Elixir port using named pipe with releasing script

from_pipe.ex

defmodule FromPipe do
  #
  # Use a helper script "from_pipe_release" to
  # release/request each line read from the
  # named pipe - effectively implementing a
  # crude backpressure mechanism
  #
  @pipe_name "/tmp/testpipe"
  @from_pipe_release "./from_pipe_release"
  @from_pipe_clean "./from_pipe_clean"

  # * terminate potential zombie OS process
  # * trash potential left over named pipe
  #
  def clean() do
    script_path = Path.expand(@from_pipe_release)
    path = Path.expand(@from_pipe_clean)
    System.cmd(path, [script_path, @pipe_name])
  end

  # Signal releasing OS process to clean up and terminate
  #
  def sig_int(os_pid) do
    System.cmd("kill", ["-INT", Integer.to_string(os_pid)])
    :ok
  end

  # Start the releasing OS process script.
  # Monitor in case process terminates
  #
  def start do
    path = Path.expand(@from_pipe_release)
    args = [@pipe_name]
    port = Port.open({:spawn_executable, path}, [:binary, args: args])
    ref = Port.monitor(port)
    {port, ref}
  end

  # Demonitor and Close and close port
  # Signal OS process to terminate
  #
  def stop({port, ref}) do
    Port.demonitor(ref, [:flush])
    info = Port.info(port, :os_pid)
    Port.close(port)

    # interrupt script reading from named pipe
    case info do
      {:os_pid, os_pid} ->
        sig_int(os_pid)

      _ ->
        :ok
    end
  end

  # Data Processing Loop
  #
  def loop({port, ref} = args) do
    # i.e. ready for next line
    Port.command(port, "ready\n")

    receive do
      {^port, {:data, "quit\n"}} ->
        stop(args)

      {^port, {:data, data}} ->
        IO.puts("port data: #{data}")
        loop(args)

      {:DOWN, ^ref, :port, ^port, _reason} ->
        # script was terminated
        :ok

      msg ->
        IO.puts("other: #{inspect(msg)}")
        loop(args)
    end
  end

  # Start "listening""
  #
  def run() do
    clean()
    loop(start())
  end
end

from_pipe_clean

#!/bin/bash
# file: from_pipe_clean script_path pipe_name

# kill script if running
pkill -KILL -f "$1 $2"

# remove pipe if present
if [[ -p $2 ]]; then
  rm -f $2
fi

from_pipe_release

#!/bin/bash
# file: from_pipe_release pipe_name
# cascade traps to prevent double cleanup
pipe=$1
trap cleanup EXIT
trap 'exit 127' HUP INT QUIT ABRT

cleanup() {
  rm -f $pipe
  exit 0
}

if [[ ! -p $pipe ]]; then
  mkfifo $pipe
fi

set -e
while read ready; do
  if read line <$pipe; then
    echo $line 2> /dev/null
  fi
done 2> /dev/null

session.md

1$ iex
Erlang/OTP 21 [erts-10.1.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]

Interactive Elixir (1.7.4) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> c("from_pipe.ex")                
[FromPipe]
iex(2)> FromPipe.run()
port data: hello

port data: world

port data: 1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ

:ok
iex(3)> 

2$ echo hello >/tmp/testpipe
2$ echo world >/tmp/testpipe
2$ echo 1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ >/tmp/testpipe
2$ echo quit >/tmp/testpipe
2$