Handle mempool requests in send loop, subject to trickle

By eliminating queued entries from the mempool response and responding only at
trickle time, this makes the mempool no longer leak transaction arrival order
information (as the mempool itself is also sorted)-- at least no more than
relay itself leaks it.

Author: sipa

src/main.cpp

@@ -5235,34 +5235,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             pfrom->fDisconnect = true;
             return true;
         }
-        LOCK2(cs_main, pfrom->cs_filter);
 
-        std::vector<uint256> vtxid;
-        mempool.queryHashes(vtxid);
-        vector<CInv> vInv;
-        BOOST_FOREACH(uint256& hash, vtxid) {
-            CInv inv(MSG_TX, hash);
-            if (pfrom->pfilter) {
-                CTransaction tx;
-                bool fInMemPool = mempool.lookup(hash, tx);
-                if (!fInMemPool) continue; // another thread removed since queryHashes, maybe...
-                if (!pfrom->pfilter->IsRelevantAndUpdate(tx)) continue;
-            }
-            if (pfrom->minFeeFilter) {
-                CFeeRate feeRate;
-                mempool.lookupFeeRate(hash, feeRate);
-                LOCK(pfrom->cs_feeFilter);
-                if (feeRate.GetFeePerK() < pfrom->minFeeFilter)
-                    continue;
-            }
-            vInv.push_back(inv);
-            if (vInv.size() == MAX_INV_SZ) {
-                pfrom->PushMessage(NetMsgType::INV, vInv);
-                vInv.clear();
-            }
-        }
-        if (vInv.size() > 0)
-            pfrom->PushMessage(NetMsgType::INV, vInv);
+        LOCK(pfrom->cs_inventory);
+        pfrom->fSendMempool = true;
     }
 
 
@@ -5811,13 +5786,52 @@ bool SendMessages(CNode* pto)
             }
             pto->vInventoryBlockToSend.clear();
 
-            // Determine transactions to relay
+            // Check whether periodic sends should happen
             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);
             }
+
+            // Respond to BIP35 mempool requests
+            if (fSendTrickle && pto->fSendMempool) {
+                std::vector<uint256> vtxid;
+                mempool.queryHashes(vtxid);
+                pto->fSendMempool = false;
+                CAmount filterrate = 0;
+                {
+                    LOCK(pto->cs_feeFilter);
+                    filterrate = pto->minFeeFilter;
+                }
+
+                LOCK(pto->cs_filter);
+
+                BOOST_FOREACH(const uint256& hash, vtxid) {
+                    CInv inv(MSG_TX, hash);
+                    pto->setInventoryTxToSend.erase(hash);
+                    if (filterrate) {
+                        CFeeRate feeRate;
+                        mempool.lookupFeeRate(hash, feeRate);
+                        if (feeRate.GetFeePerK() < filterrate)
+                            continue;
+                    }
+                    if (pto->pfilter) {
+                        CTransaction tx;
+                        bool fInMemPool = mempool.lookup(hash, tx);
+                        if (!fInMemPool) continue; // another thread removed since queryHashes, maybe...
+                        if (!pto->pfilter->IsRelevantAndUpdate(tx)) continue;
+                    }
+                    pto->filterInventoryKnown.insert(hash);
+                    vInv.push_back(inv);
+                    if (vInv.size() == MAX_INV_SZ) {
+                        pto->PushMessage(NetMsgType::INV, vInv);
+                        vInv.clear();
+                    }
+                }
+            }
+
+            // Determine transactions to relay
             if (fSendTrickle) {
                 // Produce a vector with all candidates for sending
                 vector<std::set<uint256>::iterator> vInvTx;
@@ -5847,6 +5861,10 @@ bool SendMessages(CNode* pto)
                     // Send
                     vInv.push_back(CInv(MSG_TX, hash));
                     nRelayedTransactions++;
+                    if (vInv.size() == MAX_INV_SZ) {
+                        pto->PushMessage(NetMsgType::INV, vInv);
+                        vInv.clear();
+                    }
                     pto->filterInventoryKnown.insert(hash);
                 }
             }

src/net.cpp

@@ -2370,6 +2370,7 @@ CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNa
     hashContinue = uint256();
     nStartingHeight = -1;
     filterInventoryKnown.reset();
+    fSendMempool = false;
     fGetAddr = false;
     nNextLocalAddrSend = 0;
     nNextAddrSend = 0;

src/net.h

@@ -411,6 +411,8 @@ class CNode
     // Used for headers announcements - unfiltered blocks to relay
     // Also protected by cs_inventory
     std::vector<uint256> vBlockHashesToAnnounce;
+    // Used for BIP35 mempool sending, also protected by cs_inventory
+    bool fSendMempool;
 
     // Ping time measurement:
     // The pong reply we're expecting, or 0 if no pong expected.