net/http/httputil: add X-Forwarded-{Host,Proto} headers in ReverseProxy

X-Forwarded-Host contains the original request's host.

X-Forwarded-Proto contains "http" or "https", depending on whether the
original request was made on a TLS-secured connection.

Setting either header to nil in Director disables adding the header,
same as for X-Forwarded-For.

Fixes #50465.

Change-Id: If8ed1f48d83f8ea0389c53519bc7994cb53891db
Reviewed-on: https://go-review.googlesource.com/c/go/+/407414
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/httputil/reverseproxy.go

@@ -28,14 +28,18 @@ import (
 // sends it to another server, proxying the response back to the
 // client.
 //
-// ReverseProxy by default sets the client IP as the value of the
-// X-Forwarded-For header.
+// ReverseProxy by default sets
+//   - the X-Forwarded-For header to the client IP address;
+//   - the X-Forwarded-Host header to the host of the original client
+//     request; and
+//   - the X-Forwarded-Proto header to "https" if the client request
+//     was made on a TLS-enabled connection or "http" otherwise.
 //
 // If an X-Forwarded-For header already exists, the client IP is
-// appended to the existing values. As a special case, if the header
-// exists in the Request.Header map but has a nil value (such as when
-// set by the Director func), the X-Forwarded-For header is
-// not modified.
+// appended to the existing values.
+//
+// If a header exists in the Request.Header map but has a nil value
+// (such as when set by the Director func), it is not modified.
 //
 // To prevent IP spoofing, be sure to delete any pre-existing
 // X-Forwarded-For header coming from the client or
@@ -306,6 +310,16 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 			outreq.Header.Set("X-Forwarded-For", clientIP)
 		}
 	}
+	if prior, ok := outreq.Header["X-Forwarded-Host"]; !(ok && prior == nil) {
+		outreq.Header.Set("X-Forwarded-Host", req.Host)
+	}
+	if prior, ok := outreq.Header["X-Forwarded-Proto"]; !(ok && prior == nil) {
+		if req.TLS == nil {
+			outreq.Header.Set("X-Forwarded-Proto", "http")
+		} else {
+			outreq.Header.Set("X-Forwarded-Proto", "https")
+		}
+	}
 
 	res, err := transport.RoundTrip(outreq)
 	if err != nil {

src/net/http/httputil/reverseproxy_test.go

@@ -50,6 +50,12 @@ func TestReverseProxy(t *testing.T) {
 		if r.Header.Get("X-Forwarded-For") == "" {
 			t.Errorf("didn't get X-Forwarded-For header")
 		}
+		if r.Header.Get("X-Forwarded-Host") == "" {
+			t.Errorf("didn't get X-Forwarded-Host header")
+		}
+		if r.Header.Get("X-Forwarded-Proto") == "" {
+			t.Errorf("didn't get X-Forwarded-Proto header")
+		}
 		if c := r.Header.Get("Connection"); c != "" {
 			t.Errorf("handler got Connection header value %q", c)
 		}
@@ -299,6 +305,7 @@ func TestXForwardedFor(t *testing.T) {
 	const prevForwardedFor = "client ip"
 	const backendResponse = "I am the backend"
 	const backendStatus = 404
+	const host = "some-name"
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Header.Get("X-Forwarded-For") == "" {
 			t.Errorf("didn't get X-Forwarded-For header")
@@ -306,6 +313,12 @@ func TestXForwardedFor(t *testing.T) {
 		if !strings.Contains(r.Header.Get("X-Forwarded-For"), prevForwardedFor) {
 			t.Errorf("X-Forwarded-For didn't contain prior data")
 		}
+		if got, want := r.Header.Get("X-Forwarded-Host"), host; got != want {
+			t.Errorf("X-Forwarded-Host = %q, want %q", got, want)
+		}
+		if got, want := r.Header.Get("X-Forwarded-Proto"), "http"; got != want {
+			t.Errorf("X-Forwarded-Proto = %q, want %q", got, want)
+		}
 		w.WriteHeader(backendStatus)
 		w.Write([]byte(backendResponse))
 	}))
@@ -319,7 +332,7 @@ func TestXForwardedFor(t *testing.T) {
 	defer frontend.Close()
 
 	getReq, _ := http.NewRequest("GET", frontend.URL, nil)
-	getReq.Host = "some-name"
+	getReq.Host = host
 	getReq.Header.Set("Connection", "close")
 	getReq.Header.Set("X-Forwarded-For", prevForwardedFor)
 	getReq.Close = true
@@ -336,11 +349,36 @@ func TestXForwardedFor(t *testing.T) {
 	}
 }
 
+func TestXForwardedProtoTLS(t *testing.T) {
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if got, want := r.Header.Get("X-Forwarded-Proto"), "https"; got != want {
+			t.Errorf("X-Forwarded-Proto = %q, want %q", got, want)
+		}
+	}))
+	defer backend.Close()
+	backendURL, err := url.Parse(backend.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	proxyHandler := NewSingleHostReverseProxy(backendURL)
+	frontend := httptest.NewTLSServer(proxyHandler)
+	defer frontend.Close()
+
+	getReq, _ := http.NewRequest("GET", frontend.URL, nil)
+	getReq.Host = "some-host"
+	_, err = frontend.Client().Do(getReq)
+	if err != nil {
+		t.Fatalf("Get: %v", err)
+	}
+}
+
 // Issue 38079: don't append to X-Forwarded-For if it's present but nil
 func TestXForwardedFor_Omit(t *testing.T) {
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if v := r.Header.Get("X-Forwarded-For"); v != "" {
-			t.Errorf("got X-Forwarded-For header: %q", v)
+		for _, h := range []string{"X-Forwarded-For", "X-Forwarded-Host", "X-Forwarded-Proto"} {
+			if v := r.Header.Get(h); v != "" {
+				t.Errorf("got %v header: %q", h, v)
+			}
 		}
 		w.Write([]byte("hi"))
 	}))
@@ -356,6 +394,8 @@ func TestXForwardedFor_Omit(t *testing.T) {
 	oldDirector := proxyHandler.Director
 	proxyHandler.Director = func(r *http.Request) {
 		r.Header["X-Forwarded-For"] = nil
+		r.Header["X-Forwarded-Host"] = nil
+		r.Header["X-Forwarded-Proto"] = nil
 		oldDirector(r)
 	}
 
@@ -1029,13 +1069,16 @@ func TestClonesRequestHeaders(t *testing.T) {
 	}
 	rp.ServeHTTP(httptest.NewRecorder(), req)
 
-	if req.Header.Get("From-Director") == "1" {
-		t.Error("Director header mutation modified caller's request")
+	for _, h := range []string{
+		"From-Director",
+		"X-Forwarded-For",
+		"X-Forwarded-Host",
+		"X-Forwarded-Proto",
+	} {
+		if req.Header.Get(h) != "" {
+			t.Errorf("%v header mutation modified caller's request", h)
+		}
 	}
-	if req.Header.Get("X-Forwarded-For") != "" {
-		t.Error("X-Forward-For header mutation modified caller's request")
-	}
-
 }
 
 type roundTripperFunc func(req *http.Request) (*http.Response, error)