A transport failure that states the two facts the retry rules need.

The SDK classifies Req's own errors itself (a refused connection or a DNS failure was never sent; a timeout or a reset may have been). A custom Req adapter (the :adapter entry of the client's :req_options) that knows better can return this exception instead of a response, to say exactly what happened:

• sent: whether any byte of the request may have reached the server. Say true when you cannot tell.
• timeout: whether the failure was a timeout.

A failure with sent: false is always retried. One with sent: true is retried only when the call is safe to retry (see the README's Retries section).

defmodule MyAdapter do
  def run(request) do
    {request, %Unicom360.TransportError{reason: :econnrefused, sent: false, timeout: false}}
  end
end

# On Req 0.5 and 0.6, an adapter is a function: adapter: &MyAdapter.run/1
Unicom360.client(api_key: "...", req_options: [adapter: MyAdapter])