Support setting cmsg per accepted socket

Summary:
For each `QuicServerTransport` created by `QuicServerWorker`, we are able to set the `cmsg`s to be sent whenever there's a write.

With this we can set things like TOS/SO_MARK per connection

Reviewed By: bschlinker

Differential Revision: D29313608

fbshipit-source-id: d60c97f65681086ae1079b6b95beade95158ec59

quic/api/QuicTransportBase.cpp

@@ -3298,4 +3298,12 @@ void QuicTransportBase::notifyAppRateLimited() {
   }
 }
 
+void QuicTransportBase::setCmsgs(const folly::SocketOptionMap& options) {
+  socket_->setCmsgs(options);
+}
+
+void QuicTransportBase::appendCmsgs(const folly::SocketOptionMap& options) {
+  socket_->appendCmsgs(options);
+}
+
 } // namespace quic

quic/api/QuicTransportBase.h

@@ -659,6 +659,15 @@ class QuicTransportBase : public QuicSocket {
   folly::Expected<std::vector<Buf>, LocalErrorCode> readDatagrams(
       size_t atMost = 0) override;
 
+  /**
+   * Set control messages to be sent for socket_ write, note that it's for this
+   * specific transport and does not change the other sockets sharing the same
+   * fd.
+   */
+  void setCmsgs(const folly::SocketOptionMap& options);
+
+  void appendCmsgs(const folly::SocketOptionMap& options);
+
  protected:
   void updateCongestionControlSettings(
       const TransportSettings& transportSettings);

quic/api/test/QuicTransportBaseTest.cpp

@@ -3845,5 +3845,16 @@ TEST_F(QuicTransportImplTest, DatagramCallbackDatagramAvailable) {
   transport->driveReadCallbacks();
 }
 
+TEST_F(QuicTransportImplTest, Cmsgs) {
+  transport->setServerConnectionId();
+  folly::SocketOptionMap cmsgs;
+  cmsgs[{IPPROTO_IP, IP_TOS}] = 123;
+  EXPECT_CALL(*socketPtr, setCmsgs(_)).Times(1);
+  transport->setCmsgs(cmsgs);
+
+  EXPECT_CALL(*socketPtr, appendCmsgs(_)).Times(1);
+  transport->appendCmsgs(cmsgs);
+}
+
 } // namespace test
 } // namespace quic