Add Starlink status lines for the physical gateway pane (closes #3)

When the non-VPN physical gateway is a Starlink dish, two lines are shown
under that pane: state, uptime, obstruction and alert count; then pop-ping
latency and drop rate with downlink/uplink throughput. They turn red when
the dish is not connected or an alert is active.

Detection is a TCP connect to the dish's fixed endpoint 192.168.100.1:9200,
bound to the physical interface the same way the latency probes bind. Until
a dish answers nothing is drawn and no status is fetched, so an absent dish
adds no noise. Status comes from the dish's local get_status gRPC call.

Detection and the fetch sit behind a small Client interface; the loop and
the pure Render function are tested with a fake, no dish and no network.

Model: opus-4-8

README.md

@@ -2,34 +2,85 @@
 
 rtnetmon is a WTFPL-licensed Go terminal (CLI/TUI) network monitor by
 [@sneak](https://sneak.berlin) that shows real-time network health, packet
-loss, and latency across two Linux network interfaces at once.
+loss, and latency across one or two network interfaces on Linux and macOS.
 
 ## Overview
 
 rtnetmon is a terminal-based network monitoring tool that provides real-time
-visibility into network health, packet loss, and latency across two network
-interfaces simultaneously. It's designed for Linux systems and uses ncurses
-for a clean, real-time dashboard interface.
+visibility into network health, packet loss, and latency across one or two
+network interfaces simultaneously. It runs on Linux and macOS and uses a
+terminal dashboard interface.
 
 ## Features
 
-- **Dual Interface Monitoring**: Monitor two network interfaces simultaneously
+- **Interface Monitoring**: Monitor one or two network interfaces simultaneously
 - **Real-time Updates**: Live dashboard with sub-second updates
 - **Comprehensive Metrics**:
-  - ICMP reachability tests
-  - Packet loss percentage
-  - TCP connection latency
-  - Interface health status
-- **Visual Indicators**: Color-coded status, spinners, and meters for quick status assessment
-  - Packet loss meter uses reverse coloring (empty/green = good, full/red = bad)
+    - ICMP reachability tests
+    - Packet loss percentage
+    - TCP connection latency
+    - Interface health status
+- **Visual Indicators**: Color-coded status, spinners, and meters for quick
+  status assessment
+    - Packet loss meter uses reverse coloring (empty/green = good, full/red =
+      bad)
 - **Detailed Logging**: Optional logging to file for debugging and analysis
 
 ## Requirements
 
-- Linux operating system
+- Linux or macOS
 - Go 1.21 or later
 - Root/sudo access (for raw ICMP packets)
 - `ping` command available in PATH
+- On Linux: `ip` (with `/proc/net/route` as a fallback)
+- On macOS: `netstat`
+
+## Platform support and interface detection
+
+rtnetmon monitors either one or two interfaces, chosen automatically for the
+platform it runs on. When only one interface is detected, the dashboard shows a
+single pane.
+
+**Linux.** The two named interfaces (`--ifaceA`/`--ifaceB`, default
+`gu0`/`backhaul0`) are used when both exist — this is the original dual-bridge
+setup, unchanged. When neither exists, the single default-route interface is
+monitored instead.
+
+**macOS.** The physical internet interface is found from the default route. When
+a VPN client is running (Mullvad and similar clients create a `utun` tunnel that
+carries a default route or holds a routable address), that tunnel is monitored
+as the primary pane alongside the physical interface. With no VPN running, only
+the physical interface is monitored. Interface names are detected on macOS; the
+`--ifaceA`/`--ifaceB` flags are not used there, but `--labelA`/`--labelB` still
+set the pane labels.
+
+### Supported matrix
+
+| OS    | Interfaces monitored                                        |
+| ----- | ----------------------------------------------------------- |
+| Linux | `gu0` + `backhaul0` when both exist (two panes)             |
+| Linux | the single default-route interface otherwise (one pane)     |
+| macOS | VPN tunnel + physical default-route interface (two panes)   |
+| macOS | the physical default-route interface with no VPN (one pane) |
+
+Anything outside this matrix — on Linux, only one of the named pair present, or
+no/multiple default routes when neither is present; on macOS, no default route
+or more than one physical default route — exits with a clear error.
+
+## Starlink status
+
+When the non-VPN physical gateway is a Starlink dish, two extra lines appear
+under that pane: dish state, uptime, obstruction and alert count on the first,
+and pop-ping latency and drop rate with downlink/uplink throughput on the
+second. They turn red when the dish is not connected or an alert is active.
+
+Detection is a TCP connect to the dish's fixed local endpoint,
+`192.168.100.1:9200`, made over the physical interface (the same binding the
+latency probes use). The dish sits behind the Starlink router, so this is not a
+gateway-address check. rtnetmon probes once a minute until a dish answers and
+then reads its status every few seconds; when no dish answers, nothing is drawn
+and no status is fetched. The status comes from the dish's local `get_status`
+gRPC call.
 
 ## Installation
 
@@ -67,11 +118,21 @@ rtnetmon/
 ├── internal/
 │   ├── cli/            # command-line interface using Cobra
 │   │   └── root.go
+│   ├── netdetect/      # per-platform interface/route detection and selection
+│   │   ├── netdetect.go     # selection logic and route parsers (pure)
+│   │   ├── routes_linux.go  # Linux default-route query (build-tagged)
+│   │   └── routes_darwin.go # macOS default-route query (build-tagged)
+│   ├── starlink/       # Starlink dish detection and status
+│   │   ├── starlink.go      # Status, Client interface, pure Render
+│   │   ├── client.go        # real gRPC client (get_status)
+│   │   └── pb/              # generated bindings for the get_status RPC
 │   └── monitor/        # core monitoring functionality
-│       ├── monitor.go  # monitor types, probes, logging
-│       ├── loops.go    # monitoring loops (reachability, loss, TCP)
-│       ├── styles.go   # terminal color styles
-│       └── ui.go       # user interface rendering
+│       ├── monitor.go       # monitor types, probes, logging
+│       ├── loops.go         # monitoring loops (reachability, loss, TCP)
+│       ├── styles.go        # terminal color styles
+│       ├── ui.go            # user interface rendering
+│       ├── dial_linux.go    # TCP source binding (build-tagged)
+│       └── dial_darwin.go   # TCP IP_BOUND_IF binding (build-tagged)
 ├── script/             # Scripts to Rule Them All entrypoints
 ├── .gitea/workflows/   # CI (runs script/cibuild)
 ├── Dockerfile          # lint + test gate phases and the build
@@ -84,15 +145,20 @@ rtnetmon/
 ## Development
 
 ```bash
+make check       # run test, lint, and fmt-check (the default target)
 make build       # build ./bin/rtnetmon
-make check       # run tests, lint, and fmt-check (the default target)
+make run         # build, then run ./bin/rtnetmon locally
+make dev         # go run ./cmd/rtnetmon
 make test        # run the test suite (test phase of the Dockerfile)
 make lint        # run golangci-lint (lint phase of the Dockerfile)
 make fmt         # format Go code (writes)
 make fmt-check   # verify formatting (read-only)
+make deps        # go mod download + go mod tidy
 make docker      # build the Docker image
+make cibuild     # bootstrap, check, and build the image (run by CI)
+make bootstrap   # install dependencies idempotently (git, make, go)
+make setup       # bootstrap plus install the git pre-commit hook
 make hooks       # install the git pre-commit hook
-make dev         # go run ./cmd/rtnetmon
 make clean       # remove build artifacts
 ```
 
@@ -128,8 +194,11 @@ The monitor package provides an object-oriented API for programmatic use:
 ```go
 import "git.eeqj.de/sneak/rtnetmon/internal/monitor"
 
-// Create a new monitor
-mon := monitor.NewMonitor("eth0", "Primary", "wlan0", "Backup", "/tmp/monitor.log")
+// Create a new monitor for one or two interfaces
+mon := monitor.NewMonitor([]monitor.IfaceSpec{
+    {Name: "eth0", Label: "Primary"},
+    {Name: "wlan0", Label: "Backup"},
+}, "/tmp/monitor.log")
 
 // Configure timing parameters (optional - defaults are sensible)
 mon.ICMPTimeout = 1 * time.Second

cmd/rtnetmon/main.go

@@ -1,7 +1,5 @@
-//go:build linux
-
-// Command rtnetmon is a dual-interface real-time network monitoring
-// dashboard for Linux. WTFPL, sneak@sneak.berlin.
+// Command rtnetmon is a real-time network monitoring dashboard for Linux
+// and macOS. WTFPL, sneak@sneak.berlin.
 package main
 
 import (

go.mod

@@ -6,6 +6,9 @@ require (
 	github.com/gdamore/tcell/v2 v2.8.1
 	github.com/spf13/cobra v1.8.0
 	github.com/spf13/viper v1.18.2
+	golang.org/x/sys v0.29.0
+	google.golang.org/grpc v1.67.1
+	google.golang.org/protobuf v1.36.6
 )
 
 require (
@@ -29,9 +32,10 @@ require (
 	go.uber.org/atomic v1.9.0 // indirect
 	go.uber.org/multierr v1.9.0 // indirect
 	golang.org/x/exp v0.0.0-20230905200255-921286631fa9 // indirect
-	golang.org/x/sys v0.29.0 // indirect
+	golang.org/x/net v0.28.0 // indirect
 	golang.org/x/term v0.28.0 // indirect
 	golang.org/x/text v0.21.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -91,6 +91,8 @@ golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
 golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
 golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
 golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
+golang.org/x/net v0.28.0 h1:a9JDOJc5GMUJ0+UDqmLT86WiEy7iWyIhz8gz8E4e5hE=
+golang.org/x/net v0.28.0/go.mod h1:yqtgsTWOOnlGLG9GFRrK3++bGOUEkNBoHZc8MEDWPNg=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -137,6 +139,12 @@ golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
 golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58=
 golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142 h1:e7S5W7MGGLaSu8j3YjdezkZ+m1/Nm0uRVRMEMGk26Xs=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20240814211410-ddb44dafa142/go.mod h1:UqMtugtsSgubUsoxbuAoiCXvqvErP7Gf0so0mK9tHxU=
+google.golang.org/grpc v1.67.1 h1:zWnc1Vrcno+lHZCOofnIMvycFcc0QRGIzm9dhnDX68E=
+google.golang.org/grpc v1.67.1/go.mod h1:1gLDyUQU7CTLJI90u3nXZ9ekeghjeM7pTDZlqFNg2AA=
+google.golang.org/protobuf v1.36.6 h1:z1NpPI8ku2WgiWnf+t9wTPsn6eP1L7ksHUlkfLvd9xY=
+google.golang.org/protobuf v1.36.6/go.mod h1:jduwjTPXsFjZGTmRluh+L6NjiWu7pchiJ2/5YcXBHnY=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

internal/cli/export_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package cli
 
 import "github.com/spf13/cobra"

internal/cli/root.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 // Package cli wires command-line flags to the network monitor and runs it.
 package cli
 
@@ -7,12 +5,14 @@ import (
 	"context"
 	"os"
 	"os/signal"
+	"runtime"
 	"syscall"
 
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 
 	"git.eeqj.de/sneak/rtnetmon/internal/monitor"
+	"git.eeqj.de/sneak/rtnetmon/internal/netdetect"
 )
 
 // config holds the application configuration.
@@ -59,8 +59,8 @@ func newRootCmd() *cobra.Command {
 		Short: "Real-time network monitoring dashboard",
 		Long: `rtnetmon is a dual-interface network monitoring dashboard that provides
 real-time visibility into network health, packet loss, and latency.`,
-		RunE: func(_ *cobra.Command, _ []string) error {
-			return runMonitor(cfg)
+		RunE: func(cmd *cobra.Command, _ []string) error {
+			return runMonitor(cmd, cfg)
 		},
 	}
 	registerFlags(cmd, cfg)
@@ -86,14 +86,22 @@ func registerFlags(cmd *cobra.Command, cfg *config) {
 	}
 }
 
-// runMonitor constructs and runs the monitor from cfg.
-func runMonitor(cfg *config) error {
+// runMonitor detects the interfaces to monitor, then constructs and runs the
+// monitor from cfg.
+func runMonitor(cmd *cobra.Command, cfg *config) error {
 	monitor.Logf(cfg.LogFile, "Starting rtnetmon")
-	monitor.Logf(cfg.LogFile, "Monitoring interfaces %s and %s",
-		cfg.IfaceA, cfg.IfaceB)
 
-	mon := monitor.NewMonitor(cfg.IfaceA, cfg.LabelA, cfg.IfaceB, cfg.LabelB,
-		cfg.LogFile)
+	specs, err := detectInterfaces(cmd, cfg)
+	if err != nil {
+		return err
+	}
+
+	mon := monitor.NewMonitor(specs, cfg.LogFile)
+
+	// The non-VPN physical gateway is the last pane: pane B when there are
+	// two, the only pane when there is one. That is where a Starlink dish,
+	// if present upstream, is detected and its status shown.
+	mon.EnableStarlink(specs[len(specs)-1].Name)
 
 	for _, host := range cfg.Hosts {
 		mon.AddReachabilityHost(host)
@@ -122,6 +130,45 @@ func runMonitor(cfg *config) error {
 	return mon.Run(ctx)
 }
 
+// detectInterfaces enumerates the host, reads its default routes, and applies
+// the platform selection rules to decide which interfaces to monitor.
+func detectInterfaces(
+	cmd *cobra.Command, cfg *config,
+) ([]monitor.IfaceSpec, error) {
+	ifaces, err := netdetect.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	routes, err := netdetect.DefaultRoutes()
+	if err != nil {
+		return nil, err
+	}
+
+	flags := netdetect.Flags{
+		IfaceA:    cfg.IfaceA,
+		LabelA:    cfg.LabelA,
+		IfaceB:    cfg.IfaceB,
+		LabelB:    cfg.LabelB,
+		LabelASet: cmd.Flags().Changed("labelA"),
+		LabelBSet: cmd.Flags().Changed("labelB"),
+	}
+
+	panes, err := netdetect.Select(runtime.GOOS, ifaces, routes, flags)
+	if err != nil {
+		return nil, err
+	}
+
+	specs := make([]monitor.IfaceSpec, len(panes))
+	for i, p := range panes {
+		specs[i] = monitor.IfaceSpec{Name: p.Name, Label: p.Label}
+	}
+
+	monitor.Logf(cfg.LogFile, "Monitoring %d interface(s)", len(specs))
+
+	return specs, nil
+}
+
 // Execute builds the root command and runs it.
 func Execute() error {
 	return newRootCmd().Execute()

internal/cli/root_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package cli_test
 
 import (

internal/monitor/dial_darwin.go

@@ -0,0 +1,36 @@
+//go:build darwin
+
+package monitor
+
+import (
+	"net"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+// bindControl returns a socket control hook that pins the connection to the
+// given interface with IP_BOUND_IF. On macOS a bound source address is not
+// enough: without this the kernel still routes the packets over the VPN's
+// default route, so traffic would not leave the interface we are measuring.
+func bindControl(iface string) func(network, address string, c syscall.RawConn) error {
+	ifi, err := net.InterfaceByName(iface)
+	if err != nil {
+		return nil
+	}
+
+	idx := ifi.Index
+
+	return func(_, _ string, c syscall.RawConn) error {
+		var setErr error
+
+		ctrlErr := c.Control(func(fd uintptr) {
+			setErr = unix.SetsockoptInt(int(fd), unix.IPPROTO_IP, unix.IP_BOUND_IF, idx)
+		})
+		if ctrlErr != nil {
+			return ctrlErr
+		}
+
+		return setErr
+	}
+}

internal/monitor/dial_linux.go

@@ -0,0 +1,12 @@
+//go:build linux
+
+package monitor
+
+import "syscall"
+
+// bindControl returns no socket control hook on Linux: binding the dialer's
+// local source address (as tcpDuration already does) is enough to send
+// traffic out of the chosen interface.
+func bindControl(_ string) func(network, address string, c syscall.RawConn) error {
+	return nil
+}

internal/monitor/export_test.go

@@ -1,9 +1,52 @@
-//go:build linux
-
 package monitor
 
+import (
+	"context"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/starlink"
+)
+
 // Test-only accessors exposing unexported state for white-box assertions.
 
+// SetStarlinkClient injects a Starlink client for iface, bypassing the real
+// gRPC dialer so the loop can be driven with a fake.
+func (m *Monitor) SetStarlinkClient(iface string, c starlink.Client) {
+	for _, st := range m.interfaces {
+		if st.Name == iface {
+			m.slPane = st
+			m.slState = &starlinkState{}
+			m.slClient = c
+
+			return
+		}
+	}
+}
+
+// StarlinkEnabled reports whether a Starlink client is configured.
+func (m *Monitor) StarlinkEnabled() bool { return m.slClient != nil }
+
+// StarlinkPaneName returns the name of the pane the Starlink lines attach
+// to, or "" if none.
+func (m *Monitor) StarlinkPaneName() string {
+	if m.slPane == nil {
+		return ""
+	}
+
+	return m.slPane.Name
+}
+
+// StarlinkProbeStep runs one detection step.
+func (m *Monitor) StarlinkProbeStep(ctx context.Context) { m.starlinkProbe(ctx) }
+
+// StarlinkRefreshStep runs one status-refresh step.
+func (m *Monitor) StarlinkRefreshStep(ctx context.Context) { m.starlinkRefresh(ctx) }
+
+// StarlinkSnapshot returns the current Starlink display state: detected,
+// have-status, and the latest status.
+func (m *Monitor) StarlinkSnapshot() (bool, bool, starlink.Status) {
+	return m.slState.snapshot()
+}
+
 // ReachabilityHosts returns the configured reachability hosts.
 func (m *Monitor) ReachabilityHosts() []string { return m.reachabilityHosts }
 
@@ -13,8 +56,13 @@ func (m *Monitor) PacketLossHosts() []string { return m.packetLossHosts }
 // TCPHosts returns the configured TCP hosts.
 func (m *Monitor) TCPHosts() []string { return m.tcpHosts }
 
-// InterfaceA returns the first monitored interface.
-func (m *Monitor) InterfaceA() *InterfaceStatus { return m.interfaceA }
+// Interfaces returns the monitored interfaces.
+func (m *Monitor) Interfaces() []*InterfaceStatus { return m.interfaces }
 
-// InterfaceB returns the second monitored interface.
-func (m *Monitor) InterfaceB() *InterfaceStatus { return m.interfaceB }
+// PingArgs exposes pingArgs for external tests.
+func PingArgs(goos, iface, host string) []string { return pingArgs(goos, iface, host) }
+
+// LossArgs exposes lossArgs for external tests.
+func LossArgs(goos, iface, host string, count int) []string {
+	return lossArgs(goos, iface, host, count)
+}

internal/monitor/loops.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package monitor
 
 import (

internal/monitor/monitor.go

@@ -1,8 +1,6 @@
-//go:build linux
-
-// Package monitor implements the dual-interface real-time network
-// monitoring dashboard: ICMP reachability, packet loss, TCP latency, and
-// the terminal UI that renders them.
+// Package monitor implements the real-time network monitoring dashboard:
+// ICMP reachability, packet loss, TCP latency, and the terminal UI that
+// renders them. It monitors one or two interfaces.
 package monitor
 
 import (
@@ -14,12 +12,15 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
 	"time"
 
 	tcell "github.com/gdamore/tcell/v2"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/starlink"
 )
 
 // Meter glyphs used to render the ASCII loss meter.
@@ -57,7 +58,7 @@ const (
 	ipInfoTimeout    = 2 * time.Second
 	lossQueryTimeout = 3 * time.Second
 	uiUpdateBuffer   = 100
-	logFileMode      = 0o600
+	logFileMode      = 0o644
 )
 
 // errNoIPv4 is returned when an interface has no usable IPv4 address.
@@ -88,9 +89,14 @@ type Monitor struct {
 	packetLossHosts   []string
 	tcpHosts          []string
 
-	// Interfaces
-	interfaceA *InterfaceStatus
-	interfaceB *InterfaceStatus
+	// Interfaces to monitor (one or two)
+	interfaces []*InterfaceStatus
+
+	// Starlink status for the physical (non-VPN gateway) pane. All three
+	// are nil unless EnableStarlink was called for a monitored interface.
+	slClient starlink.Client
+	slState  *starlinkState
+	slPane   *InterfaceStatus
 
 	// Logging
 	logFile string
@@ -104,9 +110,16 @@ type Monitor struct {
 	mu sync.RWMutex
 }
 
-// NewMonitor creates a new Monitor instance with default settings.
-func NewMonitor(ifaceA, labelA, ifaceB, labelB, logFile string) *Monitor {
-	return &Monitor{
+// IfaceSpec names one interface to monitor and its display label.
+type IfaceSpec struct {
+	Name  string
+	Label string
+}
+
+// NewMonitor creates a new Monitor instance with default settings,
+// monitoring the given interfaces (one or two).
+func NewMonitor(ifaces []IfaceSpec, logFile string) *Monitor {
+	m := &Monitor{
 		ICMPTimeout:      defaultICMPTimeout,
 		TCPTimeout:       defaultTCPTimeout,
 		PacketLossPings:  defaultPacketLossPings,
@@ -127,13 +140,16 @@ func NewMonitor(ifaceA, labelA, ifaceB, labelB, logFile string) *Monitor {
 		packetLossHosts:   []string{},
 		tcpHosts:          []string{},
 
-		interfaceA: NewInterfaceStatus(ifaceA, labelA),
-		interfaceB: NewInterfaceStatus(ifaceB, labelB),
-
 		logFile:   logFile,
 		startTime: time.Now(),
 		uiUpdate:  make(chan struct{}, uiUpdateBuffer),
 	}
+
+	for _, spec := range ifaces {
+		m.interfaces = append(m.interfaces, NewInterfaceStatus(spec.Name, spec.Label))
+	}
+
+	return m
 }
 
 // AddReachabilityHost adds a host for reachability monitoring.
@@ -194,12 +210,13 @@ func (m *Monitor) Run(ctx context.Context) error {
 	tcpHosts := append([]string{}, m.tcpHosts...)
 	m.mu.RUnlock()
 
-	go m.reachLoop(ctx, m.interfaceA, reachHosts)
-	go m.reachLoop(ctx, m.interfaceB, reachHosts)
-	go m.lossLoop(ctx, m.interfaceA, lossHosts)
-	go m.lossLoop(ctx, m.interfaceB, lossHosts)
-	go m.tcpLoop(ctx, m.interfaceA, tcpHosts)
-	go m.tcpLoop(ctx, m.interfaceB, tcpHosts)
+	for _, st := range m.interfaces {
+		go m.reachLoop(ctx, st, reachHosts)
+		go m.lossLoop(ctx, st, lossHosts)
+		go m.tcpLoop(ctx, st, tcpHosts)
+	}
+
+	go m.starlinkLoop(ctx)
 
 	m.logf("Starting UI loop")
 	m.uiLoop(ctx)
@@ -306,13 +323,36 @@ func fetchIPInfo(iface string) string {
 	return fmt.Sprintf("%s [%s] %s", r.IP, r.Hostname, r.Org)
 }
 
+// pingArgs builds the arguments for a single reachability ping on the given
+// OS. Linux binds the interface with -I and takes -W in seconds; macOS binds
+// with -b and takes -W in milliseconds.
+func pingArgs(goos, iface, host string) []string {
+	if goos == "darwin" {
+		return []string{"-b", iface, "-c1", "-W1000", host}
+	}
+
+	return []string{"-I", iface, "-c1", "-W1", host}
+}
+
+// lossArgs builds the arguments for a packet-loss ping burst of count pings.
+func lossArgs(goos, iface, host string, count int) []string {
+	c := strconv.Itoa(count)
+	if goos == "darwin" {
+		return []string{"-q", "-i", "0.05", "-c", c, "-W1000", "-b", iface, host}
+	}
+
+	return []string{"-q", "-i", "0.05", "-c", c, "-W1", "-I", iface, host}
+}
+
 // pingOnce performs a single ping over the named interface.
 func (m *Monitor) pingOnce(ctx context.Context, iface, host string) bool {
 	ctx, cancel := context.WithTimeout(ctx, m.ICMPTimeout)
 	defer cancel()
 
+	args := pingArgs(runtime.GOOS, iface, host)
+
 	cmd := exec.CommandContext( //nolint:gosec // G204: fixed argv, operator CLI input
-		ctx, "ping", "-I", iface, "-c1", "-W1", host)
+		ctx, "ping", args...)
 
 	return cmd.Run() == nil
 }
@@ -322,9 +362,10 @@ func (m *Monitor) lossPercent(ctx context.Context, iface, host string) float64 {
 	ctx, cancel := context.WithTimeout(ctx, lossQueryTimeout)
 	defer cancel()
 
+	args := lossArgs(runtime.GOOS, iface, host, m.PacketLossPings)
+
 	cmd := exec.CommandContext( //nolint:gosec // G204: fixed argv, operator CLI input
-		ctx, "ping", "-q", "-i", "0.05",
-		"-c", strconv.Itoa(m.PacketLossPings), "-W1", "-I", iface, host)
+		ctx, "ping", args...)
 
 	out, err := cmd.CombinedOutput()
 	if err != nil {
@@ -375,7 +416,7 @@ func (m *Monitor) tcpDuration(iface, hp string) time.Duration {
 		return m.TCPTimeout
 	}
 
-	d := net.Dialer{Timeout: m.TCPTimeout, LocalAddr: la}
+	d := net.Dialer{Timeout: m.TCPTimeout, LocalAddr: la, Control: bindControl(iface)}
 	st := time.Now()
 
 	c, err := d.Dial("tcp", hp)

internal/monitor/monitor_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package monitor_test
 
 import (
@@ -8,26 +6,33 @@ import (
 	"git.eeqj.de/sneak/rtnetmon/internal/monitor"
 )
 
+// Interface names and hosts reused across the monitor package tests.
+const (
+	ifaceTest0 = "test0"
+	ifaceTest1 = "test1"
+	ifaceEth0  = "eth0"
+	host8888   = "8.8.8.8"
+)
+
 func TestNewMonitor(t *testing.T) {
 	t.Parallel()
 
-	mon := monitor.NewMonitor("test0", "Test Interface A", "test1",
-		"Test Interface B", "/tmp/test.log")
+	mon := monitor.NewMonitor([]monitor.IfaceSpec{
+		{Name: ifaceTest0, Label: "Test Interface A"},
+		{Name: ifaceTest1, Label: "Test Interface B"},
+	}, "/tmp/test.log")
 
-	if mon.InterfaceA() == nil {
-		t.Fatal("interfaceA is nil")
+	ifaces := mon.Interfaces()
+	if len(ifaces) != 2 {
+		t.Fatalf("interfaces = %d, want 2", len(ifaces))
 	}
 
-	if mon.InterfaceB() == nil {
-		t.Fatal("interfaceB is nil")
+	if ifaces[0].Name != ifaceTest0 {
+		t.Errorf("interfaces[0].Name = %q, want %q", ifaces[0].Name, ifaceTest0)
 	}
 
-	if mon.InterfaceA().Name != "test0" {
-		t.Errorf("interfaceA.Name = %q, want %q", mon.InterfaceA().Name, "test0")
-	}
-
-	if mon.InterfaceB().Name != "test1" {
-		t.Errorf("interfaceB.Name = %q, want %q", mon.InterfaceB().Name, "test1")
+	if ifaces[1].Name != ifaceTest1 {
+		t.Errorf("interfaces[1].Name = %q, want %q", ifaces[1].Name, ifaceTest1)
 	}
 
 	if mon.ICMPTimeout.Milliseconds() != 500 {
@@ -51,12 +56,31 @@ func TestNewMonitor(t *testing.T) {
 	}
 }
 
+func TestNewMonitorSingle(t *testing.T) {
+	t.Parallel()
+
+	mon := monitor.NewMonitor(
+		[]monitor.IfaceSpec{{Name: ifaceEth0, Label: "default route"}}, "")
+
+	ifaces := mon.Interfaces()
+	if len(ifaces) != 1 {
+		t.Fatalf("interfaces = %d, want 1", len(ifaces))
+	}
+
+	if ifaces[0].Name != ifaceEth0 {
+		t.Errorf("interfaces[0].Name = %q, want %q", ifaces[0].Name, ifaceEth0)
+	}
+}
+
 func TestAddHosts(t *testing.T) {
 	t.Parallel()
 
-	mon := monitor.NewMonitor("test0", "Test A", "test1", "Test B", "")
+	mon := monitor.NewMonitor([]monitor.IfaceSpec{
+		{Name: ifaceTest0, Label: "Test A"},
+		{Name: ifaceTest1, Label: "Test B"},
+	}, "")
 
-	mon.AddReachabilityHost("8.8.8.8")
+	mon.AddReachabilityHost(host8888)
 	mon.AddReachabilityHost("google.com")
 
 	if len(mon.ReachabilityHosts()) != 2 {

internal/monitor/ping_test.go

@@ -0,0 +1,58 @@
+package monitor_test
+
+import (
+	"reflect"
+	"testing"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/monitor"
+)
+
+func TestPingArgs(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		goos string
+		want []string
+	}{
+		{"linux", []string{"-I", ifaceEth0, "-c1", "-W1", host8888}},
+		{"darwin", []string{"-b", ifaceEth0, "-c1", "-W1000", host8888}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.goos, func(t *testing.T) {
+			t.Parallel()
+
+			got := monitor.PingArgs(tt.goos, ifaceEth0, host8888)
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("PingArgs(%q) = %v, want %v", tt.goos, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestLossArgs(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		goos string
+		want []string
+	}{
+		{"linux", []string{
+			"-q", "-i", "0.05", "-c", "20", "-W1", "-I", ifaceEth0, host8888,
+		}},
+		{"darwin", []string{
+			"-q", "-i", "0.05", "-c", "20", "-W1000", "-b", ifaceEth0, host8888,
+		}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.goos, func(t *testing.T) {
+			t.Parallel()
+
+			got := monitor.LossArgs(tt.goos, ifaceEth0, host8888, 20)
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("LossArgs(%q) = %v, want %v", tt.goos, got, tt.want)
+			}
+		})
+	}
+}

internal/monitor/starlink.go

@@ -0,0 +1,166 @@
+package monitor
+
+import (
+	"context"
+	"net"
+	"sync"
+	"time"
+
+	tcell "github.com/gdamore/tcell/v2"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/starlink"
+)
+
+// Starlink probe and status cadence: detect once a minute until a dish
+// answers, then refresh the status every few seconds.
+const (
+	starlinkProbePeriod  = time.Minute
+	starlinkStatusPeriod = 5 * time.Second
+)
+
+// starlinkState holds the latest dish status for the physical pane. Nothing
+// is drawn until a dish first answers, so an absent dish adds no lines.
+type starlinkState struct {
+	mu         sync.RWMutex
+	detected   bool
+	haveStatus bool
+	status     starlink.Status
+}
+
+// snapshot returns whether a dish was detected, whether a status has been
+// read, and the latest status, all under the read lock.
+func (s *starlinkState) snapshot() (bool, bool, starlink.Status) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	return s.detected, s.haveStatus, s.status
+}
+
+// EnableStarlink turns on Starlink detection for the named interface, which
+// must be the non-VPN physical gateway pane. It is a no-op if no monitored
+// interface has that name.
+func (m *Monitor) EnableStarlink(iface string) {
+	for _, st := range m.interfaces {
+		if st.Name == iface {
+			m.slPane = st
+			m.slState = &starlinkState{}
+			m.slClient = starlink.NewClient(m.starlinkDialer(iface))
+
+			return
+		}
+	}
+}
+
+// starlinkDialer returns a dialer that binds to iface exactly as the TCP
+// latency probes do, so the dish is reached over the physical interface.
+func (m *Monitor) starlinkDialer(iface string) starlink.DialFunc {
+	return func(ctx context.Context, addr string) (net.Conn, error) {
+		la, err := localAddr(iface)
+		if err != nil {
+			return nil, err
+		}
+
+		d := net.Dialer{LocalAddr: la, Control: bindControl(iface)}
+
+		return d.DialContext(ctx, "tcp", addr)
+	}
+}
+
+// starlinkLoop probes for a dish and refreshes its status until the context
+// is cancelled. It does nothing when Starlink was not enabled.
+func (m *Monitor) starlinkLoop(ctx context.Context) {
+	if m.slClient == nil {
+		return
+	}
+
+	m.logf("Starting Starlink monitoring for %s", m.slPane.Name)
+	m.starlinkProbe(ctx)
+
+	probe := time.NewTicker(starlinkProbePeriod)
+	status := time.NewTicker(starlinkStatusPeriod)
+
+	defer probe.Stop()
+	defer status.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			m.logf("Stopping Starlink monitoring for %s", m.slPane.Name)
+
+			return
+		case <-probe.C:
+			m.starlinkProbe(ctx)
+		case <-status.C:
+			m.starlinkRefresh(ctx)
+		}
+	}
+}
+
+// starlinkProbe detects the dish; once detected it stays detected, and a
+// first status is fetched immediately.
+func (m *Monitor) starlinkProbe(ctx context.Context) {
+	if detected, _, _ := m.slState.snapshot(); detected {
+		return
+	}
+
+	if !m.slClient.Probe(ctx) {
+		return
+	}
+
+	m.slState.mu.Lock()
+	m.slState.detected = true
+	m.slState.mu.Unlock()
+
+	m.notifyUI()
+	m.starlinkRefresh(ctx)
+}
+
+// starlinkRefresh fetches status only once a dish has been detected, so an
+// absent dish produces no status traffic.
+func (m *Monitor) starlinkRefresh(ctx context.Context) {
+	if detected, _, _ := m.slState.snapshot(); !detected {
+		return
+	}
+
+	st, err := m.slClient.Status(ctx)
+	if err != nil {
+		m.logf("Starlink status error: %v", err)
+
+		return
+	}
+
+	m.slState.mu.Lock()
+	m.slState.status = st
+	m.slState.haveStatus = true
+	m.slState.mu.Unlock()
+
+	m.notifyUI()
+}
+
+// drawStarlink draws the two dish status lines under the physical pane. It
+// draws nothing until a dish has answered.
+func (m *Monitor) drawStarlink(scr tcell.Screen, y int) int {
+	detected, haveStatus, st := m.slState.snapshot()
+	if !detected {
+		return y
+	}
+
+	if !haveStatus {
+		Put(scr, colLeft, y, "Starlink: detected, status unavailable", styleBrightRed())
+
+		return y + lineStep
+	}
+
+	line1, line2, alert := starlink.Render(st)
+
+	style := tcell.StyleDefault
+	if alert {
+		style = styleBrightRed()
+	}
+
+	Put(scr, colLeft, y, line1, style)
+	y += lineStep
+	Put(scr, colLeft, y, line2, style)
+
+	return y + lineStep
+}

internal/monitor/starlink_test.go

@@ -0,0 +1,141 @@
+package monitor_test
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/monitor"
+	"git.eeqj.de/sneak/rtnetmon/internal/starlink"
+)
+
+// fakeDish is a Starlink client for tests: no dish, no network. It records
+// how often each method is called and returns programmed results.
+type fakeDish struct {
+	mu          sync.Mutex
+	probeOK     bool
+	status      starlink.Status
+	statusErr   error
+	probeCalls  int
+	statusCalls int
+}
+
+func (f *fakeDish) Probe(_ context.Context) bool {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	f.probeCalls++
+
+	return f.probeOK
+}
+
+func (f *fakeDish) Status(_ context.Context) (starlink.Status, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	f.statusCalls++
+
+	return f.status, f.statusErr
+}
+
+func (f *fakeDish) counts() (int, int) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	return f.probeCalls, f.statusCalls
+}
+
+func newTwoPaneMonitor() *monitor.Monitor {
+	return monitor.NewMonitor([]monitor.IfaceSpec{
+		{Name: ifaceTest0, Label: "A"},
+		{Name: ifaceTest1, Label: "B"},
+	}, "")
+}
+
+func TestEnableStarlinkSelectsPane(t *testing.T) {
+	t.Parallel()
+
+	mon := newTwoPaneMonitor()
+	mon.EnableStarlink(ifaceTest1)
+
+	if !mon.StarlinkEnabled() {
+		t.Fatal("StarlinkEnabled = false, want true")
+	}
+
+	if got := mon.StarlinkPaneName(); got != ifaceTest1 {
+		t.Errorf("StarlinkPaneName = %q, want %q", got, ifaceTest1)
+	}
+}
+
+func TestEnableStarlinkUnknownInterface(t *testing.T) {
+	t.Parallel()
+
+	mon := newTwoPaneMonitor()
+	mon.EnableStarlink("does-not-exist")
+
+	if mon.StarlinkEnabled() {
+		t.Error("StarlinkEnabled = true for an unknown interface, want false")
+	}
+}
+
+// TestStarlinkNoDishNoStatus verifies that when no dish answers, no status
+// is ever fetched and nothing is marked detected.
+func TestStarlinkNoDishNoStatus(t *testing.T) {
+	t.Parallel()
+
+	mon := newTwoPaneMonitor()
+	fake := &fakeDish{probeOK: false}
+	mon.SetStarlinkClient(ifaceTest1, fake)
+
+	ctx := context.Background()
+	mon.StarlinkProbeStep(ctx)
+	mon.StarlinkRefreshStep(ctx)
+
+	detected, haveStatus, _ := mon.StarlinkSnapshot()
+	if detected || haveStatus {
+		t.Errorf("detected=%v haveStatus=%v, want both false", detected, haveStatus)
+	}
+
+	if _, status := fake.counts(); status != 0 {
+		t.Errorf("status calls = %d, want 0 (no probing noise)", status)
+	}
+}
+
+// TestStarlinkDetectedFetchesStatus verifies that once a dish answers,
+// detection triggers a status fetch and later refreshes fetch again.
+func TestStarlinkDetectedFetchesStatus(t *testing.T) {
+	t.Parallel()
+
+	mon := newTwoPaneMonitor()
+	want := starlink.Status{
+		State:        "CONNECTED",
+		Uptime:       2 * time.Hour,
+		DownlinkMbps: 100,
+	}
+	fake := &fakeDish{probeOK: true, status: want}
+	mon.SetStarlinkClient(ifaceTest1, fake)
+
+	ctx := context.Background()
+	mon.StarlinkProbeStep(ctx)
+
+	detected, haveStatus, got := mon.StarlinkSnapshot()
+	if !detected || !haveStatus {
+		t.Fatalf("detected=%v haveStatus=%v, want both true", detected, haveStatus)
+	}
+
+	if got != want {
+		t.Errorf("status = %+v, want %+v", got, want)
+	}
+
+	mon.StarlinkRefreshStep(ctx)
+
+	probe, status := fake.counts()
+	if probe != 1 {
+		t.Errorf("probe calls = %d, want 1", probe)
+	}
+
+	if status != 2 {
+		t.Errorf("status calls = %d, want 2", status)
+	}
+}

internal/monitor/styles.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package monitor
 
 import tcell "github.com/gdamore/tcell/v2"

internal/monitor/styles_test.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package monitor_test
 
 import (

internal/monitor/ui.go

@@ -1,5 +1,3 @@
-//go:build linux
-
 package monitor
 
 import (
@@ -109,6 +107,11 @@ func (m *Monitor) DrawInterface(scr tcell.Screen, y, w int, st *InterfaceStatus)
 	y = m.drawTCPTable(scr, y, st, tcpHosts)
 	y = drawICMPStats(scr, y, st)
 
+	// The Starlink lines belong to the physical (non-VPN gateway) pane only.
+	if st == m.slPane {
+		y = m.drawStarlink(scr, y)
+	}
+
 	return y
 }
 
@@ -383,9 +386,11 @@ func (m *Monitor) uiLoop(ctx context.Context) {
 		runtime := time.Since(m.startTime).Round(time.Second).String()
 		Put(m.screen, colLeft, rowRuntime, "Runtime: "+runtime, tcell.StyleDefault)
 
+		// Draw one pane per interface; a single interface draws one pane.
 		y := rowFirstIface
-		y = m.DrawInterface(m.screen, y, w, m.interfaceA)
-		_ = m.DrawInterface(m.screen, y, w, m.interfaceB)
+		for _, st := range m.interfaces {
+			y = m.DrawInterface(m.screen, y, w, st)
+		}
 
 		m.screen.Show()
 	}

internal/netdetect/export_test.go

@@ -0,0 +1,12 @@
+package netdetect
+
+// Test-only accessors exposing the unexported route parsers.
+
+// ParseIPRoute exposes parseIPRoute for external tests.
+func ParseIPRoute(out string) []Route { return parseIPRoute(out) }
+
+// ParseProcNetRoute exposes parseProcNetRoute for external tests.
+func ParseProcNetRoute(out string) []Route { return parseProcNetRoute(out) }
+
+// ParseNetstat exposes parseNetstat for external tests.
+func ParseNetstat(out string) []Route { return parseNetstat(out) }

internal/netdetect/netdetect.go

@@ -0,0 +1,375 @@
+// Package netdetect chooses which network interfaces rtnetmon should monitor.
+//
+// The host-specific queries (enumerating interfaces, reading the routing
+// table) live behind small data types so the selection logic and the route
+// parsers are pure functions that can be unit-tested on any OS with fake
+// data. Only the real routing-table query is build-tagged per platform.
+package netdetect
+
+import (
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"net"
+	"sort"
+	"strings"
+)
+
+// Selection failures. Those needing the offending interface names are
+// wrapped with %w at the call site.
+var (
+	errUnsupportedOS = errors.New("unsupported operating system")
+	errOneOfPair     = errors.New(
+		"found only one of the configured interfaces; " +
+			"rtnetmon needs both, or neither (default route only)")
+	errNoDefaultRoute = errors.New(
+		"no default route found; rtnetmon needs one internet interface")
+	errManyDefaultRoutes = errors.New(
+		"multiple default-route interfaces found; rtnetmon supports only one")
+	errNoPhysRoute = errors.New(
+		"no physical default-route interface found; " +
+			"rtnetmon needs one internet interface")
+	errManyPhysRoutes = errors.New(
+		"multiple physical default-route interfaces found; " +
+			"rtnetmon supports only one")
+)
+
+// Interface is a network interface reduced to what detection needs.
+type Interface struct {
+	Name string
+	Up   bool
+	IPv4 []string
+}
+
+// Route is one routing-table entry reduced to what detection needs.
+type Route struct {
+	Iface   string
+	Gateway string
+	Default bool
+}
+
+// Pane names one interface to display, with its label.
+type Pane struct {
+	Name  string
+	Label string
+}
+
+// Flags carries the user's --iface/--label choices and whether each label was
+// set explicitly on the command line.
+type Flags struct {
+	IfaceA    string
+	LabelA    string
+	IfaceB    string
+	LabelB    string
+	LabelASet bool
+	LabelBSet bool
+}
+
+// Interfaces enumerates the host's interfaces and their IPv4 addresses. This
+// uses the standard library and is the same on every platform.
+func Interfaces() ([]Interface, error) {
+	ifs, err := net.Interfaces()
+	if err != nil {
+		return nil, fmt.Errorf("listing interfaces: %w", err)
+	}
+
+	out := make([]Interface, 0, len(ifs))
+	for _, ifi := range ifs {
+		var v4 []string
+
+		addrs, _ := ifi.Addrs()
+		for _, a := range addrs {
+			if n, ok := a.(*net.IPNet); ok && n.IP.To4() != nil {
+				v4 = append(v4, n.IP.String())
+			}
+		}
+
+		out = append(out, Interface{
+			Name: ifi.Name,
+			Up:   ifi.Flags&net.FlagUp != 0,
+			IPv4: v4,
+		})
+	}
+
+	return out, nil
+}
+
+// Select decides which one or two interfaces to monitor for the given OS.
+// See the README's supported matrix for the exact rules.
+func Select(goos string, ifaces []Interface, routes []Route, f Flags) ([]Pane, error) {
+	switch goos {
+	case "linux":
+		return selectLinux(ifaces, routes, f)
+	case "darwin":
+		return selectDarwin(ifaces, routes, f)
+	default:
+		return nil, fmt.Errorf("%w: %q", errUnsupportedOS, goos)
+	}
+}
+
+// selectLinux keeps today's behavior: if both configured interfaces exist,
+// monitor them as two panes; if neither exists, monitor the single
+// default-route interface; anything else is an error.
+func selectLinux(ifaces []Interface, routes []Route, f Flags) ([]Pane, error) {
+	haveA := hasInterface(ifaces, f.IfaceA)
+	haveB := hasInterface(ifaces, f.IfaceB)
+
+	switch {
+	case haveA && haveB:
+		return []Pane{
+			{Name: f.IfaceA, Label: f.LabelA},
+			{Name: f.IfaceB, Label: f.LabelB},
+		}, nil
+	case !haveA && !haveB:
+		name, err := onlyDefaultRoute(routes)
+		if err != nil {
+			return nil, err
+		}
+
+		return []Pane{{Name: name, Label: singleLabel(f)}}, nil
+	default:
+		return nil, fmt.Errorf("%w (%q, %q)", errOneOfPair, f.IfaceA, f.IfaceB)
+	}
+}
+
+// selectDarwin monitors the physical default-route interface, plus a VPN
+// tunnel as the primary pane when one is running.
+func selectDarwin(ifaces []Interface, routes []Route, f Flags) ([]Pane, error) {
+	vpn := findVPN(ifaces, routes)
+
+	phys, err := onlyPhysicalDefaultRoute(routes, vpn)
+	if err != nil {
+		return nil, err
+	}
+
+	if vpn == "" {
+		return []Pane{{Name: phys, Label: singleLabel(f)}}, nil
+	}
+
+	return []Pane{
+		{Name: vpn, Label: labelOr(f.LabelA, f.LabelASet, "VPN")},
+		{Name: phys, Label: labelOr(f.LabelB, f.LabelBSet, "default route")},
+	}, nil
+}
+
+// findVPN returns the name of a VPN tunnel interface, or "" if none is
+// running. A tunnel counts as a running VPN when it carries a default route,
+// or when it is up with a routable (non-link-local) IPv4 address. Idle system
+// tunnels have only a link-local IPv6 address and are skipped.
+func findVPN(ifaces []Interface, routes []Route) string {
+	routeIfaces := map[string]bool{}
+
+	for _, r := range routes {
+		if r.Default {
+			routeIfaces[r.Iface] = true
+		}
+	}
+
+	sorted := append([]Interface(nil), ifaces...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Name < sorted[j].Name })
+
+	for _, ifi := range sorted {
+		if !isTunnel(ifi.Name) {
+			continue
+		}
+
+		if routeIfaces[ifi.Name] {
+			return ifi.Name
+		}
+
+		if ifi.Up && hasRoutableIPv4(ifi) {
+			return ifi.Name
+		}
+	}
+
+	return ""
+}
+
+// onlyDefaultRoute returns the single default-route interface, or an error if
+// there is not exactly one.
+func onlyDefaultRoute(routes []Route) (string, error) {
+	names := defaultRouteIfaces(routes, "")
+
+	switch len(names) {
+	case 1:
+		return names[0], nil
+	case 0:
+		return "", errNoDefaultRoute
+	default:
+		return "", fmt.Errorf("%w (%s)",
+			errManyDefaultRoutes, strings.Join(names, ", "))
+	}
+}
+
+// onlyPhysicalDefaultRoute returns the single non-tunnel default-route
+// interface (ignoring the VPN), or an error if there is not exactly one.
+func onlyPhysicalDefaultRoute(routes []Route, vpn string) (string, error) {
+	names := defaultRouteIfaces(routes, vpn)
+
+	switch len(names) {
+	case 1:
+		return names[0], nil
+	case 0:
+		return "", errNoPhysRoute
+	default:
+		return "", fmt.Errorf("%w (%s)",
+			errManyPhysRoutes, strings.Join(names, ", "))
+	}
+}
+
+// defaultRouteIfaces returns the sorted, unique interface names that carry a
+// default route, excluding the named VPN interface and any other tunnel.
+func defaultRouteIfaces(routes []Route, vpn string) []string {
+	seen := map[string]bool{}
+
+	var names []string
+
+	for _, r := range routes {
+		if !r.Default || r.Iface == vpn || isTunnel(r.Iface) || seen[r.Iface] {
+			continue
+		}
+
+		seen[r.Iface] = true
+		names = append(names, r.Iface)
+	}
+
+	sort.Strings(names)
+
+	return names
+}
+
+// hasInterface reports whether an interface with the given name exists.
+func hasInterface(ifaces []Interface, name string) bool {
+	for _, ifi := range ifaces {
+		if ifi.Name == name {
+			return true
+		}
+	}
+
+	return false
+}
+
+// isTunnel reports whether the interface name is a macOS userspace tunnel
+// (utunN), which is what Mullvad and other WireGuard/OpenVPN clients use.
+func isTunnel(name string) bool {
+	return strings.HasPrefix(name, "utun")
+}
+
+// hasRoutableIPv4 reports whether the interface has an IPv4 address that is
+// neither loopback nor link-local.
+func hasRoutableIPv4(ifi Interface) bool {
+	for _, s := range ifi.IPv4 {
+		ip := net.ParseIP(s)
+		if ip == nil || ip.IsLoopback() || ip.IsLinkLocalUnicast() {
+			continue
+		}
+
+		return true
+	}
+
+	return false
+}
+
+// singleLabel is the label for a lone pane: the explicit --labelA if given,
+// otherwise a plain description.
+func singleLabel(f Flags) string {
+	return labelOr(f.LabelA, f.LabelASet, "default route")
+}
+
+// labelOr returns value when it was set explicitly, otherwise fallback.
+func labelOr(value string, set bool, fallback string) string {
+	if set {
+		return value
+	}
+
+	return fallback
+}
+
+// parseIPRoute reads `ip -4 route show default` output. Every printed line is
+// a default route.
+func parseIPRoute(out string) []Route {
+	var routes []Route
+
+	for _, line := range strings.Split(out, "\n") {
+		fields := strings.Fields(line)
+		if len(fields) == 0 || fields[0] != "default" {
+			continue
+		}
+
+		r := Route{Default: true}
+
+		for i := range len(fields) - 1 {
+			switch fields[i] {
+			case "dev":
+				r.Iface = fields[i+1]
+			case "via":
+				r.Gateway = fields[i+1]
+			}
+		}
+
+		if r.Iface != "" {
+			routes = append(routes, r)
+		}
+	}
+
+	return routes
+}
+
+// parseProcNetRoute reads /proc/net/route. A default route has destination
+// 00000000; the gateway is a little-endian hex IPv4 address.
+func parseProcNetRoute(out string) []Route {
+	var routes []Route
+
+	for i, line := range strings.Split(out, "\n") {
+		if i == 0 { // column header
+			continue
+		}
+
+		fields := strings.Fields(line)
+		if len(fields) < 3 || fields[1] != "00000000" {
+			continue
+		}
+
+		routes = append(routes, Route{
+			Iface:   fields[0],
+			Gateway: hexToIP(fields[2]),
+			Default: true,
+		})
+	}
+
+	return routes
+}
+
+// parseNetstat reads `netstat -rn -f inet` output (macOS). Rows whose
+// destination is "default" are default routes; the Netif column (field 4)
+// names the interface.
+func parseNetstat(out string) []Route {
+	var routes []Route
+
+	for _, line := range strings.Split(out, "\n") {
+		fields := strings.Fields(line)
+		if len(fields) < 4 || fields[0] != "default" {
+			continue
+		}
+
+		routes = append(routes, Route{
+			Iface:   fields[3],
+			Gateway: fields[1],
+			Default: true,
+		})
+	}
+
+	return routes
+}
+
+// hexToIP converts a little-endian hex IPv4 address (as found in
+// /proc/net/route) to dotted-quad form.
+func hexToIP(h string) string {
+	b, err := hex.DecodeString(h)
+	if err != nil || len(b) != net.IPv4len {
+		return ""
+	}
+
+	// /proc/net/route stores the address little-endian.
+	return net.IPv4(b[3], b[2], b[1], b[0]).String()
+}

internal/netdetect/netdetect_test.go

@@ -0,0 +1,310 @@
+package netdetect_test
+
+import (
+	"reflect"
+	"testing"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/netdetect"
+)
+
+// Values reused across the selection tests.
+const (
+	osLinux  = "linux"
+	osDarwin = "darwin"
+
+	ifaceGu0      = "gu0"
+	ifaceBackhaul = "backhaul0"
+	ifaceEth0     = "eth0"
+	ifaceWlan0    = "wlan0"
+	ifaceEn0      = "en0"
+	ifaceUtun4    = "utun4"
+
+	labelGu      = "gu LAN - VPN outbound"
+	labelCox     = "Cox cable direct"
+	labelDefault = "default route"
+
+	addrEn0 = "192.168.1.20"
+)
+
+// linuxFlags describes the Linux bridge interfaces rtnetmon was built for.
+func linuxFlags() netdetect.Flags {
+	return netdetect.Flags{
+		IfaceA: ifaceGu0, LabelA: labelGu,
+		IfaceB: ifaceBackhaul, LabelB: labelCox,
+	}
+}
+
+// selectCase is one Select scenario with fake interfaces and routes.
+type selectCase struct {
+	name    string
+	goos    string
+	ifaces  []netdetect.Interface
+	routes  []netdetect.Route
+	flags   netdetect.Flags
+	want    []netdetect.Pane
+	wantErr bool
+}
+
+// runSelectCases runs each case as a parallel subtest.
+func runSelectCases(t *testing.T, cases []selectCase) {
+	t.Helper()
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := netdetect.Select(tt.goos, tt.ifaces, tt.routes, tt.flags)
+			if tt.wantErr {
+				if err == nil {
+					t.Fatalf("Select() expected error, got panes %v", got)
+				}
+
+				return
+			}
+
+			if err != nil {
+				t.Fatalf("Select() unexpected error: %v", err)
+			}
+
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("Select() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSelectLinuxPanes(t *testing.T) {
+	t.Parallel()
+
+	runSelectCases(t, []selectCase{
+		{
+			name: "both bridge interfaces present",
+			goos: osLinux,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceGu0, Up: true},
+				{Name: ifaceBackhaul, Up: true},
+				{Name: ifaceEth0, Up: true},
+			},
+			routes: []netdetect.Route{{Iface: ifaceEth0, Default: true}},
+			flags:  linuxFlags(),
+			want: []netdetect.Pane{
+				{Name: ifaceGu0, Label: labelGu},
+				{Name: ifaceBackhaul, Label: labelCox},
+			},
+		},
+		{
+			name: "no bridge interfaces, single default route",
+			goos: osLinux,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEth0, Up: true},
+				{Name: "lo", Up: true},
+			},
+			routes: []netdetect.Route{{Iface: ifaceEth0, Default: true}},
+			flags:  linuxFlags(),
+			want:   []netdetect.Pane{{Name: ifaceEth0, Label: labelDefault}},
+		},
+		{
+			name:   "single default route keeps explicit label",
+			goos:   osLinux,
+			ifaces: []netdetect.Interface{{Name: ifaceWlan0, Up: true}},
+			routes: []netdetect.Route{{Iface: ifaceWlan0, Default: true}},
+			flags: netdetect.Flags{
+				IfaceA: ifaceGu0, LabelA: "Home WiFi", LabelASet: true,
+				IfaceB: ifaceBackhaul, LabelB: labelCox,
+			},
+			want: []netdetect.Pane{{Name: ifaceWlan0, Label: "Home WiFi"}},
+		},
+	})
+}
+
+func TestSelectLinuxErrors(t *testing.T) {
+	t.Parallel()
+
+	runSelectCases(t, []selectCase{
+		{
+			name: "only one bridge interface present",
+			goos: osLinux,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceGu0, Up: true},
+				{Name: ifaceEth0, Up: true},
+			},
+			routes:  []netdetect.Route{{Iface: ifaceEth0, Default: true}},
+			flags:   linuxFlags(),
+			wantErr: true,
+		},
+		{
+			name:    "no bridge, no default route",
+			goos:    osLinux,
+			ifaces:  []netdetect.Interface{{Name: ifaceEth0, Up: true}},
+			routes:  nil,
+			flags:   linuxFlags(),
+			wantErr: true,
+		},
+		{
+			name: "no bridge, multiple default routes",
+			goos: osLinux,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEth0, Up: true},
+				{Name: "eth1", Up: true},
+			},
+			routes: []netdetect.Route{
+				{Iface: ifaceEth0, Default: true},
+				{Iface: "eth1", Default: true},
+			},
+			flags:   linuxFlags(),
+			wantErr: true,
+		},
+	})
+}
+
+func TestSelectDarwinPanes(t *testing.T) {
+	t.Parallel()
+
+	runSelectCases(t, []selectCase{
+		{
+			name: "vpn tunnel plus physical default route",
+			goos: osDarwin,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEn0, Up: true, IPv4: []string{addrEn0}},
+				{Name: ifaceUtun4, Up: true, IPv4: []string{"10.64.0.2"}},
+				{Name: "utun0", Up: true, IPv4: nil},
+			},
+			routes: []netdetect.Route{
+				{Iface: ifaceUtun4, Default: true},
+				{Iface: ifaceEn0, Default: true},
+			},
+			flags: linuxFlags(),
+			want: []netdetect.Pane{
+				{Name: ifaceUtun4, Label: "VPN"},
+				{Name: ifaceEn0, Label: labelDefault},
+			},
+		},
+		{
+			name: "vpn detected by routable address without its own route",
+			goos: osDarwin,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEn0, Up: true, IPv4: []string{addrEn0}},
+				{Name: "utun6", Up: true, IPv4: []string{"10.2.0.2"}},
+			},
+			routes: []netdetect.Route{{Iface: ifaceEn0, Default: true}},
+			flags:  linuxFlags(),
+			want: []netdetect.Pane{
+				{Name: "utun6", Label: "VPN"},
+				{Name: ifaceEn0, Label: labelDefault},
+			},
+		},
+		{
+			name: "vpn pane honors explicit labels",
+			goos: osDarwin,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEn0, Up: true, IPv4: []string{addrEn0}},
+				{Name: ifaceUtun4, Up: true, IPv4: []string{"10.64.0.2"}},
+			},
+			routes: []netdetect.Route{
+				{Iface: ifaceUtun4, Default: true},
+				{Iface: ifaceEn0, Default: true},
+			},
+			flags: netdetect.Flags{
+				LabelA: "Mullvad", LabelASet: true,
+				LabelB: "Fiber", LabelBSet: true,
+			},
+			want: []netdetect.Pane{
+				{Name: ifaceUtun4, Label: "Mullvad"},
+				{Name: ifaceEn0, Label: "Fiber"},
+			},
+		},
+	})
+}
+
+func TestSelectDarwinSingleAndErrors(t *testing.T) {
+	t.Parallel()
+
+	runSelectCases(t, []selectCase{
+		{
+			name: "no vpn, single physical default route",
+			goos: osDarwin,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEn0, Up: true, IPv4: []string{addrEn0}},
+				{Name: "utun0", Up: true, IPv4: nil},
+				{Name: "utun1", Up: true, IPv4: []string{"169.254.1.1"}},
+			},
+			routes: []netdetect.Route{{Iface: ifaceEn0, Default: true}},
+			flags:  linuxFlags(),
+			want:   []netdetect.Pane{{Name: ifaceEn0, Label: labelDefault}},
+		},
+		{
+			name: "no default route",
+			goos: osDarwin,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEn0, Up: true, IPv4: []string{addrEn0}},
+			},
+			routes:  nil,
+			flags:   linuxFlags(),
+			wantErr: true,
+		},
+		{
+			name: "two physical default routes",
+			goos: osDarwin,
+			ifaces: []netdetect.Interface{
+				{Name: ifaceEn0, Up: true, IPv4: []string{addrEn0}},
+				{Name: "en1", Up: true, IPv4: []string{"192.168.2.20"}},
+			},
+			routes: []netdetect.Route{
+				{Iface: ifaceEn0, Default: true},
+				{Iface: "en1", Default: true},
+			},
+			flags:   linuxFlags(),
+			wantErr: true,
+		},
+		{
+			name:    "unsupported operating system",
+			goos:    "windows",
+			wantErr: true,
+		},
+	})
+}
+
+func TestParseIPRoute(t *testing.T) {
+	t.Parallel()
+
+	out := "default via 192.168.1.1 dev eth0 proto dhcp metric 100\n"
+	got := netdetect.ParseIPRoute(out)
+	want := []netdetect.Route{{Iface: ifaceEth0, Gateway: "192.168.1.1", Default: true}}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("ParseIPRoute() = %v, want %v", got, want)
+	}
+}
+
+func TestParseProcNetRoute(t *testing.T) {
+	t.Parallel()
+
+	out := "Iface\tDestination\tGateway\tFlags\tRefCnt\tUse\tMetric\tMask\n" +
+		"eth0\t00000000\t0102A8C0\t0003\t0\t0\t100\t00000000\n" +
+		"eth0\t0002A8C0\t00000000\t0001\t0\t0\t0\t00FFFFFF\n"
+	got := netdetect.ParseProcNetRoute(out)
+	want := []netdetect.Route{{Iface: ifaceEth0, Gateway: "192.168.2.1", Default: true}}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("ParseProcNetRoute() = %v, want %v", got, want)
+	}
+}
+
+func TestParseNetstat(t *testing.T) {
+	t.Parallel()
+
+	out := "Routing tables\n\nInternet:\n" +
+		"Destination        Gateway            Flags        Netif Expire\n" +
+		"default            10.0.0.1           UGScg          en0\n" +
+		"default            link#15            UCSg         utun4\n" +
+		"127.0.0.1          127.0.0.1          UH             lo0\n"
+	got := netdetect.ParseNetstat(out)
+	want := []netdetect.Route{
+		{Iface: ifaceEn0, Gateway: "10.0.0.1", Default: true},
+		{Iface: ifaceUtun4, Gateway: "link#15", Default: true},
+	}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("ParseNetstat() = %v, want %v", got, want)
+	}
+}

internal/netdetect/routes_darwin.go

@@ -0,0 +1,27 @@
+//go:build darwin
+
+package netdetect
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"time"
+)
+
+// routeQueryTimeout bounds the external route-table query.
+const routeQueryTimeout = 2 * time.Second
+
+// DefaultRoutes returns the host's IPv4 default routes, read from the macOS
+// routing table.
+func DefaultRoutes() ([]Route, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), routeQueryTimeout)
+	defer cancel()
+
+	out, err := exec.CommandContext(ctx, "netstat", "-rn", "-f", "inet").Output()
+	if err != nil {
+		return nil, fmt.Errorf("running netstat: %w", err)
+	}
+
+	return parseNetstat(string(out)), nil
+}

internal/netdetect/routes_linux.go

@@ -0,0 +1,36 @@
+//go:build linux
+
+package netdetect
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"time"
+)
+
+// routeQueryTimeout bounds the external route-table query.
+const routeQueryTimeout = 2 * time.Second
+
+// DefaultRoutes returns the host's IPv4 default routes. It prefers the `ip`
+// command and falls back to reading /proc/net/route.
+func DefaultRoutes() ([]Route, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), routeQueryTimeout)
+	defer cancel()
+
+	out, err := exec.CommandContext(ctx,
+		"ip", "-4", "route", "show", "default").Output()
+	if err == nil {
+		if routes := parseIPRoute(string(out)); len(routes) > 0 {
+			return routes, nil
+		}
+	}
+
+	data, err := os.ReadFile("/proc/net/route")
+	if err != nil {
+		return nil, fmt.Errorf("reading /proc/net/route: %w", err)
+	}
+
+	return parseProcNetRoute(string(data)), nil
+}

internal/starlink/client.go

@@ -0,0 +1,129 @@
+package starlink
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+
+	pb "git.eeqj.de/sneak/rtnetmon/internal/starlink/pb"
+)
+
+// errNoDishStatus is returned when the dish answers but the response
+// carries no dish status.
+var errNoDishStatus = errors.New("no dish status in response")
+
+// Per-call deadlines so a silent dish never wedges the monitor loop.
+const (
+	probeTimeout  = 2 * time.Second
+	statusTimeout = 3 * time.Second
+)
+
+// DialFunc opens a TCP connection to addr bound to a chosen interface. The
+// monitor supplies one that binds the same way its TCP latency probes do,
+// so the dish is reached over the physical (non-VPN) interface rather than
+// a VPN tunnel that may hold the default route.
+type DialFunc func(ctx context.Context, addr string) (net.Conn, error)
+
+// GRPCClient is the real Client: it reaches a dish at Address over whatever
+// interface dial binds to.
+type GRPCClient struct {
+	dial DialFunc
+}
+
+// NewClient returns a client that talks to a dish at Address, dialing with
+// dial so the connection leaves the intended interface.
+func NewClient(dial DialFunc) *GRPCClient {
+	return &GRPCClient{dial: dial}
+}
+
+// Probe connects to the dish's endpoint and closes it. A successful TCP
+// connect over the bound interface is the detection signal.
+func (c *GRPCClient) Probe(ctx context.Context) bool {
+	ctx, cancel := context.WithTimeout(ctx, probeTimeout)
+	defer cancel()
+
+	conn, err := c.dial(ctx, Address)
+	if err != nil {
+		return false
+	}
+
+	_ = conn.Close()
+
+	return true
+}
+
+// Status calls the dish's get_status RPC and reduces the response to the
+// fields rtnetmon shows.
+func (c *GRPCClient) Status(ctx context.Context) (Status, error) {
+	ctx, cancel := context.WithTimeout(ctx, statusTimeout)
+	defer cancel()
+
+	// passthrough:/// hands Address straight to our dialer, with no name
+	// resolution, so the connection is made over the bound interface.
+	conn, err := grpc.NewClient("passthrough:///"+Address,
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+		grpc.WithContextDialer(func(ctx context.Context, addr string) (net.Conn, error) {
+			return c.dial(ctx, addr)
+		}),
+	)
+	if err != nil {
+		return Status{}, fmt.Errorf("starlink dial: %w", err)
+	}
+	defer func() { _ = conn.Close() }()
+
+	resp, err := pb.NewDeviceClient(conn).Handle(ctx, &pb.Request{
+		Request: &pb.Request_GetStatus{GetStatus: &pb.GetStatusRequest{}},
+	})
+	if err != nil {
+		return Status{}, fmt.Errorf("starlink get_status: %w", err)
+	}
+
+	dish := resp.GetDishGetStatus()
+	if dish == nil {
+		return Status{}, errNoDishStatus
+	}
+
+	return statusFromDish(dish), nil
+}
+
+// statusFromDish reduces the dish's status message to a Status. The
+// generated getters are nil-safe, so absent sub-messages read as zero.
+func statusFromDish(d *pb.DishGetStatusResponse) Status {
+	obstruction := float64(d.GetObstructionStats().GetFractionObstructed())
+	//nolint:gosec // G115: dish uptime in seconds never approaches int64 max
+	uptime := time.Duration(d.GetDeviceState().GetUptimeS()) * time.Second
+
+	return Status{
+		State:          d.GetState().String(),
+		Uptime:         uptime,
+		ObstructionPct: obstruction * percentScale,
+		Alerts:         countAlerts(d.GetAlerts()),
+		PopPingMs:      float64(d.GetPopPingLatencyMs()),
+		PopPingDropPct: float64(d.GetPopPingDropRate()) * percentScale,
+		DownlinkMbps:   float64(d.GetDownlinkThroughputBps()) / bitsPerMegabit,
+		UplinkMbps:     float64(d.GetUplinkThroughputBps()) / bitsPerMegabit,
+	}
+}
+
+// countAlerts counts the active dish alert flags.
+func countAlerts(a *pb.DishAlerts) int {
+	n := 0
+
+	for _, on := range []bool{
+		a.GetMotorsStuck(),
+		a.GetThermalShutdown(),
+		a.GetThermalThrottle(),
+		a.GetUnexpectedLocation(),
+	} {
+		if on {
+			n++
+		}
+	}
+
+	return n
+}

internal/starlink/pb/starlink.pb.go

@@ -0,0 +1,629 @@
+// A minimal slice of the Starlink dish's local gRPC API: just the one
+// unary RPC (SpaceX.API.Device.Device/Handle) and the get_status request
+// and dish status response, reduced to the handful of fields rtnetmon
+// shows. The proto package name and field numbers must match the dish
+// exactly for the wire format to line up; every other field the dish sends
+// is ignored as an unknown field.
+//
+// Field numbers, message names and the DishState enum are transcribed from
+// the community-maintained pre-generated bindings at
+// github.com/starlink-community/starlink-grpc-go, commit
+// 2e89f3d7e3092adecbcc04e9e003e61ed5f7c6a3 (get_status = 1004,
+// dish_get_status = 2004). They are not verified against a live dish here.
+//
+// Regenerate with:
+//   protoc --go_out=. --go_opt=paths=source_relative \
+//          --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+//          internal/starlink/pb/starlink.proto
+
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.36.6
+// 	protoc        v7.36.2
+// source: internal/starlink/pb/starlink.proto
+
+package starlinkpb
+
+import (
+	reflect "reflect"
+	sync "sync"
+	unsafe "unsafe"
+
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+type DishState int32
+
+const (
+	DishState_UNKNOWN   DishState = 0
+	DishState_CONNECTED DishState = 1
+	DishState_SEARCHING DishState = 2
+	DishState_BOOTING   DishState = 3
+)
+
+// Enum value maps for DishState.
+var (
+	DishState_name = map[int32]string{
+		0: "UNKNOWN",
+		1: "CONNECTED",
+		2: "SEARCHING",
+		3: "BOOTING",
+	}
+	DishState_value = map[string]int32{
+		"UNKNOWN":   0,
+		"CONNECTED": 1,
+		"SEARCHING": 2,
+		"BOOTING":   3,
+	}
+)
+
+func (x DishState) Enum() *DishState {
+	p := new(DishState)
+	*p = x
+	return p
+}
+
+func (x DishState) String() string {
+	return protoimpl.X.EnumStringOf(x.Descriptor(), protoreflect.EnumNumber(x))
+}
+
+func (DishState) Descriptor() protoreflect.EnumDescriptor {
+	return file_internal_starlink_pb_starlink_proto_enumTypes[0].Descriptor()
+}
+
+func (DishState) Type() protoreflect.EnumType {
+	return &file_internal_starlink_pb_starlink_proto_enumTypes[0]
+}
+
+func (x DishState) Number() protoreflect.EnumNumber {
+	return protoreflect.EnumNumber(x)
+}
+
+// Deprecated: Use DishState.Descriptor instead.
+func (DishState) EnumDescriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{0}
+}
+
+type Request struct {
+	state protoimpl.MessageState `protogen:"open.v1"`
+	// Types that are valid to be assigned to Request:
+	//
+	//	*Request_GetStatus
+	Request       isRequest_Request `protobuf_oneof:"request"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *Request) Reset() {
+	*x = Request{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[0]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *Request) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Request) ProtoMessage() {}
+
+func (x *Request) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[0]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Request.ProtoReflect.Descriptor instead.
+func (*Request) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *Request) GetRequest() isRequest_Request {
+	if x != nil {
+		return x.Request
+	}
+	return nil
+}
+
+func (x *Request) GetGetStatus() *GetStatusRequest {
+	if x != nil {
+		if x, ok := x.Request.(*Request_GetStatus); ok {
+			return x.GetStatus
+		}
+	}
+	return nil
+}
+
+type isRequest_Request interface {
+	isRequest_Request()
+}
+
+type Request_GetStatus struct {
+	GetStatus *GetStatusRequest `protobuf:"bytes,1004,opt,name=get_status,json=getStatus,proto3,oneof"`
+}
+
+func (*Request_GetStatus) isRequest_Request() {}
+
+type GetStatusRequest struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *GetStatusRequest) Reset() {
+	*x = GetStatusRequest{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[1]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *GetStatusRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*GetStatusRequest) ProtoMessage() {}
+
+func (x *GetStatusRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[1]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use GetStatusRequest.ProtoReflect.Descriptor instead.
+func (*GetStatusRequest) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{1}
+}
+
+type Response struct {
+	state protoimpl.MessageState `protogen:"open.v1"`
+	// Types that are valid to be assigned to Response:
+	//
+	//	*Response_DishGetStatus
+	Response      isResponse_Response `protobuf_oneof:"response"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *Response) Reset() {
+	*x = Response{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[2]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *Response) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Response) ProtoMessage() {}
+
+func (x *Response) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[2]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Response.ProtoReflect.Descriptor instead.
+func (*Response) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{2}
+}
+
+func (x *Response) GetResponse() isResponse_Response {
+	if x != nil {
+		return x.Response
+	}
+	return nil
+}
+
+func (x *Response) GetDishGetStatus() *DishGetStatusResponse {
+	if x != nil {
+		if x, ok := x.Response.(*Response_DishGetStatus); ok {
+			return x.DishGetStatus
+		}
+	}
+	return nil
+}
+
+type isResponse_Response interface {
+	isResponse_Response()
+}
+
+type Response_DishGetStatus struct {
+	DishGetStatus *DishGetStatusResponse `protobuf:"bytes,2004,opt,name=dish_get_status,json=dishGetStatus,proto3,oneof"`
+}
+
+func (*Response_DishGetStatus) isResponse_Response() {}
+
+type DishGetStatusResponse struct {
+	state                 protoimpl.MessageState `protogen:"open.v1"`
+	DeviceState           *DeviceState           `protobuf:"bytes,2,opt,name=device_state,json=deviceState,proto3" json:"device_state,omitempty"`
+	ObstructionStats      *DishObstructionStats  `protobuf:"bytes,1004,opt,name=obstruction_stats,json=obstructionStats,proto3" json:"obstruction_stats,omitempty"`
+	Alerts                *DishAlerts            `protobuf:"bytes,1005,opt,name=alerts,proto3" json:"alerts,omitempty"`
+	State                 DishState              `protobuf:"varint,1006,opt,name=state,proto3,enum=SpaceX.API.Device.DishState" json:"state,omitempty"`
+	PopPingDropRate       float32                `protobuf:"fixed32,1003,opt,name=pop_ping_drop_rate,json=popPingDropRate,proto3" json:"pop_ping_drop_rate,omitempty"`
+	DownlinkThroughputBps float32                `protobuf:"fixed32,1007,opt,name=downlink_throughput_bps,json=downlinkThroughputBps,proto3" json:"downlink_throughput_bps,omitempty"`
+	UplinkThroughputBps   float32                `protobuf:"fixed32,1008,opt,name=uplink_throughput_bps,json=uplinkThroughputBps,proto3" json:"uplink_throughput_bps,omitempty"`
+	PopPingLatencyMs      float32                `protobuf:"fixed32,1009,opt,name=pop_ping_latency_ms,json=popPingLatencyMs,proto3" json:"pop_ping_latency_ms,omitempty"`
+	unknownFields         protoimpl.UnknownFields
+	sizeCache             protoimpl.SizeCache
+}
+
+func (x *DishGetStatusResponse) Reset() {
+	*x = DishGetStatusResponse{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[3]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *DishGetStatusResponse) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*DishGetStatusResponse) ProtoMessage() {}
+
+func (x *DishGetStatusResponse) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[3]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use DishGetStatusResponse.ProtoReflect.Descriptor instead.
+func (*DishGetStatusResponse) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{3}
+}
+
+func (x *DishGetStatusResponse) GetDeviceState() *DeviceState {
+	if x != nil {
+		return x.DeviceState
+	}
+	return nil
+}
+
+func (x *DishGetStatusResponse) GetObstructionStats() *DishObstructionStats {
+	if x != nil {
+		return x.ObstructionStats
+	}
+	return nil
+}
+
+func (x *DishGetStatusResponse) GetAlerts() *DishAlerts {
+	if x != nil {
+		return x.Alerts
+	}
+	return nil
+}
+
+func (x *DishGetStatusResponse) GetState() DishState {
+	if x != nil {
+		return x.State
+	}
+	return DishState_UNKNOWN
+}
+
+func (x *DishGetStatusResponse) GetPopPingDropRate() float32 {
+	if x != nil {
+		return x.PopPingDropRate
+	}
+	return 0
+}
+
+func (x *DishGetStatusResponse) GetDownlinkThroughputBps() float32 {
+	if x != nil {
+		return x.DownlinkThroughputBps
+	}
+	return 0
+}
+
+func (x *DishGetStatusResponse) GetUplinkThroughputBps() float32 {
+	if x != nil {
+		return x.UplinkThroughputBps
+	}
+	return 0
+}
+
+func (x *DishGetStatusResponse) GetPopPingLatencyMs() float32 {
+	if x != nil {
+		return x.PopPingLatencyMs
+	}
+	return 0
+}
+
+type DeviceState struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	UptimeS       uint64                 `protobuf:"varint,1,opt,name=uptime_s,json=uptimeS,proto3" json:"uptime_s,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *DeviceState) Reset() {
+	*x = DeviceState{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[4]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *DeviceState) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*DeviceState) ProtoMessage() {}
+
+func (x *DeviceState) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[4]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use DeviceState.ProtoReflect.Descriptor instead.
+func (*DeviceState) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{4}
+}
+
+func (x *DeviceState) GetUptimeS() uint64 {
+	if x != nil {
+		return x.UptimeS
+	}
+	return 0
+}
+
+type DishObstructionStats struct {
+	state              protoimpl.MessageState `protogen:"open.v1"`
+	FractionObstructed float32                `protobuf:"fixed32,1,opt,name=fraction_obstructed,json=fractionObstructed,proto3" json:"fraction_obstructed,omitempty"`
+	unknownFields      protoimpl.UnknownFields
+	sizeCache          protoimpl.SizeCache
+}
+
+func (x *DishObstructionStats) Reset() {
+	*x = DishObstructionStats{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[5]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *DishObstructionStats) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*DishObstructionStats) ProtoMessage() {}
+
+func (x *DishObstructionStats) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[5]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use DishObstructionStats.ProtoReflect.Descriptor instead.
+func (*DishObstructionStats) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{5}
+}
+
+func (x *DishObstructionStats) GetFractionObstructed() float32 {
+	if x != nil {
+		return x.FractionObstructed
+	}
+	return 0
+}
+
+type DishAlerts struct {
+	state              protoimpl.MessageState `protogen:"open.v1"`
+	MotorsStuck        bool                   `protobuf:"varint,1,opt,name=motors_stuck,json=motorsStuck,proto3" json:"motors_stuck,omitempty"`
+	ThermalShutdown    bool                   `protobuf:"varint,2,opt,name=thermal_shutdown,json=thermalShutdown,proto3" json:"thermal_shutdown,omitempty"`
+	ThermalThrottle    bool                   `protobuf:"varint,3,opt,name=thermal_throttle,json=thermalThrottle,proto3" json:"thermal_throttle,omitempty"`
+	UnexpectedLocation bool                   `protobuf:"varint,4,opt,name=unexpected_location,json=unexpectedLocation,proto3" json:"unexpected_location,omitempty"`
+	unknownFields      protoimpl.UnknownFields
+	sizeCache          protoimpl.SizeCache
+}
+
+func (x *DishAlerts) Reset() {
+	*x = DishAlerts{}
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[6]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *DishAlerts) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*DishAlerts) ProtoMessage() {}
+
+func (x *DishAlerts) ProtoReflect() protoreflect.Message {
+	mi := &file_internal_starlink_pb_starlink_proto_msgTypes[6]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use DishAlerts.ProtoReflect.Descriptor instead.
+func (*DishAlerts) Descriptor() ([]byte, []int) {
+	return file_internal_starlink_pb_starlink_proto_rawDescGZIP(), []int{6}
+}
+
+func (x *DishAlerts) GetMotorsStuck() bool {
+	if x != nil {
+		return x.MotorsStuck
+	}
+	return false
+}
+
+func (x *DishAlerts) GetThermalShutdown() bool {
+	if x != nil {
+		return x.ThermalShutdown
+	}
+	return false
+}
+
+func (x *DishAlerts) GetThermalThrottle() bool {
+	if x != nil {
+		return x.ThermalThrottle
+	}
+	return false
+}
+
+func (x *DishAlerts) GetUnexpectedLocation() bool {
+	if x != nil {
+		return x.UnexpectedLocation
+	}
+	return false
+}
+
+var File_internal_starlink_pb_starlink_proto protoreflect.FileDescriptor
+
+const file_internal_starlink_pb_starlink_proto_rawDesc = "" +
+	"\n" +
+	"#internal/starlink/pb/starlink.proto\x12\x11SpaceX.API.Device\"[\n" +
+	"\aRequest\x12E\n" +
+	"\n" +
+	"get_status\x18\xec\a \x01(\v2#.SpaceX.API.Device.GetStatusRequestH\x00R\tgetStatusB\t\n" +
+	"\arequest\"\x12\n" +
+	"\x10GetStatusRequest\"k\n" +
+	"\bResponse\x12S\n" +
+	"\x0fdish_get_status\x18\xd4\x0f \x01(\v2(.SpaceX.API.Device.DishGetStatusResponseH\x00R\rdishGetStatusB\n" +
+	"\n" +
+	"\bresponse\"\xea\x03\n" +
+	"\x15DishGetStatusResponse\x12A\n" +
+	"\fdevice_state\x18\x02 \x01(\v2\x1e.SpaceX.API.Device.DeviceStateR\vdeviceState\x12U\n" +
+	"\x11obstruction_stats\x18\xec\a \x01(\v2'.SpaceX.API.Device.DishObstructionStatsR\x10obstructionStats\x126\n" +
+	"\x06alerts\x18\xed\a \x01(\v2\x1d.SpaceX.API.Device.DishAlertsR\x06alerts\x123\n" +
+	"\x05state\x18\xee\a \x01(\x0e2\x1c.SpaceX.API.Device.DishStateR\x05state\x12,\n" +
+	"\x12pop_ping_drop_rate\x18\xeb\a \x01(\x02R\x0fpopPingDropRate\x127\n" +
+	"\x17downlink_throughput_bps\x18\xef\a \x01(\x02R\x15downlinkThroughputBps\x123\n" +
+	"\x15uplink_throughput_bps\x18\xf0\a \x01(\x02R\x13uplinkThroughputBps\x12.\n" +
+	"\x13pop_ping_latency_ms\x18\xf1\a \x01(\x02R\x10popPingLatencyMs\"(\n" +
+	"\vDeviceState\x12\x19\n" +
+	"\buptime_s\x18\x01 \x01(\x04R\auptimeS\"G\n" +
+	"\x14DishObstructionStats\x12/\n" +
+	"\x13fraction_obstructed\x18\x01 \x01(\x02R\x12fractionObstructed\"\xb6\x01\n" +
+	"\n" +
+	"DishAlerts\x12!\n" +
+	"\fmotors_stuck\x18\x01 \x01(\bR\vmotorsStuck\x12)\n" +
+	"\x10thermal_shutdown\x18\x02 \x01(\bR\x0fthermalShutdown\x12)\n" +
+	"\x10thermal_throttle\x18\x03 \x01(\bR\x0fthermalThrottle\x12/\n" +
+	"\x13unexpected_location\x18\x04 \x01(\bR\x12unexpectedLocation*C\n" +
+	"\tDishState\x12\v\n" +
+	"\aUNKNOWN\x10\x00\x12\r\n" +
+	"\tCONNECTED\x10\x01\x12\r\n" +
+	"\tSEARCHING\x10\x02\x12\v\n" +
+	"\aBOOTING\x10\x032K\n" +
+	"\x06Device\x12A\n" +
+	"\x06Handle\x12\x1a.SpaceX.API.Device.Request\x1a\x1b.SpaceX.API.Device.ResponseB<Z:git.eeqj.de/sneak/rtnetmon/internal/starlink/pb;starlinkpbb\x06proto3"
+
+var (
+	file_internal_starlink_pb_starlink_proto_rawDescOnce sync.Once
+	file_internal_starlink_pb_starlink_proto_rawDescData []byte
+)
+
+func file_internal_starlink_pb_starlink_proto_rawDescGZIP() []byte {
+	file_internal_starlink_pb_starlink_proto_rawDescOnce.Do(func() {
+		file_internal_starlink_pb_starlink_proto_rawDescData = protoimpl.X.CompressGZIP(unsafe.Slice(unsafe.StringData(file_internal_starlink_pb_starlink_proto_rawDesc), len(file_internal_starlink_pb_starlink_proto_rawDesc)))
+	})
+	return file_internal_starlink_pb_starlink_proto_rawDescData
+}
+
+var file_internal_starlink_pb_starlink_proto_enumTypes = make([]protoimpl.EnumInfo, 1)
+var file_internal_starlink_pb_starlink_proto_msgTypes = make([]protoimpl.MessageInfo, 7)
+var file_internal_starlink_pb_starlink_proto_goTypes = []any{
+	(DishState)(0),                // 0: SpaceX.API.Device.DishState
+	(*Request)(nil),               // 1: SpaceX.API.Device.Request
+	(*GetStatusRequest)(nil),      // 2: SpaceX.API.Device.GetStatusRequest
+	(*Response)(nil),              // 3: SpaceX.API.Device.Response
+	(*DishGetStatusResponse)(nil), // 4: SpaceX.API.Device.DishGetStatusResponse
+	(*DeviceState)(nil),           // 5: SpaceX.API.Device.DeviceState
+	(*DishObstructionStats)(nil),  // 6: SpaceX.API.Device.DishObstructionStats
+	(*DishAlerts)(nil),            // 7: SpaceX.API.Device.DishAlerts
+}
+var file_internal_starlink_pb_starlink_proto_depIdxs = []int32{
+	2, // 0: SpaceX.API.Device.Request.get_status:type_name -> SpaceX.API.Device.GetStatusRequest
+	4, // 1: SpaceX.API.Device.Response.dish_get_status:type_name -> SpaceX.API.Device.DishGetStatusResponse
+	5, // 2: SpaceX.API.Device.DishGetStatusResponse.device_state:type_name -> SpaceX.API.Device.DeviceState
+	6, // 3: SpaceX.API.Device.DishGetStatusResponse.obstruction_stats:type_name -> SpaceX.API.Device.DishObstructionStats
+	7, // 4: SpaceX.API.Device.DishGetStatusResponse.alerts:type_name -> SpaceX.API.Device.DishAlerts
+	0, // 5: SpaceX.API.Device.DishGetStatusResponse.state:type_name -> SpaceX.API.Device.DishState
+	1, // 6: SpaceX.API.Device.Device.Handle:input_type -> SpaceX.API.Device.Request
+	3, // 7: SpaceX.API.Device.Device.Handle:output_type -> SpaceX.API.Device.Response
+	7, // [7:8] is the sub-list for method output_type
+	6, // [6:7] is the sub-list for method input_type
+	6, // [6:6] is the sub-list for extension type_name
+	6, // [6:6] is the sub-list for extension extendee
+	0, // [0:6] is the sub-list for field type_name
+}
+
+func init() { file_internal_starlink_pb_starlink_proto_init() }
+func file_internal_starlink_pb_starlink_proto_init() {
+	if File_internal_starlink_pb_starlink_proto != nil {
+		return
+	}
+	file_internal_starlink_pb_starlink_proto_msgTypes[0].OneofWrappers = []any{
+		(*Request_GetStatus)(nil),
+	}
+	file_internal_starlink_pb_starlink_proto_msgTypes[2].OneofWrappers = []any{
+		(*Response_DishGetStatus)(nil),
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: unsafe.Slice(unsafe.StringData(file_internal_starlink_pb_starlink_proto_rawDesc), len(file_internal_starlink_pb_starlink_proto_rawDesc)),
+			NumEnums:      1,
+			NumMessages:   7,
+			NumExtensions: 0,
+			NumServices:   1,
+		},
+		GoTypes:           file_internal_starlink_pb_starlink_proto_goTypes,
+		DependencyIndexes: file_internal_starlink_pb_starlink_proto_depIdxs,
+		EnumInfos:         file_internal_starlink_pb_starlink_proto_enumTypes,
+		MessageInfos:      file_internal_starlink_pb_starlink_proto_msgTypes,
+	}.Build()
+	File_internal_starlink_pb_starlink_proto = out.File
+	file_internal_starlink_pb_starlink_proto_goTypes = nil
+	file_internal_starlink_pb_starlink_proto_depIdxs = nil
+}

internal/starlink/pb/starlink.proto

@@ -0,0 +1,74 @@
+// A minimal slice of the Starlink dish's local gRPC API: just the one
+// unary RPC (SpaceX.API.Device.Device/Handle) and the get_status request
+// and dish status response, reduced to the handful of fields rtnetmon
+// shows. The proto package name and field numbers must match the dish
+// exactly for the wire format to line up; every other field the dish sends
+// is ignored as an unknown field.
+//
+// Field numbers, message names and the DishState enum are transcribed from
+// the community-maintained pre-generated bindings at
+// github.com/starlink-community/starlink-grpc-go, commit
+// 2e89f3d7e3092adecbcc04e9e003e61ed5f7c6a3 (get_status = 1004,
+// dish_get_status = 2004). They are not verified against a live dish here.
+//
+// Regenerate with:
+//   protoc --go_out=. --go_opt=paths=source_relative \
+//          --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+//          internal/starlink/pb/starlink.proto
+
+syntax = "proto3";
+
+package SpaceX.API.Device;
+
+option go_package = "git.eeqj.de/sneak/rtnetmon/internal/starlink/pb;starlinkpb";
+
+service Device {
+  rpc Handle(Request) returns (Response);
+}
+
+message Request {
+  oneof request {
+    GetStatusRequest get_status = 1004;
+  }
+}
+
+message GetStatusRequest {}
+
+message Response {
+  oneof response {
+    DishGetStatusResponse dish_get_status = 2004;
+  }
+}
+
+message DishGetStatusResponse {
+  DeviceState device_state = 2;
+  DishObstructionStats obstruction_stats = 1004;
+  DishAlerts alerts = 1005;
+  DishState state = 1006;
+  float pop_ping_drop_rate = 1003;
+  float downlink_throughput_bps = 1007;
+  float uplink_throughput_bps = 1008;
+  float pop_ping_latency_ms = 1009;
+}
+
+message DeviceState {
+  uint64 uptime_s = 1;
+}
+
+message DishObstructionStats {
+  float fraction_obstructed = 1;
+}
+
+message DishAlerts {
+  bool motors_stuck = 1;
+  bool thermal_shutdown = 2;
+  bool thermal_throttle = 3;
+  bool unexpected_location = 4;
+}
+
+enum DishState {
+  UNKNOWN = 0;
+  CONNECTED = 1;
+  SEARCHING = 2;
+  BOOTING = 3;
+}

internal/starlink/pb/starlink_grpc.pb.go

@@ -0,0 +1,140 @@
+// A minimal slice of the Starlink dish's local gRPC API: just the one
+// unary RPC (SpaceX.API.Device.Device/Handle) and the get_status request
+// and dish status response, reduced to the handful of fields rtnetmon
+// shows. The proto package name and field numbers must match the dish
+// exactly for the wire format to line up; every other field the dish sends
+// is ignored as an unknown field.
+//
+// Field numbers, message names and the DishState enum are transcribed from
+// the community-maintained pre-generated bindings at
+// github.com/starlink-community/starlink-grpc-go, commit
+// 2e89f3d7e3092adecbcc04e9e003e61ed5f7c6a3 (get_status = 1004,
+// dish_get_status = 2004). They are not verified against a live dish here.
+//
+// Regenerate with:
+//   protoc --go_out=. --go_opt=paths=source_relative \
+//          --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+//          internal/starlink/pb/starlink.proto
+
+// Code generated by protoc-gen-go-grpc. DO NOT EDIT.
+// versions:
+// - protoc-gen-go-grpc v1.5.1
+// - protoc             v7.36.2
+// source: internal/starlink/pb/starlink.proto
+
+package starlinkpb
+
+import (
+	context "context"
+
+	grpc "google.golang.org/grpc"
+	codes "google.golang.org/grpc/codes"
+	status "google.golang.org/grpc/status"
+)
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+// Requires gRPC-Go v1.64.0 or later.
+const _ = grpc.SupportPackageIsVersion9
+
+const (
+	Device_Handle_FullMethodName = "/SpaceX.API.Device.Device/Handle"
+)
+
+// DeviceClient is the client API for Device service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://pkg.go.dev/google.golang.org/grpc/?tab=doc#ClientConn.NewStream.
+type DeviceClient interface {
+	Handle(ctx context.Context, in *Request, opts ...grpc.CallOption) (*Response, error)
+}
+
+type deviceClient struct {
+	cc grpc.ClientConnInterface
+}
+
+func NewDeviceClient(cc grpc.ClientConnInterface) DeviceClient {
+	return &deviceClient{cc}
+}
+
+func (c *deviceClient) Handle(ctx context.Context, in *Request, opts ...grpc.CallOption) (*Response, error) {
+	cOpts := append([]grpc.CallOption{grpc.StaticMethod()}, opts...)
+	out := new(Response)
+	err := c.cc.Invoke(ctx, Device_Handle_FullMethodName, in, out, cOpts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+// DeviceServer is the server API for Device service.
+// All implementations must embed UnimplementedDeviceServer
+// for forward compatibility.
+type DeviceServer interface {
+	Handle(context.Context, *Request) (*Response, error)
+	mustEmbedUnimplementedDeviceServer()
+}
+
+// UnimplementedDeviceServer must be embedded to have
+// forward compatible implementations.
+//
+// NOTE: this should be embedded by value instead of pointer to avoid a nil
+// pointer dereference when methods are called.
+type UnimplementedDeviceServer struct{}
+
+func (UnimplementedDeviceServer) Handle(context.Context, *Request) (*Response, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method Handle not implemented")
+}
+func (UnimplementedDeviceServer) mustEmbedUnimplementedDeviceServer() {}
+func (UnimplementedDeviceServer) testEmbeddedByValue()                {}
+
+// UnsafeDeviceServer may be embedded to opt out of forward compatibility for this service.
+// Use of this interface is not recommended, as added methods to DeviceServer will
+// result in compilation errors.
+type UnsafeDeviceServer interface {
+	mustEmbedUnimplementedDeviceServer()
+}
+
+func RegisterDeviceServer(s grpc.ServiceRegistrar, srv DeviceServer) {
+	// If the following call pancis, it indicates UnimplementedDeviceServer was
+	// embedded by pointer and is nil.  This will cause panics if an
+	// unimplemented method is ever invoked, so we test this at initialization
+	// time to prevent it from happening at runtime later due to I/O.
+	if t, ok := srv.(interface{ testEmbeddedByValue() }); ok {
+		t.testEmbeddedByValue()
+	}
+	s.RegisterService(&Device_ServiceDesc, srv)
+}
+
+func _Device_Handle_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(Request)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(DeviceServer).Handle(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: Device_Handle_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(DeviceServer).Handle(ctx, req.(*Request))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+// Device_ServiceDesc is the grpc.ServiceDesc for Device service.
+// It's only intended for direct use with grpc.RegisterService,
+// and not to be introspected or modified (even as a copy)
+var Device_ServiceDesc = grpc.ServiceDesc{
+	ServiceName: "SpaceX.API.Device.Device",
+	HandlerType: (*DeviceServer)(nil),
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "Handle",
+			Handler:    _Device_Handle_Handler,
+		},
+	},
+	Streams:  []grpc.StreamDesc{},
+	Metadata: "internal/starlink/pb/starlink.proto",
+}

internal/starlink/starlink.go

@@ -0,0 +1,81 @@
+// Package starlink detects a Starlink dish on the local network and reads a
+// short status summary from the dish's local gRPC endpoint. Detection and
+// the status fetch sit behind the Client interface, so the monitor is
+// tested with a fake and needs no dish and no network. Render turns a
+// Status into the two lines the UI draws and is a pure function.
+package starlink
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+// Address is the dish's fixed local gRPC endpoint. Every dish answers here
+// from behind the Starlink router, whatever the LAN's own addressing is, so
+// this is not the default gateway (that is the router).
+const Address = "192.168.100.1:9200"
+
+// StateConnected is the dish state string that means the link is up; any
+// other state is treated as an alert condition by Render.
+const StateConnected = "CONNECTED"
+
+// Units used when reducing the dish's raw values to display values.
+const (
+	percentScale   = 100.0
+	bitsPerMegabit = 1_000_000.0
+	hoursPerDay    = 24
+	minutesPerHour = 60
+)
+
+// Status is the subset of the dish's get_status response that rtnetmon
+// shows. Throughput is megabits per second; obstruction and drop are
+// percentages on a 0..100 scale.
+type Status struct {
+	State          string
+	Uptime         time.Duration
+	ObstructionPct float64
+	Alerts         int
+	PopPingMs      float64
+	PopPingDropPct float64
+	DownlinkMbps   float64
+	UplinkMbps     float64
+}
+
+// Client probes for a dish and reads its status. The real implementation
+// speaks gRPC to Address over one bound interface; tests use a fake.
+type Client interface {
+	// Probe reports whether a dish answers on Address over the bound
+	// interface. It is cheap: a TCP connect, no gRPC call.
+	Probe(ctx context.Context) bool
+	// Status fetches the dish's current status.
+	Status(ctx context.Context) (Status, error)
+}
+
+// Render formats a Status as the two status lines drawn under the physical
+// pane, and reports whether they warrant an alert (red) color: the dish is
+// not connected, or an alert is active.
+func Render(s Status) (string, string, bool) {
+	line1 := fmt.Sprintf(
+		"Starlink: %s  uptime %s  obstruction %.1f%%  alerts %d",
+		s.State, formatUptime(s.Uptime), s.ObstructionPct, s.Alerts)
+	line2 := fmt.Sprintf(
+		"  pop ping %.0fms / drop %.1f%%  down %.1fMbps / up %.1fMbps",
+		s.PopPingMs, s.PopPingDropPct, s.DownlinkMbps, s.UplinkMbps)
+	alert := s.State != StateConnected || s.Alerts > 0
+
+	return line1, line2, alert
+}
+
+// formatUptime renders a duration as whole days, hours and minutes.
+func formatUptime(d time.Duration) string {
+	if d < 0 {
+		d = 0
+	}
+
+	days := int64(d / (hoursPerDay * time.Hour))
+	hours := int64(d/time.Hour) % hoursPerDay
+	mins := int64(d/time.Minute) % minutesPerHour
+
+	return fmt.Sprintf("%dd %dh %dm", days, hours, mins)
+}

internal/starlink/starlink_test.go

@@ -0,0 +1,79 @@
+package starlink_test
+
+import (
+	"testing"
+	"time"
+
+	"git.eeqj.de/sneak/rtnetmon/internal/starlink"
+)
+
+func TestRender(t *testing.T) {
+	t.Parallel()
+
+	connected := starlink.Status{
+		State:          "CONNECTED",
+		Uptime:         3*24*time.Hour + 4*time.Hour + 12*time.Minute,
+		ObstructionPct: 0.1,
+		Alerts:         0,
+		PopPingMs:      34,
+		PopPingDropPct: 0.0,
+		DownlinkMbps:   145.3,
+		UplinkMbps:     12.1,
+	}
+
+	tests := []struct {
+		name      string
+		status    starlink.Status
+		wantLine1 string
+		wantLine2 string
+		wantAlert bool
+	}{
+		{
+			name:      "connected, no alert",
+			status:    connected,
+			wantLine1: "Starlink: CONNECTED  uptime 3d 4h 12m  obstruction 0.1%  alerts 0",
+			wantLine2: "  pop ping 34ms / drop 0.0%  down 145.3Mbps / up 12.1Mbps",
+			wantAlert: false,
+		},
+		{
+			name: "searching is an alert",
+			status: starlink.Status{
+				State:  "SEARCHING",
+				Uptime: 0,
+			},
+			wantLine1: "Starlink: SEARCHING  uptime 0d 0h 0m  obstruction 0.0%  alerts 0",
+			wantLine2: "  pop ping 0ms / drop 0.0%  down 0.0Mbps / up 0.0Mbps",
+			wantAlert: true,
+		},
+		{
+			name: "connected but alerts active",
+			status: starlink.Status{
+				State:  "CONNECTED",
+				Uptime: 90 * time.Minute,
+				Alerts: 2,
+			},
+			wantLine1: "Starlink: CONNECTED  uptime 0d 1h 30m  obstruction 0.0%  alerts 2",
+			wantLine2: "  pop ping 0ms / drop 0.0%  down 0.0Mbps / up 0.0Mbps",
+			wantAlert: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			line1, line2, alert := starlink.Render(tt.status)
+			if line1 != tt.wantLine1 {
+				t.Errorf("line1 = %q, want %q", line1, tt.wantLine1)
+			}
+
+			if line2 != tt.wantLine2 {
+				t.Errorf("line2 = %q, want %q", line2, tt.wantLine2)
+			}
+
+			if alert != tt.wantAlert {
+				t.Errorf("alert = %v, want %v", alert, tt.wantAlert)
+			}
+		})
+	}
+}