Use mkfifo to feed ImageMagick

lib/pleroma/helpers/media_helper.ex

@@ -7,18 +7,66 @@ defmodule Pleroma.Helpers.MediaHelper do
   Handles common media-related operations.
   """
 
-  def image_resize(url, %{max_width: max_width, max_height: max_height} = options) do
+  @tmp_base "/tmp/pleroma-media_preview-pipe"
+
+  def image_resize(url, options) do
+    with executable when is_binary(executable) <- System.find_executable("convert"),
+         {:ok, args} <- prepare_resize_args(options),
+         url = Pleroma.Web.MediaProxy.url(url),
+         {:ok, env} <- Pleroma.HTTP.get(url),
+         {:ok, fifo_path} <- mkfifo()
+    do
+      run_fifo(fifo_path, env, executable, args)
+    else
+      nil -> {:error, {:convert, :command_not_found}}
+      {:error, _} = error -> error
+    end
+  end
+
+  defp prepare_resize_args(%{max_width: max_width, max_height: max_height} = options) do
     quality = options[:quality] || 85
+    resize = Enum.join([max_width, "x", max_height, ">"])
+    args = [
+    "-auto-orient", # Support for EXIF rotation
+    "-resize", resize,
+    "-quality", to_string(quality)
+    ]
+    {:ok, args}
+  end
 
-    cmd = ~s"""
-    convert fd:0 -resize '#{max_width}x#{max_height}>' -quality #{quality} jpg:-
-    """
+  defp prepare_resize_args(_), do: {:error, :missing_options}
 
-    pid = Port.open({:spawn, cmd}, [:use_stdio, :stream, :exit_status, :binary])
-    {:ok, env} = url |> Pleroma.Web.MediaProxy.url() |> Pleroma.HTTP.get()
-    image = env.body
-    Port.command(pid, image)
+  defp run_fifo(fifo_path, env, executable, args) do
+    args = List.flatten([fifo_path, args, "jpg:fd:1"])
+    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])
+    true = Port.command(fifo, env.body)
+    :erlang.port_close(fifo)
     loop_recv(pid)
+  after
+    File.rm(fifo_path)
+  end
+
+  defp mkfifo() do
+    path = "#{@tmp_base}#{to_charlist(:erlang.phash2(self()))}"
+    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
@@ -29,12 +77,14 @@ defmodule Pleroma.Helpers.MediaHelper 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