add acceptor config for server early return

Summary:
* adds a new member field in AcceptorConfiguration to enable server early response
* for now, only enabled if underlying protocol is http/2

Reviewed By: afrind

Differential Revision: D67123903

fbshipit-source-id: e9689550ed7b7840c2d817caab9e9609d47eee13

Author: hanidamlaj

proxygen/lib/http/session/HTTPSessionAcceptor.cpp

@@ -90,6 +90,7 @@ void HTTPSessionAcceptor::onNewConnection(folly::AsyncTransport::UniquePtr sock,
   auto sessionInfoCb = sessionInfoCb_ ? sessionInfoCb_ : this;
   VLOG(4) << "Created new " << nextProtocol << " session for peer "
           << *peerAddress;
+  auto codecProtocol = codec->getProtocol();
   HTTPDownstreamSession* session =
       new HTTPDownstreamSession(getTransactionTimeoutSet(),
                                 std::move(sock),
@@ -113,6 +114,11 @@ void HTTPSessionAcceptor::onNewConnection(folly::AsyncTransport::UniquePtr sock,
   session->setFlowControl(getConfig()->initialReceiveWindow,
                           getConfig()->receiveStreamWindowSize,
                           getConfig()->receiveSessionWindowSize);
+  // TODO(@damlaj): support server early resp for http/3
+  if (getConfig()->serverEarlyResponseEnabled &&
+      codecProtocol == CodecProtocol::HTTP_2) {
+    session->enableServerEarlyResponse();
+  }
   if (getConfig()->writeBufferLimit > 0) {
     session->setWriteBufferLimit(getConfig()->writeBufferLimit);
   }

proxygen/lib/services/AcceptorConfiguration.h

@@ -96,6 +96,14 @@ struct AcceptorConfiguration : public wangle::ServerSocketConfig {
    **/
   bool HTTP2PingEnabled{false};
 
+  /**
+   * When the server sends a complete response prior to the client sending an
+   * entire request (for non-upgraded streams), the server will subsequently
+   * write RST_STREAM/NO_ERROR (h2) or STOP_SENDING/NO_ERROR (h3). This has no
+   * effect in http/1.1.
+   */
+  bool serverEarlyResponseEnabled{false};
+
   /* Strategy for which headers to insert into HPACK/QPACK dynamic table */
   const HeaderIndexingStrategy* headerIndexingStrategy{nullptr};
 };