title: Re-parse escaped subfields from json data in logstash
body: <p>I want try parse json data in logstash. but it's nested and escaped.</p>
  
  <p>I have question about re-parse escaped json in subfields in json.</p>
  
  <p>For example:</p>
  
  <pre><code>{"d1": 1, "d2": "{\"c1\": 1, \"c2\": 2}" }
  </code></pre>
  
  <p>In generally programming environments, that is so easy for solve this problem.</p>
  
  <p>but, logstash configuaration is not easily approach for this case.</p>
  
  <p>Can I get hint for this case?</p>