Attempts to parse the body of a Plumber req object.
Supports both req$body (already parsed) and req$bodyRaw (raw binary).
If the body looks like JSON ({...} or [...]), it tries to parse it
with jsonlite::fromJSON. Otherwise, it returns the raw text.
whapi_parse_body(req)A list representing the parsed body, or NULL if no body is found.
A Plumber request object (list-like).