Support Decoder lists on javax.websocket endpoints

[joakime]

Currently, the implementation of javax.websocket on Jetty does not support Decoder lists properly.
This was identified during the analysis of the Decoder.Text.willDecode() and Decoder.Binary.willDecode() reported issues.

Some apparent rules:

• If an endpoint has multiple Decoders, the decoders are supposed to be filtered by TEXT vs BINARY and then each decoder is used in the order supplied by the application.
• If the Decoder is a Decoder.Text or Decoder.Binary then the willDecode must be called. (what the previous issue addressed)
• If the Decoder is a Decoder.TextStream or Decoder.BinaryStream then that decoder is used for the appropriate raw data frame. (there is no willDecode for streaming decoders)
• If all of the application supplied decoders are skipped (presumably due to all false responses from willDecode) then the built-in decoders from jetty are used.
• If the decoded object has no matching @OnMessage method, then that object is discarded, and the application @OnError is called saying so.
• If the raw TEXT or BINARY has no decoder match, then @OnError is called indicating as such. (this isn't possible, but its a behavior that is called out in the discussion of decoders on the javax.websocket api issue tracker)

[joakime]

The rules in @OnMessage still only allow for an endpoint to have 1 each of (TEXT / BINARY / PONG).
Where TEXT and BINARY has options of (whole, partial, object/decoded).

The discovery of the methods hasn't changed, but the association of method to decoder has with this issue.

With this issue, it is possible to have a decoder list pointing to an object based onMessage method.
Only @OnMessage delivery to partial messages are immune from this issue, as they don't have decoders.

[stale]

This issue has been automatically marked as stale because it has been a full year without activity. It will be closed if no further activity occurs. Thank you for your contributions.

[joakime]

@lachlan-roberts we should look into this for Jetty 10