Validators: Add a type for the datetime used in AP.

lib/pleroma/web/activity_pub/object_validators/note_validator.ex

@@ -25,8 +25,7 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.NoteValidator do
     field(:actor, Types.ObjectID)
     field(:attributedTo, Types.ObjectID)
     field(:summary, :string)
-    # TODO: Write type
-    field(:published, :string)
+    field(:published, Types.DateTime)
     # TODO: Write type
     field(:emoji, :map, default: %{})
     field(:sensitive, :boolean, default: false)

lib/pleroma/web/activity_pub/object_validators/types/date_time.ex

@@ -0,0 +1,34 @@
+defmodule Pleroma.Web.ActivityPub.ObjectValidators.Types.DateTime do
+  @moduledoc """
+  The AP standard defines the date fields in AP as xsd:DateTime. Elixir's
+  DateTime can't parse this, but it can parse the related iso8601. This
+  module punches the date until it looks like iso8601 and normalizes to
+  it.
+
+  DateTimes without a timezone offset are treated as UTC.
+
+  Reference: https://www.w3.org/TR/activitystreams-vocabulary/#dfn-published
+  """
+  use Ecto.Type
+
+  def type, do: :string
+
+  def cast(datetime) when is_binary(datetime) do
+    with {:ok, datetime, _} <- DateTime.from_iso8601(datetime) do
+      {:ok, DateTime.to_iso8601(datetime)}
+    else
+      {:error, :missing_offset} -> cast("#{datetime}Z")
+      _e -> :error
+    end
+  end
+
+  def cast(_), do: :error
+
+  def dump(data) do
+    {:ok, data}
+  end
+
+  def load(data) do
+    {:ok, data}
+  end
+end