Fix x-forwarded-for header calculation

Setting the x-forwarded-for header is actually broken as it omit the separator between IPs passed by clients and other reverse proxies and the actual client request.

Like in the current httputil.reverseproxy library (https://golang.org/src/net/http/httputil/reverseproxy.go?s=575:1776#L188) I suggest to add the following patch.

Thank's for the work,

Salim

Author: sailor

reverse.go

@@ -215,7 +215,7 @@ func addXForwardedForHeader(req *http.Request) {
 		// X-Forwarded-For information as a comma+space
 		// separated list and fold multiple headers into one.
 		if prior, ok := req.Header["X-Forwarded-For"]; ok {
-			clientIP = strings.Join(prior, ", ") + clientIP
+			clientIP = strings.Join(prior, ", ") + ", " + clientIP
 		}
 		req.Header.Set("X-Forwarded-For", clientIP)
 	}