dhcp4: persist DHCPACK to renew existing lease after reboot

cmd/dhcp4/dhcp4.go

@@ -5,6 +5,7 @@ package main
 import (
 	"encoding/json"
 	"flag"
+	"fmt"
 	"io/ioutil"
 	"net"
 	"os"
@@ -21,16 +22,22 @@ import (
 var log = teelogger.NewConsole()
 
 func logic() error {
-	const configPath = "/perm/dhcp4/wire/lease.json"
+	const leasePath = "/perm/dhcp4/wire/lease.json"
-	if err := os.MkdirAll(filepath.Dir(configPath), 0755); err != nil {
+	if err := os.MkdirAll(filepath.Dir(leasePath), 0755); err != nil {
 		return err
 	}
 	iface, err := net.InterfaceByName("uplink0")
 	if err != nil {
 		return err
 	}
+	const ackFn = "/perm/dhcp4/wire/ack"
+	ack, err := ioutil.ReadFile(ackFn)
+	if err != nil && !os.IsNotExist(err) {
+		log.Printf("Loading previous DHCPACK packet from %s: %v", ackFn, err)
+	}
 	c := dhcp4.Client{
 		Interface: iface,
+		Ack:       ack,
 	}
 	usr2 := make(chan os.Signal, 1)
 	signal.Notify(usr2, syscall.SIGUSR2)
@@ -45,8 +52,11 @@ func logic() error {
 		if err != nil {
 			return err
 		}
-		if err := ioutil.WriteFile(configPath, b, 0644); err != nil {
+		if err := ioutil.WriteFile(leasePath, b, 0644); err != nil {
-			return err
+			return fmt.Errorf("persisting lease to %s: %v", leasePath, err)
+		}
+		if err := ioutil.WriteFile(ackFn, c.Ack, 0644); err != nil {
+			return fmt.Errorf("persisting DHCPACK to %s: %v", ackFn, err)
 		}
 		if err := notify.Process("/user/netconfi", syscall.SIGUSR1); err != nil {
 			log.Printf("notifying netconfig: %v", err)

integrationdhcpv4_test.go

@@ -88,6 +88,7 @@ func TestDHCPv4(t *testing.T) {
 	c := dhcp4.Client{
 		Interface: iface,
 	}
+	// Obtain first, then renew
 	for i := 0; i < 2; i++ {
 		if !c.ObtainOrRenew() {
 			t.Fatal(c.Err())
@@ -96,6 +97,21 @@ func TestDHCPv4(t *testing.T) {
 			t.Fatal(err)
 		}
 	}
+
+	// Renew once more, but with a new client object (simulating a dhcp4 process
+	// restart).
+	ack := c.Ack
+	c = dhcp4.Client{
+		Interface: iface,
+		Ack:       ack,
+	}
+	if !c.ObtainOrRenew() {
+		t.Fatal(c.Err())
+	}
+	if err := c.Err(); err != nil {
+		t.Fatal(err)
+	}
+
 	cfg := c.Config()
 	t.Logf("cfg = %+v", cfg)
 	if got, want := cfg.Router, "192.168.23.1"; got != want {
@@ -121,6 +137,9 @@ func TestDHCPv4(t *testing.T) {
 		"DHCPREQUEST(veth0b) 192.168.23.4 02:73:53:00:ca:fe",
 		"DHCPACK(veth0b) 192.168.23.4 02:73:53:00:ca:fe midna",
 
+		"DHCPREQUEST(veth0b) 192.168.23.4 02:73:53:00:ca:fe",
+		"DHCPACK(veth0b) 192.168.23.4 02:73:53:00:ca:fe midna",
+
 		"DHCPRELEASE(veth0b) 192.168.23.4 02:73:53:00:ca:fe",
 	}
 	trimSpace := func(line string) string {

internal/dhcp4/dhcp4.go

@@ -38,7 +38,7 @@ type Client struct {
 	generateXID  func([]byte)
 
 	// last DHCPACK packet for renewal/release
-	ack dhcp4.Packet
+	Ack dhcp4.Packet
 }
 
 // ObtainOrRenew returns false when encountering a permanent error.
@@ -76,7 +76,6 @@ func (c *Client) ObtainOrRenew() bool {
 		c.dhcp = dhcp
 	})
 	c.err = nil // clear previous error
-	// TODO: renew if c.ack != nil, fall back if renewal fails
 	ok, ack, err := c.dhcpRequest()
 	if err != nil {
 		if errno, ok := err.(syscall.Errno); ok && errno == syscall.EAGAIN {
@@ -90,7 +89,7 @@ func (c *Client) ObtainOrRenew() bool {
 		c.err = fmt.Errorf("received DHCPNAK")
 		return true // temporary error
 	}
-	c.ack = ack
+	c.Ack = ack
 	opts := ack.ParseOptions()
 
 	// DHCPACK (described in RFC2131 4.3.1)
@@ -136,8 +135,8 @@ func (c *Client) ObtainOrRenew() bool {
 }
 
 func (c *Client) Release() error {
-	err := c.dhcp.Release(c.ack)
+	err := c.dhcp.Release(c.Ack)
-	c.ack = nil
+	c.Ack = nil
 	return err
 }
 
@@ -173,7 +172,7 @@ func (c *Client) addClientId(p *dhcp4.Packet) {
 // includes the hostname.
 func (c *Client) dhcpRequest() (bool, dhcp4.Packet, error) {
 	var last dhcp4.Packet
-	if c.ack == nil {
+	if c.Ack == nil {
 		discoveryPacket := c.dhcp.DiscoverPacket()
 		c.addHostname(&discoveryPacket)
 		c.addClientId(&discoveryPacket)
@@ -189,7 +188,7 @@ func (c *Client) dhcpRequest() (bool, dhcp4.Packet, error) {
 		}
 		last = offerPacket
 	} else {
-		last = c.ack
+		last = c.Ack
 	}
 
 	requestPacket := c.dhcp.RequestPacket(&last)
@@ -208,7 +207,7 @@ func (c *Client) dhcpRequest() (bool, dhcp4.Packet, error) {
 
 	acknowledgementOptions := acknowledgement.ParseOptions()
 	if dhcp4.MessageType(acknowledgementOptions[dhcp4.OptionDHCPMessageType][0]) != dhcp4.ACK {
-		c.ack = nil // start over
+		c.Ack = nil // start over
 		return false, acknowledgement, nil
 	}