wifi(linux): query associated station directly

mdlayher/wifi only dumps stations, which some full-MAC drivers (e.g.
out-of-tree Realtek USB) answer with an empty list, leaving RSSI
unavailable. Request the associated BSSID's station directly, as
`iw link` does, and parse it with native.ParseStationInfo.

agent/wifi/wifi_linux.go

@@ -3,24 +3,85 @@
 package wifi
 
 import (
-	"bytes"
 	"context"
+	"errors"
+	"net"
 	"time"
 
 	"github.com/henrygd/beszel/internal/entities/system"
+	"github.com/mdlayher/genetlink"
+	"github.com/mdlayher/netlink"
 	native "github.com/mdlayher/wifi"
+	"golang.org/x/sys/unix"
 )
 
 type linuxClient interface {
 	Interfaces() ([]*native.Interface, error)
 	BSS(*native.Interface) (*native.BSS, error)
-	StationInfo(*native.Interface) ([]*native.StationInfo, error)
+	Station(*native.Interface, net.HardwareAddr) (*native.StationInfo, error)
 	SetDeadline(time.Time) error
 	Close() error
 }
 
-func collect(ctx context.Context) map[string]system.WiFi {
+// nl80211Client adds a targeted GET_STATION request, as used by `iw link`.
+// mdlayher/wifi only dumps stations, which some full-MAC drivers (e.g.
+// out-of-tree Realtek USB) answer with an empty list.
+type nl80211Client struct {
+	*native.Client
+	conn   *genetlink.Conn
+	family genetlink.Family
+}
+
+func newNL80211Client() (*nl80211Client, error) {
 	client, err := native.New()
+	if err != nil {
+		return nil, err
+	}
+	conn, err := genetlink.Dial(nil)
+	if err != nil {
+		client.Close()
+		return nil, err
+	}
+	family, err := conn.GetFamily(unix.NL80211_GENL_NAME)
+	if err != nil {
+		conn.Close()
+		client.Close()
+		return nil, err
+	}
+	return &nl80211Client{Client: client, conn: conn, family: family}, nil
+}
+
+func (c *nl80211Client) Station(ifi *native.Interface, mac net.HardwareAddr) (*native.StationInfo, error) {
+	ae := netlink.NewAttributeEncoder()
+	ae.Uint32(unix.NL80211_ATTR_IFINDEX, uint32(ifi.Index))
+	ae.Bytes(unix.NL80211_ATTR_MAC, mac)
+	data, err := ae.Encode()
+	if err != nil {
+		return nil, err
+	}
+	msgs, err := c.conn.Execute(genetlink.Message{
+		Header: genetlink.Header{Command: unix.NL80211_CMD_GET_STATION, Version: c.family.Version},
+		Data:   data,
+	}, c.family.ID, netlink.Request)
+	if err != nil {
+		return nil, err
+	}
+	if len(msgs) == 0 {
+		return nil, errors.New("no station info")
+	}
+	return native.ParseStationInfo(msgs[0].Data)
+}
+
+func (c *nl80211Client) SetDeadline(t time.Time) error {
+	return errors.Join(c.Client.SetDeadline(t), c.conn.SetDeadline(t))
+}
+
+func (c *nl80211Client) Close() error {
+	return errors.Join(c.conn.Close(), c.Client.Close())
+}
+
+func collect(ctx context.Context) map[string]system.WiFi {
+	client, err := newNL80211Client()
 	if err != nil {
 		return nil
 	}
@@ -59,17 +120,12 @@ func collectLinux(ctx context.Context, client linuxClient) map[string]system.WiF
 		// Station statistics may require permissions unavailable in default
 		// containers. Keep association even when RSSI cannot be read. Do not
 		// substitute cached scan signal, which may be arbitrarily old.
-		stations, err := client.StationInfo(iface)
-		if err == nil {
-			for _, station := range stations {
-				if station == nil || len(bss.BSSID) == 0 || !bytes.Equal(station.HardwareAddr, bss.BSSID) {
-					continue
-				}
+		if len(bss.BSSID) > 0 {
+			if station, err := client.Station(iface, bss.BSSID); err == nil && station != nil {
 				signal := float64(station.Signal)
 				if signal >= -150 && signal < 0 {
 					reading.Signal = &signal
 				}
-				break
 			}
 		}
 		result[iface.Name] = reading

agent/wifi/wifi_linux_test.go

@@ -3,6 +3,7 @@
 package wifi
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"net"
@@ -27,9 +28,17 @@ func (f *fakeLinuxClient) Interfaces() ([]*native.Interface, error) {
 func (f *fakeLinuxClient) BSS(i *native.Interface) (*native.BSS, error) {
 	return f.bss[i.Name], f.bssErr
 }
-func (f *fakeLinuxClient) StationInfo(i *native.Interface) ([]*native.StationInfo, error) {
+func (f *fakeLinuxClient) Station(i *native.Interface, mac net.HardwareAddr) (*native.StationInfo, error) {
 	f.stationCalls++
-	return f.stations[i.Name], f.stationErr
+	if f.stationErr != nil {
+		return nil, f.stationErr
+	}
+	for _, station := range f.stations[i.Name] {
+		if bytes.Equal(station.HardwareAddr, mac) {
+			return station, nil
+		}
+	}
+	return nil, errors.New("no such station")
 }
 func (f *fakeLinuxClient) SetDeadline(d time.Time) error { f.deadline = d; return f.deadlineErr }
 func (f *fakeLinuxClient) Close() error                  { return nil }

go.mod

@@ -10,6 +10,8 @@ require (
 	github.com/fxamacker/cbor/v2 v2.9.4
 	github.com/gliderlabs/ssh v0.3.8
 	github.com/lxzan/gws v1.10.2
+	github.com/mdlayher/genetlink v1.4.0
+	github.com/mdlayher/netlink v1.11.2
 	github.com/mdlayher/wifi v0.8.0
 	github.com/nicholas-fedor/shoutrrr v0.21.0
 	github.com/opencontainers/go-digest v1.0.0
@@ -52,8 +54,6 @@ require (
 	github.com/lufia/plan9stats v0.0.0-20260802145828-341c2f0c90b5 // indirect
 	github.com/mattn/go-colorable v0.1.15 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
-	github.com/mdlayher/genetlink v1.4.0 // indirect
-	github.com/mdlayher/netlink v1.11.2 // indirect
 	github.com/mdlayher/socket v0.6.0 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/pocketbase/ozzo-validation/v4 v4.3.0 // indirect