nghttpx: Use NGHTTP2_DATA_FLAG_NO_COPY for backend HTTP/2 session

src/shrpx_http2_downstream_connection.cc

@@ -179,24 +179,11 @@ ssize_t http2_data_read_callback(nghttp2_session *session, int32_t stream_id,
   }
   const auto &req = downstream->request();
   auto input = downstream->get_request_buf();
-  auto nread = input->remove(buf, length);
-  auto input_empty = input->rleft() == 0;
 
-  if (nread > 0) {
-    // This is important because it will handle flow control
-    // stuff.
-    if (downstream->get_upstream()->resume_read(SHRPX_NO_BUFFER, downstream,
-                                                nread) != 0) {
-      // In this case, downstream may be deleted.
-      return NGHTTP2_ERR_CALLBACK_FAILURE;
-    }
+  auto nread = std::min(input->rleft(), length);
+  auto input_empty = input->rleft() == nread;
 
-    // Check dconn is still alive because Upstream::resume_read()
-    // may delete downstream which will delete dconn.
-    if (sd->dconn == nullptr) {
-      return NGHTTP2_ERR_DEFERRED;
-    }
-  }
+  *data_flags |= NGHTTP2_DATA_FLAG_NO_COPY;
 
   if (input_empty &&
       downstream->get_request_state() == Downstream::MSG_COMPLETE &&
@@ -229,12 +216,6 @@ ssize_t http2_data_read_callback(nghttp2_session *session, int32_t stream_id,
     }
   }
 
-  if (!input_empty) {
-    downstream->reset_downstream_wtimer();
-  } else {
-    downstream->disable_downstream_wtimer();
-  }
-
   if (nread == 0 && (*data_flags & NGHTTP2_DATA_FLAG_EOF) == 0) {
     downstream->disable_downstream_wtimer();
 

src/shrpx_http2_session.cc

@@ -1362,6 +1362,54 @@ int on_frame_not_send_callback(nghttp2_session *session,
 }
 } // namespace
 
+namespace {
+constexpr auto PADDING = std::array<uint8_t, 256>{};
+} // namespace
+
+namespace {
+int send_data_callback(nghttp2_session *session, nghttp2_frame *frame,
+                       const uint8_t *framehd, size_t length,
+                       nghttp2_data_source *source, void *user_data) {
+  auto http2session = static_cast<Http2Session *>(user_data);
+  auto sd = static_cast<StreamData *>(
+      nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
+  auto dconn = sd->dconn;
+  auto downstream = dconn->get_downstream();
+  auto input = downstream->get_request_buf();
+  auto wb = http2session->get_request_buf();
+
+  size_t padlen = 0;
+
+  wb->append(framehd, 9);
+  if (frame->data.padlen > 0) {
+    padlen = frame->data.padlen - 1;
+    wb->append(static_cast<uint8_t>(padlen));
+  }
+
+  input->remove(*wb, length);
+
+  wb->append(PADDING.data(), padlen);
+
+  downstream->reset_downstream_wtimer();
+
+  if (length > 0) {
+    // This is important because it will handle flow control
+    // stuff.
+    if (downstream->get_upstream()->resume_read(SHRPX_NO_BUFFER, downstream,
+                                                length) != 0) {
+      // In this case, downstream may be deleted.
+      return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
+    }
+
+    // Here sd->dconn could be nullptr, because
+    // Upstream::resume_read() may delete downstream which will delete
+    // dconn.  Is this still really true?
+  }
+
+  return 0;
+}
+} // namespace
+
 nghttp2_session_callbacks *create_http2_downstream_callbacks() {
   int rv;
   nghttp2_session_callbacks *callbacks;
@@ -1393,6 +1441,9 @@ nghttp2_session_callbacks *create_http2_downstream_callbacks() {
   nghttp2_session_callbacks_set_on_begin_headers_callback(
       callbacks, on_begin_headers_callback);
 
+  nghttp2_session_callbacks_set_send_data_callback(callbacks,
+                                                   send_data_callback);
+
   if (get_config()->padding) {
     nghttp2_session_callbacks_set_select_padding_callback(
         callbacks, http::select_padding_callback);
@@ -2115,4 +2166,6 @@ void Http2Session::exclude_from_scheduling() {
   freelist_zone_ = FREELIST_ZONE_GONE;
 }
 
+DefaultMemchunks *Http2Session::get_request_buf() { return &wb_; }
+
 } // namespace shrpx

src/shrpx_http2_session.h

@@ -195,6 +195,8 @@ public:
   // server initiated concurrency limit.
   bool max_concurrency_reached(size_t extra = 0) const;
 
+  DefaultMemchunks *get_request_buf();
+
   enum {
     // Disconnected
     DISCONNECTED,