Golang ServeHTTP在POST请求时生成代理错误EOF

我正在使用gin和ServeHTTP开发代理服务器。
实际上，GET和OPTIONS请求工作得很好。但当我尝试多次POST请求时，两次请求中有一次出现EOF错误。我已经测试过在没有代理服务的情况下发出重复请求，并且它工作得很好，所以我的代码中有些东西不起作用。

Edit :

1. 我有一个带有https://ptsv2.com/和所有请求-响应返回200状态码的测试后代理。

// main.go

package main

import (
    "fmt"
    "../pkg/api"
)

func main() {
    fmt.Println("Starting server")
    api.InitServer()
}

// routes.go
package api

import (
    "github.com/gin-gonic/gin"
)

const serviceUrl = "http://localhost:8732"

func InitServer() {
    router := gin.Default()
    defineRoutes(router)
    router.Run()
}

func defineRoutes(router *gin.Engine) {
    router.GET("/ping", Ping)
    router.POST("/*any", Proxy(serviceUrl))
}

// controller.go

package api

import (
    "bytes"
    "fmt"
    "io/ioutil"
    "net/http"
    "net/http/httputil"
    "net/url"
    "strconv"
    "github.com/gin-gonic/gin"
)

type transport struct {
    http.RoundTripper
}

func (t *transport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
    resp, err = t.RoundTripper.RoundTrip(req)
    if err != nil {
        // EOF ERROR HERE
        return nil, err
    }
    b, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        return nil, err
    }
    err = resp.Body.Close()
    if err != nil {
        return nil, err
    }
    b = bytes.Replace(b, []byte("server"), []byte("schmerver"), -1)
    body := ioutil.NopCloser(bytes.NewReader(b))

    response := resp
    response.Body = body


    response.ContentLength = int64(len(b))
    response.Header.Set("Content-Length", strconv.Itoa(len(b)))
    response.Header.Set("Access-Control-Allow-Origin", "*")

    return response, nil
}

func Proxy(targetUrl string) gin.HandlerFunc {
    fn := func(c *gin.Context) {
        remote, err := url.Parse(targetUrl)
        if err != nil {
            panic(err)
        }
        proxy := httputil.NewSingleHostReverseProxy(remote)

        proxy.Director = func(req *http.Request) {
            req.Header = c.Request.Header
            req.Host = remote.Host
            req.URL.Scheme = remote.Scheme
            req.URL.Host = remote.Host
            req.Close = true // True / False same result
        }
        proxy.Transport = &transport{http.DefaultTransport}
        proxy.ServeHTTP(c.Writer, c.Request)
    }
    return fn
}