module HTTP::Chainable

def via(*proxy)
  proxy_hash = {}
  proxy_hash[:proxy_address]  = proxy[0] if proxy[0].is_a?(String)
  proxy_hash[:proxy_port]     = proxy[1] if proxy[1].is_a?(Integer)
  proxy_hash[:proxy_username] = proxy[2] if proxy[2].is_a?(String)
  proxy_hash[:proxy_password] = proxy[3] if proxy[3].is_a?(String)
  proxy_hash[:proxy_headers]  = proxy[2] if proxy[2].is_a?(Hash)
  proxy_hash[:proxy_headers]  = proxy[4] if proxy[4].is_a?(Hash)
  raise(RequestError, "invalid HTTP proxy: #{proxy_hash}") unless (2..5).cover?(proxy_hash.keys.size)
  branch default_options.with_proxy(proxy_hash)
end