Sending multipart message

[kodepett]

I've been scratching my head trying to figure out how to send multipart message. I've tried using the below, however an error is returned from the SMSC.

pdu = SMPPEX.Pdu.new(4, %{
      sm_length: 0, short_message: "", destination_addr: "xxxxxxxxx"
    }, %{message_payload => "Message with length over 300"})

returns the below

 %SMPPEX.Pdu{command_id: 2147483652, command_status: 4, mandatory: %{message_id: "0000000000"}, optional: %{}, ref: #Reference<0.1222358344.4153409537.176228>, sequence_number: 3}

I'm not well versed in the usage of TLV and attempt to gain insight from other documents have proven futile.
Kindly assist, thank you.

[savonarola]

Hello! The returned status is 4, i.e. RINVBNDSTS — "Incorrect BIND Status for given command".

I dare to guess you hadn't sent bind command after establishing session or it hadn't been successful.
There are examples of sending bind commands: examples.

[kodepett]

Hi, I'm binding to the SMSC, the above works when I remove the message_payload and send a normal 160 characters short_message. The command status 4 is only returned when I attempt to use message_payload optional parameter. Below is the binding function

 @impl true
  def handle_info({:bind, system_id, password}, state) do
    bind_pdu = PduFactory.bind_transceiver(system_id, password)
    Logger.info("#{inspect bind_pdu}")
    {:noreply, [bind_pdu], state}
  end

  @impl true
  def handle_resp(pdu, _original_pdu, state) do
    case Pdu.command_name(pdu) do
      :bind_transceiver_resp -> handle_bind_resp(pdu, state)
      :unbind_resp -> handle_unbind_resp(state, :response)
      :submit_sm_resp -> handle_submit_sm_resp(pdu, state)
      _ -> handle_any_resp(pdu, state)
    end
  end

Any pointers to how to send a payload greater than 160.

[savonarola]

This PDU should be valid, at least for SMSC's I generally deal with.
Probably, a tcpdump of a session could help.

[dowusu]

Below is a solution to the issue I encountered, in case anyone faces that same challenge, splits messages by 153 characters.

  def send_sms(pid, source, dest, message) do

    # msgs =
    #   message
    #   |> String.codepoints()
    #   |> Enum.chunk_every(153)
    #   |> List.to_string()

    msgs =
      message
      |> String.split(~r/.{153}/, include_captures: true, trim: true)


    ref = :rand.uniform(255)
    total = Enum.count(msgs)

    for {msg, index} <- Enum.with_index(msgs) do
      {:ok, msg} = SMPPEX.Pdu.Multipart.prepend_message_with_part_info({ref, total, index + 1}, msg)
      submit =
        SMPPEX.Pdu.Factory.submit_sm(source, dest, msg)
        |> SMPPEX.Pdu.set_mandatory_field(:esm_class, 0x40)

      SMPPEX.Session.send_pdu(pid, submit)
    end

  end

Thanks a lot for the wonderful library.

[savonarola]

Hello @dowusu , thank you for the feedback.

As far as I can see, one could use a special split_message function to make things a bit shorter:

  def send_sms(pid, source, dest, message) when byte_size(message) > 0 do
    ref = :rand.uniform(255)
    {:ok, :split, msgs} = SMPPEX.Pdu.Multipart.split_message(ref, message, 0, 153)

    for msg <- msgs do
      submit =
        SMPPEX.Pdu.Factory.submit_sm(source, dest, msg)
        |> SMPPEX.Pdu.set_mandatory_field(:esm_class, 0x40)

      SMPPEX.Session.send_pdu(pid, submit)
    end
  end

[dowusu]

Hi @savonarola, you're right.
I saw that function quite late, I think it makes the solution shorter.

Thank you.

[pmenhart]

I saw that function quite late, I think it makes the solution shorter.

There is another advantage of SMPPEX.Pdu.Multipart.split_message: it works with all target encodings.
The examples here assume ASCII (actually gsm0338, packing 160 chars into 140 octets), but generally we cannot rely on one codepoint to occupy one byte.

[dowusu]

I tried the function SMPPEX.Pdu.Multipart.split_message; it didn't work as expected, I had to rely on a GSM library for conversion before splitting the message. Not sure if I'm doing something wrong, can share the message for test if it becomes necessary

   ref = :rand.uniform(255)
    message = GSM.to_gsm(message)
    {:ok, :split, msgs} = SMPPEX.Pdu.Multipart.split_message(ref, message, 0, 153)
    for msg <- msgs do
      submit =
        SMPPEX.Pdu.Factory.submit_sm("Econtact", msisdn, msg)
        |> SMPPEX.Pdu.set_mandatory_field(:esm_class, 0x40)

      SMPPEX.Session.send_pdu(pid, submit)
    end

[pmenhart]

Please learn what coding schemes are supported by your SMSC, and which encoding or encodings do you want to use. See SMPP 3.4 specs section "5.2.19 data_coding".
Encoding 0 (implicitly set in your examples) is "SMSC Default Alphabet" that is not defined in the specification. That means each SMS operator is free to define it as they like (causing a mess in interoperability!) In North America, some operators expect the encoding 0 to be GSM03.38, some want Latin-1.
To set different encoding, use a tuple in SMPPEX.Pdu.Factory.submit_sm("Econtact", msisdn, {encoding, msg}).

And yes, message has to be converted from Elixir internal representation (UTF-8) to target encoding before calling split_message. Converted message is a binary, but not necessary a String. Note that the spec of the method split_message correctly indicates type message :: binary, unlike spec of submit_sm.