tailcfg,types/netmap: expose visible services node attr

tailcfg/tailcfg.go

@@ -2694,6 +2694,14 @@ const (
 	// (replace conflicting keys).
 	NodeAttrServiceHost NodeCapability = "service-host"
 
+	// NodeAttrVisibleServiceDetails carries the full details of VIP services
+	// that are visible (accessible) to this node, including their names,
+	// assigned IP addresses, and port requirements. This is sent to consuming
+	// client nodes so they can discover services without relying solely on DNS
+	// resolution. There is exactly one value for this key in [NodeCapMap], of
+	// type []*[ServiceDetail].
+	NodeAttrVisibleServiceDetails NodeCapability = "visible-service-details"
+
 	// NodeAttrMaxKeyDuration represents the MaxKeyDuration setting on the
 	// tailnet. The value of this key in [NodeCapMap] will be only one entry of
 	// type float64 representing the duration in seconds. This cap will be
@@ -3318,6 +3326,20 @@ const LBHeader = "Ts-Lb"
 // this client is hosting can be ignored.
 type ServiceIPMappings map[ServiceName][]netip.Addr
 
+// ServiceDetail describes a VIP service visible to or hosted by a node. It is
+// used as the element type of the []*[ServiceDetail] value sent via
+// [NodeAttrVisibleServiceDetails].
+type ServiceDetail struct {
+	// Name is the name of the service, of the form "svc:dns-label".
+	Name ServiceName
+
+	// Addrs are the IP addresses (IPv4 and IPv6) assigned to this service.
+	Addrs []netip.Addr `json:",omitempty"`
+
+	// Ports are the protocol/port combinations the service accepts.
+	Ports []ProtoPortRange `json:",omitempty"`
+}
+
 // ClientAuditAction represents an auditable action that a client can report to the
 // control plane.  These actions must correspond to the supported actions
 // in the control plane.

types/netmap/netmap.go

@@ -120,6 +120,23 @@ func (nm *NetworkMap) GetVIPServiceIPMap() tailcfg.ServiceIPMappings {
 	return ipMaps[0]
 }
 
+// GetVisibleServiceDetails returns the list of VIP services that are visible
+// (accessible) to this node, including their names, IP addresses, and ports.
+// Returns nil if no visible service details are present.
+func (nm *NetworkMap) GetVisibleServiceDetails() []*tailcfg.ServiceDetail {
+	if nm == nil {
+		return nil
+	}
+	if !nm.SelfNode.Valid() {
+		return nil
+	}
+	details, err := tailcfg.UnmarshalNodeCapViewJSON[[]*tailcfg.ServiceDetail](nm.SelfNode.CapMap(), tailcfg.NodeAttrVisibleServiceDetails)
+	if len(details) != 1 || err != nil {
+		return nil
+	}
+	return details[0]
+}
+
 // GetIPVIPServiceMap returns a map of VIP addresses to the service
 // names that has the VIP address. The service names are with the
 // prefix "svc:".