Expose TTL (on handshake) to applications

src/core/connection.c

@@ -5511,6 +5511,7 @@ QuicConnRecvDatagramBatch(
         CXPLAT_DBG_ASSERT(Packets[i]->Allocated);
         CXPLAT_ECN_TYPE ECN = CXPLAT_ECN_FROM_TOS(Packets[i]->TypeOfService);
         Packet = Packets[i];
+
         CXPLAT_DBG_ASSERT(Packet->PacketId != 0);
         if (!QuicConnRecvPrepareDecrypt(
                 Connection, Packet, HpMask + i * CXPLAT_HP_SAMPLE_LENGTH) ||
@@ -5637,6 +5638,9 @@ QuicConnRecvDatagrams(
 
         if (!IsDeferred) {
             Connection->Stats.Recv.TotalBytes += Packet->BufferLength;
+            if (Connection->Stats.Handshake.HandshakeHopLimitTTL == 0) {
+                Connection->Stats.Handshake.HandshakeHopLimitTTL = Packet->HandshakeHopLimitTTL;
+            }
             QuicConnLogInFlowStats(Connection);
 
             if (!CurrentPath->IsPeerValidated) {
@@ -6822,6 +6826,10 @@ QuicConnGetV2Statistics(
         Stats->SendEcnCongestionCount = Connection->Stats.Send.EcnCongestionCount;
     }
 
+    if (STATISTICS_HAS_FIELD(*StatsLength, HandshakeHopLimitTTL)) {
+        Stats->HandshakeHopLimitTTL = Connection->Stats.Handshake.HandshakeHopLimitTTL;
+    }
+
     *StatsLength = CXPLAT_MIN(*StatsLength, sizeof(QUIC_STATISTICS_V2));
 
     return QUIC_STATUS_SUCCESS;

src/core/connection.h

@@ -275,6 +275,7 @@ typedef struct QUIC_CONN_STATS {
         uint32_t ClientFlight1Bytes;    // Sum of TLS payloads
         uint32_t ServerFlight1Bytes;    // Sum of TLS payloads
         uint32_t ClientFlight2Bytes;    // Sum of TLS payloads
+        uint8_t HandshakeHopLimitTTL;            // TTL value in the initial packet of the handshake.
     } Handshake;
 
     struct {

src/inc/msquic.h

@@ -555,6 +555,8 @@ typedef struct QUIC_STATISTICS_V2 {
 
     uint32_t SendEcnCongestionCount;        // Number of congestion events caused by ECN.
 
+    uint8_t  HandshakeHopLimitTTL;                   // The TTL value in the initial packet of the handshake.
+
     // N.B. New fields must be appended to end
 
 } QUIC_STATISTICS_V2;

src/inc/quic_datapath.h

@@ -222,6 +222,11 @@ typedef struct CXPLAT_RECV_DATA {
     //
     uint8_t TypeOfService;
 
+    //
+    // TTL Hoplimit field of the IP header of the received packet on handshake.
+    //
+    uint8_t HandshakeHopLimitTTL;
+
     //
     // Flags.
     //

src/platform/datapath_winuser.c

@@ -153,7 +153,8 @@ typedef struct DATAPATH_RX_IO_BLOCK {
         RIO_CMSG_BASE_SIZE +
         WSA_CMSG_SPACE(sizeof(IN6_PKTINFO)) +   // IP_PKTINFO
         WSA_CMSG_SPACE(sizeof(DWORD)) +         // UDP_COALESCED_INFO
-        WSA_CMSG_SPACE(sizeof(INT))             // IP_ECN
+        WSA_CMSG_SPACE(sizeof(INT)) +           // IP_ECN
+        WSA_CMSG_SPACE(sizeof(INT))             // IP_HOP_LIMIT
         ];
 
 } DATAPATH_RX_IO_BLOCK;
@@ -1403,6 +1404,46 @@ SocketCreateUdp(
             goto Error;
         }
 
+        Option = TRUE;
+        Result =
+            setsockopt(
+                SocketProc->Socket,
+                IPPROTO_IP,
+                IP_HOPLIMIT,
+                (char*)&Option,
+                sizeof(Option));
+        if (Result == SOCKET_ERROR) {
+            int WsaError = WSAGetLastError();
+            QuicTraceEvent(
+                DatapathErrorStatus,
+                "[data][%p] ERROR, %u, %s.",
+                Socket,
+                WsaError,
+                "Set IP_HOPLIMIT");
+            Status = HRESULT_FROM_WIN32(WsaError);
+            goto Error;
+        }
+
+        Option = TRUE;
+        Result =
+            setsockopt(
+                SocketProc->Socket,
+                IPPROTO_IPV6,
+                IPV6_HOPLIMIT,
+                (char*)&Option,
+                sizeof(Option));
+        if (Result == SOCKET_ERROR) {
+            int WsaError = WSAGetLastError();
+            QuicTraceEvent(
+                DatapathErrorStatus,
+                "[data][%p] ERROR, %u, %s.",
+                Socket,
+                WsaError,
+                "Set IPV6_HOPLIMIT");
+            Status = HRESULT_FROM_WIN32(WsaError);
+            goto Error;
+        }
+
         //
         // The socket is shared by multiple endpoints, so increase the receive
         // buffer size.
@@ -3103,7 +3144,7 @@ CxPlatDataPathUdpRecvComplete(
         ULONG MessageCount = 0;
         BOOLEAN IsCoalesced = FALSE;
         INT ECN = 0;
-
+        INT HandshakeHopLimitTTL = 0;
         if (SocketProc->Parent->UseRio) {
             PRIO_CMSG_BUFFER RioRcvMsg = (PRIO_CMSG_BUFFER)IoBlock->ControlBuf;
             IoBlock->WsaMsgHdr.Control.buf = IoBlock->ControlBuf + RIO_CMSG_BASE_SIZE;
@@ -3126,6 +3167,9 @@ CxPlatDataPathUdpRecvComplete(
                 } else if (CMsg->cmsg_type == IPV6_ECN) {
                     ECN = *(PINT)WSA_CMSG_DATA(CMsg);
                     CXPLAT_DBG_ASSERT(ECN < UINT8_MAX);
+                } else if (CMsg->cmsg_type == IPV6_HOPLIMIT) {
+                    HandshakeHopLimitTTL = *(PINT)WSA_CMSG_DATA(CMsg);
+                    CXPLAT_DBG_ASSERT(HandshakeHopLimitTTL < 256);
                 }
             } else if (CMsg->cmsg_level == IPPROTO_IP) {
                 if (CMsg->cmsg_type == IP_PKTINFO) {
@@ -3138,6 +3182,9 @@ CxPlatDataPathUdpRecvComplete(
                 } else if (CMsg->cmsg_type == IP_ECN) {
                     ECN = *(PINT)WSA_CMSG_DATA(CMsg);
                     CXPLAT_DBG_ASSERT(ECN < UINT8_MAX);
+                } else if (CMsg->cmsg_type == IP_TTL) {
+                    HandshakeHopLimitTTL = *(PINT)WSA_CMSG_DATA(CMsg);
+                    CXPLAT_DBG_ASSERT(HandshakeHopLimitTTL < 256);
                 }
             } else if (CMsg->cmsg_level == IPPROTO_UDP) {
                 if (CMsg->cmsg_type == UDP_COALESCED_INFO) {
@@ -3195,6 +3242,7 @@ CxPlatDataPathUdpRecvComplete(
             Datagram->PartitionIndex =
                 SocketProc->DatapathProc->PartitionIndex % SocketProc->DatapathProc->Datapath->PartitionCount;
             Datagram->TypeOfService = (uint8_t)ECN;
+            Datagram->HandshakeHopLimitTTL = (uint8_t) HandshakeHopLimitTTL;
             Datagram->Allocated = TRUE;
             Datagram->Route->DatapathType = Datagram->DatapathType = CXPLAT_DATAPATH_TYPE_USER;
             Datagram->QueuedOnConnection = FALSE;

src/test/lib/HandshakeTest.cpp

@@ -317,6 +317,9 @@ QuicTestConnect(
                 }
                 TEST_TRUE(Client.GetIsConnected());
 
+                // After handshake, check and see if we have cached the TTL of the handshake packet.
+                TEST_TRUE(Client.GetStatistics().HandshakeHopLimitTTL > 0);
+
                 TEST_NOT_EQUAL(nullptr, Server);
                 Server->SetSslKeyLogFilePath();
                 if (!Server->WaitForConnectionComplete()) {