nghttpx: Return 503 when h1 backend connect attempt failed

integration-tests/nghttpx_test.go

@@ -89,7 +89,7 @@ func TestH1H1ConnectFailure(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Error st.http1() = %v", err)
 	}
-	want := 502
+	want := 503
 	if got := res.status; got != want {
 		t.Errorf("status: %v; want %v", got, want)
 	}
@@ -366,7 +366,7 @@ func TestH2H1ConnectFailure(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Error st.http2() = %v", err)
 	}
-	want := 502
+	want := 503
 	if got := res.status; got != want {
 		t.Errorf("status: %v; want %v", got, want)
 	}

src/shrpx_http_downstream_connection.cc

@@ -95,7 +95,7 @@ void connectcb(struct ev_loop *loop, ev_io *w, int revents) {
   auto upstream = downstream->get_upstream();
   auto handler = upstream->get_client_handler();
   if (dconn->on_connect() != 0) {
-    if (upstream->downstream_error(dconn, Downstream::EVENT_ERROR) != 0) {
+    if (upstream->on_downstream_abort_request(downstream, 503) != 0) {
       delete handler;
     }
     return;