Pull request: create aghnet package

Merge in DNS/adguard-home from mk-aghnet to master

Updates #2829.

Squashed commit of the following:

commit 519806c04b8d0517aacce9c31f2d06ab56631937
Merge: 92376c86 97361234
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Mar 16 19:13:56 2021 +0300

    Merge branch 'master' into mk-aghnet

commit 92376c8665e529191aa482432f9d5e3e2e3afdc8
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Mar 16 18:37:22 2021 +0300

    aghnet: fix linux

commit 7f36d19b0e650d4e4fc5cf9ea4b501a7f636abeb
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Mar 16 18:08:30 2021 +0300

    aghnet: mv network utils from util

commit aa68c70c1146b8c32303c6e037953a41aa7d72f9
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Mar 16 17:30:06 2021 +0300

    aghnet: mv ipDetector here

commit b033657f5c5ee91f869c36508a5eb15976a174a0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Tue Mar 16 17:24:07 2021 +0300

    all: mk aghnet package, rename sysutil package

internal/aghnet/net_darwin.go

@@ -0,0 +1,161 @@
+// +build darwin
+
+package aghnet
+
+import (
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"regexp"
+	"strings"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/util"
+)
+
+// hardwarePortInfo - information obtained using MacOS networksetup
+// about the current state of the internet connection
+type hardwarePortInfo struct {
+	name      string
+	ip        string
+	subnet    string
+	gatewayIP string
+	static    bool
+}
+
+func ifaceHasStaticIP(ifaceName string) (bool, error) {
+	portInfo, err := getCurrentHardwarePortInfo(ifaceName)
+	if err != nil {
+		return false, err
+	}
+
+	return portInfo.static, nil
+}
+
+// getCurrentHardwarePortInfo gets information the specified network interface.
+func getCurrentHardwarePortInfo(ifaceName string) (hardwarePortInfo, error) {
+	// First of all we should find hardware port name
+	m := getNetworkSetupHardwareReports()
+	hardwarePort, ok := m[ifaceName]
+	if !ok {
+		return hardwarePortInfo{}, fmt.Errorf("could not find hardware port for %s", ifaceName)
+	}
+
+	return getHardwarePortInfo(hardwarePort)
+}
+
+// getNetworkSetupHardwareReports parses the output of the `networksetup -listallhardwareports` command
+// it returns a map where the key is the interface name, and the value is the "hardware port"
+// returns nil if it fails to parse the output
+func getNetworkSetupHardwareReports() map[string]string {
+	_, out, err := util.RunCommand("networksetup", "-listallhardwareports")
+	if err != nil {
+		return nil
+	}
+
+	re, err := regexp.Compile("Hardware Port: (.*?)\nDevice: (.*?)\n")
+	if err != nil {
+		return nil
+	}
+
+	m := make(map[string]string)
+
+	matches := re.FindAllStringSubmatch(out, -1)
+	for i := range matches {
+		port := matches[i][1]
+		device := matches[i][2]
+		m[device] = port
+	}
+
+	return m
+}
+
+func getHardwarePortInfo(hardwarePort string) (hardwarePortInfo, error) {
+	h := hardwarePortInfo{}
+
+	_, out, err := util.RunCommand("networksetup", "-getinfo", hardwarePort)
+	if err != nil {
+		return h, err
+	}
+
+	re := regexp.MustCompile("IP address: (.*?)\nSubnet mask: (.*?)\nRouter: (.*?)\n")
+
+	match := re.FindStringSubmatch(out)
+	if len(match) == 0 {
+		return h, errors.New("could not find hardware port info")
+	}
+
+	h.name = hardwarePort
+	h.ip = match[1]
+	h.subnet = match[2]
+	h.gatewayIP = match[3]
+
+	if strings.Index(out, "Manual Configuration") == 0 {
+		h.static = true
+	}
+
+	return h, nil
+}
+
+func ifaceSetStaticIP(ifaceName string) (err error) {
+	portInfo, err := getCurrentHardwarePortInfo(ifaceName)
+	if err != nil {
+		return err
+	}
+
+	if portInfo.static {
+		return errors.New("IP address is already static")
+	}
+
+	dnsAddrs, err := getEtcResolvConfServers()
+	if err != nil {
+		return err
+	}
+
+	args := make([]string, 0)
+	args = append(args, "-setdnsservers", portInfo.name)
+	args = append(args, dnsAddrs...)
+
+	// Setting DNS servers is necessary when configuring a static IP
+	code, _, err := util.RunCommand("networksetup", args...)
+	if err != nil {
+		return err
+	}
+	if code != 0 {
+		return fmt.Errorf("failed to set DNS servers, code=%d", code)
+	}
+
+	// Actually configures hardware port to have static IP
+	code, _, err = util.RunCommand("networksetup", "-setmanual",
+		portInfo.name, portInfo.ip, portInfo.subnet, portInfo.gatewayIP)
+	if err != nil {
+		return err
+	}
+	if code != 0 {
+		return fmt.Errorf("failed to set DNS servers, code=%d", code)
+	}
+
+	return nil
+}
+
+// getEtcResolvConfServers returns a list of nameservers configured in
+// /etc/resolv.conf.
+func getEtcResolvConfServers() ([]string, error) {
+	body, err := ioutil.ReadFile("/etc/resolv.conf")
+	if err != nil {
+		return nil, err
+	}
+
+	re := regexp.MustCompile("nameserver ([a-zA-Z0-9.:]+)")
+
+	matches := re.FindAllStringSubmatch(string(body), -1)
+	if len(matches) == 0 {
+		return nil, errors.New("found no DNS servers in /etc/resolv.conf")
+	}
+
+	addrs := make([]string, 0)
+	for i := range matches {
+		addrs = append(addrs, matches[i][1])
+	}
+
+	return addrs, nil
+}