Makefile

@@ -1,3 +1,6 @@
-test:
+integration-test:
 	# TODO figure out needed capabilities
-	sudo go test -count=1 -v ./...
+	sudo go test -count=1 -v ./... -tags=integration
+
+test:
+	go test -count=1 -v ./...

balancer.go

@@ -37,7 +37,7 @@ func (r *roundRobin) DialContext(ctx context.Context, s *Subnet, network, addres
 
 		dd := r.d.dialer
 		dd.LocalAddr = ii.LocalAddr
-		return r.d.dialContext(&dd, ctx, "tcp", address)
+		return r.d.dialContext(&dd, ctx, network, address)
 	}
 	return nil, errors.New("(*roundRobin).DialContext: no suitale node found")
 }
@@ -55,7 +55,7 @@ func (r *firstEnabled) DialContext(ctx context.Context, s *Subnet, network, addr
 
 		dd := r.d.dialer
 		dd.LocalAddr = ii.LocalAddr
-		return r.d.dialContext(&dd, ctx, "tcp", address)
+		return r.d.dialContext(&dd, ctx, network, address)
 	}
 	return nil, errors.New("(*firstEnabled).DialContext: no suitale node found")
 }

dialer.go

@@ -8,6 +8,11 @@ import (
 	"net/netip"
 	"sort"
 	"sync"
+	"time"
+)
+
+const (
+	defaultFallbackDelay = 300 * time.Millisecond
 )
 
 // Dialer contains the single most important method from the net.Dialer.
@@ -36,8 +41,12 @@ type dialer struct {
 	restrict bool
 	// Algorithm to which picks source address for each ip.
 	balancer balancer
-	// Hook used in tests, overrides `net.Dialer.DialContext()`
-	testHookDialContext func(d *net.Dialer, ctx context.Context, network, address string) (net.Conn, error)
+	// Overrides `net.Dialer.DialContext()` if specified.
+	customDialContext func(d *net.Dialer, ctx context.Context, network, address string) (net.Conn, error)
+	// Hostname resolver
+	resolver net.Resolver
+	// See Config.FallbackDelay description.
+	fallbackDelay time.Duration
 }
 
 // Subnet represents a single subnet, possibly routable from multiple interfaces.
@@ -65,16 +74,37 @@ type Config struct {
 	Dialer net.Dialer
 	// Balancer specifies algorithm used to pick source address.
 	Balancer BalancerType
+	// FallbackDelay specifies the length of time to wait before
+	// spawning a RFC 6555 Fast Fallback connection. That is, this
+	// is the amount of time to wait for IPv6 to succeed before
+	// assuming that IPv6 is misconfigured and falling back to
+	// IPv4.
+	//
+	// If zero, a default delay of 300ms is used.
+	// A negative value disables Fast Fallback support.
+	FallbackDelay time.Duration
+	// InterfaceSource is custom `Interface`` source.
+	// If not specified, default implementation is used (`net.Interfaces()``).
+	InterfaceSource func() ([]Interface, error)
+	// DialContext is custom DialContext function.
+	// If not specified, default implemenattion is used (`d.DialContext(ctx, network, address)`).
+	DialContext func(d *net.Dialer, ctx context.Context, network, address string) (net.Conn, error)
 }
 
 // NewDialer ...
 func NewDialer(c Config) (Multidialer, error) {
-	ifaces, err := net.Interfaces()
+	var ifaces []Interface
+	var err error
+	if c.InterfaceSource != nil {
+		ifaces, err = c.InterfaceSource()
+	} else {
+		ifaces, err = systemInterfaces()
+	}
 	if err != nil {
 		return nil, err
 	}
 	sort.Slice(ifaces, func(i, j int) bool {
-		return ifaces[i].Name < ifaces[j].Name
+		return ifaces[i].Name() < ifaces[j].Name()
 	})
 
 	var sources []iface
@@ -105,16 +135,25 @@ func NewDialer(c Config) (Multidialer, error) {
 	}
 
 	d.restrict = c.Restrict
+	d.resolver.Dial = d.dialContextIP
+	d.fallbackDelay = c.FallbackDelay
+	if d.fallbackDelay == 0 {
+		d.fallbackDelay = defaultFallbackDelay
+	}
+	d.dialer = c.Dialer
+	if c.DialContext != nil {
+		d.customDialContext = c.DialContext
+	}
 
 	return &d, nil
 }
 
 type iface struct {
-	info  net.Interface
+	name  string
 	addrs []netip.Prefix
 }
 
-func processIface(info net.Interface) (iface, error) {
+func processIface(info Interface) (iface, error) {
 	ips, err := info.Addrs()
 	if err != nil {
 		return iface{}, err
@@ -129,7 +168,7 @@ func processIface(info net.Interface) (iface, error) {
 
 		addrs = append(addrs, p)
 	}
-	return iface{info: info, addrs: addrs}, nil
+	return iface{name: info.Name(), addrs: addrs}, nil
 }
 
 func processSubnet(subnet string, sources []iface) (Subnet, error) {
@@ -144,7 +183,7 @@ func processSubnet(subnet string, sources []iface) (Subnet, error) {
 			src := source.addrs[i].Addr()
 			if s.Contains(src) {
 				ifs = append(ifs, Source{
-					Name:      source.info.Name,
+					Name:      source.name,
 					LocalAddr: &net.TCPAddr{IP: net.IP(src.AsSlice())},
 				})
 			}
@@ -168,10 +207,164 @@ func processSubnet(subnet string, sources []iface) (Subnet, error) {
 // Hostnames for address are currently not supported.
 func (d *dialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
 	addr, err := netip.ParseAddrPort(address)
+	if err != nil { //try resolve as hostname
+		return d.dialContextHostname(ctx, network, address)
+	}
+	return d.dialAddr(ctx, network, address, addr)
+}
+
+func (d *dialer) dialContextIP(ctx context.Context, network, address string) (net.Conn, error) {
+	addr, err := netip.ParseAddrPort(address)
+	if err != nil {
+		return nil, err
+	}
+	return d.dialAddr(ctx, network, address, addr)
+}
+
+func (d *dialer) dialContextHostname(ctx context.Context, network, address string) (net.Conn, error) {
+	// https://github.com/golang/go/blob/release-branch.go1.21/src/net/dial.go#L488
+	addrPorts, err := d.resolveHostIPs(ctx, address, network)
 	if err != nil {
 		return nil, err
 	}
 
+	var primaries, fallbacks []netip.AddrPort
+	if d.fallbackDelay >= 0 && network == "tcp" {
+		primaries, fallbacks = splitByType(addrPorts)
+	} else {
+		primaries = addrPorts
+	}
+
+	return d.dialParallel(ctx, network, primaries, fallbacks)
+}
+
+func (d *dialer) dialSerial(ctx context.Context, network string, addrs []netip.AddrPort) (net.Conn, error) {
+	var firstErr error
+	for _, addr := range addrs {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		default:
+		}
+
+		conn, err := d.dialAddr(ctx, network, addr.String(), addr)
+		if err == nil {
+			return conn, nil
+		}
+		if firstErr == nil {
+			firstErr = err
+		}
+	}
+	return nil, fmt.Errorf("failed to connect any resolved address: %w", firstErr)
+}
+
+func (d *dialer) dialParallel(ctx context.Context, network string, primaries, fallbacks []netip.AddrPort) (net.Conn, error) {
+	if len(fallbacks) == 0 {
+		return d.dialSerial(ctx, network, primaries)
+	}
+
+	returned := make(chan struct{})
+	defer close(returned)
+
+	type dialResult struct {
+		net.Conn
+		error
+		primary bool
+		done    bool
+	}
+	results := make(chan dialResult)
+
+	dialerFunc := func(ctx context.Context, primary bool) {
+		addrs := primaries
+		if !primary {
+			addrs = fallbacks
+		}
+		c, err := d.dialSerial(ctx, network, addrs)
+		select {
+		case results <- dialResult{Conn: c, error: err, primary: primary, done: true}:
+		case <-returned:
+			if c != nil {
+				c.Close()
+			}
+		}
+	}
+
+	var primary, fallback dialResult
+
+	primaryCtx, primaryCancel := context.WithCancel(ctx)
+	defer primaryCancel()
+	go dialerFunc(primaryCtx, true)
+
+	fallbackTimer := time.NewTimer(d.fallbackDelay)
+	defer fallbackTimer.Stop()
+
+	for {
+		select {
+		case <-fallbackTimer.C:
+			fallbackCtx, fallbackCancel := context.WithCancel(ctx)
+			defer fallbackCancel()
+			go dialerFunc(fallbackCtx, false)
+
+		case res := <-results:
+			if res.error == nil {
+				return res.Conn, nil
+			}
+			if res.primary {
+				primary = res
+			} else {
+				fallback = res
+			}
+			if primary.done && fallback.done {
+				return nil, primary.error
+			}
+			if res.primary && fallbackTimer.Stop() {
+				// If we were able to stop the timer, that means it
+				// was running (hadn't yet started the fallback), but
+				// we just got an error on the primary path, so start
+				// the fallback immediately (in 0 nanoseconds).
+				fallbackTimer.Reset(0)
+			}
+		}
+	}
+}
+
+func (d *dialer) resolveHostIPs(ctx context.Context, address string, network string) ([]netip.AddrPort, error) {
+	host, port, err := net.SplitHostPort(address)
+	if err != nil {
+		return nil, fmt.Errorf("invalid address format: %w", err)
+	}
+
+	portnum, err := d.resolver.LookupPort(ctx, network, port)
+	if err != nil {
+		return nil, fmt.Errorf("invalid port format: %w", err)
+	}
+
+	ips, err := d.resolver.LookupHost(ctx, host)
+	if err != nil {
+		return nil, fmt.Errorf("failed to resolve host address: %w", err)
+	}
+
+	if len(ips) == 0 {
+		return nil, fmt.Errorf("failed to resolve address for [%s]%s", network, address)
+	}
+
+	var ipAddrs []netip.Addr
+	for _, ip := range ips {
+		ipAddr, err := netip.ParseAddr(ip)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse ip address '%s': %w", ip, err)
+		}
+		ipAddrs = append(ipAddrs, ipAddr)
+	}
+
+	var addrPorts []netip.AddrPort
+	for _, ipAddr := range ipAddrs {
+		addrPorts = append(addrPorts, netip.AddrPortFrom(ipAddr, uint16(portnum)))
+	}
+	return addrPorts, nil
+}
+
+func (d *dialer) dialAddr(ctx context.Context, network, address string, addr netip.AddrPort) (net.Conn, error) {
 	d.mtx.RLock()
 	defer d.mtx.RUnlock()
 
@@ -184,14 +377,14 @@ func (d *dialer) DialContext(ctx context.Context, network, address string) (net.
 	if d.restrict {
 		return nil, fmt.Errorf("no suitable interface for: [%s]%s", network, address)
 	}
-	return d.dialer.DialContext(ctx, network, address)
+	return d.dialContext(&d.dialer, ctx, network, address)
 }
 
 func (d *dialer) dialContext(nd *net.Dialer, ctx context.Context, network, address string) (net.Conn, error) {
-	if h := d.testHookDialContext; h != nil {
-		return h(nd, ctx, "tcp", address)
+	if h := d.customDialContext; h != nil {
+		return h(nd, ctx, network, address)
 	}
-	return nd.DialContext(ctx, "tcp", address)
+	return nd.DialContext(ctx, network, address)
 }
 
 // UpdateInterface implements the Multidialer interface.
@@ -217,3 +410,21 @@ func (d *dialer) UpdateInterface(iface string, addr netip.Addr, up bool) error {
 	}
 	return nil
 }
+
+// splitByType divides an address list into two categories:
+// the first address, and any with same type, are returned as
+// primaries, while addresses with the opposite type are returned
+// as fallbacks.
+func splitByType(addrs []netip.AddrPort) (primaries []netip.AddrPort, fallbacks []netip.AddrPort) {
+	var primaryLabel bool
+	for i, addr := range addrs {
+		label := addr.Addr().Is4()
+		if i == 0 || label == primaryLabel {
+			primaryLabel = label
+			primaries = append(primaries, addr)
+		} else {
+			fallbacks = append(fallbacks, addr)
+		}
+	}
+	return
+}

dialer_hostname_test.go

@@ -0,0 +1,308 @@
+package multinet
+
+import (
+	"context"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/dns/dnsmessage"
+)
+
+func TestHostnameResolveIPv4(t *testing.T) {
+	resolvedAddr := "10.11.12.180:8080"
+	resolved := false
+	d, err := NewDialer(Config{
+		Subnets:         []string{"10.11.12.0/24"},
+		InterfaceSource: testInterfacesV4,
+		DialContext: func(d *net.Dialer, ctx context.Context, network, address string) (net.Conn, error) {
+			if resolvedAddr == address {
+				resolved = true
+				return &testConnStub{}, nil
+			}
+			if network == "udp" {
+				return &testDnsConn{
+					wantName: "s01.storage.devnev.",
+					ipv4:     []byte{10, 11, 12, 180},
+				}, nil
+			}
+			panic("unexpected call")
+		},
+	})
+	require.NoError(t, err)
+	conn, err := d.DialContext(context.Background(), "tcp", "s01.storage.devnev:8080")
+	require.NoError(t, err)
+	require.NoError(t, conn.Close())
+	require.True(t, resolved)
+}
+
+func TestHostnameResolveIPv6(t *testing.T) {
+	resolvedAddr := "[2001:db8:85a3:8d3:1319:8a2e:370:8195]:8080"
+	ipv6 := net.ParseIP("2001:db8:85a3:8d3:1319:8a2e:370:8195")
+	resolved := false
+	d, err := NewDialer(Config{
+		Subnets:         []string{"2001:db8:85a3:8d3::/64"},
+		InterfaceSource: testInterfacesV6,
+		DialContext: func(d *net.Dialer, ctx context.Context, network, address string) (net.Conn, error) {
+			if resolvedAddr == address {
+				resolved = true
+				return &testConnStub{}, nil
+			}
+			if network == "udp" {
+				return &testDnsConn{
+					wantName: "s01.storage.devnev.",
+					ipv6:     ipv6,
+				}, nil
+			}
+			panic("unexpected call")
+		},
+	})
+	require.NoError(t, err)
+	conn, err := d.DialContext(context.Background(), "tcp", "s01.storage.devnev:8080")
+	require.NoError(t, err)
+	require.NoError(t, conn.Close())
+	require.True(t, resolved)
+}
+
+func testInterfacesV4() ([]Interface, error) {
+	return []Interface{
+		&testInterface{
+			name: "data1",
+			addrs: []net.Addr{
+				&testAddr{
+					network: "tcp",
+					str:     "10.11.12.101/24",
+				},
+			},
+		},
+		&testInterface{
+			name: "data2",
+			addrs: []net.Addr{
+				&testAddr{
+					network: "tcp",
+					str:     "10.11.12.102/24",
+				},
+			},
+		},
+	}, nil
+}
+
+func testInterfacesV6() ([]Interface, error) {
+	return []Interface{
+		&testInterface{
+			name: "data1",
+			addrs: []net.Addr{
+				&testAddr{
+					network: "tcp",
+					str:     "2001:db8:85a3:8d3:1319:8a2e:370:7348/64",
+				},
+			},
+		},
+		&testInterface{
+			name: "data2",
+			addrs: []net.Addr{
+				&testAddr{
+					network: "tcp",
+					str:     "2001:db8:85a3:8d3:1319:8a2e:370:8192/64",
+				},
+			},
+		},
+	}, nil
+}
+
+type testInterface struct {
+	name  string
+	addrs []net.Addr
+}
+
+func (i *testInterface) Name() string               { return i.name }
+func (i *testInterface) Addrs() ([]net.Addr, error) { return i.addrs, nil }
+
+type testAddr struct {
+	network string
+	str     string
+}
+
+func (a *testAddr) Network() string { return a.network }
+func (a *testAddr) String() string  { return a.str }
+
+type testDnsConn struct {
+	wantName   string
+	ipv4       []byte
+	ipv6       []byte
+	reqID      uint16
+	requested  bool
+	secondRead bool
+	questions  []dnsmessage.Question
+}
+
+// Close implements net.Conn.
+func (*testDnsConn) Close() error {
+	return nil
+}
+
+// LocalAddr implements net.Conn.
+func (*testDnsConn) LocalAddr() net.Addr {
+	panic("unimplemented")
+}
+
+// Read implements net.Conn.
+func (c *testDnsConn) Read(b []byte) (n int, err error) {
+	if c.secondRead {
+		data, err := c.data()
+		if err != nil {
+			return 0, err
+		}
+		copy(b, data)
+		return len(data), nil
+	}
+
+	data, err := c.data()
+	if err != nil {
+		return 0, err
+	}
+	l := len(data)
+	b[0] = byte(l >> 8)
+	b[1] = byte(l)
+	c.secondRead = true
+	return 2, nil
+}
+
+func (c *testDnsConn) data() ([]byte, error) {
+	if !c.requested {
+		builder := dnsmessage.NewBuilder(nil, dnsmessage.Header{RCode: dnsmessage.RCodeNameError})
+		res, err := builder.Finish()
+		if err != nil {
+			return nil, err
+		}
+		return res, nil
+	}
+
+	msg := dnsmessage.Message{
+		Header:    dnsmessage.Header{Response: true, Authoritative: true, RCode: dnsmessage.RCodeSuccess, ID: c.reqID},
+		Questions: c.questions,
+		Answers:   []dnsmessage.Resource{},
+	}
+	c.appendIPv4(&msg)
+	c.appendIPV6(&msg)
+	return msg.Pack()
+}
+
+func (c *testDnsConn) appendIPv4(msg *dnsmessage.Message) {
+	if c.ipv4 != nil {
+		msg.Answers = append(msg.Answers, dnsmessage.Resource{
+			Header: dnsmessage.ResourceHeader{
+				Name:  dnsmessage.MustNewName(c.wantName),
+				Type:  dnsmessage.TypeA,
+				Class: dnsmessage.ClassINET,
+			},
+			Body: &dnsmessage.AResource{A: [4]byte(c.ipv4)},
+		})
+	}
+}
+
+func (c *testDnsConn) appendIPV6(msg *dnsmessage.Message) {
+	if c.ipv6 != nil {
+		msg.Answers = append(msg.Answers, dnsmessage.Resource{
+			Header: dnsmessage.ResourceHeader{
+				Name:  dnsmessage.MustNewName(c.wantName),
+				Type:  dnsmessage.TypeAAAA,
+				Class: dnsmessage.ClassINET,
+			},
+			Body: &dnsmessage.AAAAResource{AAAA: [16]byte(c.ipv6)},
+		})
+	}
+}
+
+// RemoteAddr implements net.Conn.
+func (*testDnsConn) RemoteAddr() net.Addr {
+	panic("unimplemented")
+}
+
+// SetDeadline implements net.Conn.
+func (*testDnsConn) SetDeadline(t time.Time) error {
+	return nil
+}
+
+// SetReadDeadline implements net.Conn.
+func (*testDnsConn) SetReadDeadline(t time.Time) error {
+	return nil
+}
+
+// SetWriteDeadline implements net.Conn.
+func (*testDnsConn) SetWriteDeadline(t time.Time) error {
+	return nil
+}
+
+// Write implements net.Conn.
+func (c *testDnsConn) Write(b []byte) (n int, err error) {
+	var p dnsmessage.Parser
+	var h dnsmessage.Header
+	if h, err = p.Start(b[2:]); err != nil {
+		return 0, err
+	}
+
+	c.questions, err = p.AllQuestions()
+	if err != nil {
+		return 0, err
+	}
+
+	for _, q := range c.questions {
+		qStr := q.Name.String()
+		if qStr != c.wantName {
+			continue
+		}
+
+		c.requested = true
+		c.reqID = h.ID
+		if err := p.SkipAllQuestions(); err != nil {
+			return 0, err
+		}
+		break
+	}
+
+	return len(b), nil
+}
+
+type testConnStub struct{}
+
+// Close implements net.Conn.
+func (*testConnStub) Close() error {
+	return nil
+}
+
+// LocalAddr implements net.Conn.
+func (*testConnStub) LocalAddr() net.Addr {
+	panic("unimplemented")
+}
+
+// Read implements net.Conn.
+func (*testConnStub) Read(b []byte) (n int, err error) {
+	panic("unimplemented")
+}
+
+// RemoteAddr implements net.Conn.
+func (*testConnStub) RemoteAddr() net.Addr {
+	panic("unimplemented")
+}
+
+// SetDeadline implements net.Conn.
+func (*testConnStub) SetDeadline(t time.Time) error {
+	panic("unimplemented")
+}
+
+// SetReadDeadline implements net.Conn.
+func (*testConnStub) SetReadDeadline(t time.Time) error {
+	panic("unimplemented")
+}
+
+// SetWriteDeadline implements net.Conn.
+func (*testConnStub) SetWriteDeadline(t time.Time) error {
+	panic("unimplemented")
+}
+
+// Write implements net.Conn.
+func (*testConnStub) Write(b []byte) (n int, err error) {
+	panic("unimplemented")
+}

dialer_integration_test.go

@@ -1,3 +1,5 @@
+//go:build integration
+
 package multinet
 
 import (

go.mod

@@ -6,7 +6,8 @@ require (
 	github.com/stretchr/testify v1.8.4
 	github.com/vishvananda/netlink v1.1.0
 	github.com/vishvananda/netns v0.0.4
-	golang.org/x/sys v0.2.0
+	golang.org/x/net v0.17.0
+	golang.org/x/sys v0.13.0
 )
 
 require (

go.sum

@@ -9,9 +9,11 @@ github.com/vishvananda/netlink v1.1.0/go.mod h1:cTgwzPIzzgDAYoQrMm0EdrjRUBkTqKYp
 github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df/go.mod h1:JP3t17pCcGlemwknint6hfoeCVQrEMVwxRLRjXpq+BU=
 github.com/vishvananda/netns v0.0.4 h1:Oeaw1EM2JMxD51g9uhtC0D7erkIjgmj8+JZc26m1YX8=
 github.com/vishvananda/netns v0.0.4/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
+golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
+golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=
 golang.org/x/sys v0.0.0-20190606203320-7fc4e5ec1444/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.2.0 h1:ljd4t30dBnAvMZaQCevtY0xLLD0A+bRZXbgLMLU1F/A=
-golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

health_integration_test.go

@@ -1,3 +1,5 @@
+//go:build integration
+
 package multinet
 
 import (
@@ -21,8 +23,13 @@ func Test_NetlinkWatcher(t *testing.T) {
 		addr1 := &net.TCPAddr{IP: net.IP{1, 2, 30, 11}}
 		addr2 := &net.TCPAddr{IP: net.IP{1, 2, 30, 12}}
 
+		result := make(chan net.Addr, 1)
 		d, err := NewDialer(Config{
 			Subnets: []string{"1.2.30.0/23"},
+			DialContext: func(d *net.Dialer, _ context.Context, _, _ string) (net.Conn, error) {
+				result <- d.LocalAddr
+				return nil, nil
+			},
 		})
 		require.NoError(t, err)
 
@@ -30,12 +37,6 @@ func Test_NetlinkWatcher(t *testing.T) {
 		require.NoError(t, w.Start())
 		t.Cleanup(w.Stop)
 
-		result := make(chan net.Addr, 1)
-		d.(*dialer).testHookDialContext = func(d *net.Dialer, _ context.Context, _, _ string) (net.Conn, error) {
-			result <- d.LocalAddr
-			return nil, nil
-		}
-
 		checkDialAddr(t, d, result, addr1)
 		checkDialAddr(t, d, result, addr1)
 
@@ -62,8 +63,13 @@ func Test_NetlinkWatcher(t *testing.T) {
 		addr1 := &net.TCPAddr{IP: net.IP{1, 2, 30, 11}}
 		addr2 := &net.TCPAddr{IP: net.IP{1, 2, 30, 12}}
 
+		result := make(chan net.Addr, 1)
 		d, err := NewDialer(Config{
 			Subnets: []string{"1.2.30.0/23"},
+			DialContext: func(d *net.Dialer, _ context.Context, _, _ string) (net.Conn, error) {
+				result <- d.LocalAddr
+				return nil, nil
+			},
 		})
 		require.NoError(t, err)
 
@@ -71,12 +77,6 @@ func Test_NetlinkWatcher(t *testing.T) {
 		require.NoError(t, w.Start())
 		t.Cleanup(w.Stop)
 
-		result := make(chan net.Addr, 1)
-		d.(*dialer).testHookDialContext = func(d *net.Dialer, _ context.Context, _, _ string) (net.Conn, error) {
-			result <- d.LocalAddr
-			return nil, nil
-		}
-
 		checkDialAddr(t, d, result, addr1)
 		checkDialAddr(t, d, result, addr1)
 
@@ -106,9 +106,14 @@ func Test_NetlinkWatcher(t *testing.T) {
 		addr1 := &net.TCPAddr{IP: net.IP{1, 2, 30, 11}}
 		addr2 := &net.TCPAddr{IP: net.IP{1, 2, 30, 12}}
 
+		result := make(chan net.Addr, 1)
 		d, err := NewDialer(Config{
 			Subnets:  []string{"1.2.30.0/23"},
 			Balancer: BalancerTypeRoundRobin,
+			DialContext: func(d *net.Dialer, _ context.Context, _, _ string) (net.Conn, error) {
+				result <- d.LocalAddr
+				return nil, nil
+			},
 		})
 		require.NoError(t, err)
 
@@ -116,12 +121,6 @@ func Test_NetlinkWatcher(t *testing.T) {
 		require.NoError(t, w.Start())
 		t.Cleanup(w.Stop)
 
-		result := make(chan net.Addr, 1)
-		d.(*dialer).testHookDialContext = func(d *net.Dialer, _ context.Context, _, _ string) (net.Conn, error) {
-			result <- d.LocalAddr
-			return nil, nil
-		}
-
 		checkDialAddr(t, d, result, addr2)
 		checkDialAddr(t, d, result, addr1)
 		checkDialAddr(t, d, result, addr2)

interface.go

@@ -0,0 +1,33 @@
+package multinet
+
+import "net"
+
+// Interface provides information about net.Interface.
+type Interface interface {
+	Name() string
+	Addrs() ([]net.Addr, error)
+}
+
+type netInterface struct {
+	iface net.Interface
+}
+
+func (i *netInterface) Name() string {
+	return i.iface.Name
+}
+
+func (i *netInterface) Addrs() ([]net.Addr, error) {
+	return i.iface.Addrs()
+}
+
+func systemInterfaces() ([]Interface, error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	var result []Interface
+	for _, iface := range ifaces {
+		result = append(result, &netInterface{iface: iface})
+	}
+	return result, nil
+}