Support splitting STOMP messages in WebSocketStompClient

See gh-31970

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

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2024-2024 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.messaging.simp.stomp;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.util.Assert;
+
+/**
+ * An extension of {@link org.springframework.messaging.simp.stomp.StompEncoder}
+ * that splits the STOMP message to multiple incomplete STOMP frames
+ * when the encoded bytes length exceeds {@link SplittingStompEncoder#bufferSizeLimit}.
+ *
+ * @author Injae Kim
+ * @since 6.2
+ * @see StompEncoder
+ */
+public class SplittingStompEncoder {
+
+	private final StompEncoder encoder;
+
+	private final int bufferSizeLimit;
+
+	public SplittingStompEncoder(StompEncoder encoder, int bufferSizeLimit) {
+		Assert.notNull(encoder, "StompEncoder is required");
+		Assert.isTrue(bufferSizeLimit > 0, "Buffer size limit must be greater than 0");
+		this.encoder = encoder;
+		this.bufferSizeLimit = bufferSizeLimit;
+	}
+
+	/**
+	 * Encodes the given payload and headers into a list of one or more {@code byte[]}s.
+	 * @param headers the headers
+	 * @param payload the payload
+	 * @return the list of one or more encoded messages
+	 */
+	public List<byte[]> encode(Map<String, Object> headers, byte[] payload) {
+		byte[] result = this.encoder.encode(headers, payload);
+		int length = result.length;
+
+		if (length <= this.bufferSizeLimit) {
+			return List.of(result);
+		}
+
+		List<byte[]> frames = new ArrayList<>();
+		for (int i = 0; i < length; i += this.bufferSizeLimit) {
+			frames.add(Arrays.copyOfRange(result, i, Math.min(i + this.bufferSizeLimit, length)));
+		}
+		return frames;
+	}
+}

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

@@ -78,7 +78,7 @@ public class StompDecoder {
 	 * Decodes one or more STOMP frames from the given {@code ByteBuffer} into a
 	 * list of {@link Message Messages}. If the input buffer contains partial STOMP frame
 	 * content, or additional content with a partial STOMP frame, the buffer is
-	 * reset and {@code null} is returned.
+	 * reset and an empty list is returned.
 	 * @param byteBuffer the buffer to decode the STOMP frame from
 	 * @return the decoded messages, or an empty list if none
 	 * @throws StompConversionException raised in case of decoding issues