A protocol end represents one endpoint of a channel connection over which some specified FIDL protocol is spoken. The server side of this connection is the server_end, while the client side is the client_end.

Protocol ends have a required constraint, specifying the FIDL protocol being spoken over the connection. For instance, client_end:Foo represents the client endpoint of a Zircon channel over which all messages exchanged will conform to methods and events defined in that FIDL protocol, while server_end:Foo represents the opposite endpoint.

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