class Excon::Middleware::Base

def self.valid_parameter_keys

as arguments to `Connection#request` or `Connection#new`.
Returns the list of parameters that this middleware uses that are valid 
def self.valid_parameter_keys
  []
end

def error_call(datum) 

def error_call(datum)
  # do stuff
  @stack.error_call(datum)
end

def initialize(stack) 

def initialize(stack)
  @stack = stack
end

def request_call(datum) 

def request_call(datum)
  # do stuff
  @stack.request_call(datum)
end

def response_call(datum) 

def response_call(datum)
  @stack.response_call(datum)
  # do stuff
end