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net: Make Listen(":port") use IPv6 when IPv4 is not supported.

When running an experimental kernel with IPv4 disabled, Listen(":port")
currently tries to create an AF_INET socket, and fails.  Instead, it
should see !supportsIPv4, and use an AF_INET6 socket.

This sort of environment is quite esoteric at the moment, but I can
force the tests to fail on regular Linux using the following tweaks:

- net/net.go: supportsIPv4, supportsIPv6, supportsIPv4map = false, true, false
- net/sockopt_linux.go: ipv6only=true
- net/ipsock_posix.go: Revert this fix
- ./make.bash && ../bin/go test net

Also, make the arrows in server_test.go point to the left, because
server<-client is easier to read.

Fixes #12510

Change-Id: I0cc3b6b08d5e6908d2fbf8594f652ba19815aa4b
Reviewed-on: https://go-review.googlesource.com/14334
Run-TryBot: Paul Marks <pmarks@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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pmarks-net committed Sep 5, 2015
1 parent 703bd83 commit 5a3ff6c8955a5df81f6dd83e143a47bd51266b61
Showing with 10 additions and 9 deletions.
  1. +6 −5 src/net/ipsock_posix.go
  2. +1 −1 src/net/platform_test.go
  3. +3 −3 src/net/server_test.go
@@ -101,10 +101,11 @@ func probeIPv6Stack() (supportsIPv6, supportsIPv4map bool) {
//
// 1. A wild-wild listen, "tcp" + ""
// If the platform supports both IPv6 and IPv6 IPv4-mapping
// capabilities, we assume that the user want to listen on
// both IPv4 and IPv6 wildcard address over an AF_INET6
// socket with IPV6_V6ONLY=0. Otherwise we prefer an IPv4
// wildcard address listen over an AF_INET socket.
// capabilities, or does not support IPv4, we assume that
// the user wants to listen on both IPv4 and IPv6 wildcard
// addresses over an AF_INET6 socket with IPV6_V6ONLY=0.
// Otherwise we prefer an IPv4 wildcard address listen over
// an AF_INET socket.
//
// 2. A wild-ipv4wild listen, "tcp" + "0.0.0.0"
// Same as 1.
@@ -137,7 +138,7 @@ func favoriteAddrFamily(net string, laddr, raddr sockaddr, mode string) (family
}

if mode == "listen" && (laddr == nil || laddr.isWildcard()) {
if supportsIPv4map {
if supportsIPv4map || !supportsIPv4 {
return syscall.AF_INET6, false
}
if laddr == nil {
@@ -134,7 +134,7 @@ func testableListenArgs(network, address, client string) bool {

// Test functionality of IPv4 communication using AF_INET6
// sockets.
if !supportsIPv4map && (network == "tcp" || network == "udp" || network == "ip") && wildcard {
if !supportsIPv4map && supportsIPv4 && (network == "tcp" || network == "udp" || network == "ip") && wildcard {
// At this point, we prefer IPv4 when ip is nil.
// See favoriteAddrFamily for further information.
if ip.To16() != nil && ip.To4() == nil && cip.To4() != nil { // a pair of IPv6 server and IPv4 client
@@ -55,7 +55,7 @@ func TestTCPServer(t *testing.T) {

for i, tt := range tcpServerTests {
if !testableListenArgs(tt.snet, tt.saddr, tt.taddr) {
t.Logf("skipping %s test", tt.snet+" "+tt.saddr+"->"+tt.taddr)
t.Logf("skipping %s test", tt.snet+" "+tt.saddr+"<-"+tt.taddr)
continue
}

@@ -251,7 +251,7 @@ var udpServerTests = []struct {
func TestUDPServer(t *testing.T) {
for i, tt := range udpServerTests {
if !testableListenArgs(tt.snet, tt.saddr, tt.taddr) {
t.Logf("skipping %s test", tt.snet+" "+tt.saddr+"->"+tt.taddr)
t.Logf("skipping %s test", tt.snet+" "+tt.saddr+"<-"+tt.taddr)
continue
}

@@ -329,7 +329,7 @@ var unixgramServerTests = []struct {
func TestUnixgramServer(t *testing.T) {
for i, tt := range unixgramServerTests {
if !testableListenArgs("unixgram", tt.saddr, "") {
t.Logf("skipping %s test", "unixgram "+tt.saddr+"->"+tt.caddr)
t.Logf("skipping %s test", "unixgram "+tt.saddr+"<-"+tt.caddr)
continue
}

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