net/http: Response.Write adds redundant "Connection: Close" headers

[roglew]

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

go version go1.8 linux/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/user/golang"
GORACE=""
GOROOT="/home/user/go"
GOTOOLDIR="/home/user/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build896761484=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

package main

import (
	"net/http"
	"bufio"
	"bytes"
	"os"
)

func main() {
	rspbytes := []byte("HTTP/1.0 200 OK\r\n\r\nAAAA")
	buf := bytes.NewBuffer(rspbytes)
	
	httpRsp, _ := http.ReadResponse(bufio.NewReader(buf), nil)
	buf2 := bytes.NewBuffer(make([]byte, 0))
	httpRsp.Write(buf2)
	
	httpRsp2, _ := http.ReadResponse(bufio.NewReader(buf2), nil)
	buf3 := bytes.NewBuffer(make([]byte, 0))
	httpRsp2.Write(buf3)
	
	httpRsp3, _ := http.ReadResponse(bufio.NewReader(buf3), nil)
	httpRsp3.Write(os.Stdout)
}

Playground Link

What did you expect to see?

HTTP/1.0 200 OK
Connection: close

AAAA

or

HTTP/1.0 200 OK

AAAA

What did you see instead?

HTTP/1.0 200 OK
Connection: close
Connection: close
Connection: close

AAAA

[odeke-em]

/cc @bradfitz

[gopherbot]

CL https://golang.org/cl/38076 mentions this issue.