MBSF: Implement the spec-defined collection GET on all three Nmb10 resources

[davidjwbbc]

@jordijoangimenez writes:

GET on the bare /mbs-user-services, /sessions and /status-subscriptions paths (no ID) returned 400 "Invalid resource" unconditionally, even though TS 29.580 defines a real 200 (JSON array) response for all three.

[davidjwbbc]

@devbbc wrote:

@jordijoangimenez: Does the returned full collections has the resource id for each of the relevant resources returned?
This API was not implemented as we realised at that time that the three API operations were not very useful without their resource id.

Please see the standards issue 5G-MAG/Standards#191

[davidjwbbc]

We will put this implementation on hold until the Standards issue 5G-MAG/Standards#191 is resolved.