net: LookupAddr returns a zero length slice when looking up its own IP address on a Windows DNS server

[jftuga]

What version of Go are you using (go version)?

go version go1.11.4 windows/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env

set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\jftuga\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\jftuga\go
set GOPROXY=
set GORACE=
set GOROOT=C:\Go
set GOTMPDIR=
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\jftuga\AppData\Local\Temp\go-build308914574=/tmp/go-build -gno-record-gcc-switches

What did you do?

// dnstest.go
package main
import "fmt"
import "net"
import "os"

func main() {
    	ip := os.Args[1]
    	fmt.Println("LookupAddr on ", ip)
    	addresses, err := net.LookupAddr(ip)
        if err != nil {
    		fmt.Println("error:", err)
    		return
        }
    	if len(addresses) == 0 {
    		fmt.Printf("error: addresses has a length of zero")
    		return
    	}
    	fmt.Println("results:",addresses)
}

192.168.1.2 is a Active Directory server running DNS
This program is running on 192.168.1.2 and the bug is only seen in this situation.

What did you expect to see?

• Windows Server 2008 R2 Enterprise

• Windows Server 2016 Enterprise

• 192.168.1.2 is a Active Directory server running DNS

  dnstest.exe 192.168.1.2
  LookupAddr on 192.168.1.2
  results: [dns1.example.com.]

What did you see instead?

If I run this program on the DNS server itself, this is the result:

dnstest.exe 192.168.1.2
LookupAddr on  192.168.1.2
error: addresses has a length of zero

This problem only occurs when:

1. Windows OS, this does not occur under Linux
2. This program is running on the DNS server itself
3. It is looking up it's own IP address

In essence, this program does not return any hostnames when looking up it's own IP address when running on a DNS server under Windows. Instead, it returns a zero length slice. In this situation, err is nil.

Can someone else reproduce this?

Also, should err be set when len(addresses) == 0?

[julieqiu]

/cc @mikioh @bradfitz

[iwdgo]

https://golang.org/pkg/net/#InterfaceAddrs mentions

On Windows, the resolver always uses C library functions, such as GetAddrInfo and DnsQuery.

When no C compiler is installed, net.LookupAddr() is not reporting the unavailability of C like the usual exec: "gcc": executable file not found in %PATH%. Setting GODEBUG as documented does not change this behavior.

[alexbrainman]

When no C compiler is installed, net.LookupAddr() is not reporting the unavailability of C

You do not need C compiler to use net.LookupAddr on Windows.

Alex

[iwdgo]

The behavior of net.LookupAddr can be reproduced independently using the Powershell instruction Resolve-DnsName -Name 113.17.217.172.in-addr.arpa -Type 6 called here DNSQuery

Type 6 does not return a value when not registered in a public DNS in line with the in-addr domain definition rfc1035.

Using the nslookup command like in the tests of the net package resolves 192. values.

const ipname = "192.168.1.2"

func ExampleNslookupIP() {
	var out bytes.Buffer
	var err bytes.Buffer
	cmd := exec.Command("nslookup", ipname)
	cmd.Stdout = &out
	cmd.Stderr = &err
	if err := cmd.Run(); err != nil {
		log.Fatal(err)
	}
	r := strings.ReplaceAll(out.String(), "\r\n", "\n")
	// nslookup stderr output contains also debug information such as
	// "Non-authoritative answer" and it doesn't return the correct errcode
	if strings.Contains(err.String(), "can't find") {
		log.Fatal(err)
	}
	fmt.Println(r)
	// Output: <your server name>
}

[gopherbot]

Change https://golang.org/cl/178701 mentions this issue: net/lookup: fix resolving local windows machine ptr