go: net/http/httputil: ReverseProxy read error during body copy use of closed network connection

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Administrator\AppData\Local\go-build
set GOENV=C:\Users\Administrator\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=D:\wxgo
set GOPRIVATE=
set GOPROXY=https://goproxy.io,direct
set GOROOT=D:\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=D:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessag
e-length=0 -fdebug-prefix-map=C:\Users\ADMINI~1\AppData\Local\Temp\go-build74128
8550=/tmp/go-build -gno-record-gcc-switches

package main
import (
“flag”
“net/http”
“net/http/httputil”
“net/url”
“time”
)
var burl = flag.String(“u”, “”, “backend address”)
func buildProxy(target *url.URL) *httputil.ReverseProxy {
flushInterval := time.Duration(100 * time.Millisecond)
passHost := true
passHostHeader := &passHost
targetQuery := target.RawQuery
proxy := &httputil.ReverseProxy{
Director: func(req *http.Request) {
req.URL.Path = target.Path
req.URL.Host = target.Host
req.URL.Scheme = target.Scheme
		req.URL.RawPath = target.RawPath
		if targetQuery == "" || req.URL.RawQuery == "" {
			req.URL.RawQuery = targetQuery + req.URL.RawQuery
		} else {
			req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
		}
		req.RequestURI = ""
		req.Proto = "HTTP/1.1"
		req.ProtoMajor = 1
		req.ProtoMinor = 1
		if passHostHeader != nil && !*passHostHeader {
			req.Host = req.URL.Host
		}
	},
	Transport:     http.DefaultTransport,
	FlushInterval: flushInterval,
}
return proxy

}
func handler(p *httputil.ReverseProxy) func(http.ResponseWriter, *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
	p.ServeHTTP(w, r)
}

}
func main() {
flag.Parse()
remote, err := url.ParseRequestURI(“http://” + *burl)
if err != nil {
panic(err)
}
proxy := buildProxy(remote)
http.HandleFunc("/", handler(proxy))
err = http.ListenAndServe(":8081", nil)
if err != nil {
	panic(err)
}

}

package main
import (
“fmt”
“strconv”
“github.com/gin-gonic/gin”
)
type myJson struct {
Name string json:"name"
}
func createBigString(name string) string {
var bs string
for i := 1; i <= 500; i++ {
	bs += name + "abcdefghij"

}

return bs

}
func main() {
gin.SetMode(gin.ReleaseMode)
router := gin.Default()
router.POST("/test/post", func(c *gin.Context) {
	var json myJson
	c.ShouldBindJSON(&json)
	myName := createBigString(json.Name)
	lenBody := len(myName) + 11
	fmt.Println(lenBody)
	c.Header("Content-Length", strconv.Itoa(lenBody))
	c.JSON(200, gin.H{"name": myName})
})
router.Run(":8082")

}