tcp_filter_dist

Filter messages sent over Erlang distribution.

Use the -proto_dist flag to set the module to use for distribution:

iex --erl "-proto_dist Elixir.TCPFilter" -S mix

Then start your node:

Node.start(:"server@127.0.0.1")

Create a filter module that will intercept data coming into the node:

defmodule MyApp.Filter do
  @behaviour TCPFilter.Filter

  # allow genserver calls to `:increment`
  def filter({:reg_send, _sender, _unused, MyApp.MyGenServer}, {:"$gen_call", _, :increment}),
    do: :ok
  
  # block other messages to the genserver
  def filter({:reg_send, _sender, _unused, MyApp.MyGenServer}, _msg),
    do: {:error, :unauthorized}
  
  # ignore other message types
  def filter(_control_message, _message), do: :ignore
  def filter(_control_message), do: :ignore
end

Set the filter to use with TCPFilter.set_filter/1:

TCPFilter.set_filter(MyApp.Filter)

You can also set this filter when starting the TCPFilter in your supervisor:

{TCPFilter, filter: MyApp.Filter, name: TCPFilter}

TLS

To use TLS, use TCPFilter.set_socket/1 with the TCPFilter.SSLSocket module:

TCPFilter.set_socket(TCPFilter.SSLSocket)

You can also set this socket when starting the TCPFilter in your supervisor:

{TCPFilter, filter: MyApp.Filter, socket: TCPFilter.SSLSocket, name: TCPFilter}

Set the -ssl_dist_optfile option when running your application:

iex --erl "-proto_dist Elixir.TCPFilter -ssl_dist_optfile my_tls.config" -S mix

See Erlang Distribution over TLS for more information on configuring TLS in your application.

Custom Socket Modules

Besides TCPFilter.TCPSocket and TCPFilter.SSLSocket, you can implement your own socket modules to handle all of the socket operations needed for a distribution module.

For example, you could define a module that sends messages over a WebSocket.

defmodule MyApp.WebSocket do
  @behaviour TCPFilter.Socket
  # ...
end

TCPFilter.set_socket(MyApp.WebSocket)

See TCPFilter.Socket for more information.

Installation

If available in Hex, the package can be installed by adding tcp_filter_dist to your list of dependencies in mix.exs:

def deps do
  [
    {:tcp_filter_dist, "~> 0.1.0"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/tcp_filter_dist.