net: InterfaceAddrs, Interface.{Addrs,MulticastAddrs} can return addresses on administratively or operational down interface

[akevinbailey]

I found another issue in interface_windows.go: The interfaceAddrTable returns Interfaces that are not active. Need to implement the follow code after for ; paddr != nil; paddr = paddr.Next { ... (line 156):

if paddr.OperStatus == windows.IfOperStatusUp {
...
}

This will exclude inactive interfaces.

[rakyll]

/cc @alexbrainman

[rsc]

If the interface is up but it has an address, is it incorrect to return that address? Serious question.

Most down interfaces have no addresses.

[akevinbailey]

On Windows, down interfaces do have addresses.  The *IPAdaperAddresses has a field called OperStatus.  On Windows the interface is only considered up if OperStatus==1.  If you don't put in this constrain you will get all the down or dormant connections like Wifi, VPN, and virtual host interfaces.  Ideally, it would be better to just provide the OperStatus in the return and let the caller decide.
-- Kevin  

 From: Russ Cox <notifications@github.com>

To: golang/go go@noreply.github.com
Cc: A. Kevin Bailey akevinbailey@yahoo.com
Sent: Friday, October 23, 2015 12:49 PM
Subject: Re: [go] net: interfaceAddrTable returns inactive interfaces on windows (#12812)

If the interface is up but it has an address, is it incorrect to return that address? Serious question.Most down interfaces have no addresses.—
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[rsc]

OK, I guess we need to decide what InterfaceAddrs does. Does it return only "up" interfaces? I guess it does on other systems? So then maybe it should on Windows too?

[mikioh]

This is not a Windows-specific inconsistency. IIRC, there are two types of implementation on routing information. One is that simply adds and drops connected routes (and interface addresses) on link-layer events such as physical-port/{physical/logical}-link/logical-interface arrivals and departures. The other is that just keeps interface addresses and notifies each status of addresses. The former example would be BSD variants and the latter example would be Linux (and Windows probably.)