Add p2p message "wtxidrelay"

When sent to and received from a given peer, enables using wtxid's for
announcing and fetching transactions with that peer.

src/net_processing.cpp

@@ -2342,6 +2342,10 @@ void ProcessMessage(
         if (pfrom.fInbound)
             PushNodeVersion(pfrom, connman, GetAdjustedTime());
 
+        if (nVersion >= WTXID_RELAY_VERSION) {
+            connman.PushMessage(&pfrom, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::WTXIDRELAY));
+        }
+
         connman.PushMessage(&pfrom, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::VERACK));
 
         pfrom.nServices = nServices;
@@ -2478,6 +2482,18 @@ void ProcessMessage(
         return;
     }
 
+    // Feature negotiation of wtxidrelay should happen between VERSION and
+    // VERACK, to avoid relay problems from switching after a connection is up
+    if (msg_type == NetMsgType::WTXIDRELAY) {
+        if (pfrom.nVersion >= WTXID_RELAY_VERSION) {
+            LOCK(cs_main);
+            if (!State(pfrom.GetId())->m_wtxid_relay) {
+                State(pfrom.GetId())->m_wtxid_relay = true;
+            }
+        }
+        return;
+    }
+
     if (!pfrom.fSuccessfullyConnected) {
         // Must have a verack message before anything else
         LOCK(cs_main);

src/protocol.cpp

@@ -46,6 +46,7 @@ const char *GETCFHEADERS="getcfheaders";
 const char *CFHEADERS="cfheaders";
 const char *GETCFCHECKPT="getcfcheckpt";
 const char *CFCHECKPT="cfcheckpt";
+const char *WTXIDRELAY="wtxidrelay";
 } // namespace NetMsgType
 
 /** All known message types. Keep this in the same order as the list of
@@ -83,6 +84,7 @@ const static std::string allNetMessageTypes[] = {
     NetMsgType::CFHEADERS,
     NetMsgType::GETCFCHECKPT,
     NetMsgType::CFCHECKPT,
+    NetMsgType::WTXIDRELAY,
 };
 const static std::vector<std::string> allNetMessageTypesVec(allNetMessageTypes, allNetMessageTypes+ARRAYLEN(allNetMessageTypes));
 

src/protocol.h

@@ -261,6 +261,12 @@ extern const char* GETCFCHECKPT;
  * evenly spaced filter headers for blocks on the requested chain.
  */
 extern const char* CFCHECKPT;
+/**
+ * Indicates that a node prefers to relay transactions via wtxid, rather than
+ * txid.
+ * @since protocol version 70016 as described by BIP 339.
+ */
+extern const char *WTXIDRELAY;
 }; // namespace NetMsgType
 
 /* Get a vector of all valid message types (see above) */
@@ -402,7 +408,7 @@ enum GetDataMsg : uint32_t {
     MSG_TX = 1,
     MSG_BLOCK = 2,
     MSG_WTX = 5,                                      //!< Defined in BIP 339
-    // The following can only occur in getdata. Invs always use TX or BLOCK.
+    // The following can only occur in getdata. Invs always use TX/WTX or BLOCK.
     MSG_FILTERED_BLOCK = 3,                           //!< Defined in BIP37
     MSG_CMPCT_BLOCK = 4,                              //!< Defined in BIP152
     MSG_WITNESS_BLOCK = MSG_BLOCK | MSG_WITNESS_FLAG, //!< Defined in BIP144

src/version.h

@@ -9,7 +9,7 @@
  * network protocol versioning
  */
 
-static const int PROTOCOL_VERSION = 70015;
+static const int PROTOCOL_VERSION = 70016;
 
 //! initial proto version, to be increased after version/verack negotiation
 static const int INIT_PROTO_VERSION = 209;
@@ -35,4 +35,7 @@ static const int SHORT_IDS_BLOCKS_VERSION = 70014;
 //! not banning for invalid compact blocks starts with this version
 static const int INVALID_CB_NO_BAN_VERSION = 70015;
 
+//! "wtxidrelay" command for wtxid-based relay starts with this version
+static const int WTXID_RELAY_VERSION = 70016;
+
 #endif // BITCOIN_VERSION_H