From f40ef76c790bb15fc73a123b2a8dede4e6618ad9 Mon Sep 17 00:00:00 2001
From: Eugene Burkov <e.burkov@adguard.com>
Date: Thu, 22 Jun 2023 14:18:43 +0300
Subject: [PATCH] Pull request 1861: 4923-gopacket-dhcp vol.1

Merge in DNS/adguard-home from 4923-gopacket-dhcp to master

Updates #4923.

Squashed commit of the following:

commit edf36ce8b1873272c3daebe8cc8f8132793aac44
Merge: a17513d3e 123ca8738
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jun 22 14:14:39 2023 +0300

    Merge branch 'master' into 4923-gopacket-dhcp

commit a17513d3e0a9e596d56444dfa46478eee15631de
Merge: f04727c29 994906fbd
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 21 17:49:09 2023 +0300

    Merge branch 'master' into 4923-gopacket-dhcp

commit f04727c29eaf22f9eb53f3aa33d42d00e177b224
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Jun 20 15:42:31 2023 +0300

    home: revert clients container

commit c58284ac6b5b2274da5eed2e853847d757709e5b
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Jun 19 21:10:36 2023 +0300

    all: imp code, names, docs

commit 4c4613c939e1325d11655822d9dbc3f05a6d203c
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Jun 13 18:51:12 2023 +0300

    all: imp code

commit 0b4a6e0dd561d9b7bb78dea21dcc947bcd0bd583
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Jun 7 18:40:15 2023 +0300

    all: imp api

commit 0425edea03d6ca0859657df683bef6ec45bfc399
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Jun 5 15:57:23 2023 +0300

    dhcpsvc: introduce package

commit 5628ebe6cccf91e2c48778966730bcbbe9e1d9f2
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jun 1 17:49:12 2023 +0300

    WIP
---
 internal/dhcpd/bitset.go          |   5 +-
 internal/dhcpd/conn_bsd.go        |  17 ++--
 internal/dhcpd/conn_linux.go      |  17 ++--
 internal/dhcpd/dhcpd.go           |   7 +-
 internal/dhcpd/routeradv.go       |   2 +-
 internal/dhcpsvc/config.go        |  86 ++++++++++++++++++
 internal/dhcpsvc/dhcpsvc.go       | 120 ++++++++++++++++++++++++
 internal/dnsforward/dnsforward.go |  21 +++++
 internal/home/clients.go          | 146 +++++++++++++++---------------
 internal/home/rdns_test.go        |   7 +-
 10 files changed, 324 insertions(+), 104 deletions(-)
 create mode 100644 internal/dhcpsvc/config.go
 create mode 100644 internal/dhcpsvc/dhcpsvc.go

diff --git a/internal/dhcpd/bitset.go b/internal/dhcpd/bitset.go
index e726319c..7459c2f1 100644
--- a/internal/dhcpd/bitset.go
+++ b/internal/dhcpd/bitset.go
@@ -25,11 +25,8 @@ func (s *bitSet) isSet(n uint64) (ok bool) {
 
 	var word uint64
 	word, ok = s.words[wordIdx]
-	if !ok {
-		return false
-	}
 
-	return word&(1<<bitIdx) != 0
+	return ok && word&(1<<bitIdx) != 0
 }
 
 // set sets or unsets a bit.
diff --git a/internal/dhcpd/conn_bsd.go b/internal/dhcpd/conn_bsd.go
index 3a8aff93..8ec630c4 100644
--- a/internal/dhcpd/conn_bsd.go
+++ b/internal/dhcpd/conn_bsd.go
@@ -249,31 +249,30 @@ func (c *dhcpConn) buildEtherPkt(payload []byte, peer *dhcpUnicastAddr) (pkt []b
 func (s *v4Server) send(peer net.Addr, conn net.PacketConn, req, resp *dhcpv4.DHCPv4) {
 	switch giaddr, ciaddr, mtype := req.GatewayIPAddr, req.ClientIPAddr, resp.MessageType(); {
 	case giaddr != nil && !giaddr.IsUnspecified():
-		// Send any return messages to the server port on the BOOTP
-		// relay agent whose address appears in giaddr.
+		// Send any return messages to the server port on the BOOTP relay agent
+		// whose address appears in giaddr.
 		peer = &net.UDPAddr{
 			IP:   giaddr,
 			Port: dhcpv4.ServerPort,
 		}
 		if mtype == dhcpv4.MessageTypeNak {
 			// Set the broadcast bit in the DHCPNAK, so that the relay agent
-			// broadcasts it to the client, because the client may not have
-			// a correct network address or subnet mask, and the client may not
-			// be answering ARP requests.
+			// broadcasts it to the client, because the client may not have a
+			// correct network address or subnet mask, and the client may not be
+			// answering ARP requests.
 			resp.SetBroadcast()
 		}
 	case mtype == dhcpv4.MessageTypeNak:
 		// Broadcast any DHCPNAK messages to 0xffffffff.
 	case ciaddr != nil && !ciaddr.IsUnspecified():
-		// Unicast DHCPOFFER and DHCPACK messages to the address in
-		// ciaddr.
+		// Unicast DHCPOFFER and DHCPACK messages to the address in ciaddr.
 		peer = &net.UDPAddr{
 			IP:   ciaddr,
 			Port: dhcpv4.ClientPort,
 		}
 	case !req.IsBroadcast() && req.ClientHWAddr != nil:
-		// Unicast DHCPOFFER and DHCPACK messages to the client's
-		// hardware address and yiaddr.
+		// Unicast DHCPOFFER and DHCPACK messages to the client's hardware
+		// address and yiaddr.
 		peer = &dhcpUnicastAddr{
 			Addr:   raw.Addr{HardwareAddr: req.ClientHWAddr},
 			yiaddr: resp.YourIPAddr,
diff --git a/internal/dhcpd/conn_linux.go b/internal/dhcpd/conn_linux.go
index 1ebcc339..a1c26e51 100644
--- a/internal/dhcpd/conn_linux.go
+++ b/internal/dhcpd/conn_linux.go
@@ -247,31 +247,30 @@ func (c *dhcpConn) buildEtherPkt(payload []byte, peer *dhcpUnicastAddr) (pkt []b
 func (s *v4Server) send(peer net.Addr, conn net.PacketConn, req, resp *dhcpv4.DHCPv4) {
 	switch giaddr, ciaddr, mtype := req.GatewayIPAddr, req.ClientIPAddr, resp.MessageType(); {
 	case giaddr != nil && !giaddr.IsUnspecified():
-		// Send any return messages to the server port on the BOOTP
-		// relay agent whose address appears in giaddr.
+		// Send any return messages to the server port on the BOOTP relay agent
+		// whose address appears in giaddr.
 		peer = &net.UDPAddr{
 			IP:   giaddr,
 			Port: dhcpv4.ServerPort,
 		}
 		if mtype == dhcpv4.MessageTypeNak {
 			// Set the broadcast bit in the DHCPNAK, so that the relay agent
-			// broadcasts it to the client, because the client may not have
-			// a correct network address or subnet mask, and the client may not
-			// be answering ARP requests.
+			// broadcasts it to the client, because the client may not have a
+			// correct network address or subnet mask, and the client may not be
+			// answering ARP requests.
 			resp.SetBroadcast()
 		}
 	case mtype == dhcpv4.MessageTypeNak:
 		// Broadcast any DHCPNAK messages to 0xffffffff.
 	case ciaddr != nil && !ciaddr.IsUnspecified():
-		// Unicast DHCPOFFER and DHCPACK messages to the address in
-		// ciaddr.
+		// Unicast DHCPOFFER and DHCPACK messages to the address in ciaddr.
 		peer = &net.UDPAddr{
 			IP:   ciaddr,
 			Port: dhcpv4.ClientPort,
 		}
 	case !req.IsBroadcast() && req.ClientHWAddr != nil:
-		// Unicast DHCPOFFER and DHCPACK messages to the client's
-		// hardware address and yiaddr.
+		// Unicast DHCPOFFER and DHCPACK messages to the client's hardware
+		// address and yiaddr.
 		peer = &dhcpUnicastAddr{
 			Addr:   packet.Addr{HardwareAddr: req.ClientHWAddr},
 			yiaddr: resp.YourIPAddr,
diff --git a/internal/dhcpd/dhcpd.go b/internal/dhcpd/dhcpd.go
index 5a3656d1..3945c038 100644
--- a/internal/dhcpd/dhcpd.go
+++ b/internal/dhcpd/dhcpd.go
@@ -28,8 +28,9 @@ const (
 	defaultBackoff     time.Duration = 500 * time.Millisecond
 )
 
-// Lease contains the necessary information about a DHCP lease.  It's used in
-// various places.  So don't change it without good reason.
+// Lease contains the necessary information about a DHCP lease.  It's used as is
+// in the database, so don't change it until it's absolutely necessary, see
+// [dataVersion].
 type Lease struct {
 	// Expiry is the expiration time of the lease.
 	Expiry time.Time `json:"expires"`
@@ -41,8 +42,6 @@ type Lease struct {
 	HWAddr net.HardwareAddr `json:"mac"`
 
 	// IP is the IP address leased to the client.
-	//
-	// TODO(a.garipov): Migrate leases.db.
 	IP netip.Addr `json:"ip"`
 
 	// IsStatic defines if the lease is static.
diff --git a/internal/dhcpd/routeradv.go b/internal/dhcpd/routeradv.go
index a826df91..2b480b46 100644
--- a/internal/dhcpd/routeradv.go
+++ b/internal/dhcpd/routeradv.go
@@ -200,7 +200,7 @@ func createICMPv6RAPacket(params icmpv6RA) (data []byte, err error) {
 func (ra *raCtx) Init() (err error) {
 	ra.stop.Store(0)
 	ra.conn = nil
-	if !(ra.raAllowSLAAC || ra.raSLAACOnly) {
+	if !ra.raAllowSLAAC && !ra.raSLAACOnly {
 		return nil
 	}
 
diff --git a/internal/dhcpsvc/config.go b/internal/dhcpsvc/config.go
new file mode 100644
index 00000000..b01dc263
--- /dev/null
+++ b/internal/dhcpsvc/config.go
@@ -0,0 +1,86 @@
+package dhcpsvc
+
+import (
+	"net/netip"
+	"time"
+
+	"github.com/google/gopacket/layers"
+)
+
+// Config is the configuration for the DHCP service.
+type Config struct {
+	// Interfaces stores configurations of DHCP server specific for the network
+	// interface identified by its name.
+	Interfaces map[string]*InterfaceConfig
+
+	// LocalDomainName is the top-level domain name to use for resolving DHCP
+	// clients' hostnames.
+	LocalDomainName string
+
+	// ICMPTimeout is the timeout for checking another DHCP server's presence.
+	ICMPTimeout time.Duration
+
+	// Enabled is the state of the service, whether it is enabled or not.
+	Enabled bool
+}
+
+// InterfaceConfig is the configuration of a single DHCP interface.
+type InterfaceConfig struct {
+	// IPv4 is the configuration of DHCP protocol for IPv4.
+	IPv4 *IPv4Config
+
+	// IPv6 is the configuration of DHCP protocol for IPv6.
+	IPv6 *IPv6Config
+}
+
+// IPv4Config is the interface-specific configuration for DHCPv4.
+type IPv4Config struct {
+	// GatewayIP is the IPv4 address of the network's gateway.  It is used as
+	// the default gateway for DHCP clients and also used in calculating the
+	// network-specific broadcast address.
+	GatewayIP netip.Addr
+
+	// SubnetMask is the IPv4 subnet mask of the network.  It should be a valid
+	// IPv4 subnet mask (i.e. all 1s followed by all 0s).
+	SubnetMask netip.Addr
+
+	// RangeStart is the first address in the range to assign to DHCP clients.
+	RangeStart netip.Addr
+
+	// RangeEnd is the last address in the range to assign to DHCP clients.
+	RangeEnd netip.Addr
+
+	// Options is the list of DHCP options to send to DHCP clients.
+	Options layers.DHCPOptions
+
+	// LeaseDuration is the TTL of a DHCP lease.
+	LeaseDuration time.Duration
+
+	// Enabled is the state of the DHCPv4 service, whether it is enabled or not
+	// on the specific interface.
+	Enabled bool
+}
+
+// IPv6Config is the interface-specific configuration for DHCPv6.
+type IPv6Config struct {
+	// RangeStart is the first address in the range to assign to DHCP clients.
+	RangeStart netip.Addr
+
+	// Options is the list of DHCP options to send to DHCP clients.
+	Options layers.DHCPOptions
+
+	// LeaseDuration is the TTL of a DHCP lease.
+	LeaseDuration time.Duration
+
+	// RASlaacOnly defines whether the DHCP clients should only use SLAAC for
+	// address assignment.
+	RASLAACOnly bool
+
+	// RAAllowSlaac defines whether the DHCP clients may use SLAAC for address
+	// assignment.
+	RAAllowSLAAC bool
+
+	// Enabled is the state of the DHCPv6 service, whether it is enabled or not
+	// on the specific interface.
+	Enabled bool
+}
diff --git a/internal/dhcpsvc/dhcpsvc.go b/internal/dhcpsvc/dhcpsvc.go
new file mode 100644
index 00000000..0c5d1bad
--- /dev/null
+++ b/internal/dhcpsvc/dhcpsvc.go
@@ -0,0 +1,120 @@
+// Package dhcpsvc contains the AdGuard Home DHCP service.
+//
+// TODO(e.burkov): Add tests.
+package dhcpsvc
+
+import (
+	"context"
+	"net"
+	"net/netip"
+	"time"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/next/agh"
+)
+
+// Lease is a DHCP lease.
+//
+// TODO(e.burkov):  Consider it to [agh], since it also may be needed in
+// [websvc].  Also think of implementing iterating methods with appropriate
+// signatures.
+type Lease struct {
+	// IP is the IP address leased to the client.
+	IP netip.Addr
+
+	// Expiry is the expiration time of the lease.
+	Expiry time.Time
+
+	// Hostname of the client.
+	Hostname string
+
+	// HWAddr is the physical hardware address (MAC address).
+	HWAddr net.HardwareAddr
+
+	// IsStatic defines if the lease is static.
+	IsStatic bool
+}
+
+type Interface interface {
+	agh.ServiceWithConfig[*Config]
+
+	// Enabled returns true if DHCP provides information about clients.
+	Enabled() (ok bool)
+
+	// HostByIP returns the hostname of the DHCP client with the given IP
+	// address.  The address will be netip.Addr{} if there is no such client,
+	// due to an assumption that a DHCP client must always have an IP address.
+	HostByIP(ip netip.Addr) (host string)
+
+	// MACByIP returns the MAC address for the given IP address leased.  It
+	// returns nil if there is no such client, due to an assumption that a DHCP
+	// client must always have a MAC address.
+	MACByIP(ip netip.Addr) (mac net.HardwareAddr)
+
+	// IPByHost returns the IP address of the DHCP client with the given
+	// hostname.  The hostname will be an empty string if there is no such
+	// client, due to an assumption that a DHCP client must always have a
+	// hostname, either set by the client or assigned automatically.
+	IPByHost(host string) (ip netip.Addr)
+
+	// Leases returns all the DHCP leases.
+	Leases() (leases []*Lease)
+
+	// AddLease adds a new DHCP lease.  It returns an error if the lease is
+	// invalid or already exists.
+	AddLease(l *Lease) (err error)
+
+	// EditLease changes an existing DHCP lease.  It returns an error if there
+	// is no lease equal to old or if new is invalid or already exists.
+	EditLease(old, new *Lease) (err error)
+
+	// RemoveLease removes an existing DHCP lease.  It returns an error if there
+	// is no lease equal to l.
+	RemoveLease(l *Lease) (err error)
+
+	// Reset removes all the DHCP leases.
+	Reset() (err error)
+}
+
+// Empty is an [Interface] implementation that does nothing.
+type Empty struct{}
+
+// type check
+var _ Interface = Empty{}
+
+// Start implements the [Service] interface for Empty.
+func (Empty) Start() (err error) { return nil }
+
+// Shutdown implements the [Service] interface for Empty.
+func (Empty) Shutdown(_ context.Context) (err error) { return nil }
+
+var _ agh.ServiceWithConfig[*Config] = Empty{}
+
+// Config implements the [ServiceWithConfig] interface for Empty.
+func (Empty) Config() (conf *Config) { return nil }
+
+// Enabled implements the [Interface] interface for Empty.
+func (Empty) Enabled() (ok bool) { return false }
+
+// HostByIP implements the [Interface] interface for Empty.
+func (Empty) HostByIP(_ netip.Addr) (host string) { return "" }
+
+// MACByIP implements the [Interface] interface for Empty.
+func (Empty) MACByIP(_ netip.Addr) (mac net.HardwareAddr) { return nil }
+
+// IPByHost implements the [Interface] interface for Empty.
+func (Empty) IPByHost(_ string) (ip netip.Addr) { return netip.Addr{} }
+
+// Leases implements the [Interface] interface for Empty.
+func (Empty) Leases() (leases []*Lease) { return nil }
+
+// AddLease implements the [Interface] interface for Empty.
+func (Empty) AddLease(_ *Lease) (err error) { return nil }
+
+// EditLease implements the [Interface] interface for Empty.
+func (Empty) EditLease(_, _ *Lease) (err error) { return nil }
+
+// RemoveLease implements the [Interface] interface for Empty.
+func (Empty) RemoveLease(_ *Lease) (err error) { return nil }
+
+// Reset implements the [Interface] interface for Empty.
+func (Empty) Reset() (err error) { return nil }
diff --git a/internal/dnsforward/dnsforward.go b/internal/dnsforward/dnsforward.go
index 887fff41..e5ca680e 100644
--- a/internal/dnsforward/dnsforward.go
+++ b/internal/dnsforward/dnsforward.go
@@ -48,12 +48,33 @@ var webRegistered bool
 
 // hostToIPTable is a convenient type alias for tables of host names to an IP
 // address.
+//
+// TODO(e.burkov):  Use the [DHCP] interface instead.
 type hostToIPTable = map[string]netip.Addr
 
 // ipToHostTable is a convenient type alias for tables of IP addresses to their
 // host names.  For example, for use with PTR queries.
+//
+// TODO(e.burkov):  Use the [DHCP] interface instead.
 type ipToHostTable = map[netip.Addr]string
 
+// DHCP is an interface for accesing DHCP lease data needed in this package.
+type DHCP interface {
+	// HostByIP returns the hostname of the DHCP client with the given IP
+	// address.  The address will be netip.Addr{} if there is no such client,
+	// due to an assumption that a DHCP client must always have an IP address.
+	HostByIP(ip netip.Addr) (host string)
+
+	// IPByHost returns the IP address of the DHCP client with the given
+	// hostname.  The hostname will be an empty string if there is no such
+	// client, due to an assumption that a DHCP client must always have a
+	// hostname, either set by the client or assigned automatically.
+	IPByHost(host string) (ip netip.Addr)
+
+	// Enabled returns true if DHCP provides information about clients.
+	Enabled() (ok bool)
+}
+
 // Server is the main way to start a DNS server.
 //
 // Example:
diff --git a/internal/home/clients.go b/internal/home/clients.go
index 6862cf25..7771f221 100644
--- a/internal/home/clients.go
+++ b/internal/home/clients.go
@@ -11,6 +11,7 @@ import (
 
 	"github.com/AdguardTeam/AdGuardHome/internal/aghnet"
 	"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
+	"github.com/AdguardTeam/AdGuardHome/internal/dhcpsvc"
 	"github.com/AdguardTeam/AdGuardHome/internal/dnsforward"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/AdGuardHome/internal/querylog"
@@ -24,6 +25,23 @@ import (
 	"golang.org/x/exp/slices"
 )
 
+// DHCP is an interface for accesing DHCP lease data the [clientsContainer]
+// needs.
+type DHCP interface {
+	// Leases returns all the DHCP leases.
+	Leases() (leases []*dhcpsvc.Lease)
+
+	// HostByIP returns the hostname of the DHCP client with the given IP
+	// address.  The address will be netip.Addr{} if there is no such client,
+	// due to an assumption that a DHCP client must always have an IP address.
+	HostByIP(ip netip.Addr) (host string)
+
+	// MACByIP returns the MAC address for the given IP address leased.  It
+	// returns nil if there is no such client, due to an assumption that a DHCP
+	// client must always have a MAC address.
+	MACByIP(ip netip.Addr) (mac net.HardwareAddr)
+}
+
 // clientsContainer is the storage of all runtime and persistent clients.
 type clientsContainer struct {
 	// TODO(a.garipov): Perhaps use a number of separate indices for different
@@ -101,9 +119,9 @@ func (clients *clientsContainer) Init(
 		return
 	}
 
-	clients.updateFromDHCP(true)
 	if clients.dhcpServer != nil {
 		clients.dhcpServer.SetOnLeaseChanged(clients.onDHCPLeaseChanged)
+		clients.onDHCPLeaseChanged(dhcpd.LeaseChangedAdded)
 	}
 
 	if clients.etcHosts != nil {
@@ -277,15 +295,38 @@ func (clients *clientsContainer) periodicUpdate() {
 	}
 }
 
+// onDHCPLeaseChanged is a callback for the DHCP server.  It updates the list of
+// runtime clients using the DHCP server's leases.
+//
+// TODO(e.burkov):  Remove when switched to dhcpsvc.
 func (clients *clientsContainer) onDHCPLeaseChanged(flags int) {
-	switch flags {
-	case dhcpd.LeaseChangedAdded,
-		dhcpd.LeaseChangedAddedStatic,
-		dhcpd.LeaseChangedRemovedStatic:
-		clients.updateFromDHCP(true)
-	case dhcpd.LeaseChangedRemovedAll:
-		clients.updateFromDHCP(false)
+	if clients.dhcpServer == nil || !config.Clients.Sources.DHCP {
+		return
 	}
+
+	clients.lock.Lock()
+	defer clients.lock.Unlock()
+
+	clients.rmHostsBySrc(ClientSourceDHCP)
+
+	if flags == dhcpd.LeaseChangedRemovedAll {
+		return
+	}
+
+	leases := clients.dhcpServer.Leases(dhcpd.LeasesAll)
+	n := 0
+	for _, l := range leases {
+		if l.Hostname == "" {
+			continue
+		}
+
+		ok := clients.addHostLocked(l.IP, l.Hostname, ClientSourceDHCP)
+		if ok {
+			n++
+		}
+	}
+
+	log.Debug("clients: added %d client aliases from dhcp", n)
 }
 
 // clientSource checks if client with this IP address already exists and returns
@@ -301,11 +342,11 @@ func (clients *clientsContainer) clientSource(ip netip.Addr) (src clientSource)
 	}
 
 	rc, ok := clients.ipToRC[ip]
-	if !ok {
-		return ClientSourceNone
+	if ok {
+		return rc.Source
 	}
 
-	return rc.Source
+	return ClientSourceNone
 }
 
 // findMultiple is a wrapper around Find to make it a valid client finder for
@@ -466,11 +507,11 @@ func (clients *clientsContainer) findLocked(id string) (c *Client, ok bool) {
 		}
 	}
 
-	if clients.dhcpServer == nil {
-		return nil, false
+	if clients.dhcpServer != nil {
+		return clients.findDHCP(ip)
 	}
 
-	return clients.findDHCP(ip)
+	return nil, false
 }
 
 // findDHCP searches for a client by its MAC, if the DHCP server is active and
@@ -697,28 +738,27 @@ func (clients *clientsContainer) setWHOISInfo(ip netip.Addr, wi *whois.Info) {
 	_, ok := clients.findLocked(ip.String())
 	if ok {
 		log.Debug("clients: client for %s is already created, ignore whois info", ip)
+
 		return
 	}
 
+	// TODO(e.burkov):  Consider storing WHOIS information separately and
+	// potentially get rid of [RuntimeClient].
 	rc, ok := clients.ipToRC[ip]
-	if ok {
-		rc.WHOIS = wi
+	if !ok {
+		// Create a RuntimeClient implicitly so that we don't do this check
+		// again.
+		rc = &RuntimeClient{
+			Source: ClientSourceWHOIS,
+		}
+		clients.ipToRC[ip] = rc
+
+		log.Debug("clients: set whois info for runtime client with ip %s: %+v", ip, wi)
+	} else {
 		log.Debug("clients: set whois info for runtime client %s: %+v", rc.Host, wi)
-
-		return
-	}
-
-	// Create a RuntimeClient implicitly so that we don't do this check
-	// again.
-	rc = &RuntimeClient{
-		Source: ClientSourceWHOIS,
 	}
 
 	rc.WHOIS = wi
-
-	clients.ipToRC[ip] = rc
-
-	log.Debug("clients: set whois info for runtime client with ip %s: %+v", ip, wi)
 }
 
 // AddHost adds a new IP-hostname pairing.  The priorities of the sources are
@@ -742,23 +782,19 @@ func (clients *clientsContainer) addHostLocked(
 	src clientSource,
 ) (ok bool) {
 	rc, ok := clients.ipToRC[ip]
-	if ok {
-		if rc.Source > src {
-			return false
-		}
-
-		rc.Host = host
-		rc.Source = src
-	} else {
+	if !ok {
 		rc = &RuntimeClient{
-			Host:   host,
-			Source: src,
-			WHOIS:  &whois.Info{},
+			WHOIS: &whois.Info{},
 		}
 
 		clients.ipToRC[ip] = rc
+	} else if src < rc.Source {
+		return false
 	}
 
+	rc.Host = host
+	rc.Source = src
+
 	log.Debug("clients: added %s -> %q [%d]", ip, host, len(clients.ipToRC))
 
 	return true
@@ -827,38 +863,6 @@ func (clients *clientsContainer) addFromSystemARP() {
 	log.Debug("clients: added %d client aliases from arp neighborhood", added)
 }
 
-// updateFromDHCP adds the clients that have a non-empty hostname from the DHCP
-// server.
-func (clients *clientsContainer) updateFromDHCP(add bool) {
-	if clients.dhcpServer == nil || !config.Clients.Sources.DHCP {
-		return
-	}
-
-	clients.lock.Lock()
-	defer clients.lock.Unlock()
-
-	clients.rmHostsBySrc(ClientSourceDHCP)
-
-	if !add {
-		return
-	}
-
-	leases := clients.dhcpServer.Leases(dhcpd.LeasesAll)
-	n := 0
-	for _, l := range leases {
-		if l.Hostname == "" {
-			continue
-		}
-
-		ok := clients.addHostLocked(l.IP, l.Hostname, ClientSourceDHCP)
-		if ok {
-			n++
-		}
-	}
-
-	log.Debug("clients: added %d client aliases from dhcp", n)
-}
-
 // close gracefully closes all the client-specific upstream configurations of
 // the persistent clients.
 func (clients *clientsContainer) close() (err error) {
diff --git a/internal/home/rdns_test.go b/internal/home/rdns_test.go
index 4e424273..078a092f 100644
--- a/internal/home/rdns_test.go
+++ b/internal/home/rdns_test.go
@@ -228,12 +228,7 @@ func TestRDNS_WorkerLoop(t *testing.T) {
 	for _, tc := range testCases {
 		w.Reset()
 
-		cc := &clientsContainer{
-			list:    map[string]*Client{},
-			idIndex: map[string]*Client{},
-			ipToRC:  map[netip.Addr]*RuntimeClient{},
-			allTags: stringutil.NewSet(),
-		}
+		cc := newClientsContainer()
 		ch := make(chan netip.Addr)
 		rdns := &RDNS{
 			exchanger: &rDNSExchanger{