net: LookupAddr does not set IsNotFound with cgo resolver

[rudis]

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

$ go version
go version go1.19.4 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

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="$HOME/.cache/go-build"
GOENV="$HOME/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="$HOME/dev/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/go/go1.19.4"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/go/go1.19.4/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.4"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/run/user/$UID/go-build1957738364=/tmp/go-build -gno-record-gcc-switches"

What did you do?

$ cat > x.go <<EOF
package main
import (
        "fmt"
        "net"
)
func main() {
        _, err := net.LookupAddr("1.2.3.4")
        fmt.Printf("%v\n", err.(*net.DNSError).IsNotFound)
}
EOF

$ GODEBUG=netdns=go go run x.go
true

$ GODEBUG=netdns=cgo go run x.go
false

What did you expect to see?

Both go and cgo resolver correctly report IsNotFound.

What did you see instead?

Only go resolver does so.

There's already a pull request for this but it wasn't merged: #45959

[rudis]

I think this CL is unrelated because it changes cgoLookupIPCNAME and not cgoLookupAddrPTR which is used by LookupAddr.

[mateusz834]

@rudis you are right, my mistake, deleted that comment. I will make a new CL for this.

[gopherbot]

Change https://go.dev/cl/460255 mentions this issue: net: report IsNotFound when getnameinfo returns EAI_NONAME

[heschi]

cc @neild @ianlancetaylor

[rudis]

@rudis you are right, my mistake, deleted that comment. I will make a new CL for this.

Thanks for the quick response. CL looks good to me.