Thanks to Alex from Golang-nuts, I have the answer now.
This is what Alex said:
Just need to set http.Request.Host [and scheme] in the Director to get this working: http://play.golang.org/p/I17ZSM6LQb
If you read the source for SingleHostReverseProxy (http://golang.org/src/pkg/net/http/httputil/reverseproxy.go#L61), it sets its own Director which you are overriding. So you need to reimplement what it already does plus the extra Host change.
Anyway, that didn't solve de Header part of the problem: the target server was still receiving "localhost:8080" as the HTTP Host name, so I did it without the ReverseProxy package, just with http and a RoundTripper, plus a helper function that copies all the headers:
package main
import (
"flag"
"fmt"
"os"
"log"
"net/http"
"io/ioutil"
)
var target *string
func main() {
target = flag.String("target", "http://stackoverflow.com", "target URL for reverse proxy")
flag.Parse()
http.HandleFunc("/", report)
log.Fatal(http.ListenAndServe("127.0.0.1:8080", nil))
}
func report(w http.ResponseWriter, r *http.Request){
uri := *target+r.RequestURI
fmt.Println(r.Method + ": " + uri)
if r.Method == "POST" {
body, err := ioutil.ReadAll(r.Body)
fatal(err)
fmt.Printf("Body: %v\n", string(body));
}
rr, err := http.NewRequest(r.Method, uri, r.Body)
fatal(err)
copyHeader(r.Header, &rr.Header)
// Create a client and query the target
var transport http.Transport
resp, err := transport.RoundTrip(rr)
fatal(err)
fmt.Printf("Resp-Headers: %v\n", resp.Header);
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
fatal(err)
dH := w.Header()
copyHeader(resp.Header, &dH)
dH.Add("Requested-Host", rr.Host)
w.Write(body)
}
func fatal(err error) {
if err != nil {
log.Fatal(err)
os.Exit(1)
}
}
func copyHeader(source http.Header, dest *http.Header){
for n, v := range source {
for _, vv := range v {
dest.Add(n, vv)
}
}
}
Now I'm able to see StackOverflow or any other site how it's supposed to be.
I'm still working on POST calls, though, so this is a work in progress.