@spec upgrade(Plug.Conn.t(), WebSock.impl(), WebSock.state(), [connection_opt()]) ::
  Plug.Conn.t()

Upgrades the provided Plug.Conn connection request to a WebSock connection using the provided WebSock compliant module as a handler.

This function returns the passed conn set to an :upgraded state. If early_validate_upgrade is set to true (as it is by default), the request is first examined to determine if it represents a valid WebSocket upgrade. If errors are discovered in the request, a WebSockAdapter.UpgradeError is raised containing information about the failure

The provided state value will be used as the argument for WebSock.init/1 once the WebSocket connection has been successfully negotiated.

The opts keyword list argument allows a number of options to be set on the WebSocket connection. Not all options may be supported by the underlying HTTP server. Possible values are as follows:

• early_validate_upgrade: A boolean indicating whether or not WebSockAdapter should attempt to validate the WebSocket upgrade request before returning from this call. The underlying webserver may still perform its own validation during the actual upgrade process, but since this occurs after the Plug.call/2 lifecycle it can be difficult to meaningfully handle failed upgrades. Having WebSockAdapter do its own checks as part of this call helps to alleviate this. Defaults to true
• timeout: The number of milliseconds to wait after no client data is received before closing the connection. Defaults to 60_000
• compress: Whether or not to accept negotiation of a compression extension with the client. Defaults to false
• max_frame_size: The maximum frame size to accept, in octets. If a frame size larger than this is received the connection will be closed. Defaults to :infinity
• fullsweep_after: The maximum number of garbage collections before forcing a fullsweep of the WebSocket connection process. Setting this option requires OTP 24 or newer
• max_heap_size: The maximum size of the websocket process heap in words, or a configuration map. See :erlang.max_heap_size() for more info
• validate_utf8: Whether the server should verify that the payload of text and close frames is valid UTF-8. This is required by the protocol specification but in some cases it may be more interesting to disable it in order to save resources. Note that binary frames do not have this UTF-8 requirement and are what should be used under normal circumstances if necessary
• active_n: (Cowboy only) The number of packets Cowboy will request from the socket at once. This can be used to tweak the performance of the server. Higher values reduce the number of times Cowboy need to request more packets from the port driver at the expense of potentially higher memory being used. This option does not apply to Websocket over HTTP/2
• deflate_options: A keyword list of options to pass to the deflate library. See Bandit or :cow_ws documentation for more details