add default hostname to unix socket pools

lib/finch/pool_manager.ex

@@ -8,6 +8,8 @@ defmodule Finch.PoolManager do
     :versions
   ]
 
+  @default_conn_hostname "localhost"
+
   def start_link(config) do
     GenServer.start_link(__MODULE__, config, name: config.manager_name)
   end
@@ -78,6 +80,7 @@ defmodule Finch.PoolManager do
     config
     |> Map.get(shp, default)
     |> maybe_drop_tls_options(shp)
+    |> maybe_add_hostname(shp)
   end
 
   # Drop TLS options from :conn_opts for default pools with :http scheme,
@@ -95,6 +98,17 @@ defmodule Finch.PoolManager do
 
   defp maybe_drop_tls_options(config, _), do: config
 
+  # Hostname is required when the address is not a url (binary) so we need to specify
+  # a default value in case the configuration does not specify one.
+  defp maybe_add_hostname(config, {_scheme, {:local, _path}, _port} = _shp) when is_map(config) do
+    conn_opts =
+      config |> Map.get(:conn_opts, []) |> Keyword.put_new(:hostname, @default_conn_hostname)
+
+    Map.put(config, :conn_opts, conn_opts)
+  end
+
+  defp maybe_add_hostname(config, _), do: config
+
   defp pool_mod(:http1), do: Finch.HTTP1.Pool
   defp pool_mod(:http2), do: Finch.HTTP2.Pool
 end

test/finch_test.exs

@@ -84,8 +84,8 @@ defmodule FinchTest do
          pools: %{
            endpoint(bypass, "/some-path") => [count: 5, size: 5],
            endpoint(other_bypass, "/some-other-path") => [count: 10, size: 10],
-           {:http, unix_socket} => [count: 5, size: 5, conn_opts: [hostname: "localhost"]],
-           {:https, unix_socket} => [count: 10, size: 10, conn_opts: [hostname: "localhost"]]
+           {:http, unix_socket} => [count: 5, size: 5],
+           {:https, unix_socket} => [count: 10, size: 10]
          }}
       )
 
@@ -262,17 +262,9 @@ defmodule FinchTest do
     end
 
     test "successful get request when host is a unix socket" do
-      {:ok, socket_address} = MockSocketServer.start()
-
-      start_supervised!(
-        {Finch,
-          name: MyFinch,
-          pools: %{
-            {:http, socket_address} => [conn_opts: [hostname: "localhost"]]
-          }}
-      )
+      start_supervised!({Finch, name: MyFinch})
 
-      {:local, socket_path} = socket_address
+      {:ok, {:local, socket_path}} = MockSocketServer.start()
 
       Finch.build(:get, "http://localhost/", [], nil, unix_socket: socket_path)
       |> Finch.request(MyFinch)