Add automatic image detection

lib/kino/render.ex

@@ -153,3 +153,18 @@ defimpl Kino.Render, for: PID do
     end
   end
 end
+
+defimpl Kino.Render, for: BitString do
+  def to_livebook(string) do
+    case Kino.Utils.get_image_type(string) do
+      nil ->
+        Kino.Output.inspect(string)
+
+      type ->
+        raw = Kino.Inspect.new(string)
+        image = Kino.Image.new(string, type)
+        tabs = Kino.Layout.tabs(Image: image, Raw: raw)
+        Kino.Render.to_livebook(tabs)
+    end
+  end
+end

lib/kino/utils.ex

@@ -40,4 +40,18 @@ defmodule Kino.Utils do
          do: true,
          else: (_ -> false)
   end
+
+  @doc """
+  Determines image type looking for the magic number in the binary.
+  """
+  @spec get_image_type(binary()) :: Kino.Image.common_image_type() | nil
+  def get_image_type(<<0xFF, 0xD8, 0xFF, 0xE0, _rest::binary>>), do: :jpeg
+  def get_image_type(<<0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, _rest::binary>>), do: :png
+  def get_image_type(<<0x3C, 0x3F, 0x78, 0x6D, 0x6C, 0x20, _rest::binary>>), do: :svg
+
+  def get_image_type(<<0x47, 0x49, 0x46, 0x38, x::8, 0x61, _rest::binary>>)
+      when x in [0x37, 0x39],
+      do: :gif
+
+  def get_image_type(_image), do: nil
 end