net: correct address when listening on IPv4zero tcp4/udp4 on Plan 9

Since Plan 9 doesn't allow us to listen on 0.0.0.0, the Listener
address that's read in from /net is the IPv6 address ::. Convert
this address to 0.0.0.0 when the network is tcp4 or udp4.

Fixes #40045

Change-Id: Icfb69b823e5b80603742d23c3762a812996fe43f
Reviewed-on: https://go-review.googlesource.com/c/go/+/240918
Run-TryBot: David du Colombier <0intro@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David du Colombier <0intro@gmail.com>

2 files changed, 42 insertions, 7 deletions

diff --git a/src/net/ipsock_plan9.go b/src/net/ipsock_plan9.go
index 9db01b090d..99d3e3971a 100644
--- a/src/net/ipsock_plan9.go
+++ b/src/net/ipsock_plan9.go
@@ -67,7 +67,7 @@ func parsePlan9Addr(s string) (ip IP, iport int, err error) {
 	return addr, p, nil
 }
 
-func readPlan9Addr(proto, filename string) (addr Addr, err error) {
+func readPlan9Addr(net, filename string) (addr Addr, err error) {
 	var buf [128]byte
 
 	f, err := os.Open(filename)
@@ -83,13 +83,19 @@ func readPlan9Addr(proto, filename string) (addr Addr, err error) {
 	if err != nil {
 		return
 	}
-	switch proto {
-	case "tcp":
+	switch net {
+	case "tcp4", "udp4":
+		if ip.Equal(IPv6zero) {
+			ip = ip[:IPv4len]
+		}
+	}
+	switch net {
+	case "tcp", "tcp4", "tcp6":
 		addr = &TCPAddr{IP: ip, Port: port}
-	case "udp":
+	case "udp", "udp4", "udp6":
 		addr = &UDPAddr{IP: ip, Port: port}
 	default:
-		return nil, UnknownNetworkError(proto)
+		return nil, UnknownNetworkError(net)
 	}
 	return addr, nil
 }
@@ -213,7 +219,7 @@ func dialPlan9Blocking(ctx context.Context, net string, laddr, raddr Addr) (fd *
 		f.Close()
 		return nil, err
 	}
-	laddr, err = readPlan9Addr(proto, netdir+"/"+proto+"/"+name+"/local")
+	laddr, err = readPlan9Addr(net, netdir+"/"+proto+"/"+name+"/local")
 	if err != nil {
 		data.Close()
 		f.Close()
@@ -233,7 +239,7 @@ func listenPlan9(ctx context.Context, net string, laddr Addr) (fd *netFD, err er
 		f.Close()
 		return nil, &OpError{Op: "announce", Net: net, Source: laddr, Addr: nil, Err: err}
 	}
-	laddr, err = readPlan9Addr(proto, netdir+"/"+proto+"/"+name+"/local")
+	laddr, err = readPlan9Addr(net, netdir+"/"+proto+"/"+name+"/local")
 	if err != nil {
 		f.Close()
 		return nil, err
diff --git a/src/net/ipsock_plan9_test.go b/src/net/ipsock_plan9_test.go
new file mode 100644
index 0000000000..e5fb9ff965
--- /dev/null
+++ b/src/net/ipsock_plan9_test.go
@@ -0,0 +1,29 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package net
+
+import "testing"
+
+func TestTCP4ListenZero(t *testing.T) {
+	l, err := Listen("tcp4", "0.0.0.0:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer l.Close()
+	if a := l.Addr(); isNotIPv4(a) {
+		t.Errorf("address does not contain IPv4: %v", a)
+	}
+}
+
+func TestUDP4ListenZero(t *testing.T) {
+	c, err := ListenPacket("udp4", "0.0.0.0:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Close()
+	if a := c.LocalAddr(); isNotIPv4(a) {
+		t.Errorf("address does not contain IPv4: %v", a)
+	}
+}