Mismatched constant names for the HTTP session id in a websocket context

Both SessionRepositoryMessageInterceptor from SpringSession and HttpSessionHandshakeInterceptor define constants for the HTTP session id.

Spring session defines the constant as SPRING.SESSION.ID and spring-websockets defines it as HTTP.SESSION.ID.

The constants are different and this leads to an null pointer exception when HttpSessionHandshakeInterceptor is enabled. The stacktrace is below.

[ERROR] 2016-06-27 11:52:59.679 [http-nio-8080-exec-8] WebSocketConnectHandlerDecoratorFactory:87 - Error publishing org.springframework.session.web.socket.events.SessionConnectEvent[source=SessionWebSocketHandler [delegate=SubProtocolWebSocketHandler[StompSubProtocolHandler[v10.stomp, v11.stomp, v12.stomp]]]].
java.lang.NullPointerException
    at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936) ~[?:1.8.0_91]
    at org.springframework.session.web.socket.handler.WebSocketRegistryListener.registerWsSession(WebSocketRegistryListener.java:118) ~[spring-session-1.2.0.RELEASE.jar:?]
    at org.springframework.session.web.socket.handler.WebSocketRegistryListener.afterConnectionEstablished(WebSocketRegistryListener.java:86) ~[spring-session-1.2.0.RELEASE.jar:?]
    at org.springframework.session.web.socket.handler.WebSocketRegistryListener.onApplicationEvent(WebSocketRegistryListener.java:67) ~[spring-session-1.2.0.RELEASE.jar:?]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:166) ~[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:138) ~[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:382) ~[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:336) ~[spring-context-4.3.0.RELEASE.jar:4.3.0.RELEASE]

The session id is present in the attributes map under the key HTTP.SESSION.ID. Spring session version 1.2.0.RELEASE. Spring websocket version is 4.3.0.RELEASE.

Start by comparing the session-id constants in SessionRepositoryMessageInterceptor and HttpSessionHandshakeInterceptor, then trace how WebSocketRegistryListener reads the attributes map. Add a regression test for the handshake configuration using the HTTP.SESSION.ID attribute, and run the relevant Spring Session WebSocket tests; done means the shared session id is resolved without a null pointer exception.