title: REST: Correct HTTP Response Code For a POST Which Is Ignored
body: <p>We have a REST API which clients routinely POST and PUT data to.  When they do this, sometimes they POST data which results in no change on our system.  The POSTs and PUTs are  well-formed, but they data they're sending is identical to the data in our database.  When this happens, I've just found out that we're returning a 400 HTTP status.  Unfortunatly, this means "bad request" as in "request could not be understood by the server due to malformed syntax".</p>
  
  <p>Clearly this is not the case, but I'm told that we're going to use this since there's no other appropriate status code.  Choices we've considered:</p>
  
  <ul>
  <li>304 Not Modified. This, regrettably, is only for GET requests.</li>
  <li>204 No Content. Seems close, but forbids an entity-body.</li>
  </ul>
  
  <p>Other choices seem equally bad. We might go with <code>200 OK</code> and have the relevant information in the XML document we return, but this doesn't seem very "RESTish".  How does the REST world generally handle this?</p>
  
  <p>(Fixed Not Modified response code. Thanks Mkoeller)</p>