net: Dial timeout reports incorrect problem DNS entry

[dtcaciuc]

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

go version go1.7 linux/amd64

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

linux_amd64, scilinux 6.3

What did you do?

1. Have two nameserver entries in /etc/resolve.conf; first one is the invalid, second one is valid.
2. Run the test program

package main

import (
    "fmt"
    "net/http"
)

func main() {
    _, err := http.Get("https://www.google.ca/")
    if err != nil {
        fmt.Println(err)
    }
}

What did you expect to see?

Timeout message reporting the invalid nameserver IP

What did you see instead?

Timeout message erroneously reporting the second valid nameserver IP

[bradfitz]

/cc @mdempsky @mikioh

[vcabbage]

I think this was fixed in 1.7.1 by https://golang.org/cl/28057

I was able to reproduce this with the Go resolver on 1.7:

# cat /etc/resolv.conf
nameserver 8.8.8.9
nameserver 8.8.8.8
# go version
go version go1.7 linux/amd64
# GODEBUG=netdns=go+2 go run main.go
go package net: GODEBUG setting forcing use of Go's resolver
go package net: hostLookupOrder(www.google.ca) = files,dns
lookup www.google.ca on 8.8.8.8:53: dial udp 8.8.8.8:53: i/o timeout
exit status 1

With Go 1.7.1 the sample program correctly resolves the address:

# cat /etc/resolv.conf
nameserver 8.8.8.9
nameserver 8.8.8.8
# go version
go version go1.7.1 linux/amd64
# GODEBUG=netdns=go+2 go run main.go
go package net: GODEBUG setting forcing use of Go's resolver
go package net: hostLookupOrder(www.google.ca) = files,dns
[172.217.3.163 2607:f8b0:400a:801::2003]

(The cgo resolver did not exhibit the issue for 1.7 or 1.7.1)

Note that I modified the demo program to just do the DNS lookup:

package main

import (
    "fmt"
    "net"
    "os"
)

func main() {
    ips, err := net.LookupIP("www.google.ca")
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
    fmt.Println(ips)
}

[bradfitz]

@vcabbage, oh, thanks. I missed the "go1.7" in the original report.

[mikioh]

This is a duplicate of #16865.