fix(jsonrpc): correct newline state machine in StreamMessageProducer

The listener sets `newLine = false` after parsing a blank line
(end-of-headers) and then **unconditionally** sets it back to `true`,
leaving the state inconsistent. This caused a lone trailing CRLF between
messages to be misinterpreted as an additional blank line, triggering a
"Missing header Content-Length" error via `fireError`.

This fix prevents spurious errors and ensures robust parsing across
message boundaries.

Author: sebthom

org.eclipse.lsp4j.jsonrpc/src/main/java/org/eclipse/lsp4j/jsonrpc/json/StreamMessageProducer.java

@@ -101,12 +101,14 @@ public void listen(MessageConsumer callback) {
 							}
 							headers = new Headers();
 							debugBuilder = null;
-						} else if (headerBuilder != null) {
-							// A single newline ends a header line
-							parseHeader(headerBuilder.toString(), headers);
-							headerBuilder = null;
+						} else {
+							if (headerBuilder != null) {
+								// A single newline ends a header line
+								parseHeader(headerBuilder.toString(), headers);
+								headerBuilder = null;
+							}
+							newLine = true;
 						}
-						newLine = true;
 					} else if (c != '\r') {
 						// Add the input to the current header line
 						if (headerBuilder == null)

org.eclipse.lsp4j.jsonrpc/src/test/java/org/eclipse/lsp4j/jsonrpc/test/json/MessageProducerTest.java

@@ -1,21 +1,25 @@
 /******************************************************************************
  * Copyright (c) 2018 TypeFox and others.
- * 
+ *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0,
  * or the Eclipse Distribution License v. 1.0 which is available at
  * http://www.eclipse.org/org/documents/edl-v10.php.
- * 
+ *
  * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
  ******************************************************************************/
 package org.eclipse.lsp4j.jsonrpc.test.json;
 
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InterruptedIOException;
 import java.net.SocketException;
 import java.nio.channels.ClosedChannelException;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
@@ -32,27 +36,27 @@
 import org.junit.Test;
 
 public class MessageProducerTest {
-	
+
 	private static final long TIMEOUT = 2000;
-	
+
 	private ExecutorService executorService;
 	private Level logLevel;
-	
+
 	@Before
 	public void setup() {
 		executorService = Executors.newCachedThreadPool();
 		Logger logger = Logger.getLogger(StreamMessageProducer.class.getName());
 		logLevel = logger.getLevel();
 		logger.setLevel(Level.SEVERE);
 	}
-	
+
 	@After
 	public void teardown() {
 		executorService.shutdown();
 		Logger logger = Logger.getLogger(StreamMessageProducer.class.getName());
 		logger.setLevel(logLevel);
 	}
-	
+
 	@Test
 	public void testStopOnInterrrupt() throws Exception {
 		executorService.submit(() -> {
@@ -68,7 +72,7 @@ public int read() throws IOException {
 			messageProducer.close();
 		}).get(TIMEOUT, TimeUnit.MILLISECONDS);
 	}
-	
+
 	@Test
 	public void testStopOnChannelClosed() throws Exception {
 		executorService.submit(() -> {
@@ -84,7 +88,7 @@ public int read() throws IOException {
 			messageProducer.close();
 		}).get(TIMEOUT, TimeUnit.MILLISECONDS);
 	}
-	
+
 	@Test
 	public void testStopOnSocketClosed() throws Throwable {
 		executorService.submit(() -> {
@@ -100,8 +104,8 @@ public int read() throws IOException {
 			messageProducer.close();
 		}).get(TIMEOUT, TimeUnit.MILLISECONDS);
 	}
-	
-	@Test(expected=JsonRpcException.class)
+
+	@Test(expected = JsonRpcException.class)
 	public void testIOException() throws Throwable {
 		try {
 			executorService.submit(() -> {
@@ -121,4 +125,41 @@ public int read() throws IOException {
 		}
 	}
 
+	@Test
+	public void testSpuriousSingleCRLFBetweenTwoMessages() throws Exception {
+		executorService.submit(() -> {
+			// Two valid framed messages with a single extra CRLF inserted between
+			// the end of content of the first and the start of the next header block.
+			String msg1 = "{\"jsonrpc\":\"2.0\",\"method\":\"ping\",\"params\":null}";
+			String msg2 = "{\"jsonrpc\":\"2.0\",\"method\":\"pong\",\"params\":null}";
+			String inputStr = header(msg1.length()) + msg1
+					+ "\r\n" // single extra newline between messages
+					+ header(msg2.length()) + msg2;
+
+			// Override fireError to surface the bug as a failure if triggered.
+			class TestProducer extends StreamMessageProducer {
+				public TestProducer(InputStream input, MessageJsonHandler jsonHandler) {
+					super(input, jsonHandler);
+				}
+
+				@Override
+				protected void fireError(Throwable error) {
+					throw new AssertionError("fireError was called: " + error, error);
+				}
+			}
+
+			var jsonHandler = new MessageJsonHandler(Collections.emptyMap());
+			var producer = new TestProducer( new ByteArrayInputStream(inputStr.getBytes()), jsonHandler);
+			var received = new ArrayList<>();
+			producer.listen(received::add);
+			producer.close();
+
+			assertEquals("Both messages should be delivered", 2, received.size());
+		}).get(TIMEOUT, TimeUnit.MILLISECONDS);
+	}
+
+	private static String header(int contentLength) {
+		return "Content-Length: " + contentLength + "\r\n\r\n";
+	}
+
 }