Deal with clock drifts and use DateTime UTC for server data (#2787)

lib/livebook/hubs/team_client.ex

@@ -469,7 +469,7 @@ defmodule Livebook.Hubs.TeamClient do
       deployment_group_id: app_deployment.deployment_group_id,
       file: nil,
       deployed_by: app_deployment.deployed_by,
-      deployed_at: NaiveDateTime.from_gregorian_seconds(app_deployment.deployed_at)
+      deployed_at: DateTime.from_gregorian_seconds(app_deployment.deployed_at)
     }
   end
 

lib/livebook/teams/app_deployment.ex

@@ -16,7 +16,7 @@ defmodule Livebook.Teams.AppDeployment do
           deployment_group_id: String.t() | nil,
           file: binary() | nil,
           deployed_by: String.t() | nil,
-          deployed_at: NaiveDateTime.t() | nil
+          deployed_at: DateTime.t() | nil
         }
 
   @access_types Livebook.Notebook.AppSettings.access_types()
@@ -33,8 +33,7 @@ defmodule Livebook.Teams.AppDeployment do
     field :deployment_group_id, :string
     field :file, :string
     field :deployed_by, :string
-
-    timestamps(updated_at: nil, inserted_at: :deployed_at)
+    field :deployed_at, :utc_datetime
   end
 
   @doc """

lib/livebook/utils/time.ex

@@ -3,16 +3,18 @@ defmodule Livebook.Utils.Time do
 
   @doc """
   Formats the given point in time relatively to present.
+
+  ## Examples
+
+  To deal with clock-drifts when receiving timestamps from the server, we accept future times:
+
+        iex> Livebook.Utils.Time.time_ago_in_words(~N[2100-06-20 18:15:00])
+        "less than 5 seconds"
+
   """
   @spec time_ago_in_words(NaiveDateTime.t()) :: String.t()
   def time_ago_in_words(naive_date_time) when is_struct(naive_date_time, NaiveDateTime) do
-    now = NaiveDateTime.utc_now()
-
-    if NaiveDateTime.compare(naive_date_time, now) == :gt do
-      raise ArgumentError, "expected a datetime in the past, got: #{inspect(naive_date_time)}"
-    end
-
-    distance_of_time_in_words(naive_date_time, now)
+    distance_of_time_in_words(naive_date_time, NaiveDateTime.utc_now())
   end
 
   @doc """
@@ -75,6 +77,11 @@ defmodule Livebook.Utils.Time do
       iex> Livebook.Utils.Time.distance_of_time_in_words(~N[2020-06-20 18:15:00], ~N[2021-08-22 18:15:00])
       "about 14 months"
 
+  To deal with clock-drifts when receiving timestamps from another machine, we accept future times:
+
+      iex> Livebook.Utils.Time.distance_of_time_in_words(~N[2020-06-20 18:15:06], ~N[2020-06-20 18:15:04])
+      "less than 5 seconds"
+
   """
   @spec distance_of_time_in_words(NaiveDateTime.t(), NaiveDateTime.t()) :: String.t()
   def distance_of_time_in_words(from_ndt, to_ndt)
@@ -92,7 +99,7 @@ defmodule Livebook.Utils.Time do
 
   defp maybe_convert_to_minutes(duration), do: duration
 
-  defp duration_in_words({:seconds, seconds}) when seconds in 0..4 do
+  defp duration_in_words({:seconds, seconds}) when seconds <= 4 do
     "less than 5 seconds"
   end
 

lib/livebook_web/helpers/html_helpers.ex

@@ -73,7 +73,7 @@ defmodule LivebookWeb.HTMLHelpers do
   Formats the given UTC datetime relatively to present.
   """
   @spec format_datetime_relatively(DateTime.t() | NaiveDateTime.t()) :: String.t()
-  def format_datetime_relatively(%DateTime{} = date) do
+  def format_datetime_relatively(%DateTime{time_zone: "Etc/UTC"} = date) do
     date |> DateTime.to_naive() |> Livebook.Utils.Time.time_ago_in_words()
   end
 

test/livebook_teams/hubs/team_client_test.exs

@@ -663,10 +663,10 @@ defmodule Livebook.Hubs.TeamClientTest do
           version: Livebook.Utils.random_id(),
           file: nil,
           deployed_by: teams_app_deployment.app_revision.created_by.name,
-          deployed_at: teams_app_deployment.updated_at
+          deployed_at: DateTime.from_naive!(teams_app_deployment.updated_at, "Etc/UTC")
       }
 
-      {seconds, 0} = NaiveDateTime.to_gregorian_seconds(app_deployment.deployed_at)
+      {seconds, 0} = DateTime.to_gregorian_seconds(app_deployment.deployed_at)
 
       livebook_proto_app_deployment =
         %LivebookProto.AppDeployment{

test/support/factory.ex

@@ -106,10 +106,10 @@ defmodule Livebook.Factory do
     shasum = Base.encode16(md5_hash, case: :lower)
 
     deployed_at =
-      NaiveDateTime.utc_now()
-      |> NaiveDateTime.truncate(:second)
+      DateTime.utc_now()
+      |> DateTime.truncate(:second)
 
-    {seconds, 0} = NaiveDateTime.to_gregorian_seconds(deployed_at)
+    {seconds, 0} = DateTime.to_gregorian_seconds(deployed_at)
 
     %Livebook.Teams.AppDeployment{
       id: "1",