MSC4302: Exchanging FHIR resources via Matrix events

Signed-off-by: Johannes Marbach <n0-0ne+github@mailbox.org>

proposals/4302-🔥-resources.md

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+# MSC4302: Exchanging FHIR resources via Matrix events
+
+[FHIR] (pronounced 🔥) is a globally established standard for exchanging healthcare information
+electronically. The base building block of FHIR are so called resources, such as [`Patient`]. These
+resources can be serialised into JSON or XML which allows them to be transmitted via the [`m.file`]
+message type. This is insufficient, however, because a generic MIME type of `application/xml` or
+`application/json` doesn't let clients recognise the content as FHIR before downloading it. The
+`m.file` mechanism also doesn't allow clients to infer any details about the types of resources
+contained in the file ahead of downloading it. Furthermore, in many cases FHIR resources are small
+enough to be inlined into Matrix events which significantly simplifies client-side processing.
+
+This proposal introduces an event type for transmitting FHIR resources and type information over
+Matrix in either inlined or uploaded form.
+
+## Proposal
+
+A new event type `m.fhir.resource` is introduced with the following properties in `content`:
+
+- `canonical_url` (string, required): The resource's [canonical URL], that is the globally unique
+  identifier defining its schema. MAY contain a version suffix separated by `|` as per the FHIR
+  specification.
+- `m.fhir.resource` (object): The serialised JSON if it fits within the [64 KiB event size limit].
+  Required if `m.file` is missing.
+- `m.file` (object): An [MSC3551] content block describing an uploaded JSON or XML serialisation of
+  the resource if it is too large to be inlined. Required if `m.fhir.resource` is missing.
+
+``` json5
+{
+  "type": "m.fhir.resource",
+  "content": {
+    "canonical_url": "http://hl7.org/fhir/patient.html|4.0.1", 
+    "m.fhir.resource": {
+      "resourceType" : "Patient",
+      "name" : [{
+        "use" : "official",
+        "given" : ["John", "James"],
+        "family" : "Doe"
+      }],
+      "gender" : "male",
+      "birthDate" : "1970-01-01",
+      // further properties as per the Patient schema
+    },
+    "m.file": {
+      "url": "mxc://example.org/abcd1234",
+      "mimetype": "application/json",
+      // further properties as per MSC3551
+  }
+}
+```
+
+## Potential issues
+
+FHIR includes generic resources such as [`Bundle`] which wrap other resources. The `canonical_url`
+will not help clients understand the wrapped content without downloading it in these cases.
+Dedicated event types may be introduced in future to cater to these situations.
+
+## Alternatives
+
+A dedicated MIME type such as `application/fhir+xml` would allow clients to recognise an uploaded
+file as FHIR ahead of the download. It would not provide clients with information about the types of
+contained resources, however. Since FHIR supports a vast number of resources it doesn't appear
+practical to introduce dedicated mimetypes per resource, version and serialisation format
+
+## Security considerations
+
+None.
+
+## Unstable prefix
+
+While this MSC is not considered stable, the event type `m.fhir.resource` should be referred to as
+`de.gematik.msc4302.fhir.resource`.
+
+## Dependencies
+
+None.
+
+  [FHIR]: https://hl7.org/fhir/
+  [`Patient`]: http://hl7.org/fhir/R4/patient.html
+  [`m.file`]: https://spec.matrix.org/v1.14/client-server-api/#mfile
+  [canonical URL]: https://build.fhir.org/references.html#canonical
+  [64 KiB event size limit]: https://spec.matrix.org/v1.14/client-server-api/#size-limits
+  [MSC3551]: https://github.com/matrix-org/matrix-spec-proposals/pull/3551
+  [`Bundle`]: http://hl7.org/fhir/StructureDefinition/Bundle