net: missing interfaces on Windows

[AudriusButkevicius]

package main

import(
    "fmt"
    "net"
)

func main(){
    ifs, err := net.Interfaces()
    if err != nil {
        fmt.Println(err)
    }
    for _, inf := range ifs {
        x, _ := inf.Addrs()
        fmt.Printf("%#v %s", inf, x)
    }
}

In 1.4.1 returns:

net.Interface{Index:5, MTU:1500, Name:"{E36EC396-D578-48C0-82D5-F55217877570}", HardwareAddr:net.HardwareAddr{0x94, 0xde, 0x80, 0xaf, 0x4b, 0x62}, Flags:0x0} [192.168.1.70]

In 1.5 returns:

net.Interface{Index:1, MTU:4294967295, Name:"Loopback Pseudo-Interface 1", HardwareAddr:net.HardwareAddr{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, Flags:0x15} [::1/28 127.0.0.1/16]

Any code relying on net.Interfaces() breaks (for example making multicasts to all interfaces, since Windows by default multicasts to some single interface)

What version of Go are you using (go version)?
go version go1.5 windows/amd64

What operating system and processor architecture are you using?
Windows 8.1 x64

What did you do?
Called net.Interfaces()

What did you expect to see?
My one external interface

What did you see instead?
My one loopback interface

ipconfig /all

c:\Go\src\net>ipconfig /all

Windows IP Configuration

   Host Name . . . . . . . . . . . . : Audrius
   Primary Dns Suffix  . . . . . . . :
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : lan

Ethernet adapter Ethernet 5:

   Connection-specific DNS Suffix  . : lan
   Description . . . . . . . . . . . : Hyper-V Virtual Ethernet Adapter #2
   Physical Address. . . . . . . . . : 94-DE-80-AF-4B-62
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::58d9:707e:1173:32c%5(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.1.70(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : 23 August 2015 13:46:11
   Lease Expires . . . . . . . . . . : 25 August 2015 13:46:22
   Default Gateway . . . . . . . . . : 192.168.1.254
   DHCP Server . . . . . . . . . . . : 192.168.1.254
   DHCPv6 IAID . . . . . . . . . . . : 1150606976
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-1D-3C-8E-0C-94-DE-80-AF-4B-62
   DNS Servers . . . . . . . . . . . : fe80::9e97:26ff:fe78:cec2%5
                                       8.8.8.8
                                       4.4.8.8
   NetBIOS over Tcpip. . . . . . . . : Enabled

Tunnel adapter isatap.lan:

   Media State . . . . . . . . . . . : Media disconnected
   Connection-specific DNS Suffix  . : lan
   Description . . . . . . . . . . . : Microsoft ISATAP Adapter #4
   Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes

netsh interface show interface

Admin State    State          Type             Interface Name
-------------------------------------------------------------------------
Enabled        Connected      Dedicated        Ethernet 3
Enabled        Connected      Dedicated        Ethernet 5

Test output:

c:\Go\src\net>go test -v -run=Interface
=== RUN   TestInterfaces
--- PASS: TestInterfaces (0.00s)
        interface_test.go:79: "Loopback Pseudo-Interface 1": flags "up|loopback|multicast", ifindex 1, mtu 4294967295
        interface_test.go:80: hardware address "00:00:00:00:00:00:00:00"
        interface_test.go:202: interface address "::1/28"
        interface_test.go:202: interface address "127.0.0.1/16"
        interface_test.go:223: joined group address "ff02::c"
        interface_test.go:223: joined group address "239.255.255.250"
=== RUN   TestInterfaceAddrs
--- PASS: TestInterfaceAddrs (0.00s)
        interface_test.go:202: interface address "fe80::58d9:707e:1173:32c/28"
        interface_test.go:202: interface address "192.168.1.70/16"
        interface_test.go:202: interface address "::1/28"
        interface_test.go:202: interface address "127.0.0.1/16"
        interface_test.go:202: interface address "fe80::5efe:c0a8:146/28"
PASS
Socket statistical information:
(inet4, datagram, udp): opened=4, connected=0, listened=0, accepted=0, closed=4, openfailed=0, connectfailed=0, listenfailed=0, acceptfailed=0, closefailed=0

ok      net     0.124s

[AudriusButkevicius]

Strangely, net.InterfaceAddrs() returns the correct addresses, though net.InterfaceByIndex() nor net.InterfaceByName() does not.

[AudriusButkevicius]

Seems that it has been broken by ea22a08 by @mattn.

The problem seems to lie in getInterfaceInfos() which only returns info for the loopback adapter.
Though it's not obvious to me why that happens.

[mikioh]

@AudriusButkevicius,

Please take a look at https://github.com/golang/go/blob/master/CONTRIBUTING.md and let us know your environment information. Also can you show us the output of "go test -v -run=Interface at $GOROOT/src/net" and "ipconfig? ifconfig? netsh interfaces show?" on the node? (Please anonymize IDs in the output if necessary)

[AudriusButkevicius]

I edited my original post.

[mikioh]

Thanks. Just skimmed interface_windows.go and looks like the code is broken. At least about the following:

• It doesn't list up all equipped interfaces because of https://github.com/golang/go/blob/master/src/net/interface_windows.go#L110
• It makes wrong address prefixes because of https://github.com/golang/go/blob/master/src/net/interface_windows.go#L167. It should take prefixes instead of addresses, prefix lengths instead of socket structure lengths

[AudriusButkevicius]

Re 1, it does, because of for ; paddr != nil; paddr = paddr.Next {

In my case:
https://github.com/golang/go/blob/master/src/net/interface_windows.go#L93
chain contains 3 interfaces, but https://github.com/golang/go/blob/master/src/net/interface_windows.go#L98 contains only one info, hence interfaces get skipped at
https://github.com/golang/go/blob/master/src/net/interface_windows.go#L112

[alexbrainman]

@mikioh feel free to change. I know nothing about these. Happy to test / review if you need my help.

Alex

[mikioh]

@AudriusButkevicius,

Feel free to send a fix if you have a spare time. Unfortunately I'm not a windows user, have no windows box.

[mikioh]

Ah... @AudriusButkevicius, after you.

[AudriusButkevicius]

Well the win32 api is not clear to me, why it would return only info for a single interface, hence I am not sure what the right answer here is, hence pinging @mattn in hopes for comments.

[mattn]

I can reproduce. I'll look into it in later. But I don't have the old environment windowns XP 32bit that I made the change.no longer. Currently, I'm on windows 64bit.