Pull request: 2723 autogenerate hostnames

Merge in DNS/adguard-home from 2723-dhcp-hostnames to master

Updates #2723.

Squashed commit of the following:

commit f9b9d2269c25cabd225ba712730f04496ab81715
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Apr 15 16:47:31 2021 +0300

    aghnet: fix test

commit a2845d1003093ce38870b2cc89e9bd98ea2b8249
Merge: 74e450c9 0bcea347
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Apr 15 16:45:59 2021 +0300

    Merge branch 'master' into 2723-dhcp-hostnames

commit 74e450c919b4c39ed6f8489aea398b225a4c6861
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Apr 15 16:44:08 2021 +0300

    all: imp code, docs

commit 77cdb1232d18c8a2642b7131f051e318844c2c47
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Thu Apr 15 14:29:40 2021 +0300

    all: add gen func, use it

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to
 
 ### Added
 
+- Hostname generating for DHCP clients which don't provide their own ([#2723]).
 - New flag `--no-etc-hosts` to disable client domain name lookups in the
   operating system's /etc/hosts files ([#1947]).
 - The ability to set up custom upstreams to resolve PTR queries for local
@@ -67,6 +68,7 @@ and this project adheres to
 [#2533]: https://github.com/AdguardTeam/AdGuardHome/issues/2533
 [#2541]: https://github.com/AdguardTeam/AdGuardHome/issues/2541
 [#2704]: https://github.com/AdguardTeam/AdGuardHome/issues/2704
+[#2723]: https://github.com/AdguardTeam/AdGuardHome/issues/2723
 [#2824]: https://github.com/AdguardTeam/AdGuardHome/issues/2824
 [#2828]: https://github.com/AdguardTeam/AdGuardHome/issues/2828
 [#2835]: https://github.com/AdguardTeam/AdGuardHome/issues/2835

internal/aghnet/addr.go

@@ -3,6 +3,7 @@ package aghnet
 import (
 	"fmt"
 	"net"
+	"strconv"
 	"strings"
 
 	"github.com/AdguardTeam/AdGuardHome/internal/agherr"
@@ -99,3 +100,59 @@ func ValidateDomainName(name string) (err error) {
 
 	return nil
 }
+
+// The maximum lengths of generated hostnames for different IP versions.
+const (
+	ipv4HostnameMaxLen = len("192-168-100-10-")
+	ipv6HostnameMaxLen = len("ff80-f076-0000-0000-0000-0000-0000-0010")
+)
+
+// generateIPv4Hostname generates the hostname for specific IP version.
+func generateIPv4Hostname(ipv4 net.IP) (hostname string) {
+	hnData := make([]byte, 0, ipv4HostnameMaxLen)
+	for i, part := range ipv4 {
+		if i > 0 {
+			hnData = append(hnData, '-')
+		}
+		hnData = strconv.AppendUint(hnData, uint64(part), 10)
+	}
+
+	return string(hnData)
+}
+
+// generateIPv6Hostname generates the hostname for specific IP version.
+func generateIPv6Hostname(ipv6 net.IP) (hostname string) {
+	hnData := make([]byte, 0, ipv6HostnameMaxLen)
+	for i, partsNum := 0, net.IPv6len/2; i < partsNum; i++ {
+		if i > 0 {
+			hnData = append(hnData, '-')
+		}
+		for _, val := range ipv6[i*2 : i*2+2] {
+			if val < 10 {
+				hnData = append(hnData, '0')
+			}
+			hnData = strconv.AppendUint(hnData, uint64(val), 16)
+		}
+	}
+
+	return string(hnData)
+}
+
+// GenerateHostName generates the hostname from ip.  In case of using IPv4 the
+// result should be like:
+//
+//   192-168-10-1
+//
+// In case of using IPv6, the result is like:
+//
+//   ff80-f076-0000-0000-0000-0000-0000-0010
+//
+func GenerateHostName(ip net.IP) (hostname string) {
+	if ipv4 := ip.To4(); ipv4 != nil {
+		return generateIPv4Hostname(ipv4)
+	} else if ipv6 := ip.To16(); ipv6 != nil {
+		return generateIPv6Hostname(ipv6)
+	}
+
+	return ""
+}

internal/aghnet/addr_test.go

@@ -131,3 +131,43 @@ func TestValidateDomainName(t *testing.T) {
 		})
 	}
 }
+
+func TestGenerateHostName(t *testing.T) {
+	testCases := []struct {
+		name string
+		want string
+		ip   net.IP
+	}{{
+		name: "good_ipv4",
+		want: "127-0-0-1",
+		ip:   net.IP{127, 0, 0, 1},
+	}, {
+		name: "bad_ipv4",
+		want: "",
+		ip:   net.IP{127, 0, 0, 1, 0},
+	}, {
+		name: "good_ipv6",
+		want: "fe00-0000-0000-0000-0000-0000-0000-0001",
+		ip:   net.ParseIP("fe00::1"),
+	}, {
+		name: "bad_ipv6",
+		want: "",
+		ip: net.IP{
+			0xff, 0xff, 0xff, 0xff,
+			0xff, 0xff, 0xff, 0xff,
+			0xff, 0xff, 0xff, 0xff,
+			0xff, 0xff, 0xff,
+		},
+	}, {
+		name: "nil",
+		want: "",
+		ip:   nil,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			hostname := GenerateHostName(tc.ip)
+			assert.Equal(t, tc.want, hostname)
+		})
+	}
+}

internal/dhcpd/v4.go

@@ -634,13 +634,19 @@ func (s *v4Server) processRequest(req, resp *dhcpv4.DHCPv4) (lease *Lease, ok bo
 	}
 
 	if !lease.IsStatic() {
-		lease.Hostname, err = s.normalizeHostname(req.HostName())
+		var hostname string
+		hostname, err = s.normalizeHostname(req.HostName())
 		if err != nil {
 			log.Error("dhcpv4: cannot normalize hostname for %s: %s", mac, err)
 
 			return nil, false
 		}
 
+		if hostname == "" {
+			hostname = aghnet.GenerateHostName(reqIP)
+		}
+
+		lease.Hostname = hostname
 		s.commitLease(lease)
 	} else if len(lease.Hostname) != 0 {
 		o := &optFQDN{