Reject non-final txs even in testnet/regtest

Previous behavior with IsFinalTx() being an IsStandard() rule was rather
confusing and interferred with testing of protocols that depended on
nLockTime.

src/main.cpp

@@ -620,34 +620,11 @@ unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans)
 
 bool IsStandardTx(const CTransaction& tx, string& reason)
 {
-    AssertLockHeld(cs_main);
     if (tx.nVersion > CTransaction::CURRENT_VERSION || tx.nVersion < 1) {
         reason = "version";
         return false;
     }
 
-    // Treat non-final transactions as non-standard to prevent a specific type
-    // of double-spend attack, as well as DoS attacks. (if the transaction
-    // can't be mined, the attacker isn't expending resources broadcasting it)
-    // Basically we don't want to propagate transactions that can't be included in
-    // the next block.
-    //
-    // However, IsFinalTx() is confusing... Without arguments, it uses
-    // chainActive.Height() to evaluate nLockTime; when a block is accepted, chainActive.Height()
-    // is set to the value of nHeight in the block. However, when IsFinalTx()
-    // is called within CBlock::AcceptBlock(), the height of the block *being*
-    // evaluated is what is used. Thus if we want to know if a transaction can
-    // be part of the *next* block, we need to call IsFinalTx() with one more
-    // than chainActive.Height().
-    //
-    // Timestamps on the other hand don't get any special treatment, because we
-    // can't know what timestamp the next block will have, and there aren't
-    // timestamp applications where it matters.
-    if (!IsFinalTx(tx, chainActive.Height() + 1)) {
-        reason = "non-final";
-        return false;
-    }
-
     // Extremely large transactions with lots of inputs can cost the network
     // almost as much to process as they cost the sender in fees, because
     // computing signature hashes is O(ninputs*txsize). Limiting transactions
@@ -936,6 +913,26 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
                          error("AcceptToMemoryPool : nonstandard transaction: %s", reason),
                          REJECT_NONSTANDARD, reason);
 
+    // Only accept nLockTime-using transactions that can be mined in the next
+    // block; we don't want our mempool filled up with transactions that can't
+    // be mined yet.
+    //
+    // However, IsFinalTx() is confusing... Without arguments, it uses
+    // chainActive.Height() to evaluate nLockTime; when a block is accepted,
+    // chainActive.Height() is set to the value of nHeight in the block.
+    // However, when IsFinalTx() is called within CBlock::AcceptBlock(), the
+    // height of the block *being* evaluated is what is used. Thus if we want
+    // to know if a transaction can be part of the *next* block, we need to
+    // call IsFinalTx() with one more than chainActive.Height().
+    //
+    // Timestamps on the other hand don't get any special treatment, because we
+    // can't know what timestamp the next block will have, and there aren't
+    // timestamp applications where it matters.
+    if (!IsFinalTx(tx, chainActive.Height() + 1))
+        return state.DoS(0,
+                         error("AcceptToMemoryPool : non-final"),
+                         REJECT_NONSTANDARD, "non-final");
+
     // is it already in the memory pool?
     uint256 hash = tx.GetHash();
     if (pool.exists(hash))