net: fix multicast and IPv6 related issues on Plan 9

Fix issues that make these tests pass:
- TestDialerLocalAddr: return error if local address is not IPv4 for
"tcp4" network.
- TestInterfaceAddrs, TestInterfaceUnicastAddrs: don't assume each
interface has only one address. It may have more than one or none.
- TestConcurrentPreferGoResolversDial: should be skipped on Plan 9.
- TestListenMulticastUDP: remove IP from `announce` command and don't
mix IPv4 address with IPv6 address in `addmulti` command.

Fixes #34931

Change-Id: Ie0fdfe19ea282e5d6d6c938bf3c9139f8f5b0308
Reviewed-on: https://go-review.googlesource.com/c/go/+/201397
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/interface_plan9.go

@@ -143,8 +143,8 @@ func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
 		ifcs = []Interface{*ifi}
 	}
 
-	addrs := make([]Addr, len(ifcs))
-	for i, ifc := range ifcs {
+	var addrs []Addr
+	for _, ifc := range ifcs {
 		status := ifc.Name + "/status"
 		statusf, err := open(status)
 		if err != nil {
@@ -157,12 +157,8 @@ func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
 		if _, ok := statusf.readLine(); !ok {
 			return nil, errors.New("cannot read header line for interface: " + status)
 		}
-		line, ok := statusf.readLine()
-		if !ok {
-			return nil, errors.New("cannot read IP address for interface: " + status)
-		}
 
-		// This assumes only a single address for the interface.
+		for line, ok := statusf.readLine(); ok; line, ok = statusf.readLine() {
 			fields := getFields(line)
 			if len(fields) < 1 {
 				return nil, errors.New("cannot parse IP address for interface: " + status)
@@ -189,7 +185,8 @@ func interfaceAddrTable(ifi *Interface) ([]Addr, error) {
 				mask = CIDRMask(pfxlen, 8*IPv6len)
 			}
 
-		addrs[i] = &IPNet{IP: ip, Mask: mask}
+			addrs = append(addrs, &IPNet{IP: ip, Mask: mask})
+		}
 	}
 
 	return addrs, nil

src/net/ipsock_plan9.go

@@ -227,7 +227,7 @@ func listenPlan9(ctx context.Context, net string, laddr Addr) (fd *netFD, err er
 	_, err = f.WriteString("announce " + dest)
 	if err != nil {
 		f.Close()
-		return nil, err
+		return nil, &OpError{Op: "announce", Net: net, Source: laddr, Addr: nil, Err: err}
 	}
 	laddr, err = readPlan9Addr(proto, netdir+"/"+proto+"/"+name+"/local")
 	if err != nil {

src/net/lookup_test.go

@@ -972,10 +972,11 @@ func (lcr *lookupCustomResolver) dial() func(ctx context.Context, network, addre
 // TestConcurrentPreferGoResolversDial tests that multiple resolvers with the
 // PreferGo option used concurrently are all dialed properly.
 func TestConcurrentPreferGoResolversDial(t *testing.T) {
-	// The windows implementation of the resolver does not use the Dial
-	// function.
-	if runtime.GOOS == "windows" {
-		t.Skip("skip on windows")
+	// The windows and plan9 implementation of the resolver does not use
+	// the Dial function.
+	switch runtime.GOOS {
+	case "windows", "plan9":
+		t.Skipf("skip on %v", runtime.GOOS)
 	}
 
 	testenv.MustHaveExternalNetwork(t)

src/net/tcpsock_plan9.go

@@ -23,7 +23,12 @@ func (sd *sysDialer) dialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPCo
 
 func (sd *sysDialer) doDialTCP(ctx context.Context, laddr, raddr *TCPAddr) (*TCPConn, error) {
 	switch sd.network {
-	case "tcp", "tcp4", "tcp6":
+	case "tcp4":
+		// Plan 9 doesn't complain about [::]:0->127.0.0.1, so it's up to us.
+		if laddr != nil && len(laddr.IP) != 0 && laddr.IP.To4() == nil {
+			return nil, &AddrError{Err: "non-IPv4 local address", Addr: laddr.String()}
+		}
+	case "tcp", "tcp6":
 	default:
 		return nil, UnknownNetworkError(sd.network)
 	}

src/net/udpsock_plan9.go

@@ -109,7 +109,9 @@ func (sl *sysListener) listenUDP(ctx context.Context, laddr *UDPAddr) (*UDPConn,
 }
 
 func (sl *sysListener) listenMulticastUDP(ctx context.Context, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error) {
-	l, err := listenPlan9(ctx, sl.network, gaddr)
+	// Plan 9 does not like announce command with a multicast address,
+	// so do not specify an IP address when listening.
+	l, err := listenPlan9(ctx, sl.network, &UDPAddr{IP: nil, Port: gaddr.Port, Zone: gaddr.Zone})
 	if err != nil {
 		return nil, err
 	}
@@ -129,11 +131,13 @@ func (sl *sysListener) listenMulticastUDP(ctx context.Context, ifi *Interface, g
 			return nil, err
 		}
 	}
+
+	have4 := gaddr.IP.To4() != nil
 	for _, addr := range addrs {
-		if ipnet, ok := addr.(*IPNet); ok {
+		if ipnet, ok := addr.(*IPNet); ok && (ipnet.IP.To4() != nil) == have4 {
 			_, err = l.ctl.WriteString("addmulti " + ipnet.IP.String() + " " + gaddr.IP.String())
 			if err != nil {
-				return nil, err
+				return nil, &OpError{Op: "addmulti", Net: "", Source: nil, Addr: ipnet, Err: err}
 			}
 		}
 	}

src/net/udpsock_plan9_test.go

@@ -36,7 +36,7 @@ func TestListenMulticastUDP(t *testing.T) {
 
 	c1, err := ListenMulticastUDP("udp4", mifc, &UDPAddr{IP: ParseIP("224.0.0.254")})
 	if err != nil {
-		t.Fatalf("multicast not working on %s", runtime.GOOS)
+		t.Fatalf("multicast not working on %s: %v", runtime.GOOS, err)
 	}
 	c1addr := c1.LocalAddr().(*UDPAddr)
 	if err != nil {