[Housekeeping] Close system port when jobs are cancelled (#182)

* Created a test setup that works

* Refactored test setup into real-world fixes

dev.Dockerfile

@@ -8,7 +8,7 @@ FROM ${DEV_IMAGE}
 # Install debian packages
 RUN apt-get update -qq
 RUN apt-get install -y inotify-tools ffmpeg curl git openssh-client \
-  python3 python3-pip python3-setuptools python3-wheel python3-dev locales
+  python3 python3-pip python3-setuptools python3-wheel python3-dev locales procps
 
 # Install nodejs
 RUN curl -sL https://deb.nodesource.com/setup_20.x -o nodesource_setup.sh

lib/pinchflat/notifications/command_runner.ex

@@ -45,7 +45,7 @@ defmodule Pinchflat.Notifications.CommandRunner do
   """
   @impl AppriseCommandRunner
   def version do
-    case System.cmd(backend_executable(), ["--version"]) do
+    case CliUtils.wrap_cmd(backend_executable(), ["--version"]) do
       {output, 0} ->
         output
         |> String.split(~r{\r?\n})

lib/pinchflat/utils/cli_utils.ex

@@ -5,6 +5,23 @@ defmodule Pinchflat.Utils.CliUtils do
 
   alias Pinchflat.Utils.StringUtils
 
+  @doc """
+  Wraps a command in a shell script that will terminate
+  the command if stdin is closed. Useful for stopping
+  commands if the job runner is cancelled.
+
+  Delegates to `System.cmd/3` and any options/output
+  are passed through.
+
+  Returns {binary(), integer()}
+  """
+  def wrap_cmd(command, args, opts \\ []) do
+    wrapper_command = Path.join(:code.priv_dir(:pinchflat), "cmd_wrapper.sh")
+    actual_command = [command] ++ args
+
+    System.cmd(wrapper_command, actual_command, opts)
+  end
+
   @doc """
   Parses a list of command options into a list of strings suitable for passing to
   `System.cmd/3`.

lib/pinchflat/yt_dlp/command_runner.ex

@@ -37,7 +37,7 @@ defmodule Pinchflat.YtDlp.CommandRunner do
     formatted_command_opts = [url] ++ CliUtils.parse_options(all_opts)
     Logger.info("[yt-dlp] called with: #{Enum.join(formatted_command_opts, " ")}")
 
-    case System.cmd(command, formatted_command_opts, stderr_to_stdout: true) do
+    case CliUtils.wrap_cmd(command, formatted_command_opts, stderr_to_stdout: true) do
       {_, 0} ->
         # IDEA: consider deleting the file after reading it. It's in the tmp dir, so it's not
         # a huge deal, but it's still a good idea to clean up after ourselves.

priv/cmd_wrapper.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# This script is a wrapper for other programs
+# that ensures they are killed when stdin closes
+# (eg: a job terminates)
+
+# Start the program in the background
+exec "$@" &
+pid1=$!
+
+# Silence warnings from here on
+exec >/dev/null 2>&1
+
+# Read from stdin in the background and
+# kill running program when stdin closes
+exec 0<&0 $(
+  while read; do :; done
+  kill -KILL $pid1
+) &
+pid2=$!
+
+# Clean up
+wait $pid1
+ret=$?
+kill -KILL $pid2
+exit $ret

test/pinchflat/utils/cli_utils_test.exs

@@ -3,6 +3,12 @@ defmodule Pinchflat.Utils.CliUtilsTest do
 
   alias Pinchflat.Utils.CliUtils
 
+  describe "wrap_cmd/3" do
+    test "delegates to System.cmd/3" do
+      assert {"output\n", 0} = CliUtils.wrap_cmd("echo", ["output"])
+    end
+  end
+
   describe "parse_options/1" do
     test "it converts symbol k-v arg keys to kebab case" do
       assert ["--buffer-size", "1024"] = CliUtils.parse_options(buffer_size: 1024)