Healthcare API (Ruby client) returning null

I'm trying to fetch a Patient from the FHIR store via the Ruby client and it always returns null.

I am successful when querying via CURL. Here is the CURL command I'm running (full path redacted):

curl -X GET \
  -H "Authorization: Bearer $(gcloud auth application-default print-access-token)" \
"https://healthcare.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/datasets/DATASET_ID/fhirStores/FHIR_STORE_ID/fhir/Patient/PATIENT_ID"

This returns the proper FHIR Patient resource.

My Ruby code looks like:

require 'google/apis/healthcare_v1'
require 'googleauth'

service = Google::Apis::HealthcareV1::CloudHealthcareService.new

scope = 'https://www.googleapis.com/auth/cloud-platform'
service.authorization = Google::Auth::ServiceAccountCredentials.make_creds(
  json_key_io: File.open('REDACTED'), 
  scope: scope
)
service.authorization.fetch_access_token!

project_id = REDACTED
location = REDACTED
dataset_id = REDACTED
fhir_store_id = REDACTED
resource_type = 'Patient'
patient_id = REDACTED

name = "projects/#{project_id}/locations/#{location}/datasets/#{dataset_id}/fhirStores/#{fhir_store_id}/fhir/Patient/#{patient_id}"
response = service.read_project_location_dataset_fhir_store_fhir(name)
puts response.to_json

I'm not getting any authentication errors. The CURL example returns the appropriate result, while the Ruby client example returns null.

Any ideas?

The Ruby library automatically tries to parse the response as JSON. Since the responses from the Healthcare API (or any FHIR server) is Content-Type: application/fhir+json, this isn't recognized by the Ruby library, and it just returns nil for the parsed response.

I got this to work by using the skip_deserialization option for the API call (docs), so instead you should try

require 'json'

name = "projects/#{project_id}/locations/#{location}/datasets/#{dataset_id}/fhirStores/#{fhir_store_id}/fhir/Patient/#{patient_id}"
response = service.read_project_location_dataset_fhir_store_fhir(name, options: {
  skip_deserialization: true,
})

patient = JSON.parse(response)

You would actually have to parse the response yourself anyways, because the Ruby response type for these calls is Google::Apis::HealthcareV1::HttpBody, which is essentially just a wrapper around a raw JSON object.