using JettyWebSocketServlet without having a WebSocketUpgradeFilter

[lachlan-roberts]

Jetty version
10.0.x

Description
The WebSocketUpgradeFilter is added automatically by the JettyWebSocketServletContainerInitializer but the filter is not required if websocket upgrades are being done by a JettyWebSocketServlet.

There should be some option to not automatically create this this in the JettyWebSocketServerContainer.

[joakime]

This hints at a lazy initialized WebSocketUpgradeFilter.

Some things to consider ...

• The JettyWebSocketServerContainer can be accessed by the application, and it can use .addMapping() at any time.
• The WebSocketUpgradeFilter should be the first filter in the chain, if we create it.
• The WebSocketUpgradeFilter can be added by the application (such as in the WEB-INF/web.xml), and we should use that one if present. (cometd is a good example of this usage pattern)

Perhaps we should have a more fundamental component, built into ServletContextHandler, the UpgradeHandler (fitting into the same role as ServletHandler)?