HTTP: radically simplify pool checkin/checkout

Use a custom tesla middleware instead of adapter helper function +
custom redirect middleware.

This will also fix "Client died before releasing the connection"
messages when the request pool is overloaded. Since the checkout is
now done after passing ConcurrentLimiter.

This is technically less efficient, since the connection needs to be
checked in/out every time the middleware is left or entered respectively.
But I don't think the nanoseconds we might lose on redirects
to the same host are worth the complexity.

lib/pleroma/http/adapter_helper.ex

@@ -19,7 +19,6 @@ defmodule Pleroma.HTTP.AdapterHelper do
           | {Connection.proxy_type(), Connection.host(), pos_integer()}
 
   @callback options(keyword(), URI.t()) :: keyword()
-  @callback get_conn(URI.t(), keyword()) :: {:ok, term()} | {:error, term()}
 
   @spec format_proxy(String.t() | tuple() | nil) :: proxy() | nil
   def format_proxy(nil), do: nil
@@ -47,9 +46,6 @@ def options(%URI{} = uri, opts \\ []) do
     |> adapter_helper().options(uri)
   end
 
-  @spec get_conn(URI.t(), keyword()) :: {:ok, keyword()} | {:error, atom()}
-  def get_conn(uri, opts), do: adapter_helper().get_conn(uri, opts)
-
   defp adapter, do: Application.get_env(:tesla, :adapter)
 
   defp adapter_helper do

lib/pleroma/http/adapter_helper/gun.ex

@@ -6,7 +6,6 @@ defmodule Pleroma.HTTP.AdapterHelper.Gun do
   @behaviour Pleroma.HTTP.AdapterHelper
 
   alias Pleroma.Config
-  alias Pleroma.Gun.ConnectionPool
   alias Pleroma.HTTP.AdapterHelper
 
   require Logger
@@ -57,14 +56,6 @@ def pool_timeout(pool) do
     Config.get([:pools, pool, :timeout], default)
   end
 
-  @spec get_conn(URI.t(), keyword()) :: {:ok, keyword()} | {:error, atom()}
-  def get_conn(uri, opts) do
-    case ConnectionPool.get_conn(uri, opts) do
-      {:ok, conn_pid} -> {:ok, Keyword.merge(opts, conn: conn_pid, close_conn: false)}
-      err -> err
-    end
-  end
-
   @prefix Pleroma.Gun.ConnectionPool
   def limiter_setup do
     wait = Config.get([:connections_pool, :connection_acquisition_wait])

lib/pleroma/http/adapter_helper/hackney.ex

@@ -23,7 +23,4 @@ def options(connection_opts \\ [], %URI{} = uri) do
   end
 
   defp add_scheme_opts(opts, _), do: opts
-
-  @spec get_conn(URI.t(), keyword()) :: {:ok, keyword()}
-  def get_conn(_uri, opts), do: {:ok, opts}
 end

lib/pleroma/http/http.ex

@@ -62,8 +62,6 @@ def request(method, url, body, headers, options) when is_binary(url) do
     uri = URI.parse(url)
     adapter_opts = AdapterHelper.options(uri, options[:adapter] || [])
 
-    case AdapterHelper.get_conn(uri, adapter_opts) do
-      {:ok, adapter_opts} ->
     options = put_in(options[:adapter], adapter_opts)
     params = options[:params] || []
     request = build_request(method, headers, options, url, body, params)
@@ -79,11 +77,6 @@ def request(method, url, body, headers, options) when is_binary(url) do
       adapter,
       adapter_opts
     )
-
-      # Connection release is handled in a custom FollowRedirects middleware
-      err ->
-        err
-    end
   end
 
   @spec request(Client.t(), keyword()) :: {:ok, Env.t()} | {:error, any()}
@@ -110,7 +103,7 @@ defp maybe_limit(fun, _, _) do
   end
 
   defp adapter_middlewares(Tesla.Adapter.Gun) do
-    [Pleroma.HTTP.Middleware.FollowRedirects]
+    [Tesla.Middleware.FollowRedirects, Pleroma.Tesla.Middleware.ConnectionPool]
   end
 
   defp adapter_middlewares(_), do: []

lib/pleroma/tesla/middleware/connection_pool.ex

@@ -0,0 +1,35 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Tesla.Middleware.ConnectionPool do
+  @moduledoc """
+  Middleware to get/release connections from `Pleroma.Gun.ConnectionPool`
+  """
+
+  @behaviour Tesla.Middleware
+
+  alias Pleroma.Gun.ConnectionPool
+
+  @impl Tesla.Middleware
+  def call(%Tesla.Env{url: url, opts: opts} = env, next, _) do
+    uri = URI.parse(url)
+
+    case ConnectionPool.get_conn(uri, opts[:adapter]) do
+      {:ok, conn_pid} ->
+        adapter_opts = Keyword.merge(opts[:adapter], conn: conn_pid, close_conn: false)
+        opts = Keyword.put(opts, :adapter, adapter_opts)
+        env = %{env | opts: opts}
+        res = Tesla.run(env, next)
+
+        unless opts[:adapter][:body_as] == :chunks do
+          ConnectionPool.release_conn(conn_pid)
+        end
+
+        res
+
+      err ->
+        err
+    end
+  end
+end

lib/pleroma/tesla/middleware/follow_redirects.ex

@@ -1,110 +0,0 @@
-# Pleroma: A lightweight social networking server
-# Copyright © 2015-2020 Tymon Tobolski <https://github.com/teamon/tesla/blob/master/lib/tesla/middleware/follow_redirects.ex>
-# Copyright © 2020 Pleroma Authors <https://pleroma.social/>
-# SPDX-License-Identifier: AGPL-3.0-only
-
-defmodule Pleroma.HTTP.Middleware.FollowRedirects do
-  @moduledoc """
-  Pool-aware version of https://github.com/teamon/tesla/blob/master/lib/tesla/middleware/follow_redirects.ex
-
-  Follow 3xx redirects
-  ## Options
-  - `:max_redirects` - limit number of redirects (default: `5`)
-  """
-
-  alias Pleroma.Gun.ConnectionPool
-
-  @behaviour Tesla.Middleware
-
-  @max_redirects 5
-  @redirect_statuses [301, 302, 303, 307, 308]
-
-  @impl Tesla.Middleware
-  def call(env, next, opts \\ []) do
-    max = Keyword.get(opts, :max_redirects, @max_redirects)
-
-    redirect(env, next, max)
-  end
-
-  defp redirect(env, next, left) do
-    opts = env.opts[:adapter]
-
-    case Tesla.run(env, next) do
-      {:ok, %{status: status} = res} when status in @redirect_statuses and left > 0 ->
-        release_conn(opts)
-
-        case Tesla.get_header(res, "location") do
-          nil ->
-            {:ok, res}
-
-          location ->
-            location = parse_location(location, res)
-
-            case get_conn(location, opts) do
-              {:ok, opts} ->
-                %{env | opts: Keyword.put(env.opts, :adapter, opts)}
-                |> new_request(res.status, location)
-                |> redirect(next, left - 1)
-
-              e ->
-                e
-            end
-        end
-
-      {:ok, %{status: status}} when status in @redirect_statuses ->
-        release_conn(opts)
-        {:error, {__MODULE__, :too_many_redirects}}
-
-      {:error, _} = e ->
-        release_conn(opts)
-        e
-
-      other ->
-        unless opts[:body_as] == :chunks do
-          release_conn(opts)
-        end
-
-        other
-    end
-  end
-
-  defp get_conn(location, opts) do
-    uri = URI.parse(location)
-
-    case ConnectionPool.get_conn(uri, opts) do
-      {:ok, conn} ->
-        {:ok, Keyword.merge(opts, conn: conn)}
-
-      e ->
-        e
-    end
-  end
-
-  defp release_conn(opts) do
-    ConnectionPool.release_conn(opts[:conn])
-  end
-
-  # The 303 (See Other) redirect was added in HTTP/1.1 to indicate that the originally
-  # requested resource is not available, however a related resource (or another redirect)
-  # available via GET is available at the specified location.
-  # https://tools.ietf.org/html/rfc7231#section-6.4.4
-  defp new_request(env, 303, location), do: %{env | url: location, method: :get, query: []}
-
-  # The 307 (Temporary Redirect) status code indicates that the target
-  # resource resides temporarily under a different URI and the user agent
-  # MUST NOT change the request method (...)
-  # https://tools.ietf.org/html/rfc7231#section-6.4.7
-  defp new_request(env, 307, location), do: %{env | url: location}
-
-  defp new_request(env, _, location), do: %{env | url: location, query: []}
-
-  defp parse_location("https://" <> _rest = location, _env), do: location
-  defp parse_location("http://" <> _rest = location, _env), do: location
-
-  defp parse_location(location, env) do
-    env.url
-    |> URI.parse()
-    |> URI.merge(location)
-    |> URI.to_string()
-  end
-end