Replace custom fifo implementation with Exile

This is for streaming media to ffmpeg thumbnailer. The existing implementation relies on undocumented behavior.

Erlang open_port/2 does not officially support passing a string of a file path for opening. The specs clearly state you are to provide one of the following for open_port/2:

    {spawn, Command :: string() | binary()} |
    {spawn_driver, Command :: string() | binary()} |
    {spawn_executable, FileName :: file:name_all()} |
    {fd, In :: integer() >= 0, Out :: integer() >= 0}

Our method technically works but is strongly discouraged as it can block the scheduler and dialyzer throws errors as it recognizes we're breaking the contract and some of the functions we wrote may never return.

This is indirectly covered by the Erlang FAQ section "9.12 Why can't I open devices (e.g. a serial port) like normal files?"
https://www.erlang.org/faq/problems#idm1127
This commit is contained in:
Mark Felder 2024-01-22 10:01:29 -05:00
parent 548434f85c
commit 0ac010ba3f
4 changed files with 21 additions and 80 deletions

0
changelog.d/exile.skip Normal file
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@ -43,89 +43,28 @@ def image_resize(url, options) do
def video_framegrab(url) do
with executable when is_binary(executable) <- System.find_executable("ffmpeg"),
{:ok, env} <- HTTP.get(url, [], pool: :media),
{:ok, fifo_path} <- mkfifo(),
args = [
"-y",
"-i",
fifo_path,
"-vframes",
"1",
"-f",
"mjpeg",
"-loglevel",
"error",
"-"
] do
run_fifo(fifo_path, env, executable, args)
{:ok, pid} <- StringIO.open(env.body) do
body_stream = IO.binstream(pid, 1)
Exile.stream!(
[
executable,
"-i",
"pipe:0",
"-vframes",
"1",
"-f",
"mjpeg",
"pipe:1"
],
input: body_stream,
ignore_epipe: true,
stderr: :disable
)
|> Enum.into(<<>>)
else
nil -> {:error, {:ffmpeg, :command_not_found}}
{:error, _} = error -> error
end
end
defp run_fifo(fifo_path, env, executable, args) do
pid =
Port.open({:spawn_executable, executable}, [
:use_stdio,
:stream,
:exit_status,
:binary,
args: args
])
fifo = Port.open(to_charlist(fifo_path), [:eof, :binary, :stream, :out])
fix = Pleroma.Helpers.QtFastStart.fix(env.body)
true = Port.command(fifo, fix)
:erlang.port_close(fifo)
loop_recv(pid)
after
File.rm(fifo_path)
end
defp mkfifo do
path = Path.join(System.tmp_dir!(), "pleroma-media-preview-pipe-#{Ecto.UUID.generate()}")
case System.cmd("mkfifo", [path]) do
{_, 0} ->
spawn(fifo_guard(path))
{:ok, path}
{_, err} ->
{:error, {:fifo_failed, err}}
end
end
defp fifo_guard(path) do
pid = self()
fn ->
ref = Process.monitor(pid)
receive do
{:DOWN, ^ref, :process, ^pid, _} ->
File.rm(path)
end
end
end
defp loop_recv(pid) do
loop_recv(pid, <<>>)
end
defp loop_recv(pid, acc) do
receive do
{^pid, {:data, data}} ->
loop_recv(pid, acc <> data)
{^pid, {:exit_status, 0}} ->
{:ok, acc}
{^pid, {:exit_status, status}} ->
{:error, status}
after
5000 ->
:erlang.port_close(pid)
{:error, :timeout}
end
end
end

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@ -184,6 +184,7 @@ defp deps do
{:vix, "~> 0.26.0"},
{:elixir_make, "~> 0.7.7", override: true},
{:blurhash, "~> 0.1.0", hex: :rinpatch_blurhash},
{:exile, "~> 0.8.0"},
## dev & test
{:ex_doc, "~> 0.22", only: :dev, runtime: false},

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@ -46,6 +46,7 @@
"ex_doc": {:hex, :ex_doc, "0.29.4", "6257ecbb20c7396b1fe5accd55b7b0d23f44b6aa18017b415cb4c2b91d997729", [:mix], [{:earmark_parser, "~> 1.4.31", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1", [hex: :makeup_erlang, repo: "hexpm", optional: false]}], "hexpm", "2c6699a737ae46cb61e4ed012af931b57b699643b24dabe2400a8168414bc4f5"},
"ex_machina": {:hex, :ex_machina, "2.7.0", "b792cc3127fd0680fecdb6299235b4727a4944a09ff0fa904cc639272cd92dc7", [:mix], [{:ecto, "~> 2.2 or ~> 3.0", [hex: :ecto, repo: "hexpm", optional: true]}, {:ecto_sql, "~> 3.0", [hex: :ecto_sql, repo: "hexpm", optional: true]}], "hexpm", "419aa7a39bde11894c87a615c4ecaa52d8f107bbdd81d810465186f783245bf8"},
"ex_syslogger": {:hex, :ex_syslogger, "1.5.2", "72b6aa2d47a236e999171f2e1ec18698740f40af0bd02c8c650bf5f1fd1bac79", [:mix], [{:poison, ">= 1.5.0", [hex: :poison, repo: "hexpm", optional: true]}, {:syslog, "~> 1.1.0", [hex: :syslog, repo: "hexpm", optional: false]}], "hexpm", "ab9fab4136dbc62651ec6f16fa4842f10cf02ab4433fa3d0976c01be99398399"},
"exile": {:hex, :exile, "0.8.0", "7287f76add343c5dcf5e5b46066ebb93b02b7e643cce7a1a1c5eab3e7d9eb5d8", [:make, :mix], [{:elixir_make, "~> 0.6", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm", "63309c36590f3a524f513255601404e6672be4c8bea0cc4420fbae02e7ffffac"},
"expo": {:hex, :expo, "0.4.1", "1c61d18a5df197dfda38861673d392e642649a9cef7694d2f97a587b2cfb319b", [:mix], [], "hexpm", "2ff7ba7a798c8c543c12550fa0e2cbc81b95d4974c65855d8d15ba7b37a1ce47"},
"fast_html": {:hex, :fast_html, "2.0.5", "c61760340606c1077ff1f196f17834056cb1dd3d5cb92a9f2cabf28bc6221c3c", [:make, :mix], [{:elixir_make, "~> 0.4", [hex: :elixir_make, repo: "hexpm", optional: false]}, {:nimble_pool, "~> 0.2.0", [hex: :nimble_pool, repo: "hexpm", optional: false]}], "hexpm", "605f4f4829443c14127694ebabb681778712ceecb4470ec32aa31012330e6506"},
"fast_sanitize": {:hex, :fast_sanitize, "0.2.3", "67b93dfb34e302bef49fec3aaab74951e0f0602fd9fa99085987af05bd91c7a5", [:mix], [{:fast_html, "~> 2.0", [hex: :fast_html, repo: "hexpm", optional: false]}, {:plug, "~> 1.8", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm", "e8ad286d10d0386e15d67d0ee125245ebcfbc7d7290b08712ba9013c8c5e56e2"},