request_with_backoff.ex

defmodule ReqWithBackoff do
  # hakney :connect_timeout - timeout used when establishing a connection, in milliseconds
  # hakney :recv_timeout - timeout used when receiving from a connection, in milliseconds
  # poison :timeout - timeout to establish a connection, in milliseconds
  # :backoff_max - maximum backoff time, in milliseconds
  # :backoff_factor - a backoff factor to apply between attempts, in milliseconds
  defp fetch(uri) do
    options = [
      follow_redirect: true,
      recv_timeout: Application.get_env(:arc, :recv_timeout, 5_000),
      connect_timeout: Application.get_env(:arc, :connect_timeout, 10_000),
      timeout: Application.get_env(:arc, :timeout, 10_000),
      max_retries: Application.get_env(:arc, :max_retries, 3),
      backoff_factor: Application.get_env(:arc, :backoff_factor, 1000),
      backoff_max: Application.get_env(:arc, :backoff_max, 30_000),
    ]
    request(uri, options)
  end

  defp request(uri, options, tries \\ 0) do
    case HTTPoison.get(uri, [], options) do
      {:ok, %{status_code: 200, body: body}} -> {:ok, body}
      {:error, %{reason: :timeout}} ->
        case retry(tries, options) do
          {:ok, :retry} -> request(uri, options, tries + 1)
          {:error, :out_of_tries} -> {:error, :timeout}
        end

      _ -> {:error, :arc_httpoison_error}
    end
  end

  defp retry(tries, options) do
    cond do
      tries < options[:max_retries] ->
        backoff = round(options[:backoff_factor] * :math.pow(2, tries - 1))
        backoff = :erlang.min(backoff, options[:backoff_max])
        :timer.sleep(backoff)
        {:ok, :retry}

      true -> {:error, :out_of_tries}
    end
  end
end