Client exceptions refactoring

[fafhrd91]

New hierarchy of exceptions:

• ClientError
  • ClientResponseError - exceptions that could happen after we get response from server
    • WSServerHandshakeError - web socket server response error
    • ClientHttpProxyError - proxy response
  • ClientConnectionError - exceptions related to low-level connection problem
    • ClientOSError - subset of connection errors that are initiated by OSError exception
      • ClientConnectorError - connector related exceptions
        • ClientProxyConnectionError` - proxy connection initialization error
    • ServerConnectionError - server connection related errors
      • ServerDisconnectedError - server disconnected
      • ServerTimeoutError - server operation timeout, (read timeout, etc)
      • ServerFingerprintMismatch - server fingerprint mistmach

[fafhrd91]

@kxepal @asvetlov

[asvetlov]

I have strong temptation for dropping ClientError (for deprecation period we can make it as alias for Exception and deriving ClientConnectionError from OSError.
Sorry, I have no time for explaining my motivation right now but will try to describe my ideas tomorrow evening.

[fafhrd91]

we can kill ClientRequestError and replace it with ValueError

[fafhrd91]

ClientRequestError is removed

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