Fix HTTP/2 session receive window handling for small sizes

proxy/http2/Http2ConnectionState.cc

@@ -156,7 +156,7 @@ Http2ConnectionState::rcv_data_frame(const Http2Frame &frame)
   }
 
   // Check whether Window Size is acceptable
-  if (this->server_rwnd() < payload_length) {
+  if (!this->_server_rwnd_is_shrinking && this->server_rwnd() < payload_length) {
     return Http2Error(Http2ErrorClass::HTTP2_ERROR_CLASS_CONNECTION, Http2ErrorCode::HTTP2_ERROR_FLOW_CONTROL_ERROR,
                       "recv data cstate.server_rwnd < payload_length");
   }
@@ -1039,8 +1039,18 @@ Http2ConnectionState::Http2ConnectionState() : stream_list()
 void
 Http2ConnectionState::init(Http2CommonSession *ssn)
 {
-  session            = ssn;
-  this->_server_rwnd = Http2::initial_window_size;
+  session = ssn;
+
+  if (Http2::initial_window_size < HTTP2_INITIAL_WINDOW_SIZE) {
+    // There is no HTTP/2 specified way to shrink the connection window size
+    // other than to receive data and not send WINDOW_UPDATE frames for a
+    // while.
+    this->_server_rwnd              = HTTP2_INITIAL_WINDOW_SIZE;
+    this->_server_rwnd_is_shrinking = true;
+  } else {
+    this->_server_rwnd              = Http2::initial_window_size;
+    this->_server_rwnd_is_shrinking = false;
+  }
 
   local_hpack_handle  = new HpackHandle(HTTP2_HEADER_TABLE_SIZE);
   remote_hpack_handle = new HpackHandle(HTTP2_HEADER_TABLE_SIZE);
@@ -1424,6 +1434,7 @@ Http2ConnectionState::restart_receiving(Http2Stream *stream)
   if (this->server_rwnd() < min_rwnd) {
     Http2WindowSize diff_size = initial_rwnd - this->server_rwnd();
     this->increment_server_rwnd(diff_size);
+    this->_server_rwnd_is_shrinking = false;
     this->send_window_update_frame(0, diff_size);
   }
 

proxy/http2/Http2ConnectionState.h

@@ -218,6 +218,18 @@ class Http2ConnectionState : public Continuation
   ssize_t _client_rwnd = HTTP2_INITIAL_WINDOW_SIZE;
   ssize_t _server_rwnd = 0;
 
+  /** Whether the session window is in a shrinking state before we send the
+   * first WINDOW_UPDATE frame.
+   *
+   * Unlike HTTP/2 streams, the HTTP/2 session window has no way to initialize
+   * it to a value lower than 65,535. If the initial value is lower than
+   * 65,535, the session window will have to shrink while we receive DATA
+   * frames without incrementing the window via WINDOW_UPDATE frames. Once the
+   * window gets to the desired size, we start maintaining the window via
+   * WINDOW_UPDATE frames.
+   */
+  bool _server_rwnd_is_shrinking = false;
+
   std::vector<size_t> _recent_rwnd_increment = {SIZE_MAX, SIZE_MAX, SIZE_MAX, SIZE_MAX, SIZE_MAX};
   int _recent_rwnd_increment_index           = 0;
 

tests/gold_tests/h2/http2_flow_control.replay.yaml

@@ -0,0 +1,237 @@
+#  Licensed to the Apache Software Foundation (ASF) under one
+#  or more contributor license agreements.  See the NOTICE file
+#  distributed with this work for additional information
+#  regarding copyright ownership.  The ASF licenses this file
+#  to you under the Apache License, Version 2.0 (the
+#  "License"); you may not use this file except in compliance
+#  with the License.  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+meta:
+  version: "1.0"
+
+# This replay file generates an HTTP/2 session with three streams in order to
+# verify that ATS generates the expected SETTINGS and WINDOW_UPDATE frames.
+
+sessions:
+
+- protocol:
+  - name: http
+    version: 2
+  - name: tls
+    sni: www.example.com
+  - name: tcp
+  - name: ip
+
+  transactions:
+
+  - client-request:
+      headers:
+        fields:
+        - [ :method, GET ]
+        - [ :scheme, https ]
+        - [ :authority, www.example.com ]
+        - [ :path, /zero-request ]
+        - [ uuid, zero-request ]
+        - [ X-Request, zero-request ]
+        - [ Content-Length, 0 ]
+
+    proxy-request:
+      headers:
+        fields:
+        - [ X-Request, { value: 'zero-request', as: equal } ]
+
+    server-response:
+      status: 200
+      reason: OK
+      headers:
+        fields:
+        - [ X-Response, zero-response ]
+        - [ Content-Length, 28 ]
+      content:
+        size: 28
+
+    proxy-response:
+      headers:
+        fields:
+        - [ X-Response, { value: 'zero-response', as: equal } ]
+
+  - client-request:
+      delay: 500ms
+
+      headers:
+        fields:
+        - [ :method, POST ]
+        - [ :scheme, https ]
+        - [ :authority, www.example.com ]
+        - [ :path, /first-request ]
+        - [ uuid, first-request ]
+        - [ X-Request, first-request ]
+      content:
+        size: 1200
+
+    proxy-request:
+      headers:
+        fields:
+        - [ X-Request, { value: 'first-request', as: equal } ]
+
+    server-response:
+      status: 200
+      reason: OK
+      headers:
+        fields:
+        - [ X-Response, first-response ]
+        - [ Content-Length, 28 ]
+      content:
+        size: 28
+
+    proxy-response:
+      headers:
+        fields:
+        - [ X-Response, { value: 'first-response', as: equal } ]
+
+  - client-request:
+      headers:
+        fields:
+        - [ :method, POST ]
+        - [ :scheme, https ]
+        - [ :authority, www.example.com ]
+        - [ :path, /second-request ]
+        - [ uuid, second-request ]
+        - [ X-Request, second-request ]
+      content:
+        size: 1200
+
+    proxy-request:
+      headers:
+        fields:
+        - [ X-Request, {value: 'second-request', as: equal } ]
+
+    server-response:
+      status: 200
+      reason: OK
+      headers:
+        fields:
+        - [ X-Response, second-response ]
+        - [ Content-Length, 28 ]
+      content:
+        size: 28
+
+    proxy-response:
+      headers:
+        fields:
+        - [ X-Response, {value: 'second-response', as: equal } ]
+
+  - client-request:
+      headers:
+        fields:
+        - [ :method, POST ]
+        - [ :scheme, https ]
+        - [ :authority, www.example.com ]
+        - [ :path, /third-request ]
+        - [ uuid, third-request ]
+        - [ X-Request, third-request ]
+      content:
+        size: 1200
+
+    proxy-request:
+      headers:
+        fields:
+        - [ X-Request, {value: 'third-request', as: equal } ]
+
+    server-response:
+      status: 200
+      reason: OK
+      headers:
+        fields:
+        - [ X-Response, third-response ]
+        - [ Content-Length, 28 ]
+      content:
+        size: 28
+
+    proxy-response:
+      headers:
+        fields:
+        - [ X-Response, {value: 'third-response', as: equal } ]
+
+  - client-request:
+      # Intentionally test a stream after the three other parallel POST
+      # requests.
+      delay: 500ms
+
+      headers:
+        fields:
+        - [ :method, POST ]
+        - [ :scheme, https ]
+        - [ :authority, www.example.com ]
+        - [ :path, /fourth-request ]
+        - [ uuid, fourth-request ]
+        - [ X-Request, fourth-request ]
+      content:
+        # Send a very large DATA frame so that we exceed the 65,535 window
+        # size of most of the test runs.
+        size: 120000
+
+    proxy-request:
+      headers:
+        fields:
+        - [ X-Request, {value: 'fourth-request', as: equal } ]
+
+    server-response:
+      status: 200
+      reason: OK
+      headers:
+        fields:
+        - [ X-Response, fourth-response ]
+        - [ Content-Length, 28 ]
+      content:
+        size: 28
+
+    proxy-response:
+      headers:
+        fields:
+        - [ X-Response, {value: 'fourth-response', as: equal } ]
+
+  - client-request:
+      # Give the above request time to process and give us an opportunity to
+      # receive any other WINDOW_UPDATE frames.
+      delay: 500ms
+
+      headers:
+        fields:
+        - [ :method, POST ]
+        - [ :scheme, https ]
+        - [ :authority, www.example.com ]
+        - [ :path, /fifth-request ]
+        - [ uuid, fifth-request ]
+        - [ X-Request, fifth-request ]
+      content:
+        size: 10000
+
+    proxy-request:
+      headers:
+        fields:
+        - [ X-Request, {value: 'fifth-request', as: equal } ]
+
+    server-response:
+      status: 200
+      reason: OK
+      headers:
+        fields:
+        - [ X-Response, fifth-response ]
+        - [ Content-Length, 28 ]
+      content:
+        size: 28
+
+    proxy-response:
+      headers:
+        fields:
+        - [ X-Response, {value: 'fifth-response', as: equal } ]
+