Protect SseEmitter against early I/O errors

Closes gh-25442

Author: rstoyanchev

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -127,10 +127,14 @@ public Long getTimeout() {
 	synchronized void initialize(Handler handler) throws IOException {
 		this.handler = handler;
 
-		for (DataWithMediaType sendAttempt : this.earlySendAttempts) {
-			sendInternal(sendAttempt.getData(), sendAttempt.getMediaType());
+		try {
+			for (DataWithMediaType sendAttempt : this.earlySendAttempts) {
+				sendInternal(sendAttempt.getData(), sendAttempt.getMediaType());
+			}
+		}
+		finally {
+			this.earlySendAttempts.clear();
 		}
-		this.earlySendAttempts.clear();
 
 		if (this.complete) {
 			if (this.failure != null) {
@@ -147,6 +151,13 @@ synchronized void initialize(Handler handler) throws IOException {
 		}
 	}
 
+	synchronized void initializeWithError(Throwable ex) {
+		this.complete = true;
+		this.failure = ex;
+		this.earlySendAttempts.clear();
+		this.errorCallback.accept(ex);
+	}
+
 	/**
 	 * Invoked after the response is updated with the status code and headers,
 	 * if the ResponseBodyEmitter is wrapped in a ResponseEntity, but before the
@@ -182,7 +193,9 @@ public void send(Object object) throws IOException {
 	 * @throws java.lang.IllegalStateException wraps any other errors
 	 */
 	public synchronized void send(Object object, @Nullable MediaType mediaType) throws IOException {
-		Assert.state(!this.complete, "ResponseBodyEmitter is already set complete");
+		Assert.state(!this.complete,
+				"ResponseBodyEmitter has already completed" +
+						(this.failure != null ? " with error: " + this.failure : ""));
 		sendInternal(object, mediaType);
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ResponseBodyEmitterReturnValueHandler.java

@@ -176,10 +176,17 @@ public void handleReturnValue(@Nullable Object returnValue, MethodParameter retu
 		// Headers will be flushed at the first write
 		outputMessage = new StreamingServletServerHttpResponse(outputMessage);
 
-		DeferredResult<?> deferredResult = new DeferredResult<>(emitter.getTimeout());
-		WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(deferredResult, mavContainer);
+		HttpMessageConvertingHandler handler;
+		try {
+			DeferredResult<?> deferredResult = new DeferredResult<>(emitter.getTimeout());
+			WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(deferredResult, mavContainer);
+			handler = new HttpMessageConvertingHandler(outputMessage, deferredResult);
+		}
+		catch (Throwable ex) {
+			emitter.initializeWithError(ex);
+			throw ex;
+		}
 
-		HttpMessageConvertingHandler handler = new HttpMessageConvertingHandler(outputMessage, deferredResult);
 		emitter.initialize(handler);
 	}