Introduce and preferentially peer with NODE_WITNESS service bit

Service bit logic by Nicolas Dorier.

src/main.cpp

@@ -265,6 +265,8 @@ struct CNodeState {
     bool fPreferredDownload;
     //! Whether this peer wants invs or headers (when possible) for block announcements.
     bool fPreferHeaders;
+    //! Whether this peer can give us witnesses
+    bool fHaveWitness;
 
     CNodeState() {
         fCurrentlyConnected = false;
@@ -281,6 +283,7 @@ struct CNodeState {
         nBlocksInFlightValidHeaders = 0;
         fPreferredDownload = false;
         fPreferHeaders = false;
+        fHaveWitness = false;
     }
 };
 
@@ -4600,6 +4603,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
         pfrom->fClient = !(pfrom->nServices & NODE_NETWORK);
 
+        if((pfrom->nServices & NODE_WITNESS))
+        {
+            LOCK(cs_main);
+            State(pfrom->GetId())->fHaveWitness = true;
+        }
+
         // Potentially mark this peer as a preferred download peer.
         UpdatePreferredDownload(pfrom, State(pfrom->GetId()));
 
@@ -4782,14 +4791,18 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
         for (unsigned int nInv = 0; nInv < vInv.size(); nInv++)
         {
-            const CInv &inv = vInv[nInv];
+            CInv &inv = vInv[nInv];
 
             boost::this_thread::interruption_point();
             pfrom->AddInventoryKnown(inv);
 
             bool fAlreadyHave = AlreadyHave(inv);
             LogPrint("net", "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom->id);
 
+            if (inv.type == MSG_TX && State(pfrom->GetId())->fHaveWitness) {
+                inv.type = MSG_WITNESS_TX;
+            }
+
             if (inv.type == MSG_BLOCK) {
                 UpdateBlockAvailability(pfrom->GetId(), inv.hash);
                 if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
@@ -4805,6 +4818,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     CNodeState *nodestate = State(pfrom->GetId());
                     if (CanDirectFetch(chainparams.GetConsensus()) &&
                         nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
+                        if (State(pfrom->GetId())->fHaveWitness) {
+                            inv.type = MSG_WITNESS_BLOCK;
+                        }
                         vToFetch.push_back(inv);
                         // Mark block as in flight already, even though the actual "getdata" message only goes out
                         // later (within the same cs_main lock, though).
@@ -5883,7 +5899,7 @@ bool SendMessages(CNode* pto)
             NodeId staller = -1;
             FindNextBlocksToDownload(pto->GetId(), MAX_BLOCKS_IN_TRANSIT_PER_PEER - state.nBlocksInFlight, vToDownload, staller);
             BOOST_FOREACH(CBlockIndex *pindex, vToDownload) {
-                vGetData.push_back(CInv(MSG_BLOCK, pindex->GetBlockHash()));
+                vGetData.push_back(CInv(State(staller)->fHaveWitness ? MSG_WITNESS_BLOCK : MSG_BLOCK, pindex->GetBlockHash()));
                 MarkBlockAsInFlight(pto->GetId(), pindex->GetBlockHash(), consensusParams, pindex);
                 LogPrint("net", "Requesting block %s (%d) peer=%d\n", pindex->GetBlockHash().ToString(),
                     pindex->nHeight, pto->id);

src/net.cpp

@@ -72,14 +72,14 @@ namespace {
 const static std::string NET_MESSAGE_COMMAND_OTHER = "*other*";
 
 /** Services this node implementation cares about */
-static const uint64_t nRelevantServices = NODE_NETWORK;
+static const uint64_t nRelevantServices = NODE_NETWORK | NODE_WITNESS;
 
 //
 // Global state variables
 //
 bool fDiscover = true;
 bool fListen = true;
-uint64_t nLocalServices = NODE_NETWORK;
+uint64_t nLocalServices = NODE_NETWORK | NODE_WITNESS;
 CCriticalSection cs_mapLocalHost;
 map<CNetAddr, LocalServiceInfo> mapLocalHost;
 static bool vfLimited[NET_MAX] = {};
@@ -1601,6 +1601,10 @@ void ThreadOpenConnections()
             if (nANow - addr.nLastTry < 600 && nTries < 30)
                 continue;
 
+            // only consider non-witness nodes after 40 failed attemps
+            if (!(addr.nServices & NODE_WITNESS) && nTries < 40)
+                continue;
+
             // do not allow non-default ports, unless after 50 invalid addresses selected already
             if (addr.GetPort() != Params().GetDefaultPort() && nTries < 50)
                 continue;

src/protocol.h

@@ -236,6 +236,9 @@ enum {
     // Bitcoin Core nodes used to support this by default, without advertising this bit,
     // but no longer do as of protocol version 70011 (= NO_BLOOM_VERSION)
     NODE_BLOOM = (1 << 2),
+    // Indicates that a node can be asked for blocks and transactions including
+    // witness data.
+    NODE_WITNESS = (1 << 3),
 
     // Bits 24-31 are reserved for temporary experiments. Just pick a bit that
     // isn't getting used, or one not being used much, and notify the

src/version.h

@@ -39,4 +39,7 @@ static const int SENDHEADERS_VERSION = 70012;
 //! "feefilter" tells peers to filter invs to you by fee starts with this version
 static const int FEEFILTER_VERSION = 70013;
 
+//! Version after which witness support potentially exists
+static const int WITNESS_VERSION = 70013;
+
 #endif // BITCOIN_VERSION_H