net: Misleading error "no such host" when running out of file descriptiors

[polarina]

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

$ go version
go version go1.19.2 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/mce-gabrielp/.cache/go-build"
GOENV="/home/mce-gabrielp/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/mce-gabrielp/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/mce-gabrielp/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19.2"
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-build969251111=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Given the following program:

package main

import "net/http"

func main() {
	for {
		_, err := http.DefaultClient.Get("https://google.com")
		if err != nil {
			panic(err)
		}
	}
}

Then build and execute as follows:

$ go build main.go 
$ bash -c 'ulimit -n 6 && ./main'

We initially encountered this bug in a production program (where, due to our bug, a request got repeated in a loop without closing the response body) with far more gracious ulimit. This is not a fringe case limited to setting the ulimit haphazardly low.

What did you expect to see?

panic: Get "https://google.com": dial tcp: lookup google.com: too many open files

What did you see instead?

panic: Get "https://google.com": dial tcp: lookup google.com: no such host

[mateusz834]

It only happens with the cgo resolver, while using the go resolver it returns the correct error: lookup google.com on [::1]:53: dial udp [::1]:53: socket: too many open files

[gopherbot]

Change https://go.dev/cl/443255 mentions this issue: net: cgo resolver return correctly the too many open files error

[nightlyone]

@mateusz834 could you please mention which libc and version of it you are using?

https://dev.to/0xbf/how-to-get-glibc-version-c-lang-26he describes how to do that for glibc.

[mateusz834]

@nightlyone (GNU libc) 2.36

[mateusz834]

As discussed in CL 443255 this is caused by a glibc bug. I filled a bug report here: https://sourceware.org/bugzilla/show_bug.cgi?id=29717

[mateusz834]

For now it can be workarounded by forcing the go resolver, or using different libc (musl).

[bcmills]

Duplicate of #18588