net/http/httputil: DumpResponse return error when ContentLength=2 with Body length 0, but it's a response for http.MethodHead request

[lrh3321]

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

$ go version
go version go1.15.4 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

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/go/pkg/mod"
GONOPROXY="*.ucloudadmin.com"
GONOSUMDB="*.ucloudadmin.com"
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE="*.ucloudadmin.com"
GOPROXY="https://goproxy.cn,direct"
GOROOT="/root/sdk/go1.15.4"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/root/sdk/go1.15.4/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build737726766=/tmp/go-build -gno-record-gcc-switches"

What did you do?

package main

import (
	"net/http"
	"net/http/httptest"
	"net/http/httputil"
	"testing"
)

func serveHTTP(w http.ResponseWriter, r *http.Request) {
	w.Header().Add("Content-Length", "2")
	switch r.Method {
	case http.MethodHead:
	default:
		w.Write([]byte("{}"))
	}
}

func TestDumpResponse(t *testing.T) {
	t.Run("Get", func(t *testing.T) {
		rw := httptest.NewRecorder()
		r := httptest.NewRequest(http.MethodGet, "/", nil)

		serveHTTP(rw, r)
		raw, err := httputil.DumpResponse(rw.Result(), true)
		if err != nil {
			t.Errorf("DumpResponse: (%v)\nRaw: %s", err, string(raw))
		}

	})
	t.Run("Head", func(t *testing.T) {
		rw := httptest.NewRecorder()
		r := httptest.NewRequest(http.MethodHead, "/", nil)

		serveHTTP(rw, r)
		raw, err := httputil.DumpResponse(rw.Result(), true)
		if err != nil {
			t.Errorf("DumpResponse: (%v)\nRaw: %s", err, string(raw))
		}

	})
}

go test main_test.go 

What did you expect to see?

--- FAIL: TestDumpResponse (0.00s)
    --- FAIL: TestDumpResponse/Head (0.00s)
        main_test.go:38: DumpResponse: (http: ContentLength=2 with Body length 0)
            Raw: 
FAIL
FAIL    command-line-arguments  0.003s
FAIL

What did you see instead?

ok      command-line-arguments  0.003s

[imxyb]

i think you may change httputil.DumpResponse(rw.Result(), true) to httputil.DumpResponse(rw.Result(), false)

[cagedmantis]

/cc @bradfitz @empijei

[empijei]

It's not clear to me what you're trying to convey.

You wrote

What did you expect to see?

--- FAIL: TestDumpResponse (0.00s)
    --- FAIL: TestDumpResponse/Head (0.00s)
        main_test.go:38: DumpResponse: (http: ContentLength=2 with Body length 0)
            Raw: 
FAIL
FAIL    command-line-arguments  0.003s
FAIL

What did you see instead?

ok      command-line-arguments  0.003s

But if I run the tests myself I obtain the exact opposite result. I guess you meant to say that you expected "ok" and got the error instead.

Assuming my guess is right, your bug is saying that DumpResponse is erroring on an invalid response (CL mismatch with body) and you didn't expect it to?

Why did you expect httputil to work on inconsistent responses?