add function to open notebook urls (#986)

* add function to open notebook urls

* Update lib/livebook/utils.ex

Co-authored-by: José Valim <jose.valim@gmail.com>

* Update lib/livebook/utils.ex

Co-authored-by: José Valim <jose.valim@gmail.com>

* open notebook with notebook_open_url/2

* Update server.ex

* format Livebook.Utils

* Update lib/livebook_cli/server.ex

Co-authored-by: José Valim <jose.valim@gmail.com>

* correct function doc

Co-authored-by: José Valim <jose.valim@gmail.com>

lib/livebook/utils.ex

@@ -387,6 +387,24 @@ defmodule Livebook.Utils do
     |> URI.to_string()
   end
 
+  @doc """
+  Returns a URL (including localhost) to open the given `url` as a notebook
+
+      iex> Livebook.Utils.notebook_open_url("https://example.com/foo.livemd")
+      "http://localhost:4002/open?path=https%3A%2F%2Fexample.com%2Ffoo.livemd"
+
+      iex> Livebook.Utils.notebook_open_url("https://my_host", "https://example.com/foo.livemd")
+      "https://my_host/open?path=https%3A%2F%2Fexample.com%2Ffoo.livemd"  
+
+  """
+  def notebook_open_url(base_url \\ LivebookWeb.Endpoint.access_struct_url(), url) do
+    base_url
+    |> URI.parse()
+    |> Map.replace!(:path, "/open")
+    |> append_query("path=#{URI.encode_www_form(url)}")
+    |> URI.to_string()
+  end
+
   # TODO: On Elixir v1.14, use URI.append_query/2
   def append_query(%URI{query: query} = uri, query_to_add) when query in [nil, ""] do
     %{uri | query: query_to_add}

lib/livebook_cli/server.ex

@@ -168,8 +168,7 @@ defmodule LivebookCLI.Server do
 
       File.regular?(path) ->
         base_url
-        |> append_path("open")
-        |> update_query(%{"path" => path})
+        |> Livebook.Utils.notebook_open_url(url_or_file_or_dir)
         |> Livebook.Utils.browser_open()
 
       File.dir?(path) ->