Pull request: 3444 reuse port

Merge in DNS/adguard-home from 3444-dhcp-again to master

Closes AdguardTeam#3444.

Squashed commit of the following:

commit 5459ded
Merge: d655909 8e667d3
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Aug 16 15:35:30 2021 +0300

    Merge branch 'master' into 3444-dhcp-again

commit d655909
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Aug 16 15:28:38 2021 +0300

    aghnet: fix linux

commit 262f729
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Aug 16 14:30:09 2021 +0300

    aghnet: rm debug

commit c54b107
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Aug 16 14:21:07 2021 +0300

    aghnet: imp bsd compat, fix openbsd static ip

commit f9871a4
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Sat Aug 14 00:17:46 2021 +0300

    aghnet:  setsockopt

go.mod

@@ -32,4 +32,5 @@ require (
 	howett.net/plist v0.0.0-20201203080718-1454fab16a06
 )
 
+// TODO(e.burkov):  Get rid of the fork in v0.108.0.
 replace github.com/insomniacslk/dhcp => github.com/AdguardTeam/dhcp v0.0.0-20210519141215-51808c73c0bf

internal/aghnet/dhcp_unix.go

@@ -112,12 +112,12 @@ func discover4(iface *net.Interface, dstAddr *net.UDPAddr, hostname string) (ok
 	// It's also known that listening on the specified interface's address
 	// ignores broadcasted packets when reading.
 	var c net.PacketConn
-	if c, err = net.ListenPacket("udp4", ":68"); err != nil {
+	if c, err = listenPacketReusable(iface.Name, "udp4", ":68"); err != nil {
 		return false, fmt.Errorf("couldn't listen on :68: %w", err)
 	}
 	defer func() { err = errors.WithDeferred(err, c.Close()) }()
 
-	// Send to resolved broadcast.
+	// Send to broadcast.
 	if _, err = c.WriteTo(req.ToBytes(), dstAddr); err != nil {
 		return false, fmt.Errorf("couldn't send a packet to %s: %w", dstAddr, err)
 	}
@@ -154,9 +154,6 @@ func tryConn4(req *dhcpv4.DHCPv4, c net.PacketConn, iface *net.Interface) (ok, n
 
 	b := make([]byte, 1500)
 	n, _, err := c.ReadFrom(b)
-	if n > 0 {
-		log.Debug("received %d bytes: %v", n, b)
-	}
 	if err != nil {
 		if isTimeout(err) {
 			log.Debug("dhcpv4: didn't receive dhcp response")

internal/aghnet/interfaces_linux.go

@@ -0,0 +1,24 @@
+//go:build linux
+// +build linux
+
+package aghnet
+
+import (
+	"net"
+
+	"github.com/AdguardTeam/golibs/netutil"
+	"github.com/insomniacslk/dhcp/dhcpv4/nclient4"
+)
+
+// listenPacketReusable announces on the local network address additionally
+// configuring the socket to have a reusable binding.
+func listenPacketReusable(ifaceName, network, address string) (c net.PacketConn, err error) {
+	var port int
+	_, port, err = netutil.SplitHostPort(address)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO(e.burkov):  Inspect nclient4.NewRawUDPConn and implement here.
+	return nclient4.NewRawUDPConn(ifaceName, port)
+}

internal/aghnet/interfaces_unix.go

@@ -0,0 +1,51 @@
+//go:build aix || darwin || dragonfly || freebsd || netbsd || openbsd || solaris
+// +build aix darwin dragonfly freebsd netbsd openbsd solaris
+
+package aghnet
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+
+	"github.com/AdguardTeam/golibs/errors"
+	"golang.org/x/sys/unix"
+)
+
+// reuseAddrCtrl is the function to be set to net.ListenConfig.Control.  It
+// configures the socket to have a reusable port binding.
+func reuseAddrCtrl(_, _ string, c syscall.RawConn) (err error) {
+	cerr := c.Control(func(fd uintptr) {
+		// TODO(e.burkov):  Consider using SO_REUSEPORT.
+		err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
+		if err != nil {
+			err = os.NewSyscallError("setsockopt", err)
+		}
+	})
+
+	const (
+		errMsg    = "setting control options"
+		errMsgFmt = errMsg + ": %w"
+	)
+
+	if err != nil && cerr != nil {
+		err = errors.List(errMsg, err, cerr)
+	} else if err != nil {
+		err = fmt.Errorf(errMsgFmt, err)
+	} else if cerr != nil {
+		err = fmt.Errorf(errMsgFmt, cerr)
+	}
+
+	return err
+}
+
+// listenPacketReusable announces on the local network address additionally
+// configuring the socket to have a reusable binding.
+func listenPacketReusable(_, network, address string) (c net.PacketConn, err error) {
+	var lc net.ListenConfig
+	lc.Control = reuseAddrCtrl
+
+	return lc.ListenPacket(context.Background(), network, address)
+}

internal/aghnet/interfaces_windows.go

@@ -0,0 +1,18 @@
+//go:build windows
+// +build windows
+
+package aghnet
+
+import (
+	"net"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghos"
+)
+
+// listenPacketReusable announces on the local network address additionally
+// configuring the socket to have a reusable binding.
+func listenPacketReusable(_, _, _ string) (c net.PacketConn, err error) {
+	// TODO(e.burkov):  Check if we are able to control sockets on Windows
+	// in the same way as on Unix.
+	return nil, aghos.Unsupported("listening packet reusable")
+}

internal/aghnet/net_openbsd.go

@@ -31,11 +31,11 @@ func hostnameIfStaticConfig(r io.Reader) (_ []string, ok bool, err error) {
 		line := strings.TrimSpace(s.Text())
 		fields := strings.Fields(line)
 		if len(fields) >= 2 && fields[0] == "inet" && net.ParseIP(fields[1]) != nil {
-			return nil, true, s.Err()
+			return nil, false, s.Err()
 		}
 	}
 
-	return nil, false, s.Err()
+	return nil, true, s.Err()
 }
 
 func ifaceSetStaticIP(string) (err error) {