Pull request: 2302 static ip

Merge in DNS/adguard-home from 2302-static-ip to master

Closes #2302.

Squashed commit of the following:

commit e62b7b033861f1c55f0d06811ca005b3934ddc5b
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 19:38:15 2020 +0300

    all: format changelog

commit 4127aa7630674ddcfe84f712e6c7c8d06b1cab9a
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 19:24:53 2020 +0300

    all: fix changelog typo

commit f8a432056d3682facae0cdec99d7d80a5c2bd9b5
Merge: b809a866e e4383189a
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 19:22:27 2020 +0300

    Merge branch 'master' into 2302-static-ip

commit b809a866e49147354f9c6952b2f958b6b56ad873
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 19:20:05 2020 +0300

    all: log changes

commit 248c35ba411af731d6eae755a901cdbc77980628
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 18:57:15 2020 +0300

    sysutil: use bufio.Scanner

commit 0dc19dd5c232fbe9552a2b0d846e048274d73a74
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 17:26:18 2020 +0300

    sysutil: fix linux tests

commit 91202d6763595cff187040516dd1db10a20762b7
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 17:15:29 2020 +0300

    sysutil: fix linux files

commit 40fbdbb95876322ebaeef1cbdaa8e3299b83ca7e
Merge: d9a43ffb6 9b963fc77
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 16:52:35 2020 +0300

    Merge branch 'master' into 2302-static-ip

commit d9a43ffb68a2ddbbcf185b69fc75aed139cd6919
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 16:49:22 2020 +0300

    sysutil: add main test

commit bfef89186035ab0423d23246d46511584c26534c
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Dec 7 16:21:59 2020 +0300

    sysutil: improve code quality

commit a5f57a373f736971fdeb0c03371da7c8138b3a82
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Dec 4 14:14:08 2020 +0300

    all: move system functionality from dhcpd package to sysutil.

commit 020b51864f85a39ca80e2b4e06faeb47cf318e11
Merge: 967e111a6 ab8defdb0
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Dec 2 14:53:43 2020 +0300

    Merge branch 'master' into 2302-static-ip

commit 967e111a663c18b5f4a87f3ae38d076f3ab6c200
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Wed Dec 2 13:52:17 2020 +0300

    all: improve code quality

CHANGELOG.md

@@ -15,6 +15,8 @@ and this project adheres to
 
 ### Added
 
+- Detecting of network interface configurated to have static IP address via
+  `/etc/network/interfaces` ([#2302]).
 - DNSCrypt protocol support [#1361].
 - A 5 second wait period until a DHCP server's network interface gets an IP
   address ([#2304]).
@@ -22,6 +24,7 @@ and this project adheres to
 - HTTP API request body size limit ([#2305]).
 
 [#1361]: https://github.com/AdguardTeam/AdGuardHome/issues/1361
+[#2302]: https://github.com/AdguardTeam/AdGuardHome/issues/2302
 [#2304]: https://github.com/AdguardTeam/AdGuardHome/issues/2304
 [#2305]: https://github.com/AdguardTeam/AdGuardHome/issues/2305
 [#2337]: https://github.com/AdguardTeam/AdGuardHome/issues/2337

internal/dhcpd/dhcpd.go

@@ -81,11 +81,6 @@ type ServerInterface interface {
 	SetOnLeaseChanged(onLeaseChanged OnLeaseChangedT)
 }
 
-// CheckConfig checks the configuration
-func (s *Server) CheckConfig(config ServerConfig) error {
-	return nil
-}
-
 // Create - create object
 func Create(config ServerConfig) *Server {
 	s := &Server{}

internal/dhcpd/dhcphttp.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/AdguardTeam/AdGuardHome/internal/sysutil"
 	"github.com/AdguardTeam/AdGuardHome/internal/util"
 	"github.com/AdguardTeam/golibs/jsonutil"
 	"github.com/AdguardTeam/golibs/log"
@@ -205,9 +206,9 @@ func (s *Server) handleDHCPSetConfig(w http.ResponseWriter, r *http.Request) {
 	s.dbLoad()
 
 	if s.conf.Enabled {
-		staticIP, err := HasStaticIP(newconfig.InterfaceName)
+		staticIP, err := sysutil.IfaceHasStaticIP(newconfig.InterfaceName)
 		if !staticIP && err == nil {
-			err = SetStaticIP(newconfig.InterfaceName)
+			err = sysutil.IfaceSetStaticIP(newconfig.InterfaceName)
 			if err != nil {
 				httpError(r, w, http.StatusInternalServerError, "Failed to configure static IP: %s", err)
 				return
@@ -282,7 +283,7 @@ func (s *Server) handleDHCPInterfaces(w http.ResponseWriter, r *http.Request) {
 			}
 		}
 		if len(jsonIface.Addrs4)+len(jsonIface.Addrs6) != 0 {
-			jsonIface.GatewayIP = getGatewayIP(iface.Name)
+			jsonIface.GatewayIP = sysutil.GatewayIP(iface.Name)
 			response[iface.Name] = jsonIface
 		}
 	}
@@ -319,7 +320,7 @@ func (s *Server) handleDHCPFindActiveServer(w http.ResponseWriter, r *http.Reque
 	found4, err4 := CheckIfOtherDHCPServersPresentV4(interfaceName)
 
 	staticIP := map[string]interface{}{}
-	isStaticIP, err := HasStaticIP(interfaceName)
+	isStaticIP, err := sysutil.IfaceHasStaticIP(interfaceName)
 	staticIPStatus := "yes"
 	if err != nil {
 		staticIPStatus = "error"

internal/dhcpd/netutil.go

@@ -1,312 +0,0 @@
-package dhcpd
-
-import (
-	"errors"
-	"fmt"
-	"io/ioutil"
-	"net"
-	"os/exec"
-	"regexp"
-	"runtime"
-	"strings"
-
-	"github.com/AdguardTeam/AdGuardHome/internal/util"
-
-	"github.com/AdguardTeam/golibs/file"
-
-	"github.com/AdguardTeam/golibs/log"
-)
-
-// HasStaticIP check if the network interface has a static IP configured
-//
-// Supports: Raspbian.
-func HasStaticIP(ifaceName string) (bool, error) {
-	if runtime.GOOS == "linux" {
-		body, err := ioutil.ReadFile("/etc/dhcpcd.conf")
-		if err != nil {
-			return false, err
-		}
-
-		return hasStaticIPDhcpcdConf(string(body), ifaceName), nil
-	}
-
-	if runtime.GOOS == "darwin" {
-		return hasStaticIPDarwin(ifaceName)
-	}
-
-	return false, fmt.Errorf("cannot check if IP is static: not supported on %s", runtime.GOOS)
-}
-
-// SetStaticIP sets a static IP for the network interface.
-func SetStaticIP(ifaceName string) error {
-	if runtime.GOOS == "linux" {
-		return setStaticIPDhcpdConf(ifaceName)
-	}
-
-	if runtime.GOOS == "darwin" {
-		return setStaticIPDarwin(ifaceName)
-	}
-
-	return fmt.Errorf("cannot set static IP on %s", runtime.GOOS)
-}
-
-// for dhcpcd.conf
-func hasStaticIPDhcpcdConf(dhcpConf, ifaceName string) bool {
-	lines := strings.Split(dhcpConf, "\n")
-	nameLine := fmt.Sprintf("interface %s", ifaceName)
-	withinInterfaceCtx := false
-
-	for _, line := range lines {
-		line = strings.TrimSpace(line)
-
-		if withinInterfaceCtx && len(line) == 0 {
-			// an empty line resets our state
-			withinInterfaceCtx = false
-		}
-
-		if len(line) == 0 || line[0] == '#' {
-			continue
-		}
-		line = strings.TrimSpace(line)
-
-		if !withinInterfaceCtx {
-			if line == nameLine {
-				// we found our interface
-				withinInterfaceCtx = true
-			}
-		} else {
-			if strings.HasPrefix(line, "interface ") {
-				// we found another interface - reset our state
-				withinInterfaceCtx = false
-				continue
-			}
-			if strings.HasPrefix(line, "static ip_address=") {
-				return true
-			}
-		}
-	}
-	return false
-}
-
-// Get gateway IP address
-func getGatewayIP(ifaceName string) string {
-	cmd := exec.Command("ip", "route", "show", "dev", ifaceName)
-	log.Tracef("executing %s %v", cmd.Path, cmd.Args)
-	d, err := cmd.Output()
-	if err != nil || cmd.ProcessState.ExitCode() != 0 {
-		return ""
-	}
-
-	fields := strings.Fields(string(d))
-	if len(fields) < 3 || fields[0] != "default" {
-		return ""
-	}
-
-	ip := net.ParseIP(fields[2])
-	if ip == nil {
-		return ""
-	}
-
-	return fields[2]
-}
-
-// setStaticIPDhcpdConf - updates /etc/dhcpd.conf and sets the current IP address to be static
-func setStaticIPDhcpdConf(ifaceName string) error {
-	ip := util.GetSubnet(ifaceName)
-	if len(ip) == 0 {
-		return errors.New("can't get IP address")
-	}
-
-	ip4, _, err := net.ParseCIDR(ip)
-	if err != nil {
-		return err
-	}
-	gatewayIP := getGatewayIP(ifaceName)
-	add := updateStaticIPDhcpcdConf(ifaceName, ip, gatewayIP, ip4.String())
-
-	body, err := ioutil.ReadFile("/etc/dhcpcd.conf")
-	if err != nil {
-		return err
-	}
-
-	body = append(body, []byte(add)...)
-	err = file.SafeWrite("/etc/dhcpcd.conf", body)
-	if err != nil {
-		return err
-	}
-
-	return nil
-}
-
-// updates dhcpd.conf content -- sets static IP address there
-// for dhcpcd.conf
-func updateStaticIPDhcpcdConf(ifaceName, ip, gatewayIP, dnsIP string) string {
-	var body []byte
-
-	add := fmt.Sprintf("\ninterface %s\nstatic ip_address=%s\n",
-		ifaceName, ip)
-	body = append(body, []byte(add)...)
-
-	if len(gatewayIP) != 0 {
-		add = fmt.Sprintf("static routers=%s\n",
-			gatewayIP)
-		body = append(body, []byte(add)...)
-	}
-
-	add = fmt.Sprintf("static domain_name_servers=%s\n\n",
-		dnsIP)
-	body = append(body, []byte(add)...)
-
-	return string(body)
-}
-
-// Check if network interface has a static IP configured
-// Supports: MacOS.
-func hasStaticIPDarwin(ifaceName string) (bool, error) {
-	portInfo, err := getCurrentHardwarePortInfo(ifaceName)
-	if err != nil {
-		return false, err
-	}
-
-	return portInfo.static, nil
-}
-
-// setStaticIPDarwin - uses networksetup util to set the current IP address to be static
-// Additionally it configures the current DNS servers as well
-func setStaticIPDarwin(ifaceName string) 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
-}
-
-// 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
-}
-
-// 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 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
-}
-
-// Gets a list of nameservers currently configured in the /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
-}

internal/dhcpd/netutil_test.go

@@ -1,63 +0,0 @@
-// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
-
-package dhcpd
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-)
-
-func TestHasStaticIPDhcpcdConf(t *testing.T) {
-	dhcpdConf := `#comment
-# comment
-
-interface eth0
-static ip_address=192.168.0.1/24
-
-# interface wlan0
-static ip_address=192.168.1.1/24
-
-# comment
-`
-	assert.True(t, !hasStaticIPDhcpcdConf(dhcpdConf, "wlan0"))
-
-	dhcpdConf = `#comment
-# comment
-
-interface eth0
-static ip_address=192.168.0.1/24
-
-# interface wlan0
-static ip_address=192.168.1.1/24
-
-# comment
-
-interface wlan0
-# comment
-static ip_address=192.168.2.1/24
-`
-	assert.True(t, hasStaticIPDhcpcdConf(dhcpdConf, "wlan0"))
-}
-
-func TestSetStaticIPDhcpcdConf(t *testing.T) {
-	dhcpcdConf := `
-interface wlan0
-static ip_address=192.168.0.2/24
-static routers=192.168.0.1
-static domain_name_servers=192.168.0.2
-
-`
-	s := updateStaticIPDhcpcdConf("wlan0", "192.168.0.2/24", "192.168.0.1", "192.168.0.2")
-	assert.Equal(t, dhcpcdConf, s)
-
-	// without gateway
-	dhcpcdConf = `
-interface wlan0
-static ip_address=192.168.0.2/24
-static domain_name_servers=192.168.0.2
-
-`
-	s = updateStaticIPDhcpcdConf("wlan0", "192.168.0.2/24", "", "192.168.0.2")
-	assert.Equal(t, dhcpcdConf, s)
-}

internal/home/controlinstall.go

@@ -15,7 +15,7 @@ import (
 
 	"github.com/AdguardTeam/AdGuardHome/internal/util"
 
-	"github.com/AdguardTeam/AdGuardHome/internal/dhcpd"
+	"github.com/AdguardTeam/AdGuardHome/internal/sysutil"
 
 	"github.com/AdguardTeam/golibs/log"
 )
@@ -167,7 +167,7 @@ func handleStaticIP(ip string, set bool) staticIPJSON {
 
 	if set {
 		// Try to set static IP for the specified interface
-		err := dhcpd.SetStaticIP(interfaceName)
+		err := sysutil.IfaceSetStaticIP(interfaceName)
 		if err != nil {
 			resp.Static = "error"
 			resp.Error = err.Error()
@@ -177,7 +177,7 @@ func handleStaticIP(ip string, set bool) staticIPJSON {
 
 	// Fallthrough here even if we set static IP
 	// Check if we have a static IP and return the details
-	isStaticIP, err := dhcpd.HasStaticIP(interfaceName)
+	isStaticIP, err := sysutil.IfaceHasStaticIP(interfaceName)
 	if err != nil {
 		resp.Static = "error"
 		resp.Error = err.Error()

internal/sysutil/net.go

@@ -0,0 +1,44 @@
+package sysutil
+
+import (
+	"net"
+	"os/exec"
+	"strings"
+
+	"github.com/AdguardTeam/golibs/log"
+)
+
+// IfaceHasStaticIP checks if interface is configured to have static IP address.
+func IfaceHasStaticIP(ifaceName string) (has bool, err error) {
+	return ifaceHasStaticIP(ifaceName)
+}
+
+// IfaceSetStaticIP sets static IP address for network interface.
+func IfaceSetStaticIP(ifaceName string) (err error) {
+	return ifaceSetStaticIP(ifaceName)
+}
+
+// GatewayIP returns IP address of interface's gateway.
+func GatewayIP(ifaceName string) string {
+	cmd := exec.Command("ip", "route", "show", "dev", ifaceName)
+	log.Tracef("executing %s %v", cmd.Path, cmd.Args)
+	d, err := cmd.Output()
+	if err != nil || cmd.ProcessState.ExitCode() != 0 {
+		return ""
+	}
+
+	fields := strings.Fields(string(d))
+	// The meaningful "ip route" command output should contain the word
+	// "default" at first field and default gateway IP address at third
+	// field.
+	if len(fields) < 3 || fields[0] != "default" {
+		return ""
+	}
+
+	ip := net.ParseIP(fields[2])
+	if ip == nil {
+		return ""
+	}
+
+	return fields[2]
+}

internal/sysutil/net_darwin.go

@@ -0,0 +1,161 @@
+// +build darwin
+
+package sysutil
+
+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
+}

internal/sysutil/net_linux.go

@@ -0,0 +1,168 @@
+// +build linux
+
+package sysutil
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net"
+	"os"
+	"strings"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghio"
+	"github.com/AdguardTeam/AdGuardHome/internal/util"
+	"github.com/AdguardTeam/golibs/file"
+)
+
+// maxConfigFileSize is the maximum length of interfaces configuration file.
+const maxConfigFileSize = 1024 * 1024
+
+func ifaceHasStaticIP(ifaceName string) (has bool, err error) {
+	var f *os.File
+	for _, check := range []struct {
+		checker  func(io.Reader, string) (bool, error)
+		filePath string
+	}{{
+		checker:  dhcpcdStaticConfig,
+		filePath: "/etc/dhcpcd.conf",
+	}, {
+		checker:  ifacesStaticConfig,
+		filePath: "/etc/network/interfaces",
+	}} {
+		f, err = os.Open(check.filePath)
+		if errors.Is(err, os.ErrNotExist) {
+			continue
+		}
+		if err != nil {
+			return false, err
+		}
+		defer f.Close()
+
+		fileReadCloser, err := aghio.LimitReadCloser(f, maxConfigFileSize)
+		if err != nil {
+			return false, err
+		}
+		defer fileReadCloser.Close()
+
+		has, err = check.checker(fileReadCloser, ifaceName)
+		if has || err != nil {
+			break
+		}
+	}
+
+	return has, err
+}
+
+// dhcpcdStaticConfig checks if interface is configured by /etc/dhcpcd.conf to
+// have a static IP.
+func dhcpcdStaticConfig(r io.Reader, ifaceName string) (has bool, err error) {
+	s := bufio.NewScanner(r)
+	var withinInterfaceCtx bool
+
+	for s.Scan() {
+		line := strings.TrimSpace(s.Text())
+
+		if withinInterfaceCtx && len(line) == 0 {
+			// An empty line resets our state.
+			withinInterfaceCtx = false
+		}
+
+		if len(line) == 0 || line[0] == '#' {
+			continue
+		}
+
+		fields := strings.Fields(line)
+
+		if withinInterfaceCtx {
+			if len(fields) >= 2 && fields[0] == "static" && strings.HasPrefix(fields[1], "ip_address=") {
+				return true, nil
+			}
+			if len(fields) > 0 && fields[0] == "interface" {
+				// Another interface found.
+				withinInterfaceCtx = false
+			}
+			continue
+		}
+
+		if len(fields) == 2 && fields[0] == "interface" && fields[1] == ifaceName {
+			// The interface found.
+			withinInterfaceCtx = true
+		}
+	}
+
+	return false, s.Err()
+}
+
+// ifacesStaticConfig checks if interface is configured by
+// /etc/network/interfaces to have a static IP.
+func ifacesStaticConfig(r io.Reader, ifaceName string) (has bool, err error) {
+	s := bufio.NewScanner(r)
+	for s.Scan() {
+		line := strings.TrimSpace(s.Text())
+
+		if len(line) == 0 || line[0] == '#' {
+			continue
+		}
+
+		fields := strings.Fields(line)
+		// Man page interfaces(5) declares that interface definition
+		// should consist of the key word "iface" followed by interface
+		// name, and method at fourth field.
+		if len(fields) >= 4 && fields[0] == "iface" && fields[1] == ifaceName && fields[3] == "static" {
+			return true, nil
+		}
+	}
+	return false, s.Err()
+}
+
+func ifaceSetStaticIP(ifaceName string) (err error) {
+	ip := util.GetSubnet(ifaceName)
+	if len(ip) == 0 {
+		return errors.New("can't get IP address")
+	}
+
+	ip4, _, err := net.ParseCIDR(ip)
+	if err != nil {
+		return err
+	}
+	gatewayIP := GatewayIP(ifaceName)
+	add := updateStaticIPdhcpcdConf(ifaceName, ip, gatewayIP, ip4.String())
+
+	body, err := ioutil.ReadFile("/etc/dhcpcd.conf")
+	if err != nil {
+		return err
+	}
+
+	body = append(body, []byte(add)...)
+	err = file.SafeWrite("/etc/dhcpcd.conf", body)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// updateStaticIPdhcpcdConf sets static IP address for the interface by writing
+// into dhcpd.conf.
+func updateStaticIPdhcpcdConf(ifaceName, ip, gatewayIP, dnsIP string) string {
+	var body []byte
+
+	add := fmt.Sprintf("\ninterface %s\nstatic ip_address=%s\n",
+		ifaceName, ip)
+	body = append(body, []byte(add)...)
+
+	if len(gatewayIP) != 0 {
+		add = fmt.Sprintf("static routers=%s\n",
+			gatewayIP)
+		body = append(body, []byte(add)...)
+	}
+
+	add = fmt.Sprintf("static domain_name_servers=%s\n\n",
+		dnsIP)
+	body = append(body, []byte(add)...)
+
+	return string(body)
+}

internal/sysutil/net_linux_test.go

@@ -0,0 +1,109 @@
+// +build linux
+
+package sysutil
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const nl = "\n"
+
+func TestDHCPCDStaticConfig(t *testing.T) {
+	testCases := []struct {
+		name string
+		data []byte
+		want bool
+	}{{
+		name: "has_not",
+		data: []byte(`#comment` + nl +
+			`# comment` + nl +
+			`interface eth0` + nl +
+			`static ip_address=192.168.0.1/24` + nl +
+			`# interface wlan0` + nl +
+			`static ip_address=192.168.1.1/24` + nl +
+			`# comment` + nl,
+		),
+		want: false,
+	}, {
+		name: "has",
+		data: []byte(`#comment` + nl +
+			`# comment` + nl +
+			`interface eth0` + nl +
+			`static ip_address=192.168.0.1/24` + nl +
+			`# interface wlan0` + nl +
+			`static ip_address=192.168.1.1/24` + nl +
+			`# comment` + nl +
+			`interface wlan0` + nl +
+			`# comment` + nl +
+			`static ip_address=192.168.2.1/24` + nl,
+		),
+		want: true,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			r := bytes.NewReader(tc.data)
+			has, err := dhcpcdStaticConfig(r, "wlan0")
+			assert.Nil(t, err)
+			assert.Equal(t, tc.want, has)
+		})
+	}
+}
+
+func TestIfacesStaticConfig(t *testing.T) {
+	testCases := []struct {
+		name string
+		data []byte
+		want bool
+	}{{
+		name: "has_not",
+		data: []byte(`allow-hotplug enp0s3` + nl +
+			`#iface enp0s3 inet static` + nl +
+			`#  address 192.168.0.200` + nl +
+			`#  netmask 255.255.255.0` + nl +
+			`#  gateway 192.168.0.1` + nl +
+			`iface enp0s3 inet dhcp` + nl,
+		),
+		want: false,
+	}, {
+		name: "has",
+		data: []byte(`allow-hotplug enp0s3` + nl +
+			`iface enp0s3 inet static` + nl +
+			`  address 192.168.0.200` + nl +
+			`  netmask 255.255.255.0` + nl +
+			`  gateway 192.168.0.1` + nl +
+			`#iface enp0s3 inet dhcp` + nl,
+		),
+		want: true,
+	}}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			r := bytes.NewReader(tc.data)
+			has, err := ifacesStaticConfig(r, "enp0s3")
+			assert.Nil(t, err)
+			assert.Equal(t, tc.want, has)
+		})
+	}
+}
+
+func TestSetStaticIPdhcpcdConf(t *testing.T) {
+	dhcpcdConf := nl + `interface wlan0` + nl +
+		`static ip_address=192.168.0.2/24` + nl +
+		`static routers=192.168.0.1` + nl +
+		`static domain_name_servers=192.168.0.2` + nl + nl
+
+	s := updateStaticIPdhcpcdConf("wlan0", "192.168.0.2/24", "192.168.0.1", "192.168.0.2")
+	assert.Equal(t, dhcpcdConf, s)
+
+	// without gateway
+	dhcpcdConf = nl + `interface wlan0` + nl +
+		`static ip_address=192.168.0.2/24` + nl +
+		`static domain_name_servers=192.168.0.2` + nl + nl
+
+	s = updateStaticIPdhcpcdConf("wlan0", "192.168.0.2/24", "", "192.168.0.2")
+	assert.Equal(t, dhcpcdConf, s)
+}

internal/sysutil/net_others.go

@@ -0,0 +1,16 @@
+// +build !linux,!darwin
+
+package sysutil
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func ifaceHasStaticIP(string) (bool, error) {
+	return false, fmt.Errorf("cannot check if IP is static: not supported on %s", runtime.GOOS)
+}
+
+func ifaceSetStaticIP(string) error {
+	return fmt.Errorf("cannot set static IP on %s", runtime.GOOS)
+}

internal/sysutil/os.go

@@ -24,8 +24,3 @@ func HaveAdminRights() (bool, error) {
 func SendProcessSignal(pid int, sig syscall.Signal) error {
 	return sendProcessSignal(pid, sig)
 }
-
-// ConfigureSyslog reroutes standard logger output to syslog.
-func ConfigureSyslog(serviceName string) error {
-	return configureSyslog(serviceName)
-}

internal/sysutil/os_freebsd.go

@@ -1,4 +1,4 @@
-//+build freebsd
+// +build freebsd
 
 package sysutil
 

internal/sysutil/os_linux.go

@@ -1,4 +1,4 @@
-//+build linux
+// +build linux
 
 package sysutil
 

internal/sysutil/os_unix.go

@@ -1,4 +1,4 @@
-//+build aix darwin dragonfly netbsd openbsd solaris
+// +build aix darwin dragonfly netbsd openbsd solaris
 
 package sysutil
 

internal/sysutil/os_windows.go

@@ -1,4 +1,4 @@
-//+build windows
+// +build windows
 
 package sysutil
 

internal/sysutil/syslog.go

@@ -0,0 +1,6 @@
+package sysutil
+
+// ConfigureSyslog reroutes standard logger output to syslog.
+func ConfigureSyslog(serviceName string) error {
+	return configureSyslog(serviceName)
+}

internal/sysutil/syslog_others.go

@@ -1,4 +1,4 @@
-//+build !windows,!nacl,!plan9
+// +build !windows,!nacl,!plan9
 
 package sysutil
 

internal/sysutil/syslog_windows.go

@@ -1,4 +1,4 @@
-//+build windows nacl plan9
+// +build windows nacl plan9
 
 package sysutil
 

internal/sysutil/sysutil_test.go

@@ -0,0 +1,11 @@
+package sysutil
+
+import (
+	"testing"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/testutil"
+)
+
+func TestMain(m *testing.M) {
+	testutil.DiscardLogOutput(m)
+}

internal/util/network_utils.go

@@ -33,10 +33,7 @@ func GetValidNetInterfaces() ([]net.Interface, error) {
 
 	netIfaces := []net.Interface{}
 
-	for i := range ifaces {
+	netIfaces = append(netIfaces, ifaces...)
-		iface := ifaces[i]
-		netIfaces = append(netIfaces, iface)
-	}
 
 	return netIfaces, nil
 }