func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) { transport := p.Transport if transport == nil { transport = http.DefaultTransport } outreq := new(http.Request) *outreq = *req // includes shallow copies of maps, but okay p.Director(outreq) outreq.Proto = "HTTP/1.1" outreq.ProtoMajor = 1 outreq.ProtoMinor = 1 outreq.Close = false // Remove hop-by-hop headers to the backend. Especially // important is "Connection" because we want a persistent // connection, regardless of what the client sent to us. This // is modifying the same underlying map from req (shallow // copied above) so we only copy it if necessary. copiedHeaders := false for _, h := range hopHeaders { if outreq.Header.Get(h) != "" { if !copiedHeaders { outreq.Header = make(http.Header) copyHeader(outreq.Header, req.Header) copiedHeaders = true } outreq.Header.Del(h) } } if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil { // If we aren't the first proxy retain prior // X-Forwarded-For information as a comma+space // separated list and fold multiple headers into one. if prior, ok := outreq.Header["X-Forwarded-For"]; ok { clientIP = strings.Join(prior, ", ") + ", " + clientIP } outreq.Header.Set("X-Forwarded-For", clientIP) } res, err := transport.RoundTrip(outreq) if err != nil { p.logf("http: proxy error: %v", err) rw.WriteHeader(http.StatusInternalServerError) return } defer res.Body.Close() for _, h := range hopHeaders { res.Header.Del(h) } copyHeader(rw.Header(), res.Header) rw.WriteHeader(res.StatusCode) p.copyResponse(rw, res.Body) }