We use the REST module https://github.com/mendix/RestServices/blob/master/README.md#securing-published-services to communicate between Mendix and iPads. It is a small prototype and the iPad should download one JSON file, modify it and upload it afterwards to mendix again. The download part was easy, but how can I upload? Am I missing something? We prefer to send an POST request with the json data from the iPad. Or do we need a file upload? (Will be my next try...) other: How can I test the upload on my computer ? I normally test the it with this tool https://github.com/chao/RESTClient. I copied the json hash from the resonse in the download part into the Body of the request. But my params in the microflow are empty? Is there a better logging functionality for incoming requests?
For more logging, you can increase the loglevel of REST* to debug or trace. JSON should not be uploaded to the Mendix app, but POSTed (you could upload and parse it, but that doesn't make much sense). Note that the contenttype header must be set to be able to upload and parse the json data. Currently that should be text/json, but in the next release this will be changed (backward compatible) to application/json.
Any REST client should suffice for testing, but personally I advice to start with curl and small pieces of data, because then your tests are easily shareable and you are sure you know exactly what is going on.
See also: http://www.mendix.com/blog/rest-part-ii-publishing-microflows-rest/