net: pure Go resolver(netdns) can not resolve hostname.local

[atlas-comstock]

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

go version go1.13.3 darwin/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="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/atlas/Library/Caches/go-build"
GOENV="/Users/atlas/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/yonghao.hu/mycode/go_dir_path"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.13.3/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.13.3/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/yonghao.hu/mycode/go_dir_path/src/test/go.mod"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/wf/nw471wh91nj2j_dsrfrk4htnjtqhhw/T/go-build666420423=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import (
	"fmt"
	"net"
)

func main() {
	dialer := &net.Dialer{
		LocalAddr: nil,
	}

	_, err := dialer.Dial("tcp", "atalas-mac.local:4150")
	if err != nil {
		fmt.Println("resolve atalas-mac.local failed: ", err)
	} else {
		fmt.Println("resolve myaliashost success")
	}
	_, err = dialer.Dial("tcp", "myaliashost:4150")
	if err != nil {
		fmt.Println("resolve myaliashost failed: ", err)
	}
	fmt.Println("resolve myaliashost success")
}

Just run GODEBUG=netdns=go+4 go run test.go

What did you expect to see?

Resolve to 127.0.0.1

What did you see instead?

resolve mac.local failed: dial tcp: lookup mac.local on 10.22.12.45:53: no such host

[bradfitz]

Yes, that's known, as the docs at https://golang.org/pkg/net/#hdr-Name_Resolution imply, and we're unlikely to implement it.

If you need to resolve those names, use a different resolver.

[atlas-comstock]

@bradfitz Hi, thanks for your reply . I know sth about this before writing the issue. Could u plz tell me why not to implement it ? What is the consideration?

[bradfitz]

It's a lot of code for very few users and the system DNS resolver is usually fine. The advantage of using the pure Go resolver is usually to avoid cgo and expensive threads being tied up during resolution, but that only matters when you have, say, tens of thousands of outstanding lookups. (e.g. you're a web crawler binary) But if you have tens of thousands of mDNS lookups outstanding, you probably have bigger problems on your LAN.

[seankhliao]

sounds like a won't fix.