Introduce REJECT_INTERNAL codes for local AcceptToMempool errors

Add status codes specific to AcceptToMempool procession of transactions.
These can never happen due to block validation, and must never be sent
over the P2P network. Add assertions where appropriate.

src/main.cpp

@@ -811,7 +811,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
     // is it already in the memory pool?
     uint256 hash = tx.GetHash();
     if (pool.exists(hash))
-        return false;
+        return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-in-mempool");
 
     // Check for conflicts with in-memory transactions
     {
@@ -822,7 +822,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         if (pool.mapNextTx.count(outpoint))
         {
             // Disable replacement feature for now
-            return false;
+            return state.Invalid(false, REJECT_CONFLICT, "txn-mempool-conflict");
         }
     }
     }
@@ -839,7 +839,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 
         // do we already have it?
         if (view.HaveCoins(hash))
-            return false;
+            return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-known");
 
         // do all inputs exist?
         // Note that this does not check for the presence of actual outputs (see the next check for that),
@@ -848,7 +848,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
             if (!view.HaveCoins(txin.prevout.hash)) {
                 if (pfMissingInputs)
                     *pfMissingInputs = true;
-                return false;
+                return false; // fMissingInputs and !state.IsInvalid() is used to detect this condition, don't set state.Invalid()
             }
         }
 
@@ -868,7 +868,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 
         // Check for non-standard pay-to-script-hash in inputs
         if (fRequireStandard && !AreInputsStandard(tx, view))
-            return error("AcceptToMemoryPool: nonstandard transaction input");
+            return state.Invalid(false, REJECT_NONSTANDARD, "bad-txns-nonstandard-inputs");
 
         // Check that the transaction doesn't have an excessive number of
         // sigops, making it impossible to mine. Since the coinbase transaction
@@ -1239,7 +1239,7 @@ void static InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state
     if (state.IsInvalid(nDoS)) {
         std::map<uint256, NodeId>::iterator it = mapBlockSource.find(pindex->GetBlockHash());
         if (it != mapBlockSource.end() && State(it->second)) {
-            assert(state.GetRejectCode() < 0x100);
+            assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
             CBlockReject reject = {(unsigned char)state.GetRejectCode(), state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), pindex->GetBlockHash()};
             State(it->second)->rejects.push_back(reject);
             if (nDoS > 0)
@@ -4358,6 +4358,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             LogPrint("mempool", "%s from peer=%d %s was not accepted into the memory pool: %s\n", tx.GetHash().ToString(),
                 pfrom->id, pfrom->cleanSubVer,
                 state.GetRejectReason());
+            if (state.GetRejectCode() < REJECT_INTERNAL) // Never send AcceptToMemoryPool's internal codes over P2P
                 pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),
                                    state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
             if (nDoS > 0)
@@ -4439,6 +4440,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         ProcessNewBlock(state, pfrom, &block, forceProcessing, NULL);
         int nDoS;
         if (state.IsInvalid(nDoS)) {
+            assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
             pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),
                                state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
             if (nDoS > 0) {

src/main.h

@@ -455,7 +455,16 @@ extern CBlockTreeDB *pblocktree;
  */
 int GetSpendHeight(const CCoinsViewCache& inputs);
 
-/** local "reject" message codes for RPC which can not be triggered by p2p trasactions */
+/** Reject codes greater or equal to this can be returned by AcceptToMemPool
+ * for transactions, to signal internal conditions. They cannot and should not
+ * be sent over the P2P network.
+ */
+static const unsigned int REJECT_INTERNAL = 0x100;
+/** Too high fee. Can not be triggered by P2P transactions */
 static const unsigned int REJECT_HIGHFEE = 0x100;
+/** Transaction is already known (either in mempool or blockchain) */
+static const unsigned int REJECT_ALREADY_KNOWN = 0x101;
+/** Transaction conflicts with a transaction already known */
+static const unsigned int REJECT_CONFLICT = 0x102;
 
 #endif // BITCOIN_MAIN_H