feature/conn25,types/appctype: serve active Conn25 state over localapi

At /v0/conn25-state.

State includes whether the node is configured for Connectors 2025, as
well as client-specific and connector-specific state, if the node is
acting in those contexts.

Client-specific state includes the reserved Magic IPs and Transit IPs on
the client that have not been returned to their IP pools, and their
associated apps, domains, real destination IPs, and active flow counts.

We also report IP pool utilization: the number of magic and transit IPs
in use versus each pool's capacity, split by IP family.

Connector-specific state includes a peer list of clients that have
registered Transit IPs with the connector, and the apps are real
destination IPs the Transit IPs map to.

Updates tailscale/corp#40125

Signed-off-by: Michael Ben-Ami <mzb@tailscale.com>

types/appctype/appconnector.go

@@ -7,9 +7,11 @@ package appctype
 
 import (
 	"net/netip"
+	"time"
 
 	"go4.org/netipx"
 	"tailscale.com/tailcfg"
+	"tailscale.com/util/dnsname"
 )
 
 // ConfigID is an opaque identifier for a configuration.
@@ -113,3 +115,81 @@ type Conn25PoolsAttr struct {
 	V6MagicIPPool   []netipx.IPRange `json:"v6MagicIPPool,omitempty"`
 	V6TransitIPPool []netipx.IPRange `json:"v6TransitIPPool,omitempty"`
 }
+
+// Conn25ActiveState holds the active client and connector state.
+type Conn25ActiveState struct {
+	Configured bool                 `json:"configured"`
+	Client     Conn25ClientState    `json:"client,omitzero"`
+	Connector  Conn25ConnectorState `json:"connector,omitzero"`
+}
+
+// Conn25ClientState holds the active client state.
+type Conn25ClientState struct {
+	Apps        []Conn25ClientAppState  `json:"apps,omitempty"`
+	IPPoolStats Conn25ClientIPPoolStats `json:"ipPoolStats,omitzero"`
+}
+
+// Conn25ClientIPPoolStats holds the in-use and total capacity counts for the
+// client's magic and transit IP pools, split by address family. If a count
+// exceeds [math.MaxInt64], that maximum is used instead.
+type Conn25ClientIPPoolStats struct {
+	IPv4MagicIPsInUse      int64 `json:"ipv4MagicIPsInUse"`
+	IPv4MagicIPsCapacity   int64 `json:"ipv4MagicIPsCapacity"`
+	IPv6MagicIPsInUse      int64 `json:"ipv6MagicIPsInUse"`
+	IPv6MagicIPsCapacity   int64 `json:"ipv6MagicIPsCapacity"`
+	IPv4TransitIPsInUse    int64 `json:"ipv4TransitIPsInUse"`
+	IPv4TransitIPsCapacity int64 `json:"ipv4TransitIPsCapacity"`
+	IPv6TransitIPsInUse    int64 `json:"ipv6TransitIPsInUse"`
+	IPv6TransitIPsCapacity int64 `json:"ipv6TransitIPsCapacity"`
+}
+
+// Conn25ClientAppState holds the active client state for a single app,
+// grouped by domain.
+type Conn25ClientAppState struct {
+	App     string                    `json:"app,omitempty"`
+	Domains []Conn25ClientDomainState `json:"domains,omitempty"`
+}
+
+// Conn25ClientDomainState holds the address mappings the client has allocated
+// for a single domain.
+type Conn25ClientDomainState struct {
+	Domain    dnsname.FQDN               `json:"domain"`
+	Addresses []Conn25ClientAddressState `json:"addresses,omitempty"`
+}
+
+// Conn25ClientAddressState describes a single address mapping the client has
+// allocated: the destination it resolves to, the magic and transit IPs handed
+// out for it, its active flow count, and when the mapping expires.
+type Conn25ClientAddressState struct {
+	ActiveFlowCount int       `json:"activeFlowCount"`
+	DestinationIP   string    `json:"destinationIP,omitempty"`
+	MagicIP         string    `json:"magicIP,omitempty"`
+	TransitIP       string    `json:"transitIP,omitempty"`
+	ExpiresAt       time.Time `json:"expiresAt,omitzero"`
+}
+
+// Conn25ConnectorState holds the active connector state.
+type Conn25ConnectorState struct {
+	Peers []Conn25ConnectorPeerState `json:"peers,omitempty"`
+}
+
+// Conn25ConnectorPeerState holds the active connector state for a single peer
+// (client) that has registered addresses with the connector, grouped by app.
+type Conn25ConnectorPeerState struct {
+	ClientIP string                    `json:"clientIP,omitempty"`
+	Apps     []Conn25ConnectorAppState `json:"apps,omitempty"`
+}
+
+// Conn25ConnectorAppState holds the address mappings a peer has registered
+// with the connector for a single app.
+type Conn25ConnectorAppState struct {
+	App       string                        `json:"app,omitempty"`
+	Addresses []Conn25ConnectorAddressState `json:"addresses,omitempty"`
+}
+
+// Conn25ConnectorAddressState describes a single transit-to-destination IP
+// mapping the connector routes on behalf of a peer.
+type Conn25ConnectorAddressState struct {
+	DestinationIP string `json:"destinationIP,omitempty"`
+	TransitIP     string `json:"transitIP,omitempty"`
+}