I am developing a RESTful web service. The web service receives XML from clients, it should reject some bad requests containing some error related to our business logic(say, the payment value below a minimum value). If rejecting request, a customised error code and error message will be written in a response XML(inside http response body). I also want to return a HTTP code in the status line, so client can recognize rejection right away without looking into the response boday. Some people suggest using HTTP code 412, however by looking at the definition of HTTP 412:
412 Precondition Failed
The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This response code allows the client to place preconditions on the current resource metainformation (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.
I don't quite understand what it represents for. Could someone explain the appropriate usage of 412 please? or in this case are there any better choices?
