affected/package: net

[alexchowle]

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

$ go version
go version go1.19.3 linux/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
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/me/.cache/go-build"
GOENV="/home/me/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/me/sourcecode/me/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/me/sourcecode/me/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/me/bin/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/me/bin/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.3"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2805608787=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Attempt to resolve a UDP hostname and port combination on a Centos7.9 VM. Works with go 1.17.6, but doesn't work with go 1.19.3.

https://go.dev/play/p/ZWWcqrwO0gv

What did you expect to see?

address my-lan-server:514 resolved successfully: <MY_LAN_SERVER_IP_ADDRESS>

What did you see instead?

failed to resolve my-lan-server:514: lookup my-lan-server on <MY_DNS_SERVER>:53: server misbehaving

[mateusz834]

Can you show the file contents of /etc/nsswitch.conf and /etc/resolv.conf?
Also try running your program with GODEBUG=netdns=go+2 or GODEBUG=netdns=cgo+2 env vars.

[alexchowle]

GODEBUG=netdns=go+2

go package net: confVal.netCgo = false  netGo = true
go package net: GODEBUG setting forcing use of Go's resolver
go package net: hostLookupOrder(my-lan-server) = files,dns
failed to resolve my-lan-server:514: lookup my-lan-server on <MY_DNS_SERVER>:53: server misbehaving

GODEBUG=netdns=cgo+2

go package net: confVal.netCgo = true  netGo = false
go package net: using cgo DNS resolver
go package net: hostLookupOrder(my-lan-server) = cgo
address my-lan-server:514 resolved successfully: <VALID_IP>:514

So, GODEBUG=netdns=cgo+2 has corrected the issue.

[mateusz834]

Ok, so it seems that we are doing something differently that the glibc does.
What is the response code of the dns query to my-lan-server? Try running dig my-lan-server.
Do you have any search/domain directives in /etc/resolv.conf?

[seankhliao]

how is the lan server address propagated? mdns? or some other way?

[alexchowle]

I have a search directive: search localdomain

which looks odd. When I correct that to the correct domain, my software works, even with Go/s resolver (via GODEBUG=netdns=go+2)

[mateusz834]

When I correct that to the correct domain, my software works, even with Go/s resolver (via GODEBUG=netdns=go+2)

What did you change the search domain to?

[alexchowle]

The correct one for my enterprise - sorry for being coy but it's private information.

[alexchowle]

So it looks like the cgo resolver copes with a dodgy search entry in resolv.conf, but the Go one doesn't. Unsure if this is a bug or not - I'll leave that to you guys.

[seankhliao]

i don't think this is enough information for us to do anything about it.