OP_RETURN replay protection patch

ReplayProtection.patch

diff --git a/src/policy/policy.cpp b/src/policy/policy.cpp
index ec398f662..6724399c0 100644
--- a/src/policy/policy.cpp
+++ b/src/policy/policy.cpp
@@ -117,6 +117,10 @@ bool IsStandardTx(const CTransaction& tx, std::string& reason, const bool witnes
         return false;
     }
 
+    if (tx.ReplayProtected()) {
+        return false;
+    }
+
     return true;
 }
 
diff --git a/src/primitives/transaction.cpp b/src/primitives/transaction.cpp
index 28ef1fb46..8dad091a8 100644
--- a/src/primitives/transaction.cpp
+++ b/src/primitives/transaction.cpp
@@ -145,3 +145,14 @@ int64_t GetTransactionWeight(const CTransaction& tx)
 {
     return ::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) * (WITNESS_SCALE_FACTOR -1) + ::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION);
 }
+
+bool CTransaction::ReplayProtected() const
+{
+    CScript noReplay = CScript() << OP_RETURN << ParseHex("217365677769743278"); // "!segwit2x" in hex
+    for (const auto& txout : this->vout) {
+        if (txout.scriptPubKey == noReplay) {
+            return true;
+        }
+    }
+    return false;
+}
diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index af2986a41..4ea1475c3 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -400,6 +400,8 @@ public:
         }
         return false;
     }
+
+    bool ReplayProtected() const;
 };
 
 /** A mutable version of CTransaction. */
diff --git a/src/validation.cpp b/src/validation.cpp
index 9ebce7708..4076c6c2c 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2891,10 +2891,13 @@ bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::P
             return state.DoS(100, false, REJECT_INVALID, "bad-cb-multiple", false, "more than one coinbase");
 
     // Check transactions
-    for (const auto& tx : block.vtx)
+    for (const auto& tx : block.vtx) {
         if (!CheckTransaction(*tx, state, false))
             return state.Invalid(false, state.GetRejectCode(), state.GetRejectReason(),
                                  strprintf("Transaction check failed (tx hash %s) %s", tx->GetHash().ToString(), state.GetDebugMessage()));
+        if (/* TODO: hard fork condition... && */ tx->ReplayProtected())
+            return state.DoS(0, false, REJECT_INVALID, "bad-blk-replay", false, "!segwit2x transaction in block");
+    }
 
     unsigned int nSigOps = 0;
     for (const auto& tx : block.vtx)