我想定义一个http.Client自动将表单值附加到所有GET / POST请求的。

我天真地尝试将其实现http.RoundTripper为从另一个库中复制/粘贴，并使用此技术为每个请求修改标头。

type Transport struct {
    // Transport is the HTTP transport to use when making requests.
    // It will default to http.DefaultTransport if nil.
    // (It should never be an oauth.Transport.)
    Transport http.RoundTripper
}

// Client returns an *http.Client that makes OAuth-authenticated requests.
func (t *Transport) Client() *http.Client {
    return &http.Client{Transport: t}
}

func (t *Transport) transport() http.RoundTripper {
    if t.Transport != nil {
        return t.Transport
    }
    return http.DefaultTransport
}

func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
    // To set the Authorization header, we must make a copy of the Request
    // so that we don't modify the Request we were given.
    // This is required by the specification of http.RoundTripper.
    req = cloneRequest(req)
 >> req.Form.Set("foo", bar)

    // Make the HTTP request.
    return t.transport().RoundTrip(req)
}

// cloneRequest returns a clone of the provided *http.Request.
// The clone is a shallow copy of the struct and its Header map.
func cloneRequest(r *http.Request) *http.Request {
    // shallow copy of the struct
    r2 := new(http.Request)
    *r2 = *r
    // deep copy of the Header
    r2.Header = make(http.Header)
    for k, s := range r.Header {
        r2.Header[k] = s
    }
    return r2
}

但是，这不起作用。该req.Form数值地图似乎并不在此阶段存在，所以我得到的恐慌： panic: runtime error: assignment to entry in nil map

我尝试将其添加到中(t *Transport) RoundTrip，但没有运气：

err := req.ParseForm()
misc.PanicIf(err)

我不知道我在做什么，有什么建议吗？

编辑：尝试复制方法中的req.Form值没有意义cloneRequest，因为r.Form无论如何都是空映射。