Poll Telegram API until response

kannix

I am currently stuck with an implementation of a function that has to poll the Telegram API periodically and wait for a response from this. I guess there is some async / await magic that will help me to solve this problem in an elegant way. Maybe someone can jump in an give me a hint

Other suggestions for improvement are also very welcome

defmodule TelegramHelper do
  @moduledoc """
  Documentation for TelegramHelper.
  """

  import Nadia

  @chat_id 123456

  @spec get_sms_verification_code() :: any()
  def get_sms_verification_code do
    # telegram api will return some old messages from time to time
    # so we have to check if there are old message and get the update_id to poll later only for newer messages
    update_id = 0
    {:ok, result} = get_updates
    if length(result) > 0 do
      update_id = List.last(result).update_id + 1
    end

    send_message(@chat_id, "Please send the Auth Code")
    get_reply(update_id)
  end

  defp get_reply(update_id) do
    Process.sleep(1000)
    {:ok, result} = get_updates(%{:update_id => update_id})
    if length(result) == 0 do
      # this should stop after a timeout of e.g. 5 Minutes
      # and is obviously the wrong way of doing it
      get_reply(update_id)
    end
    # this is only for reference on what i want to return if i get back a new message from telegram
    List.first(result).message.text
  end
end

9 comments

#asynchronous

0 2036 9

2018-09-03 10:52:51 UTC

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idi527

Have you considered using webhooks?

Post #1

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david_ex

I believe you should be returning a tuple from handle_info/2:

  def handle_info(:poll, state) do
    case get_updates(last_update_id) do
      [] ->
        Process.send_after(self(), :poll, 5000)
        {:noreply, state}
      new_messages ->
        state = handle_new_messages(state, new_messages)
        {:noreply, state}
    end
  end

Post #4

Last Post!

idi527

I don’t think you need a looping async functions … I’d do something like

# in Auther

def wait_for_chat(server , chat_id, timeout \\ 5000) do
  GenServer.call(server, {:wait_for_chat, chat_id}, timeout)
end

@doc false
def handle_call({:wait_for_chat, chat_id}, from, state) do
  # note that `Map.put` would override any previous "subscription" (from)
  # if this is a problem, store `from`s in a list
  # auth_codes = %{chat_id => [from1, from2, from3, ...]}
  {:noreply, %{state | auth_codes: Map.put(state.auth_codes, chat_id, from)}}
end

defp handle_new_messages(state, new_messages) do
  # go over new messages and check if there are any auth codes from
  # the chat ids in state.auth_codes, if there are, reply to 
  # the client process in the corresponding to that chat_id's `from`
  auth_codes = Enum.reduce(new_messages, state.auth_codes, fn %{"chat" => %{"id" => chat_id}, "text" => message}, auth_codes ->
    with true <- auth_code?(message),
         {from, auth_codes} when not is_nil(from) <- Map.pop(auth_codes, chat_id) do
      GenServer.reply(from, message)
      auth_codes
    else
      _ -> auth_codes
    end
  end)
  %{state | auth_codes: auth_codes}
end

Then in your browser automation program you can do

fill_email_password("mail", "password")
click_auth_button
auth_code = Auther.wait_for_chat(auther_pid, chat_id, :infinity) # or just a large number for timeout
fill_auth_code(code_from_telegram)

state.auth_codes should probably be renamed to state.awaiting_auth_codes or awaiting_chats_auth_code something like that. It was named incorrectly the first time since I misunderstood your problem again, it seems.

Post #9