net/http.Request.URL.Host返回空字符串

我试图将我的客户端重定向到https url。我试过这个：

func index(w http.ResponseWriter, r *http.Request) {
        if r.URL.Scheme != "https" {
                http.Redirect(w, r, "https://"+r.URL.Host+r.URL.Path, 301)
                return
        }
//....
}

但它给了我这样的回答：

$ curl -i http://localhost
HTTP/1.1 301 Moved Permanently
Content-Type: text/html; charset=utf-8
Location: https:///
Date: Sat, 24 Nov 2018 20:02:33 GMT
Content-Length: 44

<a href="https:///">Moved Permanently</a>.

然后我理解了为什么它返回

r.URL.Host

的空字符串

我还尝试了

r.Header.Get（“主机”）

和

r.Header.Get（“源代码”）

。它也给了我一个空字符串

是否有其他方法获取主机名？

尝试使用r.host

文件说：

// For server requests Host specifies the host on which the URL
// is sought. Per RFC 7230, section 5.4, this is either the value
// of the "Host" header or the host name given in the URL itself.

那就试试吧

func index(w http.ResponseWriter, r *http.Request) {
    if r.URL.Scheme != "https" {
            http.Redirect(w, r, "https://"+r.Host+r.URL.Path, 301)
            return
    }
//....
}

---

从

转到文档http.request

：

type Request struct {
        ...
        // For incoming requests, the Host header is promoted to the
        // Request.Host field and removed from the Header map.
       ...
        Header Header
       ...
        // For server requests Host specifies the host on which the
        // URL is sought. Per RFC 2616, this is either the value of
        // the "Host" header or the host name given in the URL itself.
        ...
        Host string

---

因此，对于//大多数请求，使用

r.Host

而不是

r.Header.Get（“主机”）

，除Path和RawQuery之外的字段将//为空。（参见RFC 7230，第5.3节）godoc的这一行很好地描述了

r.URL.Host

为空的原因。但是，还有其他方法可以获得非空主机名吗？谢谢，它起到了作用，并被接受为回答示例的答案。对于非代理请求，r.URL.Scheme始终是空字符串。您可以将处理程序主体简化为

http.Redirect

调用。

type Request struct {
        ...
        // For incoming requests, the Host header is promoted to the
        // Request.Host field and removed from the Header map.
       ...
        Header Header
       ...
        // For server requests Host specifies the host on which the
        // URL is sought. Per RFC 2616, this is either the value of
        // the "Host" header or the host name given in the URL itself.
        ...
        Host string