Go ReverseProxy handle redirect error: "http: invalid Read on closed Body"

here is my code, when origin server return 302, reverse proxy will modify the request and serve it again, but if the request with a body, it print an error: http: invalid Read on closed Body

                proxy = httputil.NewSingleHostReverseProxy(url)
		proxy.ErrorLog = proxyLogger
		proxy.ModifyResponse = func(response *http.Response) error {
			if response.StatusCode > 300 && response.StatusCode < 400 {
				location, err := response.Location()
				if err != nil {
					return err
				}
				return &RedirectErr{location: location}
			}
			return nil
		}
		var rewindBody func(r *http.Request)

		proxy.Director = func(request *http.Request) {
			if redirect := request.Header.Get("redirect"); redirect != "" {
				request.Header.Del("redirect")
				u, _ := urlpkg.Parse(redirect)
				rewriteRequestURL(request, u)
				return
			}
			rewriteRequestURL(request, url)
		}
		proxy.ErrorHandler = func(writer http.ResponseWriter, request *http.Request, err error) {
			var redirect *RedirectErr
			if redirect, ok = err.(*RedirectErr); !ok {
				proxy.ErrorLog.Printf("http: proxy error: %v", err)
				writer.WriteHeader(http.StatusBadGateway)
			} else {
				request.Header.Set("redirect", redirect.location.String())
				proxy.ServeHTTP(writer, request)
				return
			}
		}

I try to use fakeCloseReadCloser, but it comes new error: "error: net/http: HTTP/1.x transport connection broken: http: ContentLength=75 with Body length 0"

Finally , I resoled this. We need ensure that the request body not close.
and we should rewind the body before second transport.

// after transport, the request body will close,
// so if we need redirect it, we have to wrap the body and ensure that it won't be close
// we will handle it after we finished.
// see this issue: https://github.com/flynn/flynn/issues/872
type fakeCloseReadCloser struct {
io.ReadCloser
}
func (w *fakeCloseReadCloser) Close() error {
return nil
}
func (w *fakeCloseReadCloser) RealClose() error {
if w.ReadCloser == nil {
return nil
}
return w.ReadCloser.Close()
}
type Proxy struct {
*httputil.ReverseProxy
}
func (p *Proxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
req.Body = &fakeCloseReadCloser{req.Body}
// The body can only be read once, so we use this func to make the body available on the second forwarding
if req.Body != nil {
bodyBytes, _ := io.ReadAll(req.Body)
_ = req.Body.(*fakeCloseReadCloser).RealClose()
req.Body = &fakeCloseReadCloser{io.NopCloser(bytes.NewBuffer(bodyBytes))}
req.GetBody = func() (io.ReadCloser, error) {
body := io.NopCloser(bytes.NewBuffer(bodyBytes))
return body, nil
}
}
p.ReverseProxy.ServeHTTP(rw, req)
_ = req.Body.(*fakeCloseReadCloser).RealClose()
}
// Get returns a proxy for the given shard.
func (pp *ProxyPool) Get(url *urlpkg.URL) *Proxy {
pp.mutex.Lock()
defer pp.mutex.Unlock()
p, ok := pp.pool[url.String()]
if !ok {
// When the original target server returns 302,
// proxy.ModifyResponse will return a customized redirect error containing location,
// proxy.ErrorHandler catches the error and modifies the request,
// adds a "redirect" header field to it, and Serve it again.
// At this point proxy.Director will detect the "redirect" field in the request header
// and send the request to the final target server.
rp := httputil.NewSingleHostReverseProxy(url)
px := &Proxy{ReverseProxy: rp}
px.ErrorLog = proxyLogger
px.ModifyResponse = func(response *http.Response) error {
if response.StatusCode > 300 && response.StatusCode < 400 {
location, err := response.Location()
if err != nil {
return err
}
return &RedirectErr{location: location}
}
return nil
}
px.Director = func(request *http.Request) {
if redirect := request.Header.Get("redirect"); redirect != "" {
request.Header.Del("redirect")
u, _ := urlpkg.Parse(redirect)
// rewind
if request.GetBody != nil {
b, _ := request.GetBody()
request.Body = b
}
rewriteRequestURL(request, u)
return
}
rewriteRequestURL(request, url)
}
px.ErrorHandler = func(writer http.ResponseWriter, request *http.Request, err error) {
var redirect *RedirectErr
if redirect, ok = err.(*RedirectErr); !ok {
p.ErrorLog.Printf("http: proxy error: %v", err)
writer.WriteHeader(http.StatusBadGateway)
} else {
request.Header.Set("redirect", redirect.location.String())
px.ReverseProxy.ServeHTTP(writer, request)
return
}
}
pp.pool[url.Host] = px
p = px
}
return p
}