What configuration am I missing for httputil.NewSingleHostReverseProxy? - go

Question

The code below produces the error further below. When I type "http://www.cnn.com/favicon.ico" straight into any browser it works without issue. I am guessing that I am missing some critical configuration for the reverse proxy. What is the minimum config needed for getting this to work?
package main
import (
"net/http"
"net/http/httputil"
"net/url"
"log"
)
func main(){
url, _ := url.Parse("http://www.cnn.com/favicon.ico")
proxy := httputil.NewSingleHostReverseProxy(url)
http.HandleFunc("/", proxy.ServeHTTP)
log.Fatal(http.ListenAndServe(":9090", nil))
}
Fastly error: unknown domain: localhost. Please check that this domain
has been added to a service.
Details: cache-lax8625-LAX
Happy 4th of July!

Answer 1

I made the following 2 changes to get it working:
Firstly, point the proxy at www.cnn.com instead of www.cnn.com/favicon.ico. Of course, now we must make our request to localhost:9090/favicon.ico.
Next, set the proxied request's Host field to the target host, not the host of the proxy which is localhost.
The code ends up looking like this:
package main
import (
"log"
"net/http"
"net/http/httputil"
"net/url"
)
type Director func(*http.Request)
func (f Director) Then(g Director) Director {
return func(req *http.Request) {
f(req)
g(req)
}
}
func hostDirector(host string) Director {
return func(req *http.Request) {
req.Host = host
}
}
func main() {
url, _ := url.Parse("http://www.cnn.com")
proxy := httputil.NewSingleHostReverseProxy(url)
d := proxy.Director
// sequence the default director with our host director
proxy.Director = Director(d).Then(hostDirector(url.Hostname()))
http.Handle("/", proxy)
log.Fatal(http.ListenAndServe(":9090", nil))
}