Auto merge of #1411 - bitcartel:master_bitcoin_7106, r=daira

Upstream patch: Fix and improve relay from whitelisted peers

https://github.com/bitcoin/bitcoin/pull/7106
a9f3d3db5c0c8d1697998ed9b3e192ddbf9a31f4

An extra commit modifies the log message string, otherwise there are are a number of commits that need be to backported to add methods e.g. GetDebugMessage.  These commits modify the interface in consensus/validation.h so there are conflicts to be resolved. e.g.
9003c7c
a9ac95c
5f12263
fbf44e6

src/main.cpp

@@ -4660,11 +4660,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         pfrom->setAskFor.erase(inv.hash);
         mapAlreadyAskedFor.erase(inv);
 
-        // Check for recently rejected (and do other quick existence checks)
-        if (AlreadyHave(inv))
-            return true;
-
-        if (AcceptToMemoryPool(mempool, state, tx, true, &fMissingInputs))
+        if (!AlreadyHave(inv) && AcceptToMemoryPool(mempool, state, tx, true, &fMissingInputs))
         {
             mempool.check(pcoinsTip);
             RelayTransaction(tx);
@@ -4745,13 +4741,21 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
             if (pfrom->fWhitelisted) {
                 // Always relay transactions received from whitelisted peers, even
-                // if they were rejected from the mempool, allowing the node to
-                // function as a gateway for nodes hidden behind it.
+                // if they were already in the mempool or rejected from it due
+                // to policy, allowing the node to function as a gateway for
+                // nodes hidden behind it.
                 //
-                // FIXME: This includes invalid transactions, which means a
-                // whitelisted peer could get us banned! We may want to change
-                // that.
-                RelayTransaction(tx);
+                // Never relay transactions that we would assign a non-zero DoS
+                // score for, as we expect peers to do the same with us in that
+                // case.
+                int nDoS = 0;
+                if (!state.IsInvalid(nDoS) || nDoS == 0) {
+                    LogPrintf("Force relaying tx %s from whitelisted peer=%d\n", tx.GetHash().ToString(), pfrom->id);
+                    RelayTransaction(tx);
+                } else {
+                    LogPrintf("Not relaying invalid transaction %s from whitelisted peer=%d (%s (code %d))\n",
+                        tx.GetHash().ToString(), pfrom->id, state.GetRejectReason(), state.GetRejectCode());
+                }
             }
         }
         int nDoS = 0;