A RESTful Web Services API was added to the product with XPP 9.3.
It is available, and is distributed for use with any new installation or upgrade as of the XPP 9.3 release.
Replace Web Services with a RESTful API that is URL addressable for XPP functionality.
Low-level "micro" services (toxsf, compose, print, citi, etc) supported by XPP, that can be built upon for more high level customized functionality.
Or alternatively it could be that in the 'completed' JSON status object you return also the url to the resulting file.
So that when we do a GET to that url we simply get the resulting PDF or XML or whatever file ...
And talking about files, how do plan to send the content of a file? Inside a JSON object as a base64 encoded string?
And if you send it as a JSON object you could maybe also include the path of the file and its name on the XPP system?