Pull request 2019: 1700-update-static-lease

Updates #1700.

Squashed commit of the following:

commit b3fdf0a492e38be594500b1db4da20bf70cd7096
Merge: 507cb9bc7 4479b32ad
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Oct 5 12:53:30 2023 +0300

    Merge branch 'master' into 1700-update-static-lease

commit 507cb9bc7bec9884ce7db2f42688d0a409015756
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Wed Oct 4 18:54:06 2023 +0300

    all: upd chlog

commit 0736b97bdd652a3da13bce4177c64daa0a3da2af
Author: Ildar Kamalov <ik@adguard.com>
Date:   Wed Oct 4 16:05:35 2023 +0300

    client: fix update action

commit 351986bb03b1c525f00b1e7cd44a3dab8dd9eb97
Author: Ildar Kamalov <ik@adguard.com>
Date:   Wed Oct 4 16:01:38 2023 +0300

    client: update static lease

commit 3c328283c8374480132a9907e1738978c0b0384f
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Sep 28 20:06:29 2023 +0300

    dhcpd: fix err msg

commit 5b2f8f51b427ae07b227357fa3cc073a3278079b
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Thu Sep 28 16:28:07 2023 +0300

    dhcpd: imp code

commit a9d24e816f602ad207e42124ddbb56ecdb0e03f6
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Wed Sep 27 17:43:04 2023 +0300

    all: add tests

commit 453785796191179ef4136b613f4dd8665703b364
Author: Stanislav Chzhen <s.chzhen@adguard.com>
Date:   Tue Sep 26 20:14:17 2023 +0300

    dhcpd: update static lease

internal/dhcpd/v4_unix.go

@@ -309,9 +309,15 @@ func (s *v4Server) rmDynamicLease(lease *Lease) (err error) {
 	return nil
 }
 
-// ErrDupHostname is returned by addLease when the added lease has a not empty
-// non-unique hostname.
-const ErrDupHostname = errors.Error("hostname is not unique")
+const (
+	// ErrDupHostname is returned by addLease, validateStaticLease when the
+	// modified lease has a not empty non-unique hostname.
+	ErrDupHostname = errors.Error("hostname is not unique")
+
+	// ErrDupIP is returned by addLease, validateStaticLease when the modified
+	// lease has a non-unique IP address.
+	ErrDupIP = errors.Error("ip address is not unique")
+)
 
 // addLease adds a dynamic or static lease.
 func (s *v4Server) addLease(l *Lease) (err error) {
@@ -428,6 +434,81 @@ func (s *v4Server) AddStaticLease(l *Lease) (err error) {
 	return nil
 }
 
+// UpdateStaticLease updates IP, hostname of the static lease.
+func (s *v4Server) UpdateStaticLease(l *Lease) (err error) {
+	defer func() {
+		if err != nil {
+			err = errors.Annotate(err, "dhcpv4: updating static lease: %w")
+
+			return
+		}
+
+		s.conf.notify(LeaseChangedDBStore)
+		s.conf.notify(LeaseChangedRemovedStatic)
+	}()
+
+	s.leasesLock.Lock()
+	defer s.leasesLock.Unlock()
+
+	found := s.findLease(l.HWAddr)
+	if found == nil {
+		return fmt.Errorf("can't find lease %s", l.HWAddr)
+	}
+
+	err = s.validateStaticLease(l)
+	if err != nil {
+		return err
+	}
+
+	err = s.rmLease(found)
+	if err != nil {
+		return fmt.Errorf("removing previous lease for %s (%s): %w", l.IP, l.HWAddr, err)
+	}
+
+	err = s.addLease(l)
+	if err != nil {
+		return fmt.Errorf("adding updated static lease for %s (%s): %w", l.IP, l.HWAddr, err)
+	}
+
+	return nil
+}
+
+// validateStaticLease returns an error if the static lease is invalid.
+func (s *v4Server) validateStaticLease(l *Lease) (err error) {
+	hostname, err := normalizeHostname(l.Hostname)
+	if err != nil {
+		// Don't wrap the error, because it's informative enough as is.
+		return err
+	}
+
+	err = netutil.ValidateHostname(hostname)
+	if err != nil {
+		return fmt.Errorf("validating hostname: %w", err)
+	}
+
+	dup, ok := s.hostsIndex[hostname]
+	if ok && !bytes.Equal(dup.HWAddr, l.HWAddr) {
+		return ErrDupHostname
+	}
+
+	dup, ok = s.ipIndex[l.IP]
+	if ok && !bytes.Equal(dup.HWAddr, l.HWAddr) {
+		return ErrDupIP
+	}
+
+	l.Hostname = hostname
+
+	if gwIP := s.conf.GatewayIP; gwIP == l.IP {
+		return fmt.Errorf("can't assign the gateway IP %q to the lease", gwIP)
+	}
+
+	if sn := s.conf.subnet; !sn.Contains(l.IP) {
+		return fmt.Errorf("subnet %s does not contain the ip %q", sn, l.IP)
+	}
+
+	return nil
+}
+
 // updateStaticLease safe removes dynamic lease with the same properties and
 // then adds a static lease l.
 func (s *v4Server) updateStaticLease(l *Lease) (err error) {