Fix timezone issue

neurow/lib/neurow/ecs_log_formatter.ex

@@ -4,16 +4,16 @@ defmodule Neurow.EcsLogFormatter do
 
   # ECS Reference: https://www.elastic.co/guide/en/ecs/current/index.html
 
-  def format(level, message, timestamp, metadata) do
-    {{year, month, day}, {hour, minute, second, millisecond}} = timestamp
-    {:ok, date} = Date.new(year, month, day)
-    {:ok, time} = Time.new(hour, minute, second, millisecond * 1000)
-    {:ok, datetime} = DateTime.new(date, time)
+  def format(level, message, _timestamp, metadata) do
+    # The timestamp provided in input parameter is in the system timezone,
+    # but there is no clean way to get the system timezone in Elixir/Erlang to convert it to UTC and/or format it in ISO8601.
+    # So we use the unix timestamp provided in the metadata to get the event datetime time in UTC
+    {:ok, event_datetime} = DateTime.from_unix(metadata[:time], :microsecond)
 
     {module, function, arity} = metadata[:mfa]
 
     %{
-      "@timestamp" => datetime |> DateTime.to_iso8601(),
+      "@timestamp" => event_datetime |> DateTime.to_iso8601(),
       "log.level" => level,
       "log.name" => "#{module}.#{function}/#{arity}",
       "log.source" => %{

neurow/test/neurow/ecs_log_formatter_test.exs

@@ -2,20 +2,19 @@ defmodule Neurow.EcsLogFormatterTest do
   use ExUnit.Case
 
   test "generates ECS compliant logs with default metadata" do
-    timestamp = {{2024, 10, 23}, {12, 25, 45, 123}}
-
     metadata = %{
+      time: 1_728_556_213_722_376,
       mfa: {Neurow.EcsLogFormatterTest, :fake_function, 4},
       file: "test/neurow/ecs_log_formatter_test.exs",
       line: 10
     }
 
     json_log =
-      Neurow.EcsLogFormatter.format(:info, "Hello, world!", timestamp, metadata)
+      Neurow.EcsLogFormatter.format(:info, "Hello, world!", nil, metadata)
       |> :jiffy.decode([:return_maps])
 
     assert json_log == %{
-             "@timestamp" => "2024-10-23T12:25:45.123000Z",
+             "@timestamp" => "2024-10-10T10:30:13.722376Z",
              "log.level" => "info",
              "log.name" => "Elixir.Neurow.EcsLogFormatterTest.fake_function/4",
              "log.source" => %{
@@ -35,21 +34,20 @@ defmodule Neurow.EcsLogFormatterTest do
   end
 
   test "supports optional trace_id metadata" do
-    timestamp = {{2024, 10, 23}, {12, 25, 45, 123}}
-
     metadata = %{
+      time: 1_728_556_213_722_376,
       mfa: {Neurow.EcsLogFormatterTest, :fake_function, 4},
       file: "test/neurow/ecs_log_formatter_test.exs",
       line: 10,
       trace_id: "1234567890"
     }
 
     json_log =
-      Neurow.EcsLogFormatter.format(:info, "Hello, world!", timestamp, metadata)
+      Neurow.EcsLogFormatter.format(:info, "Hello, world!", nil, metadata)
       |> :jiffy.decode([:return_maps])
 
     assert json_log == %{
-             "@timestamp" => "2024-10-23T12:25:45.123000Z",
+             "@timestamp" => "2024-10-10T10:30:13.722376Z",
              "log.level" => "info",
              "log.name" => "Elixir.Neurow.EcsLogFormatterTest.fake_function/4",
              "log.source" => %{
@@ -70,21 +68,20 @@ defmodule Neurow.EcsLogFormatterTest do
   end
 
   test "supports optional error_code metadata" do
-    timestamp = {{2024, 10, 23}, {12, 25, 45, 123}}
-
     metadata = %{
+      time: 1_728_556_213_722_376,
       mfa: {Neurow.EcsLogFormatterTest, :fake_function, 4},
       file: "test/neurow/ecs_log_formatter_test.exs",
       line: 10,
       error_code: "invalid_last_event_id"
     }
 
     json_log =
-      Neurow.EcsLogFormatter.format(:info, "Hello, world!", timestamp, metadata)
+      Neurow.EcsLogFormatter.format(:info, "Hello, world!", nil, metadata)
       |> :jiffy.decode([:return_maps])
 
     assert json_log == %{
-             "@timestamp" => "2024-10-23T12:25:45.123000Z",
+             "@timestamp" => "2024-10-10T10:30:13.722376Z",
              "log.level" => "info",
              "log.name" => "Elixir.Neurow.EcsLogFormatterTest.fake_function/4",
              "log.source" => %{