Pull request: dhcpd: add purge, imp code

Updates AdguardTeam#1691.

Squashed commit of the following:

commit 2ce6cc0
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jun 16 16:42:57 2021 +0300

    dhcp: imp code

commit 8f2bd70
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jun 16 16:27:06 2021 +0300

    dhcpd: add purge, imp code

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to
 
 ### Added
 
+- The ability to completely purge DHCP leases ([#1691]).
 - The ability to set the timeout for querying the upstream servers ([#2280]).
 - The ability to change group and user ID on startup on Unix ([#2763]).
 - Experimental OpenBSD support for AMD64 and 64-bit ARM CPUs ([#2439]).
@@ -62,6 +63,7 @@ released by then.
 
 - Go 1.15 support.
 
+[#1691]: https://github.com/AdguardTeam/AdGuardHome/issues/1691
 [#2280]: https://github.com/AdguardTeam/AdGuardHome/issues/2280
 [#2439]: https://github.com/AdguardTeam/AdGuardHome/issues/2439
 [#2441]: https://github.com/AdguardTeam/AdGuardHome/issues/2441

internal/aghnet/addr.go

@@ -10,6 +10,24 @@ import (
 	"golang.org/x/net/idna"
 )
 
+// CloneIP returns a clone of an IP address.
+func CloneIP(ip net.IP) (clone net.IP) {
+	if ip != nil && len(ip) == 0 {
+		return net.IP{}
+	}
+
+	return append(clone, ip...)
+}
+
+// CloneMAC returns a clone of a MAC address.
+func CloneMAC(mac net.HardwareAddr) (clone net.HardwareAddr) {
+	if mac != nil && len(mac) == 0 {
+		return net.HardwareAddr{}
+	}
+
+	return append(clone, mac...)
+}
+
 // IPFromAddr returns an IP address from addr.  If addr is neither
 // a *net.TCPAddr nor a *net.UDPAddr, it returns nil.
 func IPFromAddr(addr net.Addr) (ip net.IP) {
@@ -31,6 +49,12 @@ func IsValidHostOuterRune(r rune) (ok bool) {
 		(r >= '0' && r <= '9')
 }
 
+// JoinHostPort is a convinient wrapper for net.JoinHostPort with port of type
+// int.
+func JoinHostPort(host string, port int) (hostport string) {
+	return net.JoinHostPort(host, strconv.Itoa(port))
+}
+
 // isValidHostRune returns true if r is a valid rune for a hostname label.
 func isValidHostRune(r rune) (ok bool) {
 	return r == '-' || IsValidHostOuterRune(r)

internal/aghnet/addr_test.go

@@ -9,6 +9,26 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestCloneIP(t *testing.T) {
+	assert.Equal(t, net.IP(nil), CloneIP(nil))
+	assert.Equal(t, net.IP{}, CloneIP(net.IP{}))
+
+	ip := net.IP{1, 2, 3, 4}
+	clone := CloneIP(ip)
+	assert.Equal(t, ip, clone)
+	assert.NotSame(t, &ip[0], &clone[0])
+}
+
+func TestCloneMAC(t *testing.T) {
+	assert.Equal(t, net.HardwareAddr(nil), CloneMAC(nil))
+	assert.Equal(t, net.HardwareAddr{}, CloneMAC(net.HardwareAddr{}))
+
+	mac := net.HardwareAddr{0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC}
+	clone := CloneMAC(mac)
+	assert.Equal(t, mac, clone)
+	assert.NotSame(t, &mac[0], &clone[0])
+}
+
 func TestIPFromAddr(t *testing.T) {
 	ip := net.IP{1, 2, 3, 4}
 	assert.Equal(t, net.IP(nil), IPFromAddr(nil))
@@ -66,6 +86,14 @@ func TestValidateHardwareAddress(t *testing.T) {
 	}
 }
 
+func TestJoinHostPort(t *testing.T) {
+	assert.Equal(t, ":0", JoinHostPort("", 0))
+	assert.Equal(t, "host:12345", JoinHostPort("host", 12345))
+	assert.Equal(t, "1.2.3.4:12345", JoinHostPort("1.2.3.4", 12345))
+	assert.Equal(t, "[1234::5678]:12345", JoinHostPort("1234::5678", 12345))
+	assert.Equal(t, "[1234::5678%lo]:12345", JoinHostPort("1234::5678%lo", 12345))
+}
+
 func repeatStr(b *strings.Builder, s string, n int) {
 	for i := 0; i < n; i++ {
 		_, _ = b.WriteString(s)

internal/aghnet/net.go

@@ -424,9 +424,3 @@ func CollectAllIfacesAddrs() (addrs []string, err error) {
 
 	return addrs, nil
 }
-
-// JoinHostPort is a convinient wrapper for net.JoinHostPort with port of type
-// int.
-func JoinHostPort(host string, port int) (hostport string) {
-	return net.JoinHostPort(host, strconv.Itoa(port))
-}

internal/dhcpd/db.go

@@ -4,6 +4,7 @@ package dhcpd
 
 import (
 	"encoding/json"
+	"fmt"
 	"net"
 	"os"
 	"time"
@@ -31,7 +32,7 @@ func normalizeIP(ip net.IP) net.IP {
 }
 
 // Load lease table from DB
-func (s *Server) dbLoad() {
+func (s *Server) dbLoad() (err error) {
 	dynLeases := []*Lease{}
 	staticLeases := []*Lease{}
 	v6StaticLeases := []*Lease{}
@@ -40,17 +41,16 @@ func (s *Server) dbLoad() {
 	data, err := os.ReadFile(s.conf.DBFilePath)
 	if err != nil {
 		if !errors.Is(err, os.ErrNotExist) {
-			log.Error("dhcp: can't read file %q: %v", s.conf.DBFilePath, err)
+			return fmt.Errorf("reading db: %w", err)
 		}
 
-		return
+		return nil
 	}
 
 	obj := []leaseJSON{}
 	err = json.Unmarshal(data, &obj)
 	if err != nil {
-		log.Error("dhcp: invalid DB: %v", err)
-		return
+		return fmt.Errorf("decoding db: %w", err)
 	}
 
 	numLeases := len(obj)
@@ -85,15 +85,23 @@ func (s *Server) dbLoad() {
 	}
 
 	leases4 := normalizeLeases(staticLeases, dynLeases)
-	s.srv4.ResetLeases(leases4)
+	err = s.srv4.ResetLeases(leases4)
+	if err != nil {
+		return fmt.Errorf("resetting dhcpv4 leases: %w", err)
+	}
 
 	leases6 := normalizeLeases(v6StaticLeases, v6DynLeases)
 	if s.srv6 != nil {
-		s.srv6.ResetLeases(leases6)
+		err = s.srv6.ResetLeases(leases6)
+		if err != nil {
+			return fmt.Errorf("resetting dhcpv6 leases: %w", err)
+		}
 	}
 
 	log.Info("dhcp: loaded leases v4:%d  v6:%d  total-read:%d from DB",
 		len(leases4), len(leases6), numLeases)
+
+	return nil
 }
 
 // Skip duplicate leases
@@ -124,20 +132,24 @@ func normalizeLeases(staticLeases, dynLeases []*Lease) []*Lease {
 }
 
 // Store lease table in DB
-func (s *Server) dbStore() {
-	var leases []leaseJSON
+func (s *Server) dbStore() (err error) {
+	// Use an empty slice here as opposed to nil so that it doesn't write
+	// "null" into the database file if leases are empty.
+	leases := []leaseJSON{}
 
 	leases4 := s.srv4.getLeasesRef()
 	for _, l := range leases4 {
 		if l.Expiry.Unix() == 0 {
 			continue
 		}
+
 		lease := leaseJSON{
 			HWAddr:   l.HWAddr,
 			IP:       l.IP,
 			Hostname: l.Hostname,
 			Expiry:   l.Expiry.Unix(),
 		}
+
 		leases = append(leases, lease)
 	}
 
@@ -147,29 +159,30 @@ func (s *Server) dbStore() {
 			if l.Expiry.Unix() == 0 {
 				continue
 			}
+
 			lease := leaseJSON{
 				HWAddr:   l.HWAddr,
 				IP:       l.IP,
 				Hostname: l.Hostname,
 				Expiry:   l.Expiry.Unix(),
 			}
+
 			leases = append(leases, lease)
 		}
 	}
 
-	data, err := json.Marshal(leases)
+	var data []byte
+	data, err = json.Marshal(leases)
 	if err != nil {
-		log.Error("json.Marshal: %v", err)
-		return
+		return fmt.Errorf("encoding db: %w", err)
 	}
 
 	err = maybe.WriteFile(s.conf.DBFilePath, data, 0o644)
 	if err != nil {
-		log.Error("dhcp: can't store lease table on disk: %v  filename: %s",
-			err, s.conf.DBFilePath)
-
-		return
+		return fmt.Errorf("writing db: %w", err)
 	}
 
-	log.Info("dhcp: stored %d leases in DB", len(leases))
+	log.Info("dhcp: stored %d leases in db", len(leases))
+
+	return nil
 }