nghttpx: Use send_data_callback for higher throughput

src/memchunk.h

@@ -222,7 +222,7 @@ template <typename Memchunk> struct Memchunks {
     }
     return ndata - count;
   }
-  int riovec(struct iovec *iov, int iovcnt) {
+  int riovec(struct iovec *iov, int iovcnt) const {
     if (!head) {
       return 0;
     }

src/shrpx_client_handler.cc

@@ -731,7 +731,7 @@ int ClientHandler::perform_http2_upgrade(HttpsUpstream *http) {
                       "Connection: Upgrade\r\n"
                       "Upgrade: " NGHTTP2_CLEARTEXT_PROTO_VERSION_ID "\r\n"
                       "\r\n";
-  upstream->response_write(res, sizeof(res) - 1);
+  upstream->get_response_buf()->write(res, sizeof(res) - 1);
   upstream_ = std::move(upstream);
 
   signal_write();

src/shrpx_downstream.cc

@@ -1241,4 +1241,8 @@ bool Downstream::can_detach_downstream_connection() const {
          !response_connection_close_;
 }
 
+DefaultMemchunks Downstream::pop_response_buf() {
+  return std::move(response_buf_);
+}
+
 } // namespace shrpx

src/shrpx_downstream.h

@@ -342,6 +342,8 @@ public:
   // Returns true if downstream_connection can be detached and reused.
   bool can_detach_downstream_connection() const;
 
+  DefaultMemchunks pop_response_buf();
+
   enum {
     EVENT_ERROR = 0x1,
     EVENT_TIMEOUT = 0x2,

src/shrpx_http2_upstream.cc

@@ -647,6 +647,57 @@ int on_frame_not_send_callback(nghttp2_session *session,
 }
 } // namespace
 
+void Http2Upstream::set_pending_data_downstream(Downstream *downstream,
+                                                size_t n) {
+  pending_data_downstream_ = downstream;
+  data_pendinglen_ = n;
+}
+
+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 downstream = static_cast<Downstream *>(source->ptr);
+  auto upstream = static_cast<Http2Upstream *>(downstream->get_upstream());
+  auto body = downstream->get_response_buf();
+
+  auto wb = upstream->get_response_buf();
+
+  if (wb->wleft() < 9) {
+    return NGHTTP2_ERR_WOULDBLOCK;
+  }
+
+  wb->write(framehd, 9);
+
+  auto nwrite = std::min(length, wb->wleft());
+  body->remove(wb->last, nwrite);
+  wb->write(nwrite);
+  if (nwrite < length) {
+    // We must store unsent amount of data to somewhere.  We just tell
+    // libnghttp2 that we wrote everything, so downstream could be
+    // deleted.  We handle this situation in
+    // Http2Upstream::remove_downstream().
+    upstream->set_pending_data_downstream(downstream, length - nwrite);
+  }
+
+  if (wb->rleft() == 0) {
+    downstream->disable_upstream_wtimer();
+  } else {
+    downstream->reset_upstream_wtimer();
+  }
+
+  if (length > 0 && downstream->resume_read(SHRPX_NO_BUFFER, length) != 0) {
+    return NGHTTP2_ERR_CALLBACK_FAILURE;
+  }
+
+  if (length > 0) {
+    downstream->add_response_sent_bodylen(length);
+  }
+
+  return nwrite < length ? NGHTTP2_ERR_PAUSE : 0;
+}
+} // namespace
+
 namespace {
 uint32_t infer_upstream_rst_stream_error_code(uint32_t downstream_error_code) {
   // NGHTTP2_REFUSED_STREAM is important because it tells upstream
@@ -748,6 +799,9 @@ nghttp2_session_callbacks *create_http2_upstream_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);
@@ -764,8 +818,9 @@ Http2Upstream::Http2Upstream(ClientHandler *handler)
                     ? get_config()->downstream_connections_per_frontend
                     : 0,
           !get_config()->http2_proxy),
-      handler_(handler), session_(nullptr), data_pending_(nullptr),
-      data_pendinglen_(0), shutdown_handled_(false) {
+      pending_response_buf_(handler->get_worker()->get_mcpool()),
+      pending_data_downstream_(nullptr), handler_(handler), session_(nullptr),
+      data_pending_(nullptr), data_pendinglen_(0), shutdown_handled_(false) {
 
   int rv;
 
@@ -870,17 +925,42 @@ int Http2Upstream::on_write() {
     wb_.reset();
   }
 
-  if (data_pending_) {
-    auto n = std::min(wb_.wleft(), data_pendinglen_);
-    wb_.write(data_pending_, n);
-    if (n < data_pendinglen_) {
+  if (data_pendinglen_ > 0) {
+    if (data_pending_) {
+      auto n = std::min(wb_.wleft(), data_pendinglen_);
+      wb_.write(data_pending_, n);
       data_pending_ += n;
       data_pendinglen_ -= n;
-      return 0;
-    }
 
-    data_pending_ = nullptr;
-    data_pendinglen_ = 0;
+      if (data_pendinglen_ > 0) {
+        return 0;
+      }
+
+      data_pending_ = nullptr;
+    } else {
+      auto n = std::min(wb_.wleft(), data_pendinglen_);
+      DefaultMemchunks *body;
+      if (pending_data_downstream_) {
+        body = pending_data_downstream_->get_response_buf();
+      } else {
+        body = &pending_response_buf_;
+      }
+      body->remove(wb_.last, n);
+      wb_.write(n);
+      data_pendinglen_ -= n;
+
+      if (data_pendinglen_ > 0) {
+        return 0;
+      }
+
+      if (pending_data_downstream_) {
+        pending_data_downstream_ = nullptr;
+      } else {
+        // Downstream was already deleted, and we don't need its
+        // response data.
+        body->reset();
+      }
+    }
   }
 
   for (;;) {
@@ -1118,8 +1198,10 @@ ssize_t downstream_data_read_callback(nghttp2_session *session,
     }
   }
 
-  auto nread = body->remove(buf, length);
-  auto body_empty = body->rleft() == 0;
+  auto nread = std::min(body->rleft(), length);
+  auto body_empty = body->rleft() == nread;
+
+  *data_flags |= NGHTTP2_DATA_FLAG_NO_COPY;
 
   if (body_empty &&
       downstream->get_response_state() == Downstream::MSG_COMPLETE) {
@@ -1147,24 +1229,10 @@ ssize_t downstream_data_read_callback(nghttp2_session *session,
     }
   }
 
-  if (body_empty) {
-    downstream->disable_upstream_wtimer();
-  } else {
-    downstream->reset_upstream_wtimer();
-  }
-
-  if (nread > 0 && downstream->resume_read(SHRPX_NO_BUFFER, nread) != 0) {
-    return NGHTTP2_ERR_CALLBACK_FAILURE;
-  }
-
   if (nread == 0 && ((*data_flags) & NGHTTP2_DATA_FLAG_EOF) == 0) {
     return NGHTTP2_ERR_DEFERRED;
   }
 
-  if (nread > 0) {
-    downstream->add_response_sent_bodylen(nread);
-  }
-
   return nread;
 }
 } // namespace
@@ -1275,6 +1343,11 @@ void Http2Upstream::remove_downstream(Downstream *downstream) {
   nghttp2_session_set_stream_user_data(session_, downstream->get_stream_id(),
                                        nullptr);
 
+  if (downstream == pending_data_downstream_) {
+    pending_data_downstream_ = nullptr;
+    pending_response_buf_ = downstream->pop_response_buf();
+  }
+
   auto next_downstream = downstream_queue_.remove_and_get_blocked(downstream);
 
   if (next_downstream) {
@@ -1771,8 +1844,6 @@ void Http2Upstream::response_drain(size_t n) { wb_.drain(n); }
 
 bool Http2Upstream::response_empty() const { return wb_.rleft() == 0; }
 
-void Http2Upstream::response_write(void *data, size_t len) {
-  wb_.write(data, len);
-}
+Http2Upstream::WriteBuffer *Http2Upstream::get_response_buf() { return &wb_; }
 
 } // namespace shrpx

src/shrpx_http2_upstream.h

@@ -87,8 +87,6 @@ public:
   virtual void response_drain(size_t n);
   virtual bool response_empty() const;
 
-  void response_write(void *data, size_t len);
-
   bool get_flow_control() const;
   // Perform HTTP/2 upgrade from |upstream|. On success, this object
   // takes ownership of the |upstream|. This function returns 0 if it
@@ -114,6 +112,10 @@ public:
 
   using WriteBuffer = Buffer<32_k>;
 
+  WriteBuffer *get_response_buf();
+
+  void set_pending_data_downstream(Downstream *downstream, size_t n);
+
 private:
   WriteBuffer wb_;
   std::unique_ptr<HttpsUpstream> pre_upstream_;
@@ -121,9 +123,26 @@ private:
   ev_timer settings_timer_;
   ev_timer shutdown_timer_;
   ev_prepare prep_;
+  // A response buffer used to belong to Downstream object.  This is
+  // moved here when response is partially written to wb_ in
+  // send_data_callback, but before writing them all, Downstream
+  // object was destroyed.  On destruction of Downstream,
+  // pending_data_downstream_ becomes nullptr.
+  DefaultMemchunks pending_response_buf_;
+  // Downstream object whose DATA frame payload is partillay written
+  // to wb_ in send_data_callback.  This field exists to keep track of
+  // its lifetime.  When it is destroyed, its response buffer is
+  // transferred to pending_response_buf_, and this field becomes
+  // nullptr.
+  Downstream *pending_data_downstream_;
   ClientHandler *handler_;
   nghttp2_session *session_;
   const uint8_t *data_pending_;
+  // The length of lending data to be written into wb_.  If
+  // data_pending_ is not nullptr, data_pending_ points to the data to
+  // write.  Otherwise, pending_data_downstream_->get_response_buf()
+  // if pending_data_downstream_ is not nullptr, or
+  // pending_response_buf_ holds data to write.
   size_t data_pendinglen_;
   bool flow_control_;
   bool shutdown_handled_;

src/shrpx_http_downstream_connection.cc

@@ -455,7 +455,7 @@ void HttpDownstreamConnection::pause_read(IOCtrlReason reason) {
 
 int HttpDownstreamConnection::resume_read(IOCtrlReason reason,
                                           size_t consumed) {
-  if (!downstream_->response_buf_full()) {
+  if (downstream_->get_response_buf()->rleft() == 0) {
     ioctrl_.resume_read(reason);
   }