Allow Tesla middleware to be configured

lib/ex_force/client/tesla/tesla.ex

@@ -29,6 +29,7 @@ defmodule ExForce.Client.Tesla do
   - `:headers`: set additional headers; default: `[{"user-agent", "#{@default_user_agent}"}]`
   - `:api_version`: use the given api_version; default: `"#{@default_api_version}"`
   - `:adapter`: use the given adapter with custom opts; default: `nil`, which causes Tesla to use the default adapter or the one set in config.
+  - `:middleware`: set additional middleware to use in the Tesla Client
   """
   @impl ExForce.Client
   def build_client(instance_url_or_map, opts \\ [headers: [{"user-agent", @default_user_agent}]])
@@ -42,16 +43,18 @@ defmodule ExForce.Client.Tesla do
   end
 
   def build_client(instance_url, opts) when is_binary(instance_url) do
-    Tesla.client(
-      [
-        {ExForce.Client.Tesla.Middleware,
-         {instance_url, Keyword.get(opts, :api_version, @default_api_version)}},
-        {Tesla.Middleware.Compression, format: "gzip"},
-        {Tesla.Middleware.JSON, engine: Jason},
-        {Tesla.Middleware.Headers, Keyword.get(opts, :headers, [])}
-      ],
-      Keyword.get(opts, :adapter)
-    )
+    additional_middleware = Keyword.get(opts, :middleware, [])
+
+    middleware = [
+      {ExForce.Client.Tesla.Middleware,
+       {instance_url, Keyword.get(opts, :api_version, @default_api_version)}},
+      additional_middleware,
+      {Tesla.Middleware.Compression, format: "gzip"},
+      {Tesla.Middleware.JSON, engine: Jason},
+      {Tesla.Middleware.Headers, Keyword.get(opts, :headers, [])}
+    ] |> List.flatten
+
+    Tesla.client(middleware, Keyword.get(opts, :adapter))
   end
 
   @doc """

test/ex_force/client/tesla_test.exs

@@ -0,0 +1,53 @@
+defmodule ExForce.Client.TeslaTest do
+  use ExUnit.Case, async: false
+  alias ExForce.{Client, Request}
+  alias Plug.Conn
+
+  defmodule TestMiddleware do
+    @behaviour Tesla.Middleware
+
+    @impl Tesla.Middleware
+    def call(env, next, test_pid: test_pid, id: id) when is_pid(test_pid) do
+      send(test_pid, {:before, id})
+      result = Tesla.run(env, next)
+      send(test_pid, {:after, id})
+
+      result
+    end
+  end
+
+  setup do
+    %{bypass: Bypass.open()}
+  end
+
+  test "it will use the custom middleware provided to it", %{bypass: bypass} do
+    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.Client.Tesla.build_client(%{instance_url: bypass_url(bypass), access_token: "foo"},
+        middleware: [
+          {TestMiddleware, test_pid: self(), id: 1},
+          {TestMiddleware, test_pid: self(), id: 2},
+          {TestMiddleware, test_pid: self(), id: 3}
+        ]
+      )
+
+    {:ok, _response} = Client.request(client, %Request{url: "/foo", method: :get})
+
+    assert {:messages,
+            [
+              before: 1,
+              before: 2,
+              before: 3,
+              after: 3,
+              after: 2,
+              after: 1
+            ]} = Process.info(self(), :messages)
+  end
+
+  defp bypass_url(bypass), do: "http://127.0.0.1:#{bypass.port}"
+end