Allow own formatter and fix flaky tests

config/config.exs

@@ -1,6 +1,6 @@
 # This file is responsible for configuring your application
 # and its dependencies with the aid of the Mix.Config module.
-use Mix.Config
+import Config
 
 # This configuration is loaded before any dependency and is restricted
 # to this project. If another project depends on this project, this

config/dev.exs

@@ -1,4 +1,4 @@
-use Mix.Config
+import Config
 
 config :logger,
   backends: [{LoggerFileBackend, :dev_backend}],

config/test.exs

@@ -1,4 +1,4 @@
-use Mix.Config
+import Config
 
 config :logger, backends: []
 

lib/logger_file_backend.ex

@@ -8,9 +8,10 @@ defmodule LoggerFileBackend do
   @type path :: String.t()
   @type file :: :file.io_device()
   @type inode :: integer
-  @type format :: String.t()
+  @type format :: {atom(), atom()} | [Logger.Formatter.pattern() | binary()]
   @type level :: Logger.level()
   @type metadata :: [atom]
+  @type formatter :: module()
 
   require Record
   Record.defrecordp(:file_info, Record.extract(:file_info, from_lib: "kernel/include/file.hrl"))
@@ -114,7 +115,7 @@ defmodule LoggerFileBackend do
   defp rename_file(path, keep) do
     File.rm("#{path}.#{keep}")
 
-    Enum.each((keep - 1)..1, fn x -> File.rename("#{path}.#{x}", "#{path}.#{x + 1}") end)
+    Enum.each((keep - 1)..1//-1, fn x -> File.rename("#{path}.#{x}", "#{path}.#{x + 1}") end)
 
     case File.rename(path, "#{path}.1") do
       :ok -> false
@@ -148,10 +149,30 @@ defmodule LoggerFileBackend do
     end
   end
 
-  defp format_event(level, msg, ts, md, %{format: format, metadata: keys}) do
+  defp format_event(level, msg, ts, md, %{
+         format: format,
+         formatter: Logger.Formatter,
+         metadata: keys
+       }) do
     Logger.Formatter.format(format, level, msg, ts, take_metadata(md, keys))
   end
 
+  # md should be a map
+  defp format_event(level, msg, ts, md, opts) when is_list(md) do
+    format_event(level, msg, ts, Enum.into(md, %{}), opts)
+  end
+
+  defp format_event(level, msg, ts, md, %{
+         format: _format,
+         formatter: {formatter_module, formatter_opts},
+         metadata: _metadata
+       }) do
+    apply(formatter_module, :format, [
+      %{level: level, msg: {:string, msg}, meta: Map.put(md, :time, ts)},
+      formatter_opts
+    ])
+  end
+
   @doc false
   @spec metadata_matches?(Keyword.t(), nil | Keyword.t()) :: true | false
   def metadata_matches?(_md, nil), do: true
@@ -208,6 +229,7 @@ defmodule LoggerFileBackend do
       io_device: nil,
       inode: nil,
       format: nil,
+      formatter: nil,
       level: nil,
       metadata: nil,
       metadata_filter: nil,
@@ -225,8 +247,9 @@ defmodule LoggerFileBackend do
 
     level = Keyword.get(opts, :level)
     metadata = Keyword.get(opts, :metadata, [])
-    format_opts = Keyword.get(opts, :format, @default_format)
-    format = Logger.Formatter.compile(format_opts)
+    format_opts = Keyword.get(opts, :format)
+    format = Logger.Formatter.compile(format_opts || @default_format)
+    formatter = Keyword.get(opts, :formatter)
     path = Keyword.get(opts, :path)
     metadata_filter = Keyword.get(opts, :metadata_filter)
     metadata_reject = Keyword.get(opts, :metadata_reject)
@@ -237,6 +260,7 @@ defmodule LoggerFileBackend do
       | name: name,
         path: path,
         format: format,
+        formatter: formatter || Logger.Formatter,
         level: level,
         metadata: metadata,
         metadata_filter: metadata_filter,

mix.exs

@@ -42,6 +42,7 @@ defmodule LoggerFileBackend.Mixfile do
   defp deps do
     [
       {:credo, "~> 1.7.5", only: [:dev, :test]},
+      {:logger_json, "~> 7.0", only: [:dev, :test]},
       {:ex_doc, ">= 0.32.1", only: :dev, runtime: false}
     ]
   end

mix.lock

@@ -5,6 +5,7 @@
   "ex_doc": {:hex, :ex_doc, "0.32.1", "21e40f939515373bcdc9cffe65f3b3543f05015ac6c3d01d991874129d173420", [:mix], [{:earmark_parser, "~> 1.4.39", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_c, ">= 0.1.1", [hex: :makeup_c, repo: "hexpm", optional: true]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1", [hex: :makeup_erlang, repo: "hexpm", optional: false]}], "hexpm", "5142c9db521f106d61ff33250f779807ed2a88620e472ac95dc7d59c380113da"},
   "file_system": {:hex, :file_system, "1.0.0", "b689cc7dcee665f774de94b5a832e578bd7963c8e637ef940cd44327db7de2cd", [:mix], [], "hexpm", "6752092d66aec5a10e662aefeed8ddb9531d79db0bc145bb8c40325ca1d8536d"},
   "jason": {:hex, :jason, "1.4.1", "af1504e35f629ddcdd6addb3513c3853991f694921b1b9368b0bd32beb9f1b63", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "fbb01ecdfd565b56261302f7e1fcc27c4fb8f32d56eab74db621fc154604a7a1"},
+  "logger_json": {:hex, :logger_json, "7.0.4", "e315f2b9a755504658a745f3eab90d88d2cd7ac2ecfd08c8da94d8893965ab5c", [:mix], [{:decimal, ">= 0.0.0", [hex: :decimal, repo: "hexpm", optional: true]}, {:ecto, "~> 3.11", [hex: :ecto, repo: "hexpm", optional: true]}, {:jason, "~> 1.4", [hex: :jason, repo: "hexpm", optional: true]}, {:plug, "~> 1.15", [hex: :plug, repo: "hexpm", optional: true]}, {:telemetry, "~> 1.0", [hex: :telemetry, repo: "hexpm", optional: true]}], "hexpm", "d1369f8094e372db45d50672c3b91e8888bcd695fdc444a37a0734e96717c45c"},
   "makeup": {:hex, :makeup, "1.1.1", "fa0bc768698053b2b3869fa8a62616501ff9d11a562f3ce39580d60860c3a55e", [:mix], [{:nimble_parsec, "~> 1.2.2 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "5dc62fbdd0de44de194898b6710692490be74baa02d9d108bc29f007783b0b48"},
   "makeup_elixir": {:hex, :makeup_elixir, "0.16.2", "627e84b8e8bf22e60a2579dad15067c755531fea049ae26ef1020cad58fe9578", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}, {:nimble_parsec, "~> 1.2.3 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "41193978704763f6bbe6cc2758b84909e62984c7752b3784bd3c218bb341706b"},
   "makeup_erlang": {:hex, :makeup_erlang, "0.1.5", "e0ff5a7c708dda34311f7522a8758e23bfcd7d8d8068dc312b5eb41c6fd76eba", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm", "94d2e986428585a21516d7d7149781480013c56e30c6a233534bedf38867a59a"},