Deprecate writePrelude in AbstractHttpSockJsSession

A logical follow-up on commit 43d937, this change also removes (or
rather deprecates for now) writePrelude that is only of concern to
streaming SockJS session implementations.

Issue: SPR-12427

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/handler/EventSourceTransportHandler.java

@@ -16,12 +16,10 @@
 
 package org.springframework.web.socket.sockjs.transport.handler;
 
-import java.io.IOException;
 import java.util.Map;
 
 import org.springframework.http.MediaType;
 import org.springframework.http.server.ServerHttpRequest;
-import org.springframework.http.server.ServerHttpResponse;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.frame.DefaultSockJsFrameFormat;
 import org.springframework.web.socket.sockjs.frame.SockJsFrameFormat;
@@ -70,10 +68,8 @@ public class EventSourceTransportHandler extends AbstractHttpSendingTransportHan
 		}
 
 		@Override
-		protected void writePrelude(ServerHttpRequest request, ServerHttpResponse response) throws IOException {
-			response.getBody().write('\r');
-			response.getBody().write('\n');
-			response.flush();
+		protected byte[] getPrelude(ServerHttpRequest request) {
+			return new byte[] { '\r', '\n' };
 		}
 	}
 

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/handler/HtmlFileTransportHandler.java

@@ -134,18 +134,11 @@ public class HtmlFileTransportHandler extends AbstractHttpSendingTransportHandle
 		}
 
 		@Override
-		protected void writePrelude(ServerHttpRequest request, ServerHttpResponse response) {
+		protected byte[] getPrelude(ServerHttpRequest request) {
 			// We already validated the parameter above...
 			String callback = getCallbackParam(request);
 			String html = String.format(PARTIAL_HTML_CONTENT, callback);
-			try {
-				response.getBody().write(html.getBytes(UTF8_CHARSET));
-				response.flush();
-			}
-			catch (IOException ex) {
-				tryCloseWithSockJsTransportError(ex, CloseStatus.SERVER_ERROR);
-				throw new SockJsTransportFailureException("Failed to write HTML content", getId(), ex);
-			}
+			return html.getBytes(UTF8_CHARSET);
 		}
 	}
 

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/handler/XhrStreamingTransportHandler.java

@@ -16,12 +16,10 @@
 
 package org.springframework.web.socket.sockjs.transport.handler;
 
-import java.io.IOException;
 import java.util.Map;
 
 import org.springframework.http.MediaType;
 import org.springframework.http.server.ServerHttpRequest;
-import org.springframework.http.server.ServerHttpResponse;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.frame.DefaultSockJsFrameFormat;
 import org.springframework.web.socket.sockjs.frame.SockJsFrameFormat;
@@ -38,6 +36,16 @@ import org.springframework.web.socket.sockjs.transport.session.StreamingSockJsSe
  */
 public class XhrStreamingTransportHandler extends AbstractHttpSendingTransportHandler {
 
+	private static final byte[] PRELUDE = new byte[2049];
+
+	static {
+		for (int i = 0; i < 2048; i++) {
+			PRELUDE[i] = 'h';
+		}
+		PRELUDE[2048] = '\n';
+	}
+
+
 	@Override
 	public TransportType getTransportType() {
 		return TransportType.XHR_STREAMING;
@@ -70,12 +78,8 @@ public class XhrStreamingTransportHandler extends AbstractHttpSendingTransportHa
 		}
 
 		@Override
-		protected void writePrelude(ServerHttpRequest request, ServerHttpResponse response) throws IOException {
-			for (int i = 0; i < 2048; i++) {
-				response.getBody().write('h');
-			}
-			response.getBody().write('\n');
-			response.flush();
+		protected byte[] getPrelude(ServerHttpRequest request) {
+			return PRELUDE;
 		}
 	}
 

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/session/AbstractHttpSockJsSession.java

@@ -168,7 +168,7 @@ public abstract class AbstractHttpSockJsSession extends AbstractSockJsSession {
 	}
 
 	/**
-	 * @deprecated as of 4.2 this method is no longer used for anything
+	 * @deprecated as of 4.2 this method is no longer used.
 	 */
 	@Deprecated
 	protected abstract boolean isStreaming();
@@ -292,6 +292,11 @@ public abstract class AbstractHttpSockJsSession extends AbstractSockJsSession {
 	protected abstract void flushCache() throws SockJsTransportFailureException;
 
 
+	/**
+	 * @deprecated as of 4.2 this method is deprecated since the prelude is written
+	 * in {@link #handleRequestInternal} of the StreamingSockJsSession subclass.
+	 */
+	@Deprecated
 	protected void writePrelude(ServerHttpRequest request, ServerHttpResponse response) throws IOException {
 	}
 

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/session/PollingSockJsSession.java

@@ -44,7 +44,7 @@ public class PollingSockJsSession extends AbstractHttpSockJsSession {
 
 
 	/**
-	 * @deprecated as of 4.2 this method is no longer used for anything
+	 * @deprecated as of 4.2 this method is no longer used.
 	 */
 	@Override
 	@Deprecated

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/session/StreamingSockJsSession.java

@@ -21,6 +21,8 @@ import java.util.Map;
 
 import org.springframework.http.server.ServerHttpRequest;
 import org.springframework.http.server.ServerHttpResponse;
+import org.springframework.util.Assert;
+import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.SockJsTransportFailureException;
 import org.springframework.web.socket.sockjs.frame.SockJsFrame;
@@ -33,7 +35,7 @@ import org.springframework.web.socket.sockjs.transport.SockJsServiceConfig;
  * @author Rossen Stoyanchev
  * @since 4.0
  */
-public class StreamingSockJsSession extends AbstractHttpSockJsSession {
+public abstract class StreamingSockJsSession extends AbstractHttpSockJsSession {
 
 	private int byteCount;
 
@@ -46,7 +48,7 @@ public class StreamingSockJsSession extends AbstractHttpSockJsSession {
 
 
 	/**
-	 * @deprecated as of 4.2 this method is no longer used for anything
+	 * @deprecated as of 4.2 this method is no longer used.
 	 */
 	@Override
 	@Deprecated
@@ -54,11 +56,21 @@ public class StreamingSockJsSession extends AbstractHttpSockJsSession {
 		return true;
 	}
 
+	/**
+	 * Get the prelude to write to the response before any other data.
+	 * @since 4.2
+	 */
+	protected abstract byte[] getPrelude(ServerHttpRequest request);
+
 	@Override
 	protected void handleRequestInternal(ServerHttpRequest request, ServerHttpResponse response,
 			boolean initialRequest) throws IOException {
 
-		writePrelude(request, response);
+		byte[] prelude = getPrelude(request);
+		Assert.notNull(prelude);
+		response.getBody().write(prelude);
+		response.flush();
+
 		if (initialRequest) {
 			writeFrame(SockJsFrame.openFrame());
 		}

spring-websocket/src/test/java/org/springframework/web/socket/sockjs/transport/session/HttpSockJsSessionTests.java

@@ -118,13 +118,8 @@ public class HttpSockJsSessionTests extends AbstractSockJsSessionTests<TestAbstr
 		}
 
 		@Override
-		protected boolean isStreaming() {
-			return true;
-		}
-
-		@Override
-		protected void writePrelude(ServerHttpRequest request, ServerHttpResponse response) throws IOException {
-			response.getBody().write("hhh\n".getBytes());
+		protected byte[] getPrelude(ServerHttpRequest request) {
+			return "hhh\n".getBytes();
 		}
 
 		public boolean wasCacheFlushed() {

spring-websocket/src/test/java/org/springframework/web/socket/sockjs/transport/session/TestHttpSockJsSession.java

@@ -22,7 +22,6 @@ import java.util.List;
 import java.util.Map;
 
 import org.springframework.http.server.ServerHttpRequest;
-import org.springframework.http.server.ServerHttpResponse;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.SockJsTransportFailureException;
@@ -56,8 +55,8 @@ public class TestHttpSockJsSession extends StreamingSockJsSession {
 	}
 
 	@Override
-	protected boolean isStreaming() {
-		return true;
+	protected byte[] getPrelude(ServerHttpRequest request) {
+		return new byte[0];
 	}
 
 	@Override