nghttpx: Migrate backend stream to another h2 session on graceful shutdown

src/shrpx_client_handler.cc

@@ -770,9 +770,24 @@ Http2Session *ClientHandler::select_http2_session(
   auto &http2_avail_freelist = shared_addr->http2_avail_freelist;
 
   if (http2_avail_freelist.size() >= min) {
-    auto session = http2_avail_freelist.head;
+    for (auto session = http2_avail_freelist.head; session;) {
+      auto next = session->dlnext;
+
       session->remove_from_freelist();
 
+      // session may be in graceful shutdown period now.
+      if (session->max_concurrency_reached(0)) {
+        if (LOG_ENABLED(INFO)) {
+          CLOG(INFO, this)
+              << "Maximum streams have been reached for Http2Session("
+              << session << ").  Skip it";
+        }
+
+        session = next;
+
+        continue;
+      }
+
       if (LOG_ENABLED(INFO)) {
         CLOG(INFO, this) << "Use Http2Session " << session
                          << " from http2_avail_freelist";
@@ -788,16 +803,40 @@ Http2Session *ClientHandler::select_http2_session(
       }
       return session;
     }
+  }
 
   DownstreamAddr *selected_addr = nullptr;
 
   for (auto &addr : shared_addr->addrs) {
-    if (addr.proto != PROTO_HTTP2 || (addr.http2_extra_freelist.size() == 0 &&
+    if (addr.in_avail || addr.proto != PROTO_HTTP2 ||
+        (addr.http2_extra_freelist.size() == 0 &&
          addr.connect_blocker->blocked())) {
       continue;
     }
 
-    if (addr.in_avail) {
+    for (auto session = addr.http2_extra_freelist.head; session;) {
+      auto next = session->dlnext;
+
+      // session may be in graceful shutdown period now.
+      if (session->max_concurrency_reached(0)) {
+        if (LOG_ENABLED(INFO)) {
+          CLOG(INFO, this)
+              << "Maximum streams have been reached for Http2Session("
+              << session << ").  Skip it";
+        }
+
+        session->remove_from_freelist();
+
+        session = next;
+
+        continue;
+      }
+
+      break;
+    }
+
+    if (addr.http2_extra_freelist.size() == 0 &&
+        addr.connect_blocker->blocked()) {
       continue;
     }
 

src/shrpx_downstream.cc

@@ -137,7 +137,8 @@ Downstream::Downstream(Upstream *upstream, MemchunkPool *mcpool,
       chunked_request_(false),
       chunked_response_(false),
       expect_final_response_(false),
-      request_pending_(false) {
+      request_pending_(false),
+      request_header_sent_(false) {
 
   auto &timeoutconf = get_config()->http2.timeout;
 
@@ -885,7 +886,7 @@ bool Downstream::accesslog_ready() const { return resp_.http_status > 0; }
 
 void Downstream::add_retry() { ++num_retry_; }
 
-bool Downstream::no_more_retry() const { return num_retry_ > 5; }
+bool Downstream::no_more_retry() const { return num_retry_ > 50; }
 
 void Downstream::set_request_downstream_host(const StringRef &host) {
   request_downstream_host_ = host;
@@ -895,10 +896,13 @@ void Downstream::set_request_pending(bool f) { request_pending_ = f; }
 
 bool Downstream::get_request_pending() const { return request_pending_; }
 
+void Downstream::set_request_header_sent(bool f) { request_header_sent_ = f; }
+
 bool Downstream::request_submission_ready() const {
   return (request_state_ == Downstream::HEADER_COMPLETE ||
           request_state_ == Downstream::MSG_COMPLETE) &&
-         request_pending_ && response_state_ == Downstream::INITIAL;
+         (request_pending_ || !request_header_sent_) &&
+         response_state_ == Downstream::INITIAL;
 }
 
 int Downstream::get_dispatch_state() const { return dispatch_state_; }

src/shrpx_downstream.h

@@ -302,7 +302,11 @@ public:
   DefaultMemchunks *get_request_buf();
   void set_request_pending(bool f);
   bool get_request_pending() const;
+  void set_request_header_sent(bool f);
   // Returns true if request is ready to be submitted to downstream.
+  // When sending pending request, get_request_pending() should be
+  // checked too because this function may return true when
+  // get_request_pending() returns false.
   bool request_submission_ready() const;
 
   // downstream response API
@@ -471,6 +475,8 @@ private:
   // has not been established or should be checked before use;
   // currently used only with HTTP/2 connection.
   bool request_pending_;
+  // true if downstream request header is considered to be sent.
+  bool request_header_sent_;
 };
 
 } // namespace shrpx

src/shrpx_http2_downstream_connection.cc

@@ -117,11 +117,11 @@ void Http2DownstreamConnection::detach_downstream(Downstream *downstream) {
 
   auto &resp = downstream_->response();
 
+  if (downstream_->get_downstream_stream_id() != -1) {
     if (submit_rst_stream(downstream) == 0) {
       http2session_->signal_write();
     }
 
-  if (downstream_->get_downstream_stream_id() != -1) {
     http2session_->consume(downstream_->get_downstream_stream_id(),
                            resp.unconsumed_body_length);
 

src/shrpx_http2_session.cc

@@ -665,7 +665,6 @@ int Http2Session::submit_request(Http2DownstreamConnection *dconn,
   }
 
   dconn->attach_stream_data(sd.get());
-  dconn->get_downstream()->set_downstream_stream_id(stream_id);
   streams_.append(sd.release());
 
   return 0;
@@ -1396,8 +1395,17 @@ int on_frame_send_callback(nghttp2_session *session, const nghttp2_frame *frame,
 
     auto downstream = sd->dconn->get_downstream();
 
-    if (!downstream ||
-        downstream->get_downstream_stream_id() != frame->hd.stream_id) {
+    if (!downstream) {
+      return 0;
+    }
+
+    if (frame->hd.type == NGHTTP2_HEADERS &&
+        frame->headers.cat == NGHTTP2_HCAT_REQUEST) {
+      assert(downstream->get_downstream_stream_id() == -1);
+
+      downstream->set_downstream_stream_id(frame->hd.stream_id);
+      downstream->set_request_header_sent(true);
+    } else if (downstream->get_downstream_stream_id() != frame->hd.stream_id) {
       return 0;
     }
 
@@ -1422,13 +1430,15 @@ int on_frame_not_send_callback(nghttp2_session *session,
   if (LOG_ENABLED(INFO)) {
     SSLOG(INFO, http2session) << "Failed to send control frame type="
                               << static_cast<uint32_t>(frame->hd.type)
-                              << "lib_error_code=" << lib_error_code << ":"
+                              << ", lib_error_code=" << lib_error_code << ": "
                               << nghttp2_strerror(lib_error_code);
   }
-  if (frame->hd.type == NGHTTP2_HEADERS &&
-      lib_error_code != NGHTTP2_ERR_STREAM_CLOSED &&
-      lib_error_code != NGHTTP2_ERR_STREAM_CLOSING) {
-    // To avoid stream hanging around, flag Downstream::MSG_RESET.
+  if (frame->hd.type != NGHTTP2_HEADERS ||
+      lib_error_code == NGHTTP2_ERR_STREAM_CLOSED ||
+      lib_error_code == NGHTTP2_ERR_STREAM_CLOSING) {
+    return 0;
+  }
+
   auto sd = static_cast<StreamData *>(
       nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
   if (!sd) {
@@ -1438,13 +1448,31 @@ int on_frame_not_send_callback(nghttp2_session *session,
     return 0;
   }
   auto downstream = sd->dconn->get_downstream();
-    if (!downstream ||
-        downstream->get_downstream_stream_id() != frame->hd.stream_id) {
+  if (!downstream) {
     return 0;
   }
+
+  if (lib_error_code == NGHTTP2_ERR_START_STREAM_NOT_ALLOWED) {
+    // Migrate to another downstream connection.
+    auto upstream = downstream->get_upstream();
+
+    if (upstream->on_downstream_reset(downstream, false)) {
+      // This should be done for h1 upstream only.  Deleting
+      // ClientHandler for h2 or SPDY upstream may lead to crash.
+      delete upstream->get_client_handler();
+    }
+
+    return 0;
+  }
+
+  if (downstream->get_downstream_stream_id() != frame->hd.stream_id) {
+    return 0;
+  }
+
+  // To avoid stream hanging around, flag Downstream::MSG_RESET.
   downstream->set_response_state(Downstream::MSG_RESET);
   call_downstream_readcb(http2session, downstream);
-  }
+
   return 0;
 }
 } // namespace
@@ -1815,7 +1843,8 @@ void Http2Session::submit_pending_requests() {
   for (auto dconn = dconns_.head; dconn; dconn = dconn->dlnext) {
     auto downstream = dconn->get_downstream();
 
-    if (!downstream || !downstream->request_submission_ready()) {
+    if (!downstream || !downstream->get_request_pending() ||
+        !downstream->request_submission_ready()) {
       continue;
     }
 
@@ -2153,6 +2182,7 @@ int Http2Session::handle_downstream_push_promise_complete(
   auto upstream = promised_downstream->get_upstream();
 
   promised_downstream->set_request_state(Downstream::MSG_COMPLETE);
+  promised_downstream->set_request_header_sent(true);
 
   if (upstream->on_downstream_push_promise_complete(downstream,
                                                     promised_downstream) != 0) {

src/shrpx_http_downstream_connection.cc

@@ -344,6 +344,10 @@ int HttpDownstreamConnection::push_request_headers() {
 
   auto &httpconf = get_config()->http;
 
+  // Set request_sent to true because we write request into buffer
+  // here.
+  downstream_->set_request_header_sent(true);
+
   // For HTTP/1.0 request, there is no authority in request.  In that
   // case, we use backend server's host nonetheless.
   auto authority = StringRef(downstream_hostport);