Add Kino.Proxy module

lib/kino/proxy.ex

@@ -0,0 +1,22 @@
+defmodule Kino.Proxy do
+  @moduledoc """
+  A kino for handling proxy requests from the host.
+
+  ## Examples
+
+      Kino.Proxy.listen(fn conn ->
+        conn
+        |> Plug.Conn.put_resp_header("content-type", "application/text;charset=utf-8")
+        |> Plug.Conn.send_resp(200, "used " <> conn.method <> " method")
+      end)
+  """
+
+  @doc """
+  Persists the function to be listened by the proxy handler.
+  """
+  @spec listen(atom(), module(), (Plug.Conn.t() -> Plug.Conn.t())) ::
+          DynamicSupervisor.on_start_child()
+  def listen(name \\ __MODULE__, mod \\ Livebook.Proxy.Handler, fun) when is_function(fun, 1) do
+    Kino.start_child({mod, name: name, listen: fun})
+  end
+end