Bucket for inbound when scheduling invs to hide tx time

4 files changed, 45 insertions, 19 deletions

diff --git a/src/net.cpp b/src/net.cpp
index 55043ffe30..12bdcb465a 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2864,8 +2864,20 @@ bool CConnman::ForNode(NodeId id, std::function<bool(CNode* pnode)> func)
     return found != nullptr && NodeFullyConnected(found) && func(found);
 }
 
-int64_t PoissonNextSend(int64_t nNow, int average_interval_seconds) {
-    return nNow + (int64_t)(log1p(GetRand(1ULL << 48) * -0.0000000000000035527136788 /* -1/2^48 */) * average_interval_seconds * -1000000.0 + 0.5);
+int64_t CConnman::PoissonNextSendInbound(int64_t now, int average_interval_seconds)
+{
+    if (m_next_send_inv_to_incoming < now) {
+        // If this function were called from multiple threads simultaneously
+        // it would possible that both update the next send variable, and return a different result to their caller.
+        // This is not possible in practice as only the net processing thread invokes this function.
+        m_next_send_inv_to_incoming = PoissonNextSend(now, average_interval_seconds);
+    }
+    return m_next_send_inv_to_incoming;
+}
+
+int64_t PoissonNextSend(int64_t now, int average_interval_seconds)
+{
+    return now + (int64_t)(log1p(GetRand(1ULL << 48) * -0.0000000000000035527136788 /* -1/2^48 */) * average_interval_seconds * -1000000.0 + 0.5);
 }
 
 CSipHasher CConnman::GetDeterministicRandomizer(uint64_t id) const
diff --git a/src/net.h b/src/net.h
index 1bcc3cbb44..e542201163 100644
--- a/src/net.h
+++ b/src/net.h
@@ -310,6 +310,13 @@ public:
     unsigned int GetReceiveFloodSize() const;
 
     void WakeMessageHandler();
+
+    /** Attempts to obfuscate tx time through exponentially distributed emitting.
+        Works assuming that a single interval is used.
+        Variable intervals will result in privacy decrease.
+    */
+    int64_t PoissonNextSendInbound(int64_t now, int average_interval_seconds);
+
 private:
     struct ListenSocket {
         SOCKET socket;
@@ -434,6 +441,8 @@ private:
      *  This takes the place of a feeler connection */
     std::atomic_bool m_try_another_outbound_peer;
 
+    std::atomic<int64_t> m_next_send_inv_to_incoming;
+
     friend struct CConnmanTest;
 };
 extern std::unique_ptr<CConnman> g_connman;
@@ -863,6 +872,6 @@ public:
 
 
 /** Return a timestamp in the future (in microseconds) for exponentially distributed events. */
-int64_t PoissonNextSend(int64_t nNow, int average_interval_seconds);
+int64_t PoissonNextSend(int64_t now, int average_interval_seconds);
 
 #endif // BITCOIN_NET_H
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index ed9debc95a..473a4b8c55 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -71,6 +71,21 @@ static const int STALE_RELAY_AGE_LIMIT = 30 * 24 * 60 * 60;
 /// limiting block relay. Set to one week, denominated in seconds.
 static const int HISTORICAL_BLOCK_AGE = 7 * 24 * 60 * 60;
 
+/** Average delay between local address broadcasts in seconds. */
+static constexpr unsigned int AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL = 24 * 60 * 60;
+/** Average delay between peer address broadcasts in seconds. */
+static const unsigned int AVG_ADDRESS_BROADCAST_INTERVAL = 30;
+/** Average delay between trickled inventory transmissions in seconds.
+ *  Blocks and whitelisted receivers bypass this, outbound peers get half this delay. */
+static const unsigned int INVENTORY_BROADCAST_INTERVAL = 5;
+/** Maximum number of inventory items to send per transmission.
+ *  Limits the impact of low-fee transaction floods. */
+static constexpr unsigned int INVENTORY_BROADCAST_MAX = 7 * INVENTORY_BROADCAST_INTERVAL;
+/** Average delay between feefilter broadcasts in seconds. */
+static constexpr unsigned int AVG_FEEFILTER_BROADCAST_INTERVAL = 10 * 60;
+/** Maximum feefilter broadcast delay after significant change. */
+static constexpr unsigned int MAX_FEEFILTER_CHANGE_DELAY = 5 * 60;
+
 // Internal stuff
 namespace {
     /** Number of nodes with fSyncStarted. */
@@ -3496,8 +3511,12 @@ bool PeerLogicValidation::SendMessages(CNode* pto, std::atomic<bool>& interruptM
             bool fSendTrickle = pto->fWhitelisted;
             if (pto->nNextInvSend < nNow) {
                 fSendTrickle = true;
-                // Use half the delay for outbound peers, as there is less privacy concern for them.
-                pto->nNextInvSend = PoissonNextSend(nNow, INVENTORY_BROADCAST_INTERVAL >> !pto->fInbound);
+                if (pto->fInbound) {
+                    pto->nNextInvSend = connman->PoissonNextSendInbound(nNow, INVENTORY_BROADCAST_INTERVAL);
+                } else {
+                    // Use half the delay for outbound peers, as there is less privacy concern for them.
+                    pto->nNextInvSend = PoissonNextSend(nNow, INVENTORY_BROADCAST_INTERVAL >> 1);
+                }
             }
 
             // Time to send but the peer has requested we not relay transactions.
diff --git a/src/validation.h b/src/validation.h
index b9c2f6c023..cd29083f21 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -104,20 +104,6 @@ static const unsigned int DATABASE_WRITE_INTERVAL = 60 * 60;
 static const unsigned int DATABASE_FLUSH_INTERVAL = 24 * 60 * 60;
 /** Maximum length of reject messages. */
 static const unsigned int MAX_REJECT_MESSAGE_LENGTH = 111;
-/** Average delay between local address broadcasts in seconds. */
-static const unsigned int AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL = 24 * 60 * 60;
-/** Average delay between peer address broadcasts in seconds. */
-static const unsigned int AVG_ADDRESS_BROADCAST_INTERVAL = 30;
-/** Average delay between trickled inventory transmissions in seconds.
- *  Blocks and whitelisted receivers bypass this, outbound peers get half this delay. */
-static const unsigned int INVENTORY_BROADCAST_INTERVAL = 5;
-/** Maximum number of inventory items to send per transmission.
- *  Limits the impact of low-fee transaction floods. */
-static const unsigned int INVENTORY_BROADCAST_MAX = 7 * INVENTORY_BROADCAST_INTERVAL;
-/** Average delay between feefilter broadcasts in seconds. */
-static const unsigned int AVG_FEEFILTER_BROADCAST_INTERVAL = 10 * 60;
-/** Maximum feefilter broadcast delay after significant change. */
-static const unsigned int MAX_FEEFILTER_CHANGE_DELAY = 5 * 60;
 /** Block download timeout base, expressed in millionths of the block interval (i.e. 10 min) */
 static const int64_t BLOCK_DOWNLOAD_TIMEOUT_BASE = 1000000;
 /** Additional block download timeout per parallel downloading peer (i.e. 5 min) */