Better serialize errors

exe/referator

@@ -14,8 +14,17 @@ def success(data = nil)
   puts "OK #{data.to_json}"
 end
 
-def failure(msg)
-  puts "ERR #{String(msg).lines.join(' ')}"
+def failure(data = nil)
+  puts "ERR #{data.to_json}"
+end
+
+def serialize_err(err)
+  {
+    class: err.class.name.freeze,
+    message: err.message.freeze,
+    stacktrace: err.backtrace.map(&:freeze).freeze,
+    cause: err.cause.nil? ? nil : serialize_err(err.cause),
+  }.freeze
 end
 
 workdir = ARGV.first
@@ -24,7 +33,6 @@ workdir = File.expand_path(workdir).freeze
 
 config = Referator::Config.new workdir
 footnotes = Referator::Footnotes.new config
-stacktrace = nil
 
 while (line = $stdin.gets)
   begin
@@ -38,9 +46,6 @@ while (line = $stdin.gets)
       exit
     when :ping
       success :pong
-    when :stacktrace
-      success stacktrace
-      stacktrace = nil
     ##########
     # Config #
     ##########
@@ -91,7 +96,6 @@ while (line = $stdin.gets)
       raise 'Invalid command'
     end
   rescue => e
-    stacktrace = e.backtrace.map(&:freeze).freeze
-    failure e.detailed_message
+    failure serialize_err e
   end
 end