Cleanup and modularize receive path, improve timestamp support [22/x]

Summary:
This diff changes `WriteAckFrameState::ReceivedPacket` so that it stores a complete `ReceivedUdpPacket::Timings` object, instead of just one field extracted from that object. This lets us have access to both user space and socket timestamps in our ACK RX timestamp handling code. See D48785086 for a similar change.

--

This diff is part of a larger stack focused on the following:

- **Cleaning up client and server UDP packet receive paths while improving testability.** We currently have multiple receive paths for client and server. Capabilities vary significantly and there are few tests. For instance:
  - The server receive path supports socket RX timestamps, abet incorrectly in that it does not store timestamp per packet. In comparison, the client receive path does not currently support socket RX timestamps, although the code in `QuicClientTransport::recvmsg` and `QuicClientTransport::recvmmsg` makes reference to socket RX timestamps, making it confusing to understand the capabilities available when tracing through the code. This complicates the tests in `QuicTypedTransportTests`, as we have to disable test logic that depends on socket RX timestamps for client tests.
  - The client currently has three receive paths, and none of them are well tested.

- **Modularize and abstract components in the receive path.** This will make it easier to mock/fake the UDP socket and network layers.
  - `QuicClientTransport` and `QuicServerTransport` currently contain UDP socket handling logic that operates over lower layer primitives such `cmsg` and `io_vec` (see `QuicClientTransport::recvmmsg` and `...::recvmsg` as examples).
  - Because this UDP socket handling logic is inside of the mvfst transport implementations, it is difficult to test this logic in isolation and mock/fake the underlying socket and network layers. For instance, injecting a user space network emulator that operates at the socket layer would require faking `folly::AsyncUDPSocket`, which is non-trivial given that `AsyncUDPSocket` does not abstract away intricacies arising from the aforementioned lower layer primitives.
  - By shifting this logic into an intermediate layer between the transport and the underlying UDP socket, it will be easier to mock out the UDP socket layer when testing functionality at higher layers, and inject fake components when we want to emulate the network between a mvfst client and server. It will also be easier for us to have unit tests focused on testing interactions between the UDP socket implementation and this intermediate layer.

- **Improving receive path timestamping.** We only record a single timestamp per `NetworkData` at the moment, but (1) it is possible for a `NetworkData` to have multiple packets, each with their own timestamps, and (2) we should be able to record both userspace and socket timestamps.

Reviewed By: silver23arrow

Differential Revision: D48795108

fbshipit-source-id: 70471d2654a09cbf25e711af583c18084eb90ca0

quic/codec/QuicWriteCodec.cpp

@@ -332,13 +332,16 @@ static size_t fillPacketReceiveTimestamps(
            timestampIt->pktNum <= timestampIntervalsIt->end) {
       std::chrono::microseconds deltaDuration;
       if (timestampIt == recvdPacketInfos.crbegin()) {
-        deltaDuration = (timestampIt->timeStamp > ackFrameMetaData.connTime)
+        deltaDuration =
+            (timestampIt->timings.receiveTimePoint > ackFrameMetaData.connTime)
             ? std::chrono::duration_cast<std::chrono::microseconds>(
-                  timestampIt->timeStamp - ackFrameMetaData.connTime)
+                  timestampIt->timings.receiveTimePoint -
+                  ackFrameMetaData.connTime)
             : 0us;
       } else {
         deltaDuration = std::chrono::duration_cast<std::chrono::microseconds>(
-            (timestampIt - 1)->timeStamp - timestampIt->timeStamp);
+            (timestampIt - 1)->timings.receiveTimePoint -
+            timestampIt->timings.receiveTimePoint);
       }
       auto delta = deltaDuration.count() >> receiveTimestampsExponent;
       // Check if adding a new time-stamp delta from the current time-stamp
@@ -424,10 +427,11 @@ folly::Optional<WriteAckFrame> writeAckFrameToPacketBuilder(
       maybeLastPktNum = ackState.lastRecvdPacketInfo.value().pktNum;
 
     maybeLastPktTsDelta =
-        (ackState.lastRecvdPacketInfo.value().timeStamp >
+        (ackState.lastRecvdPacketInfo.value().timings.receiveTimePoint >
                  ackFrameMetaData.connTime
              ? std::chrono::duration_cast<std::chrono::microseconds>(
-                   ackState.lastRecvdPacketInfo.value().timeStamp -
+                   ackState.lastRecvdPacketInfo.value()
+                       .timings.receiveTimePoint -
                    ackFrameMetaData.connTime)
              : 0us);
 
@@ -507,10 +511,11 @@ folly::Optional<WriteAckFrameResult> writeAckFrameWithReceivedTimestamps(
   if (ackState.lastRecvdPacketInfo) {
     lastPktNum = ackState.lastRecvdPacketInfo.value().pktNum;
     lastPktTsDelta =
-        (ackState.lastRecvdPacketInfo.value().timeStamp >
+        (ackState.lastRecvdPacketInfo.value().timings.receiveTimePoint >
                  ackFrameMetaData.connTime
              ? std::chrono::duration_cast<std::chrono::microseconds>(
-                   ackState.lastRecvdPacketInfo.value().timeStamp -
+                   ackState.lastRecvdPacketInfo.value()
+                       .timings.receiveTimePoint -
                    ackFrameMetaData.connTime)
              : 0us);
   }

quic/codec/Types.h

@@ -19,6 +19,7 @@
 #include <quic/common/BufUtil.h>
 #include <quic/common/CircularDeque.h>
 #include <quic/common/IntervalSet.h>
+#include <quic/common/NetworkData.h>
 #include <quic/common/SmallCollections.h>
 #include <quic/common/Variant.h>
 
@@ -219,7 +220,7 @@ struct WriteAckFrameState {
    */
   struct ReceivedPacket {
     PacketNum pktNum;
-    TimePoint timeStamp;
+    ReceivedUdpPacket::Timings timings;
   };
 
   AckBlocks acks;

quic/codec/test/QuicWriteCodecTest.cpp

@@ -147,7 +147,6 @@ void setupCommonExpects(MockQuicPacketBuilder& pktBuilder) {
 }
 using PacketsReceivedTimestampsDeque =
     CircularDeque<WriteAckFrameState::ReceivedPacket>;
-
 const auto kDefaultTimestampsDelta = 10us;
 const AckReceiveTimestampsConfig defaultAckReceiveTimestmpsConfig = {
     .receiveTimestampsExponent = kDefaultReceiveTimestampsExponent};
@@ -171,9 +170,9 @@ PacketsReceivedTimestampsDeque populateReceiveTimestamps(
         auto diff = std::chrono::microseconds(
             lastPacketDelta -= kDefaultTimestampsDelta);
         if ((connTime + diff) > connTime) {
-          rpi.timeStamp = connTime + diff;
+          rpi.timings.receiveTimePoint = connTime + diff;
         } else {
-          rpi.timeStamp = connTime;
+          rpi.timings.receiveTimePoint = connTime;
         }
         pktsReceivedTimestamps.emplace_front(rpi);
       } else {
@@ -198,7 +197,8 @@ size_t computeBytesForAckReceivedTimestamps(
       ackFrameMetadata.ackState.lastRecvdPacketInfo.value().pktNum;
   std::chrono::duration lastTimeStampDelta =
       std::chrono::duration_cast<std::chrono::microseconds>(
-          ackFrameMetadata.ackState.lastRecvdPacketInfo.value().timeStamp -
+          ackFrameMetadata.ackState.lastRecvdPacketInfo.value()
+              .timings.receiveTimePoint -
           connTime);
 
   // When FrameType == ACK_RECEIVE_TIMESTAMPS, the minimum additional
@@ -232,10 +232,11 @@ WriteAckFrameState createTestWriteAckState(
   if (frameType == FrameType::ACK_RECEIVE_TIMESTAMPS) {
     ackState.recvdPacketInfos =
         populateReceiveTimestamps(ackBlocks, connTime, countTimestampsToStore);
-    ackState.lastRecvdPacketInfo.assign({
-        ackState.recvdPacketInfos.back().pktNum,
-        ackState.recvdPacketInfos.back().timeStamp,
-    });
+    ackState.lastRecvdPacketInfo.assign(
+        {ackState.recvdPacketInfos.back().pktNum,
+         ReceivedUdpPacket::Timings{
+             .receiveTimePoint =
+                 ackState.recvdPacketInfos.back().timings.receiveTimePoint}});
   }
   return ackState;
 }
@@ -255,7 +256,8 @@ void assertsOnDecodedReceiveTimestamps(
   EXPECT_EQ(
       readAckFrame.maybeLatestRecvdPacketTime.value(),
       std::chrono::duration_cast<std::chrono::microseconds>(
-          ackFrameMetaData.ackState.lastRecvdPacketInfo.value().timeStamp -
+          ackFrameMetaData.ackState.lastRecvdPacketInfo.value()
+              .timings.receiveTimePoint -
           ackFrameMetaData.connTime));
   EXPECT_EQ(
       readAckFrame.recvdPacketsTimestampRanges.size(),
@@ -947,7 +949,7 @@ TEST_P(QuicWriteCodecTest, AckFrameVeryLargeAckRange) {
           rpi.pktNum = i;
           auto diff = std::chrono::microseconds(
               lastPacketDelta -= kDefaultTimestampsDelta);
-          rpi.timeStamp = connTime + diff;
+          rpi.timings.receiveTimePoint = connTime + diff;
           pktsReceivedTimestamps.emplace_front(rpi);
         } else {
           break;
@@ -957,7 +959,9 @@ TEST_P(QuicWriteCodecTest, AckFrameVeryLargeAckRange) {
     ackState.recvdPacketInfos = pktsReceivedTimestamps;
     ackState.lastRecvdPacketInfo.assign({
         ackState.recvdPacketInfos.back().pktNum,
-        ackState.recvdPacketInfos.back().timeStamp,
+        ReceivedUdpPacket::Timings{
+            .receiveTimePoint =
+                ackState.recvdPacketInfos.back().timings.receiveTimePoint},
     });
   }
 

quic/state/QuicStateFunctions.cpp

@@ -424,15 +424,15 @@ uint64_t addPacketToAckState(
   }
   static_assert(Clock::is_steady, "Needs steady clock");
 
-  ackState.lastRecvdPacketInfo.assign({packetNum, timings.receiveTimePoint});
+  ackState.lastRecvdPacketInfo.assign({packetNum, timings});
 
   if (packetNum >= expectedNextPacket) {
     if (ackState.recvdPacketInfos.size() ==
         conn.transportSettings.maxReceiveTimestampsPerAckStored) {
       ackState.recvdPacketInfos.pop_front();
     }
-    ackState.recvdPacketInfos.emplace_back(WriteAckFrameState::ReceivedPacket{
-        packetNum, timings.receiveTimePoint});
+    ackState.recvdPacketInfos.emplace_back(
+        WriteAckFrameState::ReceivedPacket{packetNum, timings});
   }
 
   if (expectedNextPacket) {

quic/state/test/AckHandlersTest.cpp

@@ -1635,7 +1635,9 @@ TEST_P(AckHandlersTest, purgeAckReceiveTimestamps) {
     // Fill up the last 25 timestamps ending at PN 40.
     for (PacketNum pktNum = 15; pktNum <= 40; ++pktNum) {
       conn.ackStates.initialAckState->recvdPacketInfos.emplace_back(
-          WriteAckFrameState::ReceivedPacket{pktNum, expectedTime});
+          WriteAckFrameState::ReceivedPacket{
+              pktNum,
+              ReceivedUdpPacket::Timings{.receiveTimePoint = expectedTime}});
     }
 
     commonAckVisitorForAckFrame(*conn.ackStates.initialAckState, ackFrame);
@@ -1656,7 +1658,9 @@ TEST_P(AckHandlersTest, purgeAckReceiveTimestamps) {
     // Local ACK state has timestamps for {15, 40}
     for (PacketNum pktNum = 15; pktNum <= 40; ++pktNum) {
       conn.ackStates.initialAckState->recvdPacketInfos.emplace_back(
-          WriteAckFrameState::ReceivedPacket{pktNum, expectedTime});
+          WriteAckFrameState::ReceivedPacket{
+              pktNum,
+              ReceivedUdpPacket::Timings{.receiveTimePoint = expectedTime}});
     }
     // ACK frame in the ACKed packet has ACKs for {10, 20}, {25, 35}
     ackFrame.ackBlocks.emplace_back(10, 20);
@@ -1691,7 +1695,9 @@ TEST_P(AckHandlersTest, purgeAckReceiveTimestamps) {
     // Local ACK state has timestamps for {15, 40}
     for (PacketNum pktNum = 15; pktNum <= 40; ++pktNum) {
       conn.ackStates.initialAckState->recvdPacketInfos.emplace_back(
-          WriteAckFrameState::ReceivedPacket{pktNum, expectedTime});
+          WriteAckFrameState::ReceivedPacket{
+              pktNum,
+              ReceivedUdpPacket::Timings{.receiveTimePoint = expectedTime}});
     }
     // Selectively ACK some packets in the middle - {18, 20}, {25, 35}
     ackFrame.ackBlocks.emplace_back(25, 35);

quic/state/test/QuicStateFunctionsTest.cpp

@@ -224,15 +224,21 @@ TEST_P(
   // Packets 1 and 5 are out of order and will not be stored.
   auto& ackState = getAckState(conn, PacketNumberSpace::AppData);
   std::deque<WriteAckFrameState::ReceivedPacket> expectedPktsInfo = {
-      {0, recvdTs}, {2, recvdTs}, {3, recvdTs}, {4, recvdTs}, {6, recvdTs}};
+      {0, ReceivedUdpPacket::Timings{.receiveTimePoint = recvdTs}},
+      {2, ReceivedUdpPacket::Timings{.receiveTimePoint = recvdTs}},
+      {3, ReceivedUdpPacket::Timings{.receiveTimePoint = recvdTs}},
+      {4, ReceivedUdpPacket::Timings{.receiveTimePoint = recvdTs}},
+      {6, ReceivedUdpPacket::Timings{.receiveTimePoint = recvdTs}}};
   EXPECT_EQ(expectedPktsInfo.size(), ackState.recvdPacketInfos.size());
   for (unsigned long i = 0; i < expectedPktsInfo.size(); i++) {
     EXPECT_EQ(expectedPktsInfo[i].pktNum, ackState.recvdPacketInfos[i].pktNum);
     EXPECT_EQ(
-        expectedPktsInfo[i].timeStamp, ackState.recvdPacketInfos[i].timeStamp);
+        expectedPktsInfo[i].timings.receiveTimePoint,
+        ackState.recvdPacketInfos[i].timings.receiveTimePoint);
   }
   EXPECT_EQ(ackState.lastRecvdPacketInfo.value().pktNum, 5);
-  EXPECT_EQ(ackState.lastRecvdPacketInfo.value().timeStamp, recvdTs);
+  EXPECT_EQ(
+      ackState.lastRecvdPacketInfo.value().timings.receiveTimePoint, recvdTs);
 }
 
 INSTANTIATE_TEST_SUITE_P(