add logs scrubber to config for removing secrets, includes test

lib/slack_logger_backend/format_helper.ex

@@ -3,8 +3,6 @@ defmodule SlackLoggerBackend.FormatHelper do
   Simple formatter for Slack messages.
   """
 
-  import Poison, only: [encode: 1]
-
   @doc """
   Formats a log event for Slack.
   """
@@ -22,7 +20,12 @@ defmodule SlackLoggerBackend.FormatHelper do
       ]
       |> Enum.reject(&is_nil/1)
 
-    message = messge_to_string(detail.message)
+    scrubber = Application.get_env(:slack_logger_backend, :scrubber)
+
+    message =
+      detail.message
+      |> messge_to_string()
+      |> scrub(scrubber)
 
     {:ok, json} =
       %{
@@ -34,7 +37,7 @@ defmodule SlackLoggerBackend.FormatHelper do
           }
         ]
       }
-      |> encode
+      |> Poison.encode()
 
     json
   end
@@ -49,6 +52,14 @@ defmodule SlackLoggerBackend.FormatHelper do
     )
   end
 
+  defp scrub(message, nil), do: message
+
+  defp scrub(message, {regex, substitution}),
+    do: String.replace(message, regex, substitution, global: true)
+
+  defp scrub(message, regex),
+    do: String.replace(message, regex, "--redacted--", global: true)
+
   defp field(title, map, key), do: field(title, map[key])
   defp field(_, nil), do: nil
 

test/slack_logger_backend/format_helper_test.exs

@@ -0,0 +1,26 @@
+defmodule SlackLoggerBackend.FormatHelperTest do
+  alias SlackLoggerBackend.FormatHelper
+
+  use ExUnit.Case
+
+  test "scrubber redacts secrets" do
+    scrubber = {~r/(password: \")(.+)(\")/, "\\1--redadacted--\\3"}
+    Application.put_env(:slack_logger_backend, :scrubber, scrubber)
+
+    message =
+      %{level: "error", message: "username: \"user\",  password: \"password\""}
+      |> FormatHelper.format_event()
+      |> get_message()
+
+    assert message == "username: \"user\",  password: \"--redadacted--\""
+  end
+
+  defp get_message(message) do
+    message
+    |> Poison.decode()
+    |> elem(1)
+    |> Map.get("attachments")
+    |> List.first()
+    |> Map.get("pretext")
+  end
+end

test/slack_logger_backend/pool_worker_test.exs

@@ -2,7 +2,7 @@ ExUnit.start()
 
 defmodule SlackLoggerBackend.PoolWorkerTest do
   use ExUnit.Case
-  alias SlackLoggerBackend.{PoolWorker}
+  alias SlackLoggerBackend.PoolWorker
 
   setup do
     bypass = Bypass.open()