Getting Water from a FHIR Operation

According to the FHIR Operation specification (STU2 and 3 say the same thing):

---

If there is only one out parameter, which is a Resource with the parameter name "return" then the parameter format is not used, and the response is simply the resource itself.

---

So, if you want to return non-FHIR content in your operation, return a Binary resource. The FHIR Server (if properly implemented) would interpret the resource as content to be returned in the usual web way.  

I've verified that the HAPI 3.0 Server does in fact operate correctly when you return a Binary resource for an operation.

So, if you want your FHIR operation to return a CDA document, you can get it to do so.  Heck, if you really wanted to, you could get it to return V3 or even better (sic) a V2 message.  DICOM anyone?

   Keith