PerMessageDeflateExtension *_no_context_takeover negotiation is faulty, leading to mismatch

[robert-s-ubi]

Describe the bug
The PerMessageDeflateExtension#getProvidedExtensionAsClient() method unconditionally includes client_no_context_takeover and server_no_context_takeover in the extensions to send to the server, ignoring the clientNoContextTakeover and serverNoContextTakeover configuration variables.

The acceptProvidedExtensionAsServer() on the server will thus ALWAYS set its clientNoContextTakeover variable to true, but the acceptProvidedExtensionAsClient() does NOT update its clientNoContextTakeover configuration variable upon receiving this, leading to a mismatch.

As a result, the second compressed response the client receives from the server yields an exception:

org.java_websocket.exceptions.InvalidDataException: invalid distance too far back
at org.java_websocket.extensions.permessage_deflate.PerMessageDeflateExtension.decodeFrame(PerMessageDeflateExtension.java:193)
at org.java_websocket.drafts.Draft_6455.translateSingleFrame(Draft_6455.java:589)

To Reproduce
Steps to reproduce the behavior:

1. Set up WebSocketClient and WebSocketServer with the PerMessageDelateExtension
2. Connect them
3. Send messages back and forth
4. The client side will bail out at the second message it receives from the server

Example application to reproduce the issue
https://github.com/ChargeTimeEU/Java-OCA-OCPP was recently enhanced with WebSocket compression support, but it's broken due to this bug.

Expected behavior
Behavior must be as follows:

1. getProvidedExtensionsAsClient() must add the extensions following the clientNoContextTakeover and serverNoContextTakeover configuration variables (i.e. leave them out if false).
2. acceptProvidedExtensionsAsServer() must enable the clientNoContextTakeover and/or serverNoContextTakeover if their corresponding extensions are received, effectively ORing them with the locally configured settings.
3. getProviderExtensionsAsServer() must add the extensions following the (potentially updated) clientNoContextTakeover and serverNoContextTakeover configuration variables (i.e. leave them out if false).
4. acceptProvidedExtensionsAsClient() must enable the clientNoContextTakeover and/or serverNoContextTakeover if their corresponding extensions are received, effectively ORing them with the locally configured settings.

This ensures these configuration settings are always properly synchronized on both ends, and allows operation with context takeover on both ends (both configuration variables set to false on both ends), which maximizes the compression efficiency.

[robert-s-ubi]

The logic to reset the deflater and inflater is also bugged: You cannot directly infer which to reset by the two configuration variables. Instead, it is swapped on client and server. So if one no_context_takeover is set, it must cause one side to reset the inflater, and the other to reset the deflater.

Right now both sides will reset the same of these two for one of these variables, that's why it blows up in case both are not the same. I.e. the code works for true/true and false/false, but not for true/false or false/true combinations of clientNoContextTakeover and serverNoContextTakeover.

[robert-s-ubi]

I have submitted PR #1497 to fix this. Note that the last verifier run failed, presumably because the server ran out of sockets. Unfortunately, I cannot find a button to rerun the verifier.