feat: let the router set the ready GPIO pin after startup

debian/arduino-router/etc/systemd/system/arduino-router.service

@@ -7,9 +7,8 @@ Requires=
 [Service]
 # Put the micro in a ready state.
 ExecStartPre=-/usr/bin/gpioset -c /dev/gpiochip1 -t0 37=0
-ExecStart=/usr/bin/arduino-router --unix-port /var/run/arduino-router.sock --serial-port /dev/ttyHS1 --serial-baudrate 115200
-# End the boot animation after the router is started.
-ExecStartPost=/usr/bin/gpioset -c /dev/gpiochip1 -t0 70=1
+# Launch router and end the boot animation after the router is started (--after-start).
+ExecStart=/usr/bin/arduino-router --unix-port /var/run/arduino-router.sock --serial-port /dev/ttyHS1 --serial-baudrate 115200 --after-start "/usr/bin/gpioset -c /dev/gpiochip1 -t0 70=1"
 StandardOutput=journal
 StandardError=journal
 Restart=always

main.go

@@ -25,6 +25,7 @@ import (
 	"net"
 	"os"
 	"os/signal"
+	"strings"
 	"sync"
 	"syscall"
 	"time"
@@ -35,6 +36,7 @@ import (
 	"github.com/arduino/arduino-router/msgpackrpc"
 	networkapi "github.com/arduino/arduino-router/network-api"
 
+	"github.com/arduino/go-paths-helper"
 	"github.com/spf13/cobra"
 	"go.bug.st/f"
 	"go.bug.st/serial"
@@ -51,6 +53,7 @@ type Config struct {
 	SerialPortAddr  string
 	SerialBaudRate  int
 	MonitorPortAddr string
+	StartCallback   string
 }
 
 func main() {
@@ -86,6 +89,7 @@ func main() {
 	cmd.Flags().StringVarP(&cfg.SerialPortAddr, "serial-port", "p", "", "Serial port address")
 	cmd.Flags().IntVarP(&cfg.SerialBaudRate, "serial-baudrate", "b", 115200, "Serial port baud rate")
 	cmd.Flags().StringVarP(&cfg.MonitorPortAddr, "monitor-port", "m", "127.0.0.1:7500", "Listening port for MCU monitor proxy")
+	cmd.Flags().StringVar(&cfg.StartCallback, "after-start", "", "Command to execute when the router has successfully completed startup")
 	if err := cmd.Execute(); err != nil {
 		slog.Error("Error executing command.", "error", err)
 	}
@@ -214,6 +218,10 @@ func startRouter(cfg Config) error {
 			return true, nil
 		})
 		f.Assert(err == nil, "Failed to register $/serial/close method")
+
+		var started sync.WaitGroup
+		started.Add(1)
+		initialized := sync.OnceFunc(started.Done)
 		go func() {
 			for {
 				serialOpened.L.Lock()
@@ -236,6 +244,7 @@ func startRouter(cfg Config) error {
 					time.Sleep(5 * time.Second)
 					continue
 				}
+				initialized()
 				slog.Info("Opened serial connection", "serial", cfg.SerialPortAddr)
 				wr := &MsgpackDebugStream{Name: cfg.SerialPortAddr, Upstream: serialPort}
 
@@ -252,6 +261,7 @@ func startRouter(cfg Config) error {
 				<-routerExit
 			}
 		}()
+		started.Wait()
 	}
 
 	// Wait for incoming connections on all listeners
@@ -270,6 +280,20 @@ func startRouter(cfg Config) error {
 		}()
 	}
 
+	// Execute start callback if specified
+	if cfg.StartCallback != "" {
+		slog.Info("Executing start callback", "cmd", cfg.StartCallback)
+		cb, err := paths.NewProcess(nil, strings.Split(cfg.StartCallback, " ")...)
+		if err != nil {
+			slog.Error("Failed to start callback process", "err", err)
+			return err
+		}
+		if err := cb.Run(); err != nil {
+			slog.Error("Start callback process failed", "err", err)
+			return err
+		}
+	}
+
 	// Sleep forever until interrupted
 	signalChan := make(chan os.Signal, 1)
 	signal.Notify(signalChan, os.Interrupt, syscall.SIGTERM)