net/http/httputil: NewSingleHostReverseProxy fails to transparently send requests #10342
Description
I seems that NewSingleHostReverseProxy does not work, at least not how I would expected it to.
The program below demonstrates the correct and incorrect behavior.
The problem is that the director function do not reset the Host field of the request received by the proxy.
This is ok if the server is used as a real proxy:
curl -x http://localhost:8000/ http://golang.org/
works perfectly well.
However it was my understanding that the goal of NewSingleHostReverseProxy was to transparently proxy requests to a given http server:
curl http://localhost:8000/
won't work as localhost:8000 is sent as the Host header of the request to the proxied server.
package main
import (
"fmt"
"net/http"
"net/http/httputil"
"net/url"
"strings"
)
func singleJoiningSlash(a, b string) string {
aslash := strings.HasSuffix(a, "/")
bslash := strings.HasPrefix(b, "/")
switch {
case aslash && bslash:
return a + b[1:]
case !aslash && !bslash:
return a + "/" + b
}
return a + b
}
func NewSingleHostReverseProxy(target *url.URL) *httputil.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)
fmt.Println(req.Host)
// this fixes the bug
req.Host = ""
// --
if targetQuery == "" || req.URL.RawQuery == "" {
req.URL.RawQuery = targetQuery + req.URL.RawQuery
} else {
req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
}
}
return &httputil.ReverseProxy{Director: director}
}
func main() {
url, _ := url.Parse("http://golang.org/")
go func() {
http.ListenAndServe(":8001", NewSingleHostReverseProxy(url))
}()
http.ListenAndServe(":8000", httputil.NewSingleHostReverseProxy(url))
}