Add default config in config.exs + ability to configure Tesla middleware

lib/ex_force.ex

@@ -14,6 +14,21 @@ defmodule ExForce do
   end
   ```
 
+  Configure default settings for the Tesla client (currently the only
+  client supported) in config/config.exs (optional).
+
+  ```elixir
+  # config/config.exs
+
+  config :ex_force, ExForce.Client.Tesla,
+    api_version: "43.0",
+    adapter: {Tesla.Adapter.Hackney, [recv_timeout: 1_000]},
+    append_middleware: [
+      Tesla.Middleware.Telemetry,
+      {Tesla.Middleware.Timeout, timeout: :timer.seconds(1)}
+    ]
+  ```
+
   Check out [Choosing a Tesla Adapter](https://github.com/chulkilee/ex_force/wiki/Choosing-a-Tesla-Adapter).
 
   ## Usage

lib/ex_force/client/tesla/tesla.ex

@@ -41,19 +41,23 @@ defmodule ExForce.Client.Tesla do
   end
 
   def build_client(instance_url, opts) when is_binary(instance_url) do
-    Tesla.client(
+    adapter = get_from_opts_or_config(opts, :adapter)
+    headers = get_headers(opts)
+
+    middleware =
       [
         {ExForce.Client.Tesla.Middleware,
-         {instance_url, Keyword.get(opts, :api_version, @default_api_version)}},
+         {instance_url, get_from_opts_or_config(opts, :api_version, @default_api_version)}},
         {Tesla.Middleware.Compression, format: "gzip"},
         {Tesla.Middleware.JSON, engine: Jason},
-        {Tesla.Middleware.Headers, get_headers(opts)}
-      ],
-      Keyword.get(opts, :adapter)
-    )
+        {Tesla.Middleware.Headers, headers}
+      ] ++ get_from_opts_or_config(opts, :append_middleware, [])
+
+    Tesla.client(middleware, adapter)
   end
 
-  defp get_headers(opts), do: Keyword.get(opts, :headers, [{"user-agent", @default_user_agent}])
+  defp get_headers(opts),
+    do: get_from_opts_or_config(opts, :headers, [{"user-agent", @default_user_agent}])
 
   @doc """
   Returns a `Tesla` client for `ExForce.OAuth` functions
@@ -65,16 +69,18 @@ defmodule ExForce.Client.Tesla do
   """
   @impl ExForce.Client
   def build_oauth_client(instance_url, opts \\ []) do
-    Tesla.client(
+    adapter = get_from_opts_or_config(opts, :adapter)
+
+    middleware =
       [
+        {Tesla.Middleware.DecodeJson, engine: Jason},
         {Tesla.Middleware.BaseUrl, instance_url},
         {Tesla.Middleware.Compression, format: "gzip"},
         Tesla.Middleware.FormUrlencoded,
-        {Tesla.Middleware.DecodeJson, engine: Jason},
         {Tesla.Middleware.Headers, get_headers(opts)}
-      ],
-      Keyword.get(opts, :adapter)
-    )
+      ] ++ get_from_opts_or_config(opts, :append_middleware, [])
+
+    Tesla.client(middleware, adapter)
   end
 
   @doc """
@@ -87,6 +93,15 @@ defmodule ExForce.Client.Tesla do
     |> cast_response()
   end
 
+  defp get_from_opts_or_config(opts, key, default \\ nil) do
+    from_opts = Keyword.get(opts, key)
+
+    app_config = Application.get_env(:ex_force, __MODULE__, [])
+    from_app_config = Keyword.get(app_config, key)
+
+    from_opts || from_app_config || default
+  end
+
   defp cast_tesla_request(%Request{} = request) do
     request
     |> convert_struct(Tesla.Env)

test/config_test.exs

@@ -0,0 +1,59 @@
+defmodule ExForce.ConfigTest do
+  # Must be set to async: false since this is manipulating global application config
+  use ExUnit.Case, async: false
+
+  alias ExForce.{
+    Client,
+    Request
+  }
+
+  alias Plug.Conn
+
+  test "build_client/2 - custom config" do
+    bypass = Bypass.open()
+    bypass_url = "http://127.0.0.1:#{bypass.port}"
+
+    api_version = "456.0"
+
+    custom_middleware = [
+      Tesla.Middleware.Telemetry,
+      {Tesla.Middleware.Timeout, timeout: :timer.seconds(1)}
+    ]
+
+    custom_middleware_representation = [
+      {Tesla.Middleware.Telemetry, :call, [[]]},
+      {Tesla.Middleware.Timeout, :call, [[timeout: 1000]]}
+    ]
+
+    Application.put_env(:ex_force, ExForce.Client.Tesla,
+      api_version: api_version,
+      append_middleware: custom_middleware
+    )
+
+    on_exit(fn -> Application.delete_env(:ex_force, ExForce.Client.Tesla) end)
+
+    Bypass.expect_once(bypass, "GET", "/foo", fn conn ->
+      conn
+      |> Conn.put_resp_content_type("application/json")
+      |> Conn.resp(200, ~w({"hello": "world"}))
+    end)
+
+    client = ExForce.build_client(bypass_url)
+
+    assert %Tesla.Client{
+             adapter: nil,
+             fun: nil,
+             post: [],
+             pre:
+               [
+                 {ExForce.Client.Tesla.Middleware, :call, [{^bypass_url, ^api_version}]},
+                 {Tesla.Middleware.Compression, :call, [[format: "gzip"]]},
+                 {Tesla.Middleware.JSON, :call, [[engine: Jason]]},
+                 {Tesla.Middleware.Headers, :call, [[{"user-agent", "ex_force"}]]}
+               ] ++ ^custom_middleware_representation
+           } = client
+
+    assert {:ok, %{status: 200, body: %{"hello" => "world"}}} =
+             Client.request(client, %Request{url: "/foo", method: :get})
+  end
+end

test/ex_force/oauth_test.exs

@@ -335,10 +335,10 @@ defmodule ExForce.OAuthTest do
              fun: nil,
              post: [],
              pre: [
+               {Tesla.Middleware.DecodeJson, :call, [[engine: Jason]]},
                {Tesla.Middleware.BaseUrl, :call, ["http://257.0.0.0:0"]},
                {Tesla.Middleware.Compression, :call, [[format: "gzip"]]},
                {Tesla.Middleware.FormUrlencoded, :call, [[]]},
-               {Tesla.Middleware.DecodeJson, :call, [[engine: Jason]]},
                {Tesla.Middleware.Headers, :call, [[{"user-agent", "agent"}]]}
              ]
            }