golang/go

net: LookupHost shows different results between GODEBUG=netdns=cgo and go

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#22,902 opened on Nov 28, 2017

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Description

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

go version go1.9.2 darwin/amd64

What did you do?

package main

import (
	"net"
	"fmt"
)

func main() {
	fmt.Println(net.LookupHost("10.256"))
	fmt.Println(net.LookupHost("10.256.1"))
	fmt.Println(net.LookupHost("10.10.256"))
	fmt.Println(net.LookupHost("10.10.256.1"))
	fmt.Println(net.LookupHost("10.10.10.256"))
}

What did you expect to see?

This program works fine on both Linux & Windows and does show below output, but not on Mac

[] lookup 10.256: no such host
[] lookup 10.256.1: no such host
[] lookup 10.10.256: no such host
[] lookup 10.10.256.1: no such host
[] lookup 10.10.10.256: no such host

What did you see instead?

[10.0.1.0] <nil>
[] lookup 10.256.1: no such host
[10.10.1.0] <nil>
[] lookup 10.10.256.1: no such host
[] lookup 10.10.10.256: no such host

Contributor guide

Research direction
Investigate the difference between the pure Go DNS resolver and cgo's resolver in the net package, specifically how invalid IPs like 10.256 are handled on macOS.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70