Auto merge of #1407 - bitcartel:master_bitcoin_7079, r=daira

Upstream patch: Prevent peer flooding inv request queue

https://github.com/bitcoin/bitcoin/pull/7079
5029698186445bf3cd69d0e720f019c472661bff
ebb25f4c23adbcb55796c402bafd6064a136f16f

src/main.cpp

@@ -4657,6 +4657,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         bool fMissingInputs = false;
         CValidationState state;
 
+        pfrom->setAskFor.erase(inv.hash);
         mapAlreadyAskedFor.erase(inv);
 
         // Check for recently rejected (and do other quick existence checks)
@@ -5451,6 +5452,9 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                     pto->PushMessage("getdata", vGetData);
                     vGetData.clear();
                 }
+            } else {
+                //If we're not going to ask, don't expect a response.
+                pto->setAskFor.erase(inv.hash);
             }
             pto->mapAskFor.erase(pto->mapAskFor.begin());
         }

src/net.cpp

@@ -2178,8 +2178,12 @@ CNode::~CNode()
 
 void CNode::AskFor(const CInv& inv)
 {
-    if (mapAskFor.size() > MAPASKFOR_MAX_SZ)
+    if (mapAskFor.size() > MAPASKFOR_MAX_SZ || setAskFor.size() > SETASKFOR_MAX_SZ)
         return;
+    // a peer may not have multiple non-responded queue positions for a single inv item
+    if (!setAskFor.insert(inv.hash).second)
+        return;
+
     // We're using mapAskFor as a priority queue,
     // the key is the earliest time the request can be sent
     int64_t nRequestTime;

src/net.h

@@ -59,6 +59,8 @@ static const bool DEFAULT_UPNP = false;
 #endif
 /** The maximum number of entries in mapAskFor */
 static const size_t MAPASKFOR_MAX_SZ = MAX_INV_SZ;
+/** The maximum number of entries in setAskFor (larger due to getdata latency)*/
+static const size_t SETASKFOR_MAX_SZ = 2 * MAX_INV_SZ;
 
 unsigned int ReceiveFloodSize();
 unsigned int SendBufferSize();
@@ -310,6 +312,7 @@ public:
     mruset<CInv> setInventoryKnown;
     std::vector<CInv> vInventoryToSend;
     CCriticalSection cs_inventory;
+    std::set<uint256> setAskFor;
     std::multimap<int64_t, CInv> mapAskFor;
 
     // Ping time measurement: