache.get(inputToUse);
+		}
+		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);
 	}
 
 	/**
@@ -157,26 +182,38 @@ public class StompEncoder  {
 	 * <a href="http://stomp.github.io/stomp-specification-1.2.html#Value_Encoding">"Value Encoding"</a>.
 	 */
 	private String escape(String inString) {
-		StringBuilder sb = new StringBuilder(inString.length());
+		StringBuilder sb = null;
 		for (int i = 0; i < inString.length(); i++) {
 			char c = inString.charAt(i);
 			if (c == '\\') {
+				sb = getStringBuilder(sb, inString, i);
 				sb.append("\\\\");
 			}
 			else if (c == ':') {
+				sb = getStringBuilder(sb, inString, i);
 				sb.append("\\c");
 			}
 			else if (c == '\n') {
-				 sb.append("\\n");
+				sb = getStringBuilder(sb, inString, i);
+				sb.append("\\n");
 			}
 			else if (c == '\r') {
+				sb = getStringBuilder(sb, inString, i);
 				sb.append("\\r");
 			}
-			else {
+			else if (sb != null){
 				sb.append(c);
 			}
 		}
-		return sb.toString();
+		return (sb != null ? sb.toString() : inString);
+	}
+
+	private StringBuilder getStringBuilder(StringBuilder sb, String inString, int i) {
+		if (sb == null) {
+			sb = new StringBuilder(inString.length());
+			sb.append(inString.substring(0, i));
+		}
+		return sb;
 	}
 
 	private void writeBody(byte[] payload, DataOutputStream output) throws IOException {