input

{
    duck:true,
    "french":"fries"
}

logstash.conf

input { 
	stdin { 
		type => json
		codec => json_lines
	} 
	tcp {
    	port => 28777
    	type => "winston"
  	}
}

filter {
	json {
      source => "message"
    }
}

output {
  stdout { codec => rubydebug }
}

output

{
       "message" => "{\"app\":\"logstash-dev-test\",\"level\":\"info\",\"message\":\"{\\\"duck\\\":true,\\\"french\\\":\\\"fries\\\"}\"}",
      "@version" => "1",
    "@timestamp" => "2015-07-28T19:49:32.063Z",
          "host" => "73.212.109.60",
          "type" => "winston"
}