Add compatibility with websockets 11.0.

[aaugustin]

I failed at naming things in the Sans-I/O layer of websockets. I ended up with Connection and Protocol swapped vs. what one would expect: Protocol was managing the network and Connection didn't know about the network.

I am about to rename in python-websockets/websockets#1269. Since Sanic was an early adopter — actually, the first mainstream library to adopt it — it will need an update. I'm sorry.

This PR provides compatibility both with websockets 10.0 (without deprecation warnings) and with the upcoming release websockets 11.0.

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sanic currently imports private APIs for which websockets won't provide backwards-compatibility. Specifically, it imports OPEN, CLOSING, CLOSED directly rather than the State enum. To avoid breaking Sanic users, I am planning to keep websockets 11.0 on hold until you release Sanic 22.12, with this PR included.

This is why I have to support both versions of websockets: I cannot simply release websockets 11.0 then update Sanic (bumping the dependency to websockets >= 11.0 to avoid deprecation warnings).

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In detail:

• The first commit switches to the correct import paths for websockets 11.0, with fallback to import paths for websockets 10.x.
• The second commit renames a variable for consistency with the new name in websockets. It is optional; I can remove it if you don't want it.
• The third commit ensures that Sanic only uses public APIs of websockets, for which backwards-compatibility is guaranteed a minimum of 5 years.

[aaugustin]

Actually, I have to use the websockets 10.x imports and fallback to the websockets 11.0 imports, or else mypy gets confused.

It will get confused again when I release websockets 11.0. Fortunately, at that point, we can remove the fallback and bump the dependency to websockets >= 11.0.

[aaugustin]

CI failures look unrelated to my changes. Other PR suffer from the same failures. I am planning to wait until this is cleared and then rebase this PR.

[ashleysommer]

@aaugustin Thank you very much for your work to adapt this, and for your continued work on the Websockets library. These changes look good to me.

[ahopkins]

I really have no clue what happened to those TLS tests. They run fine locally. Some package somewhere must have changed. Regardless, I have disabled them for now so we can get the ball rolling again.

@aaugustin as always, your continued support and efforts with websockets and assistance with sanic is greatly appreciated.

[ahopkins]

Before we merge this, I want to make one tweak to add a property for connection that will handle any backwards compat. Will push to your branch.

[codecov]

Codecov Report

Base: 88.047% // Head: 87.882% // Decreases project coverage by -0.165% ⚠️

Coverage data is based on head (adaa580) compared to base (beae35f).
Patch coverage: 47.058% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2609       +/-   ##
=============================================
- Coverage   88.047%   87.882%   -0.166%     
=============================================
  Files           71        71               
  Lines         5338      5356       +18     
  Branches       893       893               
=============================================
+ Hits          4700      4707        +7     
- Misses         461       471       +10     
- Partials       177       178        +1     

Impacted Files	Coverage Δ
sanic/server/websockets/impl.py	37.788% <42.857%> (-0.274%)	⬇️
sanic/server/protocols/websocket_protocol.py	71.428% <66.666%> (-1.588%)	⬇️

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