1 files changed, 133 insertions, 0 deletions
diff --git a/lib/pleroma/gun/connection_pool/worker.ex b/lib/pleroma/gun/connection_pool/worker.ex
new file mode 100644
index 000000000..fec9d0efa
--- /dev/null
+++ b/lib/pleroma/gun/connection_pool/worker.ex
@@ -0,0 +1,133 @@
+defmodule Pleroma.Gun.ConnectionPool.Worker do
+  alias Pleroma.Gun
+  use GenServer, restart: :temporary
+
+  @registry Pleroma.Gun.ConnectionPool
+
+  def start_link([key | _] = opts) do
+    GenServer.start_link(__MODULE__, opts, name: {:via, Registry, {@registry, key}})
+  end
+
+  @impl true
+  def init([_key, _uri, _opts, _client_pid] = opts) do
+    {:ok, nil, {:continue, {:connect, opts}}}
+  end
+
+  @impl true
+  def handle_continue({:connect, [key, uri, opts, client_pid]}, _) do
+    with {:ok, conn_pid} <- Gun.Conn.open(uri, opts),
+         Process.link(conn_pid) do
+      time = :erlang.monotonic_time(:millisecond)
+
+      {_, _} =
+        Registry.update_value(@registry, key, fn _ ->
+          {conn_pid, [client_pid], 1, time}
+        end)
+
+      send(client_pid, {:conn_pid, conn_pid})
+
+      {:noreply,
+       %{key: key, timer: nil, client_monitors: %{client_pid => Process.monitor(client_pid)}},
+       :hibernate}
+    else
+      err ->
+        {:stop, {:shutdown, err}, nil}
+    end
+  end
+
+  @impl true
+  def handle_cast({:add_client, client_pid}, state) do
+    case handle_call(:add_client, {client_pid, nil}, state) do
+      {:reply, conn_pid, state, :hibernate} ->
+        send(client_pid, {:conn_pid, conn_pid})
+        {:noreply, state, :hibernate}
+    end
+  end
+
+  @impl true
+  def handle_cast({:remove_client, client_pid}, state) do
+    case handle_call(:remove_client, {client_pid, nil}, state) do
+      {:reply, _, state, :hibernate} ->
+        {:noreply, state, :hibernate}
+    end
+  end
+
+  @impl true
+  def handle_call(:add_client, {client_pid, _}, %{key: key} = state) do
+    time = :erlang.monotonic_time(:millisecond)
+
+    {{conn_pid, _, _, _}, _} =
+      Registry.update_value(@registry, key, fn {conn_pid, used_by, crf, last_reference} ->
+        {conn_pid, [client_pid | used_by], crf(time - last_reference, crf), time}
+      end)
+
+    state =
+      if state.timer != nil do
+        Process.cancel_timer(state[:timer])
+        %{state | timer: nil}
+      else
+        state
+      end
+
+    ref = Process.monitor(client_pid)
+
+    state = put_in(state.client_monitors[client_pid], ref)
+    {:reply, conn_pid, state, :hibernate}
+  end
+
+  @impl true
+  def handle_call(:remove_client, {client_pid, _}, %{key: key} = state) do
+    {{_conn_pid, used_by, _crf, _last_reference}, _} =
+      Registry.update_value(@registry, key, fn {conn_pid, used_by, crf, last_reference} ->
+        {conn_pid, List.delete(used_by, client_pid), crf, last_reference}
+      end)
+
+    {ref, state} = pop_in(state.client_monitors[client_pid])
+    Process.demonitor(ref)
+
+    timer =
+      if used_by == [] do
+        max_idle = Pleroma.Config.get([:connections_pool, :max_idle_time], 30_000)
+        Process.send_after(self(), :idle_close, max_idle)
+      else
+        nil
+      end
+
+    {:reply, :ok, %{state | timer: timer}, :hibernate}
+  end
+
+  @impl true
+  def handle_info(:idle_close, state) do
+    # Gun monitors the owner process, and will close the connection automatically
+    # when it's terminated
+    {:stop, :normal, state}
+  end
+
+  # Gracefully shutdown if the connection got closed without any streams left
+  @impl true
+  def handle_info({:gun_down, _pid, _protocol, _reason, []}, state) do
+    {:stop, :normal, state}
+  end
+
+  # Otherwise, shutdown with an error
+  @impl true
+  def handle_info({:gun_down, _pid, _protocol, _reason, _killed_streams} = down_message, state) do
+    {:stop, {:error, down_message}, state}
+  end
+
+  @impl true
+  def handle_info({:DOWN, _ref, :process, pid, reason}, state) do
+    :telemetry.execute(
+      [:pleroma, :connection_pool, :client_death],
+      %{client_pid: pid, reason: reason},
+      %{key: state.key}
+    )
+
+    handle_cast({:remove_client, pid}, state)
+  end
+
+  # LRFU policy: https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.55.1478
+  defp crf(time_delta, prev_crf) do
+    1 + :math.pow(0.5, 0.0001 * time_delta) * prev_crf
+  end
+end