Workaround for WFLY-3474 NullPointerException

Prior to this commit, the ServletResponseHttpHeaders.get method
would throw an NPE when used under Wildfly 8.0.0.Final and 8.1.0.Final.
This can be traced to WFLY-3474, which throws an NPE when calling
HttpServletResponse.getHeaders("foo") and that header has not
been defined prior to that.
This would cause NPE being thrown by AbstractSockJsService when
checking for CORS HTTP headers in the server HTTP response.

This commit surrounds that method call in AbstractSockJsService and
guards against this issue.

Issue: SPR-11919

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/support/AbstractSockJsService.java

@@ -367,10 +367,15 @@ public abstract class AbstractSockJsService implements SockJsService {
 		HttpHeaders requestHeaders = request.getHeaders();
 		HttpHeaders responseHeaders = response.getHeaders();
 
-		// Perhaps a CORS Filter has already added this?
-		if (!CollectionUtils.isEmpty(responseHeaders.get("Access-Control-Allow-Origin"))) {
-			logger.debug("Skip adding CORS headers, response already contains \"Access-Control-Allow-Origin\"");
-			return;
+		try {
+			// Perhaps a CORS Filter has already added this?
+			if (!CollectionUtils.isEmpty(responseHeaders.get("Access-Control-Allow-Origin"))) {
+				logger.debug("Skip adding CORS headers, response already contains \"Access-Control-Allow-Origin\"");
+				return;
+			}
+		}
+		catch (NullPointerException npe) {
+			// See SPR-11919 and https://issues.jboss.org/browse/WFLY-3474
 		}
 
 		String origin = requestHeaders.getFirst("origin");

spring-websocket/src/test/java/org/springframework/web/socket/sockjs/support/SockJsServiceTests.java

@@ -23,6 +23,7 @@ import org.junit.Test;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.server.ServerHttpRequest;
 import org.springframework.http.server.ServerHttpResponse;
+import org.springframework.http.server.ServletServerHttpResponse;
 import org.springframework.scheduling.TaskScheduler;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
 import org.springframework.web.socket.AbstractHttpRequestTests;
@@ -30,6 +31,10 @@ import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.SockJsException;
 
 import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
+
+import javax.servlet.ServletOutputStream;
+import javax.servlet.http.HttpServletResponse;
 
 /**
  * Test fixture for {@link AbstractSockJsService}.
@@ -106,6 +111,21 @@ public class SockJsServiceTests extends AbstractHttpRequestTests {
 		assertEquals("foobar:123", this.servletResponse.getHeader("Access-Control-Allow-Origin"));
 	}
 
+	// SPR-11919
+
+	@Test
+	public void handleInfoGetWildflyNPE() throws Exception {
+		HttpServletResponse mockResponse = mock(HttpServletResponse.class);
+		ServletOutputStream ous = mock(ServletOutputStream.class);
+		when(mockResponse.getHeaders("Access-Control-Allow-Origin")).thenThrow(NullPointerException.class);
+		when(mockResponse.getOutputStream()).thenReturn(ous);
+		this.response = new ServletServerHttpResponse(mockResponse);
+
+		handleRequest("GET", "/echo/info", HttpStatus.OK);
+
+		verify(mockResponse.getOutputStream(), times(1));
+	}
+
 	@Test
 	public void handleInfoOptions() throws Exception {