Fix IP deduplication and filter link interfaces in JSON

link.go

@@ -1,6 +1,9 @@
 package tendrils
 
-import "fmt"
+import (
+	"encoding/json"
+	"fmt"
+)
 
 type Link struct {
 	TypeID     string `json:"typeid"`
@@ -10,6 +13,24 @@ type Link struct {
 	InterfaceB string `json:"interface_b,omitempty"`
 }
 
+func (l *Link) MarshalJSON() ([]byte, error) {
+	type linkJSON struct {
+		TypeID     string      `json:"typeid"`
+		NodeA      interface{} `json:"node_a"`
+		InterfaceA string      `json:"interface_a,omitempty"`
+		NodeB      interface{} `json:"node_b"`
+		InterfaceB string      `json:"interface_b,omitempty"`
+	}
+
+	return json.Marshal(linkJSON{
+		TypeID:     l.TypeID,
+		NodeA:      l.NodeA.WithInterface(l.InterfaceA),
+		InterfaceA: l.InterfaceA,
+		NodeB:      l.NodeB.WithInterface(l.InterfaceB),
+		InterfaceB: l.InterfaceB,
+	})
+}
+
 func (l *Link) String() string {
 	nameA := l.NodeA.DisplayName()
 	if nameA == "" {

nodes.go

@@ -308,6 +308,10 @@ func (n *Nodes) updateNodeInterface(node *Node, nodeID int, mac net.HardwareAddr
 		}
 		iface.IPs.Add(ip)
 		n.ipIndex[ipKey] = nodeID
+
+		if ipOnlyIface, exists := node.Interfaces[ipKey]; exists && ipOnlyIface != iface {
+			delete(node.Interfaces, ipKey)
+		}
 	}
 
 	return added

types.go

@@ -130,6 +130,25 @@ type Node struct {
 	pollTrigger        chan struct{}
 }
 
+func (n *Node) WithInterface(ifaceKey string) *Node {
+	if ifaceKey == "" {
+		return n
+	}
+	iface, exists := n.Interfaces[ifaceKey]
+	if !exists {
+		return n
+	}
+	return &Node{
+		TypeID:             n.TypeID,
+		Names:              n.Names,
+		Interfaces:         InterfaceMap{ifaceKey: iface},
+		MACTableSize:       n.MACTableSize,
+		PoEBudget:          n.PoEBudget,
+		IsDanteClockMaster: n.IsDanteClockMaster,
+		DanteTxChannels:    n.DanteTxChannels,
+	}
+}
+
 func (i *Interface) String() string {
 	var parts []string
 	parts = append(parts, string(i.MAC))