Pull request: 3597 arpdb

Merge in DNS/adguard-home from 3597-wrt-netlink to master

Updates #3597.

Squashed commit of the following:

commit 1709582cd204bb80c84775feabae8723ed3340f6
Merge: 0507b6ed e7b3c996
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 15 20:25:18 2022 +0300

    Merge branch 'master' into 3597-wrt-netlink

commit 0507b6ede1162554ca8ac7399d827264aca64f98
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 15 20:21:29 2022 +0300

    all: imp code

commit 71f9758d854b3e2cf90cbd3655ae4818cfbcf528
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Mar 9 18:03:48 2022 +0500

    aghnet: imp naming

commit c949e765104f130aa3e5ba465bdebc3286bebe44
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Mar 9 17:26:30 2022 +0500

    all: imp code, docs

commit cf605ddb401b6e7b0a7a4bb1b175a4dc588d253a
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Mar 8 15:33:52 2022 +0500

    all: imp code, docs

commit 2960c6549a7e4944cc0072ca47a0cd4e82ec850e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Sun Mar 6 21:34:58 2022 +0500

    all: imp code & docs, fix tests

commit 29c049f3aee91a826c3416961686396d562a7066
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Mar 2 20:45:34 2022 +0300

    all: add arpdb

internal/aghnet/arpdb_windows.go

@@ -0,0 +1,70 @@
+//go:build windows
+// +build windows
+
+package aghnet
+
+import (
+	"bufio"
+	"io"
+	"net"
+	"strings"
+	"sync"
+)
+
+func newARPDB() *cmdARPDB {
+	return &cmdARPDB{
+		runcmd: rcArpA,
+		ns: &neighs{
+			mu: &sync.RWMutex{},
+			ns: make([]Neighbor, 0),
+		},
+		parse: parseArpA,
+	}
+}
+
+// rcArpA runs "arp /a".
+func rcArpA() (r io.Reader, err error) {
+	return runCmd("arp", "/a")
+}
+
+// parseArpA parses the output of the "arp /a" command on Windows.  The expected
+// input format (the first line is empty):
+//
+//
+//   Interface: 192.168.56.16 --- 0x7
+//     Internet Address      Physical Address      Type
+//     192.168.56.1          0a-00-27-00-00-00     dynamic
+//     192.168.56.255        ff-ff-ff-ff-ff-ff     static
+//
+func parseArpA(sc *bufio.Scanner, lenHint int) (ns []Neighbor) {
+	ns = make([]Neighbor, 0, lenHint)
+	for sc.Scan() {
+		ln := sc.Text()
+		if ln == "" {
+			continue
+		}
+
+		fields := strings.Fields(ln)
+		if len(fields) != 3 {
+			continue
+		}
+
+		n := Neighbor{}
+
+		if ip := net.ParseIP(fields[0]); ip == nil {
+			continue
+		} else {
+			n.IP = ip
+		}
+
+		if mac, err := net.ParseMAC(fields[1]); err != nil {
+			continue
+		} else {
+			n.MAC = mac
+		}
+
+		ns = append(ns, n)
+	}
+
+	return ns
+}