golang reverse proxy cannot be accessed

First, let’s take a look at how to get a reverse proxy structure

func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
	targetQuery := target.RawQuery
	director := func(req *http.Request) {
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
		if targetQuery == "" || req.URL.RawQuery == "" {
			req.URL.RawQuery = targetQuery + req.URL.RawQuery
		} else {
			req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
		}
		if _, ok := req.Header["User-Agent"]; !ok {
			req.Header.Set("User-Agent", "")
		}
	}
	return &ReverseProxy{Director: director}
}

NewSingleHostReverseProxy uses a closure as the Director to create a new ReverseProxy structure, and the director is It is the proxy function we implement by default. In this function, the protocol, Host and Path of the request URL are rewritten. But it does not rewrite req.Host, which results in our reverse proxy only being able to proxy locally. So we only need to modify this function. There are two ways to modify it.

(Recommended tutorial: golang tutorial)

Modification method:

1. We can copy the NewSingleHostReverseProxy function and modify it. Anyway, this function is also It's not complicated, and then use our custom function to create a new proxy where the reverse proxy structure is needed.

func NewProxy(target *url.URL) *httputil.ReverseProxy {
	targetQuery := target.RawQuery
	director := func(req *http.Request) {
		req.Host = target.Host // -- 加入这句 --
		req.URL.Scheme = target.Scheme
		req.URL.Host = target.Host
		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
		if targetQuery == "" || req.URL.RawQuery == "" {
			req.URL.RawQuery = targetQuery + req.URL.RawQuery
		} else {
			req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
		}
		if _, ok := req.Header["User-Agent"]; !ok {
			// explicitly disable User-Agent so it's not set to default value
			req.Header.Set("User-Agent", "")
		}
	}
	return &httputil.ReverseProxy{Director: director}
}

Then replace httputil.NewSingleHostReverseProxy(u) with NewProxy(u) to proxy to other domain names.

2. Customize Director function. We still use the NewSingleHostReverseProxy function to create a new proxy, and then customize a Director function for it.

p := httputil.NewSingleHostReverseProxy(u)
d := p.Director
p.Director = func(r *http.Request) {
	d(r)
	r.Host = u.Host
}

Recommended related video tutorials: golang video tutorial

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