feat: coinjoin promotion / demotion

src/coinjoin/client.h

@@ -143,6 +143,11 @@ class CCoinJoinClientSession : public CCoinJoinBaseSession
 
     CKeyHolderStorage keyHolderStorage; // storage for keys used in PrepareDenominate
 
+    // Post-V24: Promotion/demotion session state
+    bool m_fPromotion{false};  // True if this session is promoting smaller -> larger denom
+    bool m_fDemotion{false};   // True if this session is demoting larger -> smaller denom
+    std::vector<COutPoint> m_vecPromotionInputs;  // Selected inputs for promotion (10 coins)
+
     /// Create denominations
     bool CreateDenominated(CAmount nBalanceToDenominate);
     bool CreateDenominated(CAmount nBalanceToDenominate, const wallet::CompactTallyItem& tallyItem, bool fCreateMixingCollaterals)
@@ -156,15 +161,27 @@ class CCoinJoinClientSession : public CCoinJoinBaseSession
     bool CreateCollateralTransaction(CMutableTransaction& txCollateral, std::string& strReason)
         EXCLUSIVE_LOCKS_REQUIRED(m_wallet->cs_wallet);
 
-    bool JoinExistingQueue(CAmount nBalanceNeedsAnonymized, CConnman& connman);
+    bool JoinExistingQueue(CAmount nBalanceNeedsAnonymized, CConnman& connman,
+                           int nTargetDenom = 0, bool fPromotion = false, bool fDemotion = false);
     bool StartNewQueue(CAmount nBalanceNeedsAnonymized, CConnman& connman);
+    bool StartNewQueue(CAmount nBalanceNeedsAnonymized, CConnman& connman,
+                       int nTargetDenom, bool fPromotion, bool fDemotion);
 
     /// step 0: select denominated inputs and txouts
     bool SelectDenominate(std::string& strErrorRet, std::vector<CTxDSIn>& vecTxDSInRet);
     /// step 1: prepare denominated inputs and outputs
     bool PrepareDenominate(int nMinRounds, int nMaxRounds, std::string& strErrorRet, const std::vector<CTxDSIn>& vecTxDSIn,
                            std::vector<std::pair<CTxDSIn, CTxOut>>& vecPSInOutPairsRet, bool fDryRun = false)
         EXCLUSIVE_LOCKS_REQUIRED(m_wallet->cs_wallet);
+
+    /// Post-V24: prepare promotion entry (10 inputs of smaller denom -> 1 output of larger denom)
+    bool PreparePromotionEntry(std::string& strErrorRet, std::vector<std::pair<CTxDSIn, CTxOut>>& vecPSInOutPairsRet)
+        EXCLUSIVE_LOCKS_REQUIRED(m_wallet->cs_wallet);
+
+    /// Post-V24: prepare demotion entry (1 input of larger denom -> 10 outputs of smaller denom)
+    bool PrepareDemotionEntry(std::string& strErrorRet, std::vector<std::pair<CTxDSIn, CTxOut>>& vecPSInOutPairsRet)
+        EXCLUSIVE_LOCKS_REQUIRED(m_wallet->cs_wallet);
+
     /// step 2: send denominated inputs and outputs prepared in step 1
     bool SendDenominate(const std::vector<std::pair<CTxDSIn, CTxOut> >& vecPSInOutPairsIn, CConnman& connman) EXCLUSIVE_LOCKS_REQUIRED(!cs_coinjoin);
 
@@ -315,6 +332,22 @@ class CCoinJoinClientManager
         EXCLUSIVE_LOCKS_REQUIRED(!cs_deqsessions);
 
     void GetJsonInfo(UniValue& obj) const EXCLUSIVE_LOCKS_REQUIRED(!cs_deqsessions);
+
+    /**
+     * Post-V24: Check if we should promote smaller denominations into larger ones
+     * @param nSmallerDenom The smaller denomination to promote from
+     * @param nLargerDenom The larger denomination to promote into
+     * @return true if promotion is recommended
+     */
+    bool ShouldPromote(int nSmallerDenom, int nLargerDenom) const;
+
+    /**
+     * Post-V24: Check if we should demote larger denominations into smaller ones
+     * @param nLargerDenom The larger denomination to demote from
+     * @param nSmallerDenom The smaller denomination to demote into
+     * @return true if demotion is recommended
+     */
+    bool ShouldDemote(int nLargerDenom, int nSmallerDenom) const;
 };
 
 #endif // BITCOIN_COINJOIN_CLIENT_H

src/coinjoin/coinjoin.cpp

@@ -6,6 +6,7 @@
 
 #include <chain.h>
 #include <chainparams.h>
+#include <deploymentstatus.h>
 #include <txmempool.h>
 #include <util/moneystr.h>
 #include <util/system.h>
@@ -89,24 +90,47 @@ bool CCoinJoinBroadcastTx::IsExpired(const CBlockIndex* pindex, const llmq::CCha
     return clhandler.HasChainLock(pindex->nHeight, *pindex->phashBlock);
 }
 
-bool CCoinJoinBroadcastTx::IsValidStructure() const
+bool CCoinJoinBroadcastTx::IsValidStructure(const CBlockIndex* pindex) const
 {
     // some trivial checks only
     if (masternodeOutpoint.IsNull() && m_protxHash.IsNull()) {
         return false;
     }
-    if (tx->vin.size() != tx->vout.size()) {
+
+    const bool fV24Active = pindex && DeploymentActiveAt(*pindex, Params().GetConsensus(), Consensus::DEPLOYMENT_V24);
+
+    // Pre-V24: require balanced input/output counts (1:1 mixing only)
+    // Post-V24: allow unbalanced counts (promotion/demotion)
+    if (!fV24Active && tx->vin.size() != tx->vout.size()) {
         return false;
     }
+
     if (tx->vin.size() < size_t(CoinJoin::GetMinPoolParticipants())) {
         return false;
     }
-    if (tx->vin.size() > CoinJoin::GetMaxPoolParticipants() * COINJOIN_ENTRY_MAX_SIZE) {
+
+    // Post-V24: allow up to 200 inputs (20 participants * 10 inputs for promotions)
+    // Pre-V24: max 180 inputs (20 participants * 9 entries)
+    const size_t nMaxInputs = fV24Active
+        ? CoinJoin::GetMaxPoolParticipants() * CoinJoin::PROMOTION_RATIO
+        : CoinJoin::GetMaxPoolParticipants() * COINJOIN_ENTRY_MAX_SIZE;
+
+    if (tx->vin.size() > nMaxInputs) {
         return false;
     }
-    return ranges::all_of(tx->vout, [] (const auto& txOut){
+
+    // All outputs must be valid denominations and P2PKH
+    if (!ranges::all_of(tx->vout, [] (const auto& txOut){
         return CoinJoin::IsDenominatedAmount(txOut.nValue) && txOut.scriptPubKey.IsPayToPublicKeyHash();
-    });
+    })) {
+        return false;
+    }
+
+    // Note: For post-V24 unbalanced transactions (promotion/demotion),
+    // value sum validation (inputs == outputs) requires UTXO access and
+    // is performed in IsValidInOuts() when the transaction is processed.
+
+    return true;
 }
 
 void CCoinJoinBaseSession::SetNull()
@@ -192,17 +216,80 @@ bool CCoinJoinBaseSession::IsValidInOuts(CChainState& active_chainstate, const l
     nMessageIDRet = MSG_NOERR;
     if (fConsumeCollateralRet) *fConsumeCollateralRet = false;
 
-    if (vin.size() != vout.size()) {
+    // Check if V24 is active for promotion/demotion support
+    bool fV24Active{false};
+    {
+        LOCK(::cs_main);
+        const CBlockIndex* pindex = active_chainstate.m_chain.Tip();
+        fV24Active = pindex && DeploymentActiveAt(*pindex, Params().GetConsensus(), Consensus::DEPLOYMENT_V24);
+    }
+
+    // Determine entry type based on input/output counts
+    // Standard: N inputs, N outputs (same denom)
+    // Promotion: PROMOTION_RATIO inputs of session denom, 1 output of larger adjacent denom
+    // Demotion: 1 input of larger adjacent denom, PROMOTION_RATIO outputs of session denom
+    enum class EntryType { STANDARD, PROMOTION, DEMOTION, INVALID };
+    EntryType entryType = EntryType::STANDARD;
+
+    if (vin.size() == vout.size()) {
+        entryType = EntryType::STANDARD;
+    } else if (fV24Active) {
+        if (vin.size() == static_cast<size_t>(CoinJoin::PROMOTION_RATIO) && vout.size() == 1) {
+            entryType = EntryType::PROMOTION;
+        } else if (vin.size() == 1 && vout.size() == static_cast<size_t>(CoinJoin::PROMOTION_RATIO)) {
+            entryType = EntryType::DEMOTION;
+        } else {
+            entryType = EntryType::INVALID;
+        }
+    } else {
+        // Pre-V24: only standard entries allowed
         LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::%s -- ERROR: inputs vs outputs size mismatch! %d vs %d\n", __func__, vin.size(), vout.size());
         nMessageIDRet = ERR_SIZE_MISMATCH;
         if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
         return false;
     }
 
-    auto checkTxOut = [&](const CTxOut& txout) {
-        if (int nDenom = CoinJoin::AmountToDenomination(txout.nValue); nDenom != nSessionDenom) {
-            LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::IsValidInOuts -- ERROR: incompatible denom %d (%s) != nSessionDenom %d (%s)\n",
-                    nDenom, CoinJoin::DenominationToString(nDenom), nSessionDenom, CoinJoin::DenominationToString(nSessionDenom));
+    if (entryType == EntryType::INVALID) {
+        LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::%s -- ERROR: invalid entry structure! %d inputs, %d outputs\n", __func__, vin.size(), vout.size());
+        nMessageIDRet = ERR_SIZE_MISMATCH;
+        if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
+        return false;
+    }
+
+    const int nLargerAdjacentDenom = CoinJoin::GetLargerAdjacentDenom(nSessionDenom);
+
+    // Determine expected denominations based on entry type
+    int nExpectedInputDenom = nSessionDenom;
+    int nExpectedOutputDenom = nSessionDenom;
+
+    if (entryType == EntryType::PROMOTION) {
+        // Promotion: inputs = session denom (smaller), output = larger adjacent
+        nExpectedInputDenom = nSessionDenom;
+        nExpectedOutputDenom = nLargerAdjacentDenom;
+        if (nLargerAdjacentDenom == 0) {
+            LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::%s -- ERROR: no larger adjacent denom for promotion\n", __func__);
+            nMessageIDRet = ERR_DENOM;
+            if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
+            return false;
+        }
+    } else if (entryType == EntryType::DEMOTION) {
+        // Demotion: input = larger adjacent, outputs = session denom (smaller)
+        nExpectedInputDenom = nLargerAdjacentDenom;
+        nExpectedOutputDenom = nSessionDenom;
+        if (nLargerAdjacentDenom == 0) {
+            LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::%s -- ERROR: no larger adjacent denom for demotion\n", __func__);
+            nMessageIDRet = ERR_DENOM;
+            if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
+            return false;
+        }
+    }
+
+    auto checkTxOut = [&](const CTxOut& txout, int nExpectedDenom) {
+        const int nDenom = CoinJoin::AmountToDenomination(txout.nValue);
+
+        if (nDenom != nExpectedDenom) {
+            LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::IsValidInOuts -- ERROR: incompatible denom %d (%s) != expected %d (%s)\n",
+                    nDenom, CoinJoin::DenominationToString(nDenom), nExpectedDenom, CoinJoin::DenominationToString(nExpectedDenom));
             nMessageIDRet = ERR_DENOM;
             if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
             return false;
@@ -213,21 +300,20 @@ bool CCoinJoinBaseSession::IsValidInOuts(CChainState& active_chainstate, const l
             if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
             return false;
         }
+        // Check for duplicate scripts across all inputs and outputs (privacy requirement)
         if (!setScripPubKeys.insert(txout.scriptPubKey).second) {
             LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::IsValidInOuts -- ERROR: already have this script! scriptPubKey=%s\n", ScriptToAsmStr(txout.scriptPubKey));
             nMessageIDRet = ERR_ALREADY_HAVE;
             if (fConsumeCollateralRet) *fConsumeCollateralRet = true;
             return false;
         }
-        // IsPayToPublicKeyHash() above already checks for scriptPubKey size,
-        // no need to double-check, hence no usage of ERR_NON_STANDARD_PUBKEY
         return true;
     };
 
     CAmount nFees{0};
 
     for (const auto& txout : vout) {
-        if (!checkTxOut(txout)) {
+        if (!checkTxOut(txout, nExpectedOutputDenom)) {
             return false;
         }
         nFees -= txout.nValue;
@@ -253,21 +339,26 @@ bool CCoinJoinBaseSession::IsValidInOuts(CChainState& active_chainstate, const l
             return false;
         }
 
-        if (!checkTxOut(coin.out)) {
+        if (!checkTxOut(coin.out, nExpectedInputDenom)) {
             return false;
         }
 
         nFees += coin.out.nValue;
     }
 
-    // The same size and denom for inputs and outputs ensures their total value is also the same,
-    // no need to double-check. If not, we are doing something wrong, bail out.
+    // Value sum must match: inputs == outputs (no fees in CoinJoin)
+    // This holds for standard mixing (same denom) and promotion/demotion (value preserved)
     if (nFees != 0) {
         LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::%s -- ERROR: non-zero fees! fees: %lld\n", __func__, nFees);
         nMessageIDRet = ERR_FEES;
         return false;
     }
 
+    LogPrint(BCLog::COINJOIN, "CCoinJoinBaseSession::%s -- Valid %s entry: %d inputs, %d outputs\n",
+             __func__,
+             entryType == EntryType::PROMOTION ? "PROMOTION" : (entryType == EntryType::DEMOTION ? "DEMOTION" : "STANDARD"),
+             vin.size(), vout.size());
+
     return true;
 }
 
@@ -487,3 +578,96 @@ void CDSTXManager::BlockDisconnected(const std::shared_ptr<const CBlock>& pblock
 
 int CoinJoin::GetMinPoolParticipants() { return Params().PoolMinParticipants(); }
 int CoinJoin::GetMaxPoolParticipants() { return Params().PoolMaxParticipants(); }
+
+bool CoinJoin::ValidatePromotionEntry(const std::vector<CTxIn>& vecTxIn, const std::vector<CTxOut>& vecTxOut,
+                                       int nSessionDenom, PoolMessage& nMessageIDRet)
+{
+    // Promotion: 10 inputs of smaller denom → 1 output of larger denom
+    // Session denom is the smaller denom (inputs)
+    nMessageIDRet = MSG_NOERR;
+
+    // Check input count
+    if (vecTxIn.size() != static_cast<size_t>(PROMOTION_RATIO)) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidatePromotionEntry -- ERROR: wrong input count %zu, expected %d\n",
+                vecTxIn.size(), PROMOTION_RATIO);
+        nMessageIDRet = ERR_SIZE_MISMATCH;
+        return false;
+    }
+
+    // Check output count
+    if (vecTxOut.size() != 1) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidatePromotionEntry -- ERROR: wrong output count %zu, expected 1\n",
+                vecTxOut.size());
+        nMessageIDRet = ERR_SIZE_MISMATCH;
+        return false;
+    }
+
+    // Get the larger adjacent denomination
+    const int nLargerDenom = GetLargerAdjacentDenom(nSessionDenom);
+    if (nLargerDenom == 0) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidatePromotionEntry -- ERROR: no larger adjacent denom for %s\n",
+                DenominationToString(nSessionDenom));
+        nMessageIDRet = ERR_DENOM;
+        return false;
+    }
+
+    // Validate output is at larger denomination
+    const int nOutputDenom = AmountToDenomination(vecTxOut[0].nValue);
+    if (nOutputDenom != nLargerDenom) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidatePromotionEntry -- ERROR: output denom %s != expected %s\n",
+                DenominationToString(nOutputDenom), DenominationToString(nLargerDenom));
+        nMessageIDRet = ERR_DENOM;
+        return false;
+    }
+
+    // Validate output is P2PKH
+    if (!vecTxOut[0].scriptPubKey.IsPayToPublicKeyHash()) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidatePromotionEntry -- ERROR: output is not P2PKH\n");
+        nMessageIDRet = ERR_INVALID_SCRIPT;
+        return false;
+    }
+
+    return true;
+}
+
+bool CoinJoin::ValidateDemotionEntry(const std::vector<CTxIn>& vecTxIn, const std::vector<CTxOut>& vecTxOut,
+                                      int nSessionDenom, PoolMessage& nMessageIDRet)
+{
+    // Demotion: 1 input of larger denom → 10 outputs of smaller denom
+    // Session denom is the smaller denom (outputs)
+    nMessageIDRet = MSG_NOERR;
+
+    // Check input count
+    if (vecTxIn.size() != 1) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidateDemotionEntry -- ERROR: wrong input count %zu, expected 1\n",
+                vecTxIn.size());
+        nMessageIDRet = ERR_SIZE_MISMATCH;
+        return false;
+    }
+
+    // Check output count
+    if (vecTxOut.size() != static_cast<size_t>(PROMOTION_RATIO)) {
+        LogPrint(BCLog::COINJOIN, "CoinJoin::ValidateDemotionEntry -- ERROR: wrong output count %zu, expected %d\n",
+                vecTxOut.size(), PROMOTION_RATIO);
+        nMessageIDRet = ERR_SIZE_MISMATCH;
+        return false;
+    }
+
+    // Validate all outputs are at session denomination and P2PKH
+    for (const auto& txout : vecTxOut) {
+        const int nDenom = AmountToDenomination(txout.nValue);
+        if (nDenom != nSessionDenom) {
+            LogPrint(BCLog::COINJOIN, "CoinJoin::ValidateDemotionEntry -- ERROR: output denom %s != session denom %s\n",
+                    DenominationToString(nDenom), DenominationToString(nSessionDenom));
+            nMessageIDRet = ERR_DENOM;
+            return false;
+        }
+        if (!txout.scriptPubKey.IsPayToPublicKeyHash()) {
+            LogPrint(BCLog::COINJOIN, "CoinJoin::ValidateDemotionEntry -- ERROR: output is not P2PKH\n");
+            nMessageIDRet = ERR_INVALID_SCRIPT;
+            return false;
+        }
+    }
+
+    return true;
+}