From d95da694b90bf0599f8054b8a591b91c33617ded Mon Sep 17 00:00:00 2001
From: Duke <duke@hush.is>
Date: Fri, 8 Aug 2025 14:53:21 -0400
Subject: [PATCH] WIP donation via z_shieldcoinbase

---
 .../asyncrpcoperation_shieldcoinbase.cpp      | 65 ++++++++++---------
 src/wallet/asyncrpcoperation_shieldcoinbase.h |  9 +--
 2 files changed, 37 insertions(+), 37 deletions(-)

diff --git a/src/wallet/asyncrpcoperation_shieldcoinbase.cpp b/src/wallet/asyncrpcoperation_shieldcoinbase.cpp
index 57113f930..ce4da86fe 100644
--- a/src/wallet/asyncrpcoperation_shieldcoinbase.cpp
+++ b/src/wallet/asyncrpcoperation_shieldcoinbase.cpp
@@ -161,24 +161,7 @@ void AsyncRPCOperation_shieldcoinbase::main() {
 bool AsyncRPCOperation_shieldcoinbase::main_impl() {
 
     CAmount minersFee = fee_;
-
-    size_t numInputs = inputs_.size();
-
-    /*
-    // Check mempooltxinputlimit to avoid creating a transaction which the local mempool rejects
-    size_t limit = (size_t)GetArg("-mempooltxinputlimit", 0);
-    {
-        LOCK(cs_main);
-        if (NetworkUpgradeActive(chainActive.Height() + 1, Params().GetConsensus(), Consensus::UPGRADE_OVERWINTER)) {
-            limit = 0;
-        }
-    }
-    if (limit>0 && numInputs > limit) {
-        throw JSONRPCError(RPC_WALLET_ERROR,
-            strprintf("Number of inputs %d is greater than mempooltxinputlimit of %d",
-            numInputs, limit));
-    }
-    */
+    size_t numInputs  = inputs_.size();
 
     CAmount targetAmount = 0;
     for (ShieldCoinbaseUTXO & utxo : inputs_) {
@@ -192,10 +175,12 @@ bool AsyncRPCOperation_shieldcoinbase::main_impl() {
     }
 
     CAmount sendAmount = targetAmount - minersFee;
-    LogPrint("zrpc", "%s: spending %s to shield %s with fee %s\n",
+    LogPrint("zrpc", "%s: spending %s to shield %s with fee %s, donation=%d\n",
             getId(), FormatMoney(targetAmount), FormatMoney(sendAmount), FormatMoney(minersFee));
 
-    return boost::apply_visitor(ShieldToAddress(this, sendAmount), tozaddr_);
+    //TODO: pass this in from RPC
+    CAmount donation = 2;
+    return boost::apply_visitor(ShieldToAddress(this, sendAmount, donation), tozaddr_);
 }
 
 extern UniValue signrawtransaction(const UniValue& params, bool fHelp, const CPubKey& mypk);
@@ -229,19 +214,37 @@ bool ShieldToAddress::operator()(const libzcash::SaplingPaymentAddress &zaddr) c
         }
     }
 
+    //TODO: if donation==true, send X% of value to zaddr and Y% of of value to donatezaddr
     // Send all value to the target z-addr
-    m_op->builder_.SendChangeTo(zaddr, ovk);
+    if(donation) {
+        // add original recipient as first output
+        m_op->builder_.AddSaplingOutput(ovk, zaddr, sendAmount);
+
+        CAmount donationAmount = 0; //TODO calculate exact donation amount in puposhis
+        // donation recipient as second output
+        m_op->builder_.AddSaplingOutput(ovk, donationZaddr, donationAmount);
+    
+        // zdust as third output, so donation txs are indistinguishable from
+        // non-donation z_shieldcoinbase txs
+        auto zdust1        = DecodePaymentAddress(randomSietchZaddr());
+        auto sietchZout1   = boost::get<libzcash::SaplingPaymentAddress>(zdust1);
+        m_op->builder_.AddSaplingOutput(ovk, sietchZout1, 0);
+
+    } else {
+        m_op->builder_.SendChangeTo(zaddr, ovk);
+
+        // Sietchified Shielding of Coinbase Funds
+        // Add Sietch zouts so it's unclear which zout contains value :)
+        // This reduces metadata leakage of coinbase t=>z tx's
+        CAmount amount     = 0;
+        auto zdust1        = DecodePaymentAddress(randomSietchZaddr());
+        auto zdust2        = DecodePaymentAddress(randomSietchZaddr());
+        auto sietchZout1   = boost::get<libzcash::SaplingPaymentAddress>(zdust1);
+        auto sietchZout2   = boost::get<libzcash::SaplingPaymentAddress>(zdust2);
+        m_op->builder_.AddSaplingOutput(ovk, sietchZout1, amount);
+        m_op->builder_.AddSaplingOutput(ovk, sietchZout2, amount);
+    }
 
-    // Sietchified Shielding of Coinbase Funds
-    // Add Sietch zouts so it's unclear which zout contains value :)
-    // This reduces metadata leakage of coinbase t=>z tx's
-    CAmount amount     = 0;
-    auto zdust1        = DecodePaymentAddress(randomSietchZaddr());
-    auto zdust2        = DecodePaymentAddress(randomSietchZaddr());
-    auto sietchZout1   = boost::get<libzcash::SaplingPaymentAddress>(zdust1);
-    auto sietchZout2   = boost::get<libzcash::SaplingPaymentAddress>(zdust2);
-    m_op->builder_.AddSaplingOutput(ovk, sietchZout1, amount);
-    m_op->builder_.AddSaplingOutput(ovk, sietchZout2, amount);
 
     // Build the transaction
     auto maybe_tx = m_op->builder_.Build();
diff --git a/src/wallet/asyncrpcoperation_shieldcoinbase.h b/src/wallet/asyncrpcoperation_shieldcoinbase.h
index bd606e23e..7a018e0d7 100644
--- a/src/wallet/asyncrpcoperation_shieldcoinbase.h
+++ b/src/wallet/asyncrpcoperation_shieldcoinbase.h
@@ -63,7 +63,6 @@ public:
     virtual UniValue getStatus() const;
 
     bool testmode = false;  // Set to true to disable sending txs and generating proofs
-    bool cheatSpend = false; // set when this is shielding a cheating coinbase
 
 private:
     friend class ShieldToAddress;
@@ -96,15 +95,15 @@ class ShieldToAddress : public boost::static_visitor<bool>
 private:
     AsyncRPCOperation_shieldcoinbase *m_op;
     CAmount sendAmount;
+    CAmount donation = 0;
 public:
-    ShieldToAddress(AsyncRPCOperation_shieldcoinbase *op, CAmount sendAmount) :
-        m_op(op), sendAmount(sendAmount) {}
+    ShieldToAddress(AsyncRPCOperation_shieldcoinbase *op, CAmount sendAmount, bool donation) :
+        m_op(op), sendAmount(sendAmount), donation(donation) {}
 
     bool operator()(const libzcash::SaplingPaymentAddress &zaddr) const;
     bool operator()(const libzcash::InvalidEncoding& no) const;
 };
 
-
 // To test private methods, a friend class can act as a proxy
 class TEST_FRIEND_AsyncRPCOperation_shieldcoinbase {
 public:
@@ -135,6 +134,4 @@ public:
     }
 };
 
-
 #endif /* ASYNCRPCOPERATION_SHIELDCOINBASE_H */
-