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/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
+}

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 }