HTTP: Implement max request limits

lib/pleroma/application.ex

@@ -244,7 +244,8 @@ defmodule Pleroma.Application do
   end
 
   defp http_children(Tesla.Adapter.Gun, _) do
-    Pleroma.Gun.ConnectionPool.children()
+    Pleroma.Gun.ConnectionPool.children() ++
+      [{Task, &Pleroma.HTTP.AdapterHelper.Gun.limiter_setup/0}]
   end
 
   defp http_children(_, _), do: []

lib/pleroma/http/adapter_helper/gun.ex

@@ -49,4 +49,25 @@ defmodule Pleroma.HTTP.AdapterHelper.Gun do
       err -> err
     end
   end
+
+  @prefix Pleroma.Gun.ConnectionPool
+  def limiter_setup do
+    wait = Pleroma.Config.get([:connections_pool, :connection_acquisition_wait])
+    retries = Pleroma.Config.get([:connections_pool, :connection_acquisition_retries])
+
+    :pools
+    |> Pleroma.Config.get([])
+    |> Enum.each(fn {name, opts} ->
+      max_running = Keyword.get(opts, :size, 50)
+      max_waiting = Keyword.get(opts, :max_waiting, 10)
+
+      :ok =
+        ConcurrentLimiter.new(:"#{@prefix}.#{name}", max_running, max_waiting,
+          wait: wait,
+          max_retries: retries
+        )
+    end)
+
+    :ok
+  end
 end

lib/pleroma/http/http.ex

@@ -71,7 +71,13 @@ defmodule Pleroma.HTTP do
         adapter = Application.get_env(:tesla, :adapter)
         client = Tesla.client([Pleroma.HTTP.Middleware.FollowRedirects], adapter)
 
-        request(client, request)
+        maybe_limit(
+          fn ->
+            request(client, request)
+          end,
+          adapter,
+          adapter_opts
+        )
 
       # Connection release is handled in a custom FollowRedirects middleware
       err ->
@@ -92,4 +98,13 @@ defmodule Pleroma.HTTP do
     |> Builder.add_param(:query, :query, params)
     |> Builder.convert_to_keyword()
   end
+
+  @prefix Pleroma.Gun.ConnectionPool
+  defp maybe_limit(fun, Tesla.Adapter.Gun, opts) do
+    ConcurrentLimiter.limit(:"#{@prefix}.#{opts[:pool] || :default}", fun)
+  end
+
+  defp maybe_limit(fun, _, _) do
+    fun.()
+  end
 end