nghttpx: Always expect response trailer fields

src/shrpx_downstream.cc

@@ -744,6 +744,13 @@ bool Downstream::expect_response_body() const {
          http2::expect_response_body(req_.method, resp_.http_status);
 }
 
+bool Downstream::expect_response_trailer() const {
+  // In HTTP/2, if final response HEADERS does not bear END_STREAM it
+  // is possible trailer fields might come, regardless of request
+  // method or status code.
+  return !resp_.headers_only && resp_.http_major == 2;
+}
+
 namespace {
 void reset_timer(struct ev_loop *loop, ev_timer *w) { ev_timer_again(loop, w); }
 } // namespace

src/shrpx_downstream.h

@@ -278,6 +278,7 @@ public:
   bool validate_request_recv_body_length() const;
   void set_request_downstream_host(const StringRef &host);
   bool expect_response_body() const;
+  bool expect_response_trailer() const;
   enum {
     INITIAL,
     HEADER_COMPLETE,

src/shrpx_http2_upstream.cc

@@ -1520,7 +1520,8 @@ int Http2Upstream::on_downstream_header_complete(Downstream *downstream) {
 
   nghttp2_data_provider *data_prdptr;
 
-  if (downstream->expect_response_body()) {
+  if (downstream->expect_response_body() ||
+      downstream->expect_response_trailer()) {
     data_prdptr = &data_prd;
   } else {
     data_prdptr = nullptr;

src/shrpx_http_downstream_connection.cc

@@ -604,6 +604,13 @@ int htp_hdrs_completecb(http_parser *htp) {
   resp.http_major = htp->http_major;
   resp.http_minor = htp->http_minor;
 
+  if (resp.http_major > 1) {
+    // Normalize HTTP version, since we use http_major == 2 specially
+    // in Downstream::expect_response_trailer().
+    resp.http_major = 1;
+    resp.http_minor = 1;
+  }
+
   if (resp.fs.parse_content_length() != 0) {
     downstream->set_response_state(Downstream::MSG_BAD_HEADER);
     return -1;