Merge branch 'ffmpeg-limiter' into 'develop'

Prevent Media Helper from respawning ffmpeg for bad media

See merge request pleroma/pleroma!4086

changelog.d/ffmpeg-limiter.add

@@ -0,0 +1 @@
+Framegrabs with ffmpeg will execute with a 5 second timeout and cache the URLs of failures with a TTL of 15 minutes to prevent excessive retries.

lib/pleroma/application.ex

@@ -156,6 +156,7 @@ defp cachex_children do
       build_cachex("web_resp", limit: 2500),
       build_cachex("emoji_packs", expiration: emoji_packs_expiration(), limit: 10),
       build_cachex("failed_proxy_url", limit: 2500),
+      build_cachex("failed_media_helper_url", default_ttl: :timer.minutes(15), limit: 2_500),
       build_cachex("banned_urls", default_ttl: :timer.hours(24 * 30), limit: 5_000),
       build_cachex("chat_message_id_idempotency_key",
         expiration: chat_message_id_idempotency_key_expiration(),

lib/pleroma/helpers/media_helper.ex

@@ -12,6 +12,8 @@ defmodule Pleroma.Helpers.MediaHelper do
 
   require Logger
 
+  @cachex Pleroma.Config.get([:cachex, :provider], Cachex)
+
   def missing_dependencies do
     Enum.reduce([ffmpeg: "ffmpeg"], [], fn {sym, executable}, acc ->
       if Pleroma.Utils.command_available?(executable) do
@@ -43,11 +45,13 @@ def image_resize(url, options) do
   @spec video_framegrab(String.t()) :: {:ok, binary()} | {:error, any()}
   def video_framegrab(url) do
     with executable when is_binary(executable) <- System.find_executable("ffmpeg"),
+         false <- @cachex.exists?(:failed_media_helper_cache, url),
          {:ok, env} <- HTTP.get(url, [], pool: :media),
          {:ok, pid} <- StringIO.open(env.body) do
       body_stream = IO.binstream(pid, 1)
 
-      result =
+      task =
+        Task.async(fn ->
           Exile.stream!(
             [
               executable,
@@ -64,8 +68,17 @@ def video_framegrab(url) do
             stderr: :disable
           )
           |> Enum.into(<<>>)
+        end)
 
+      case Task.yield(task, 5_000) do
+        nil ->
+          Task.shutdown(task)
+          @cachex.put(:failed_media_helper_cache, url, nil)
+          {:error, {:ffmpeg, :timeout}}
+
+        result ->
           {:ok, result}
+      end
     else
       nil -> {:error, {:ffmpeg, :command_not_found}}
       {:error, _} = error -> error