Disallow v0 transactions as a consensus rule

Closes #1557

src/consensus/consensus.h

@@ -6,6 +6,8 @@
 #ifndef BITCOIN_CONSENSUS_CONSENSUS_H
 #define BITCOIN_CONSENSUS_CONSENSUS_H
 
+/** The minimum allowed transaction version (network rule) */
+static const int32_t MIN_TX_VERSION = 1;
 /** The maximum allowed size for a serialized block, in bytes (network rule) */
 static const unsigned int MAX_BLOCK_SIZE = 2000000;
 /** The maximum allowed number of signature check operations in a block (network rule) */

src/gtest/test_checktransaction.cpp

@@ -94,6 +94,16 @@ TEST(checktransaction_tests, valid_transaction) {
     EXPECT_TRUE(CheckTransactionWithoutProofVerification(tx, state));
 }
 
+TEST(checktransaction_tests, BadVersionTooLow) {
+    CMutableTransaction mtx = GetValidTransaction();
+    mtx.nVersion = 0;
+
+    CTransaction tx(mtx);
+    MockCValidationState state;
+    EXPECT_CALL(state, DoS(100, false, REJECT_INVALID, "bad-version-too-low", false)).Times(1);
+    CheckTransactionWithoutProofVerification(tx, state);
+}
+
 TEST(checktransaction_tests, bad_txns_vin_empty) {
     CMutableTransaction mtx = GetValidTransaction();
     mtx.vjoinsplit.resize(0);

src/main.cpp

@@ -851,6 +851,12 @@ bool CheckTransactionWithoutProofVerification(const CTransaction& tx, CValidatio
 {
     // Basic checks that don't depend on any context
 
+    // Check transaction version
+    if (tx.nVersion < MIN_TX_VERSION) {
+        return state.DoS(100, error("CheckTransaction(): version too low"),
+                         REJECT_INVALID, "bad-version-too-low");
+    }
+
     // Transactions can contain empty `vin` and `vout` so long as
     // `vjoinsplit` is non-empty.
     if (tx.vin.empty() && tx.vjoinsplit.empty())