gistfile1.ex

#Supervisor
defmodule Torrentex.TrackerSupervisor do
  use Supervisor.Behaviour

  @udp_port 9998
  @tcp_port 9999

  def start_link do
    :supervisor.start_link(__MODULE__, [])
  end

  def init(_) do
    IO.inspect "starting tracker supervisor..."
    supervise([], strategy: :one_for_one)
  end

  def start_tracker(:tcp, torrent) do    
    :supervisor.start_child(__MODULE__, worker(Torrentex.TCPTracker, [@tcp_port, torrent], []))
  end

  def start_tracker(:udp, torrent) do
    IO.inspect "starting udp tracker..."
    IO.inspect worker(Torrentex.UDPTracker, [@udp_port, torrent], [])
    :supervisor.start_child(__MODULE__, worker(Torrentex.UDPTracker, [@udp_port, torrent], []))
  end

end


#Gen_Server

defmodule Torrentex.UDPTracker do
  use GenServer.Behaviour
  alias Torrentex.Url

  @actions %{:connect   => 0,
             :announce  => 1,
             :scrape    => 2,
             :error     => 3}

  #External API
  def start_link(port, torrent) do
    :gen_server.start_link(__MODULE__, [port, torrent], [])
  end

  #GenServer Callbacks
  def init([port, torrent]) do
    {:ok, socket} = :gen_udp.open(port, [:binary, {:active, true}])
    {:ok, %{:socket => socket, :torrent => torrent}, 0}
  end


  #Utilities
  defp generate_transaction_id do
    :crypto.rand_bytes(4)
  end

  #Outgoing messages
  defp send_message({socket, torrent}, :announce) do
    [domain, port] = Url.host(torrent[:announce])
    :ok = :gen_udp.send(socket, domain, port, "data")
  end

  defp send_message({socket, torrent}, :connect) do
    [domain, port] = Url.host(torrent[:announce])
    :ok = :gen_udp.send(socket, domain, port, <<4497486125440::64,@actions[:connect]::32, generate_transaction_id::binary>>)
  end

  #initializer
  def handle_info(:timeout, %{:socket => socket, :torrent => torrent} = state) do
    send_message({socket, torrent}, :connect)
    {:noreply, state}
  end

  #Incoming messages from socket
  def handle_info({:udp, _, _ip, _port, packet}, state) do
    {:noreply, state}
  end

end

Hi.
I wasn't at irc when you sent this. I took a look, and I think your problem is in how you call start_child. Take a look at erlang docs for the function.

Essentially, you need to send supervisor pid to the function, and the child specification.

So your function should look like:

def start_tracker(supervisor_pid, :udp, torrent) do
  IO.inspect "starting udp tracker..."
  IO.inspect worker(Torrentex.UDPTracker, [@udp_port, torrent], [])
  :supervisor.start_child(supervisor_pid, worker(Torrentex.UDPTracker, [@udp_port, torrent], []))
end

You'd then do:

{:ok, pid} = Torrentex.TrackerSupervisor.start_link
Torrentex.TrackerSupervisor.start_tracker(pid, ...)

If you don't want to keep track of the supervisor pid, you can register it with a local alias, and use that alias as first argument to start_child.