hook up SIGUSR2 to DHCPRELEASE

cmd/dhcp4/dhcp4.go

@@ -32,6 +32,8 @@ func logic() error {
 	c := dhcp4.Client{
 		Interface: iface,
 	}
+	usr2 := make(chan os.Signal, 1)
+	signal.Notify(usr2, syscall.SIGUSR2)
 	for c.ObtainOrRenew() {
 		if err := c.Err(); err != nil {
 			log.Printf("Temporary error: %v", err)
@@ -48,7 +50,15 @@ func logic() error {
 		if err := notify.Process("/user/netconfi", syscall.SIGUSR1); err != nil {
 			log.Printf("notifying netconfig: %v", err)
 		}
-		time.Sleep(time.Until(c.Config().RenewAfter))
+		select {
+		case <-time.After(time.Until(c.Config().RenewAfter)):
+			// fallthrough and renew the DHCP lease
+		case <-usr2:
+			if err := c.Release(); err != nil {
+				return err
+			}
+			os.Exit(125) // quit supervision by gokrazy
+		}
 	}
 	return c.Err() // permanent error
 }

internal/dhcp4/dhcp4.go

@@ -36,6 +36,9 @@ type Client struct {
 	cfg          Config
 	timeNow      func() time.Time
 	randRead     func([]byte) (int, error)
+
+	// last DHCPACK packet for renewal/release
+	ack dhcp4.Packet
 }
 
 // ObtainOrRenew returns false when encountering a permanent error.
@@ -87,6 +90,7 @@ func (c *Client) ObtainOrRenew() bool {
 		c.err = fmt.Errorf("received DHCPNAK")
 		return true // temporary error
 	}
+	c.ack = ack
 	opts := ack.ParseOptions()
 
 	// DHCPACK (described in RFC2131 4.3.1)
@@ -131,6 +135,12 @@ func (c *Client) ObtainOrRenew() bool {
 	return true
 }
 
+func (c *Client) Release() error {
+	err := c.dhcp.Release(c.ack)
+	c.ack = nil
+	return err
+}
+
 func (c *Client) Err() error {
 	return c.err
 }