Writing a file to NFS server

Hi,

Could you please suggest how to proceed to the below scenario.

     Scenario is from SOAP-IDOC.Client is sending the XML document through SOAP,in which we are sending the payload to ECC as general case.But at the same time they are sending the whole document in one of the fields using BASE 64.

     So in PI we have to read that field and have to write it to File and place it in NFS server.

Could you please help how can we write that file using UDF.