How to register custom media handlers with only some resources?

[dkbarn]

What is the correct way to support a specific Content-Type for only a subset of resources?

Example: I have a falcon App with multiple resources/endpoints, some are GET only and return health check statuses, etc. Some of the endpoints allow GraphQL queries via POST. For these resources, I want to register a custom media handler for the "application/graphql" content type.

It seems that media handlers are assigned to the RequestOptions of the application as a whole. But it doesn't make sense for all of my endpoints to receive GraphQL queries. What is the recommended way of handling this scenario?

[vytas7]

Hi @dkbarn!
I don't think there is idiomatic support for that out of the box.

One way could be simply adding all handlers, and checking req.content_type in hooks applied only to a specific subset of resources/responders, or doing the same thing in middleware (in process_resource).

See, for instance, this type of check in our Quickstart docs (performed in middleware):

        if req.method in ('POST', 'PUT'):
            if 'application/json' not in req.content_type:
                raise falcon.HTTPUnsupportedMediaType(
                    title='This API only supports requests encoded as JSON.',
                    href='http://docs.examples.com/api/json')

Furthermore, maybe it's not a big deal to have all media handlers registered for the whole app?
When it comes to request media parsing, Falcon does nothing automagical behind your back unless you actually call req.get_media() (or reference the req.media property). So those GET health check responders shouldn't be affected in any way.

If the above doesn't fit your bill, we could file a new enhancement proposal issue.
Normally, I would think global handlers are more than enough for small and medium sized (micro)services, but if you are pooling lots of different functionality in a large Falcon app, this functionality might actually make sense.