REST api example for decode a Base64 data

Hi all,

It's me again 😁. In the pervious article Writing a REST api service for exporting the generated FHIR bundle in JSON, we actually generated a resource DocumentReference, with the content data encoded in Base64

Question!! Is it possible to write a REST service for decoding it? Because I am very curious what is the message data talking about🤔🤔🤔

OK, Let's start!

1. Create a new utility class datagen.utli.decodefhirjson.cls for decoding the data inside the DocumentReference
 

Class datagen.utli.decodefhirjson Extends%RegisteredObject
{
}

2. Write a Python function decodebase64docref to 
a. loop through the FHIR bundle
b. find out the resource DocumentReference
  - get the 1st element in the content
   - get the attachment from the content
     - get the data from the attachment
c. decode the data by Base64
 (this part I asked Chat-GPT to help me😂🤫) 

Class datagen.utli.decodefhirjson Extends%RegisteredObject
{

ClassMethod decodebase64docref(fhirbundle = "") As%String [ Language = python ]
{
    # w##class(datagen.utli.decodefhirjson).decodebase64docref()
    import base64
    import json

    def decode_discharge_summary(bundle_json):
        """
        Extracts and decodes the Base64-encoded discharge summary note
        from a FHIR Bundle containing a DocumentReference.
        """for entry in bundle_json.get("entry", []):
            resource = entry.get("resource", {})
            if resource.get("resourceType") == "DocumentReference":
                # Traverse to the attachment
                content_list = resource.get("content", [])
                if not content_list:
                    continue
                attachment = content_list[0].get("attachment", {})
                base64_data = attachment.get("data")
                if base64_data:
                    decoded_text = base64.b64decode(base64_data).decode("utf-8")
                    return decoded_text
        return None


    # Example usage
    # Load your FHIR Bundle JSON from a file or object
    #with open("fhir_bundle.json", "r") as f:
    #    fhir_bundle = json.loads(f)
    if fhirbundle=="":
        rtstr=f"⚠️ No input found - JSON string is required."
        jsstr={"operation_outcome" : rtstr}
        return json.dumps(jsstr, indent=2)

    fhir_bundle = json.loads(fhirbundle)
    decoded_note = decode_discharge_summary(fhir_bundle)

    if decoded_note:
        #print("📝 Decoded Discharge Summary:\n")
        #print(decoded_note)
        rtstr=f"📝 Decoded Discharge Summary:\n {decoded_note}"else:
        #print("⚠️ No DocumentReference with Base64 note found.")
        rtstr=f"⚠️ No DocumentReference with Base64 note found."
    jsstr={"data" : rtstr}
    return json.dumps(jsstr, indent=2)
}

}

For testing this function, I try do some trick, which is making use of the function genfhirbundle to generate FHIR bundle in JSON string,  in the pervious article Writing a REST api service for exporting the generated FHIR bundle in JSON.  

Let's generated a FHIR bundle and store into a variable jsonstr

set jsonstr=##class(datagen.utli.genfhirjson).genfhirbundle(1)

The test the decode function decodebase64docref  with the jsonstr

w##class(datagen.utli.decodefhirjson).decodebase64docref(jsonstr)

OK 😉 Looks good. Now I can read the decode message.

Now, go back the pervious and pervious article Writing a REST api service for exporting the generated patient data in .csv

We would like to add a new function and update the route for the datagen.restservice class.

1. Add a new function DecodeDocRef, which is expecting to handle the FHIR bundle  attached in the body in JSON format.

i.e. In this case, we are expecting a POST.

the body content is packaged as %CSP.BinaryStream by default and stored in the variable %request.Content, so we can use the .Read() function  from the class %CSP.BinaryStream to read the BinaryStream

ClassMethod DecodeDocRef() As%Status
{
    // get body - json string#dim bistream As%CSP.BinaryStream =""set bistream=%request.Contentset jsstr=bistream.Read()
    
    //decode the Document Reference dataw##class(datagen.utli.decodefhirjson).decodebase64docref(jsstr)
    return$$$OK
}

2. Then we add a route for the REST service and compile😀

<Route Url="/decode/docref" Method="POST" Call="DecodeDocRef" />

the updated  datagen.restservice class will look like the following.

Great!! That's all we need to do!😁

Let's test in postman!!

POST the following path

localhost/irishealth/csp/mpapp/decode/docref

with the following body ( I simplified FHIR bundle, you may test the full one😀)

{
    "resourceType": "Bundle",
    "type": "transaction",
    "id": "98bfce83-7eb1-4afe-bf2b-42916512244e",
    "meta": {
        "lastUpdated": "2025-10-13T05:49:07Z"
    },
    "entry": [
        {
            "fullUrl": "urn:uuid:5be1037d-a481-45ca-aea9-2034e27ebdcd",
            "resource": {
                "resourceType": "DocumentReference",
                "id": "5be1037d-a481-45ca-aea9-2034e27ebdcd",
                "status": "current",
                "type": {
                    "coding": [
                        {
                            "system": "http://loinc.org",
                            "code": "18842-5",
                            "display": "Discharge summary"
                        }
                    ]
                },
                "subject": {
                    "reference": "9e3a2636-4e87-4dee-b202-709d6f94ed18"
                },
                "author": [
                    {
                        "reference": "2aa54642-6743-4153-a171-7b8a8004ce5b"
                    }
                ],
                "context": {
                    "encounter": [
                        {
                            "reference": "98cd848b-251f-4d0b-bf36-e35c9fe68956"
                        }
                    ]
                },
                "content": [
                    {
                        "attachment": {
                            "contentType": "text/plain",
                            "language": "en",
                            "data": "RGlzY2hhcmdlIHN1bW1hcnkgZm9yIHBhdGllbnQgOWUzYTI2MzYtNGU4Ny00ZGVlLWIyMDItNzA5ZDZmOTRlZDE4LiBEaWFnbm9zaXM6IFN0YWJsZS4gRm9sbG93LXVwIGluIDIgd2Vla3Mu",
                            "title": "Discharge Summary Note"
                        }
                    }
                ]
            },
            "request": {
                "method": "POST",
                "url": "DocumentReference"
            }
        }
    ]
}

Works well!!!😆😉

Thank you very much for reading. 😘