nghttpx: Return 413 if request header is too large

For now, if request has request body, we'll issue RST_STREAM to inform
the peer to stop sending body.  RST_STREAM may be sent before error
page header or data, so peer may receive RST_STREAM only.

src/shrpx_http2_upstream.cc

@@ -212,12 +212,21 @@ int on_header_callback(nghttp2_session *session,
     return 0;
   }
   if(downstream->get_request_headers_sum() > Downstream::MAX_HEADERS_SUM) {
+    if(downstream->get_response_state() == Downstream::MSG_COMPLETE) {
+      return 0;
+    }
+
     if(LOG_ENABLED(INFO)) {
       ULOG(INFO, upstream) << "Too large header block size="
                            << downstream->get_request_headers_sum();
     }
+
+    if(upstream->error_reply(downstream, 413) != 0) {
       return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
     }
+
+    return 0;
+  }
   if(!http2::check_nv(name, namelen, value, valuelen)) {
     return 0;
   }
@@ -267,6 +276,10 @@ int on_request_headers(Http2Upstream *upstream,
 {
   int rv;
 
+  if(downstream->get_response_state() == Downstream::MSG_COMPLETE) {
+    return 0;
+  }
+
   downstream->normalize_request_headers();
   auto& nva = downstream->get_request_headers();