A genserver which handles data packet transfers between the TFTP service and hungry clients. By being spawned off of Trivial.Daemon after accept, it allows transactions to be concurrent and asynchronous.

Generally, you should not be initiating from this module, except possibly for testing puroposes.

This module also serves as a behaviour module defining the API that you should use to service TFTP transactions.

Example

The following example shows how to set up a TFTP module which can transmit both templated and file data. Note that in general, you should not use stateful reading techinques in the read/5 callback since UDP has no delivery guarantees and the client may re-request a data block, meaning that your data transmission may be nonlinear.

defmodule MyTftpModule do
  @behaviour Trivial.Server

  @impl true
  # forbids transactions from the evil ip address 42.42.42.42
  def init(_, {42, 42, 42, 42}, _), do: {:error, :eacces}
  # forbids transactions to unwanted files
  def init("secret.txt", _client, _), do: {:error, :eacces}

  # set up a templated transaction
  def init("/templated", _client, data) do
    str = "template for #{inet.ntoa client}"
    size = :erlang.size(str)
    {:ok, {str, size}}
  end

  # set up file transaction
  def init(file, _client, data) do
    bin = File.read!(file)
    size = :erlang.size(bin)
    {:ok, {bin, size}}
  end

  @impl true
  def read(_request, pos, len, _client, data = {str, size}) when pos > size do
    :done
  end
  def read(_request, pos, len, _client, data = {str, size}) pos + len > size do
    {:ok, :erlang.binary_part(str, pos, size - pos), data}
  end
  def read(_request, pos, len, _client, data = {str, size}) do
    {:ok, :erlang.binary_part(str, pos, len), data}
  end

  @impl true
  def tsize(_request, _client, data = {_, size}) do
    {:ok, size, data}
  end
end