tailcfg,types/netmap: add (visible) Services to SelfNode Caps (#19335)

Updates #40052

Signed-off-by: Adriano Sela Aviles <adriano@tailscale.com>

tailcfg/tailcfg.go

@@ -2447,6 +2447,18 @@ type Oauth2Token struct {
 // These are also referred to as "Node Attributes" in the ACL policy file.
 type NodeCapability string
 
+// NodeCapabilityPrefix is a prefix for [NodeCapMap] keys that share a common
+// namespace, where each entry represents a distinct named instance (e.g. one
+// per service). The full key is formed by concatenating the prefix with the
+// instance name.
+type NodeCapabilityPrefix string
+
+// ToAttribute returns the full [NodeCapability] key for the given value under
+// this prefix, of the form prefix+value.
+func (p NodeCapabilityPrefix) ToAttribute(value string) NodeCapability {
+	return NodeCapability(string(p) + value)
+}
+
 const (
 	CapabilityFileSharing        NodeCapability = "https://tailscale.com/cap/file-sharing"
 	CapabilityAdmin              NodeCapability = "https://tailscale.com/cap/is-admin"
@@ -2780,6 +2792,14 @@ const (
 	NodeAttrCacheNetworkMaps NodeCapability = "cache-network-maps"
 )
 
+const (
+	// NodeAttrPrefixServices is the prefix for per-service [NodeCapMap]
+	// entries describing Services visible (accessible) to this node. The full
+	// key for a service named "svc:foo" is NodeAttrPrefixServices+"foo".
+	// Each value under such a key is of type [ServiceDetails].
+	NodeAttrPrefixServices NodeCapabilityPrefix = "services/"
+)
+
 // SetDNSRequest is a request to add a DNS record.
 //
 // This is used to let tailscaled clients complete their ACME DNS-01 challenges
@@ -3318,6 +3338,19 @@ const LBHeader = "Ts-Lb"
 // this client is hosting can be ignored.
 type ServiceIPMappings map[ServiceName][]netip.Addr
 
+// ServiceDetails describes a Service visible to this node.
+// It is the value type stored under [NodeAttrPrefixServices]+serviceName keys in [NodeCapMap].
+type ServiceDetails 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

@@ -146,6 +146,27 @@ func (nm *NetworkMap) GetIPVIPServiceMap() IPServiceMappings {
 	return res
 }
 
+// Services returns the Services visible (accessible) to this node,
+// decoded from [tailcfg.NodeAttrPrefixServices]+serviceName entries in the
+// self node's CapMap. Returns nil if nm is nil or SelfNode is invalid.
+func (nm *NetworkMap) Services() map[tailcfg.ServiceName]tailcfg.ServiceDetails {
+	if nm == nil || !nm.SelfNode.Valid() {
+		return nil
+	}
+	result := make(map[tailcfg.ServiceName]tailcfg.ServiceDetails)
+	for cap := range nm.SelfNode.CapMap().All() {
+		if !strings.HasPrefix(string(cap), string(tailcfg.NodeAttrPrefixServices)) {
+			continue
+		}
+		svcs, err := tailcfg.UnmarshalNodeCapViewJSON[tailcfg.ServiceDetails](nm.SelfNode.CapMap(), cap)
+		if err != nil || len(svcs) < 1 {
+			continue
+		}
+		result[svcs[0].Name] = svcs[0]
+	}
+	return result
+}
+
 // SelfNodeOrZero returns the self node, or a zero value if nm is nil.
 func (nm *NetworkMap) SelfNodeOrZero() tailcfg.NodeView {
 	if nm == nil {