Add env var for debug logs (#2292)

README.md

@@ -224,6 +224,9 @@ The following environment variables can be used to configure Livebook on boot:
     configuration. Defaults to "livebook" under the default user data
     directory.
 
+  * LIVEBOOK_DEBUG - enables verbose logging, when set to "true". Disabled
+    by default.
+
   * LIVEBOOK_DEFAULT_RUNTIME - sets the runtime type that is used by default
     when none is started explicitly for the given notebook. Must be either
     "standalone" (Elixir standalone), "attached:NODE:COOKIE" (Attached node)

lib/livebook.ex

@@ -91,6 +91,10 @@ defmodule Livebook do
         Livebook.Config.secret!("LIVEBOOK_SECRET_KEY_BASE") ||
           Base.encode64(:crypto.strong_rand_bytes(48))
 
+    if Livebook.Config.debug!("LIVEBOOK_DEBUG") do
+      config :logger, level: :debug
+    end
+
     if port = Livebook.Config.port!("LIVEBOOK_PORT") do
       config :livebook, LivebookWeb.Endpoint, http: [port: port]
     end

lib/livebook/config.ex

@@ -420,6 +420,19 @@ defmodule Livebook.Config do
     end
   end
 
+  @doc """
+  Parses and validates debug mode from env.
+  """
+  def debug!(env) do
+    if debug = System.get_env(env) do
+      cond do
+        debug in ["1", "true"] -> true
+        debug in ["0", "false"] -> false
+        true -> abort!("expected #{env} to be a boolean, got: #{inspect(debug)}")
+      end
+    end
+  end
+
   @doc """
   Parses and validates the port from env.
   """