GetBody() the Method in Golang is not define in gentleman.

[leleyi]

When creating a new request, the GetBody property of the request is set according to the body parameter.
This attribute will affect the client's behavior after receiving the 307, 308 response code. If it is empty, it is likely that it will not follow redirect.

if body != nil {
		switch v := body.(type) {
		case *bytes.Buffer:
			req.ContentLength = int64(v.Len())
			buf := v.Bytes()
			req.GetBody = func() (io.ReadCloser, error) {
				r := bytes.NewReader(buf)
				return io.NopCloser(r), nil
			}
}

if ireq.GetBody == nil && ireq.outgoingLength() != 0 {
	// We had a request body, and 307/308 require
	// re-sending it, but GetBody is not defined. So just
	// return this response to the user instead of an
	// error, like we did in Go 1.7 and earlier.
	shouldRedirect = false
}

But in gentleman the 'body.go ' and the createRequest the GetBody（） Method is not define.

// String defines the HTTP request body based on the given string.
func String(data string) p.Plugin {
	return p.NewRequestPlugin(func(ctx *c.Context, h c.Handler) {
		ctx.Request.Method = getMethod(ctx)
		ctx.Request.Body = utils.StringReader(data)
		ctx.Request.ContentLength = int64(bytes.NewBufferString(data).Len())
		h.Next(ctx)
	})
}


// JSON defines a JSON body in the outgoing request.
// Supports strings, array of bytes or buffer.
func JSON(data interface{}) p.Plugin {
	return p.NewRequestPlugin(func(ctx *c.Context, h c.Handler) {
		buf := &bytes.Buffer{}
	switch data.(type) {
	case string:
		buf.WriteString(data.(string))
	case []byte:
		buf.Write(data.([]byte))
	default:
		if err := json.NewEncoder(buf).Encode(data); err != nil {
			h.Error(ctx, err)
			return
		}
	}

	ctx.Request.Method = getMethod(ctx)
	ctx.Request.Body = ioutil.NopCloser(buf)
	ctx.Request.ContentLength = int64(buf.Len())
	ctx.Request.Header.Set("Content-Type", "application/json")
	h.Next(ctx)
})
..........
}

// createRequest creates a default http.Request instance.
func createRequest() *http.Request {
	// Create HTTP request
	req := &http.Request{
		Method:     "GET",
		URL:        &url.URL{},
		Host:       "",
		ProtoMajor: 1,
		ProtoMinor: 1,
		Proto:      "HTTP/1.1",
		Header:     make(http.Header),
		Body:       utils.NopCloser(),
	}
	// Return shallow copy of Request with the new context
	return req.WithContext(emptyContext())
}