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XML-RPC – Response Format

Responses are much like requests, with a few extra twists. If the response is successful – the procedure was found, executed correctly, and returned results – then the XML-RPC response will look much like a request, except that the methodCall element is replaced by a methodResponse element and there is no methodName element:

<?xml version="1.0"?>
<methodResponse>
   <params>
      <param>
         <value><double>18.24668429131</double></value>
      </param>
   </params>
</methodResponse>
  • An XML-RPC response can only contain one parameter.
  • That parameter may be an array or a struct, so it is possible to return multiple values.
  • It is always required to return a value in response. A “success value” – perhaps a Boolean set to true (1).

Like requests, responses are packaged in HTTP and have HTTP headers. All XML-RPC responses use the 200 OK response code, even if a fault is contained in the message. Headers use a common structure similar to that of requests, and a typical set of headers might look like:

HTTP/1.1 200 OK
Date: Sat, 06 Oct 2001 23:20:04 GMT
Server: Apache.1.3.12 (Unix)
Connection: close
Content-Type: text/xml
Content-Length: 124
  • XML-RPC only requires HTTP 1.0 support, but HTTP 1.1 is compatible.
  • The Content-Type must be set to text/xml.
  • The Content-Length header specifies the length of the response in bytes.

A complete response, with both headers and a response payload, would look like:

HTTP/1.1 200 OK
Date: Sat, 06 Oct 2001 23:20:04 GMT
Server: Apache.1.3.12 (Unix)
Connection: close
Content-Type: text/xml
Content-Length: 124

<?xml version="1.0"?>
<methodResponse>
   <params>
      <param>
         <value><double>18.24668429131</double></value>
      </param>
   </params>
</methodResponse>

After the response is delivered from the XML-RPC server to the XML-RPC client, the connection is closed. Follow-up requests need to be sent as separate XML-RPC connections.

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