refactor: introduce UPNode as common interface for UPF and gNB nodes

[LaumiH]

I worked on refactoring the SMF code, and this is a change I found very helpful to improve code reuse and readability.

For simpler management of UPNodes in the UserPlaneTopology, a new struct is added:

type UPNode struct {
	Name   string
	Type   UPNodeType
	ID     uuid.UUID
	NodeID pfcpType.NodeID
	Links  UPPath
}

The gNB and UPF structs "inherit" these fields using Golang's struct embedding (similar to inheritance).
The *UPNode pointer is given to the constructors of gNB and UPF structs (e.g., the NewUPF method).

E.g.,

type GNB struct {
	UPNode
	ANIP net.IP
}

and

type UPF struct {
	*UPNode
...
}

Additionally, both gNB and UPF structs implement the UPNodeInterface:

type UPNodeInterface interface {
	String() string
	GetName() string
	GetID() uuid.UUID
	GetType() UPNodeType
	GetLinks() UPPath
	AddLink(link UPNodeInterface) bool
	RemoveLink(link UPNodeInterface) bool
	GetNodeID() pfcpType.NodeID
	GetNodeIDString() string
}

This makes the UUID of each UPF a uuid.UUID instead of a string.

Now, the UPPath consists of UPNodes that implement the interface:

type UPPath []UPNodeInterface

This makes the code more concise and removes unnecessary empty fields from objects.

Additional smaller changes:

• The MatchedSelection method is moved to the upf.go file for clarity.
• Add method configToNodeIDto convert the single NodeID string from the SMF config to either IPv4, IPv6, or FQDN NodeID type.
• Use existing LinksFromConfiguration method in NewUserPlaneInformation method instead of code duplication.
• The UPF UUID is now a uuid.UUID and not a string.
• Reformat UPFSelectionParams.String() output for better readability.
• Added a bit of logging here and there, mainly traces.
• Replace every occurence of UPF.NodeID.ResolveNodeIdToIp().String() and similar with a method.

[andy89923]

Hi @LaumiH,

Do you test the functionalities with this PR? And which scenarios did you take?
I'm going to fix the linter and test this PR, and I'm wondering about the progress you made.
Thanks!

[LaumiH]

Hi @andy89923, I tested only session establishment with 1 gNB and 1 UE so far. In addition, I have tested the heartbeat procedure and UPF failure detection. I have also checked the unit tests.

Are there any test scenarios/cases that you typically do? I can help with testing.

[andy89923]

I haven't reviewed all the details, but here are some suggestions.

Also, I think we should test with ULCL scnario for more than 1 GNB and 1 UPF as UPNode in SMF.