Auto merge of #4812 - str4d:shielded-reqs-reject-reasons, r=str4d

Improve reject reasons for unmet shielded requirements

These reject messages end up bubbling up to users via the RPC interface.
Distinguishing between the various failure cases will help users figure
out why their transaction is being rejected.

Closes zcash/zcash#3114.

src/coins.cpp

@@ -11,6 +11,8 @@
 
 #include <assert.h>
 
+#include <tracing.h>
+
 /**
  * calculate number of bytes for the bitmask, and its number of non-zero bytes
  * each bit in the bitmask represents the availability of one output, but the
@@ -914,7 +916,7 @@ CAmount CCoinsViewCache::GetValueIn(const CTransaction& tx) const
     return nResult;
 }
 
-bool CCoinsViewCache::HaveShieldedRequirements(const CTransaction& tx) const
+std::optional<UnsatisfiedShieldedReq> CCoinsViewCache::HaveShieldedRequirements(const CTransaction& tx) const
 {
     boost::unordered_map<uint256, SproutMerkleTree, CCoinsKeyHasher> intermediates;
 
@@ -925,7 +927,12 @@ bool CCoinsViewCache::HaveShieldedRequirements(const CTransaction& tx) const
             if (GetNullifier(nullifier, SPROUT)) {
                 // If the nullifier is set, this transaction
                 // double-spends!
-                return false;
+                auto txid = tx.GetHash().ToString();
+                auto nf = nullifier.ToString();
+                TracingWarn("consensus", "Sprout double-spend detected",
+                    "txid", txid.c_str(),
+                    "nf", nf.c_str());
+                return UnsatisfiedShieldedReq::SproutDuplicateNullifier;
             }
         }
 
@@ -934,7 +941,12 @@ bool CCoinsViewCache::HaveShieldedRequirements(const CTransaction& tx) const
         if (it != intermediates.end()) {
             tree = it->second;
         } else if (!GetSproutAnchorAt(joinsplit.anchor, tree)) {
-            return false;
+            auto txid = tx.GetHash().ToString();
+            auto anchor = joinsplit.anchor.ToString();
+            TracingWarn("consensus", "Transaction uses unknown Sprout anchor",
+                "txid", txid.c_str(),
+                "anchor", anchor.c_str());
+            return UnsatisfiedShieldedReq::SproutUnknownAnchor;
         }
 
         BOOST_FOREACH(const uint256& commitment, joinsplit.commitments)
@@ -946,16 +958,27 @@ bool CCoinsViewCache::HaveShieldedRequirements(const CTransaction& tx) const
     }
 
     for (const SpendDescription &spendDescription : tx.vShieldedSpend) {
-        if (GetNullifier(spendDescription.nullifier, SAPLING)) // Prevent double spends
+        if (GetNullifier(spendDescription.nullifier, SAPLING)) { // Prevent double spends
-            return false;
+            auto txid = tx.GetHash().ToString();
+            auto nf = spendDescription.nullifier.ToString();
+            TracingWarn("consensus", "Sapling double-spend detected",
+                "txid", txid.c_str(),
+                "nf", nf.c_str());
+            return UnsatisfiedShieldedReq::SaplingDuplicateNullifier;
+        }
 
         SaplingMerkleTree tree;
         if (!GetSaplingAnchorAt(spendDescription.anchor, tree)) {
-            return false;
+            auto txid = tx.GetHash().ToString();
+            auto anchor = spendDescription.anchor.ToString();
+            TracingWarn("consensus", "Transaction uses unknown Sapling anchor",
+                "txid", txid.c_str(),
+                "anchor", anchor.c_str());
+            return UnsatisfiedShieldedReq::SaplingUnknownAnchor;
         }
     }
 
-    return true;
+    return std::nullopt;
 }
 
 bool CCoinsViewCache::HaveInputs(const CTransaction& tx) const

src/coins.h

@@ -447,6 +447,14 @@ public:
     friend class CCoinsViewCache;
 };
 
+/** The set of shielded requirements that might be unsatisfied. */
+enum class UnsatisfiedShieldedReq {
+    SproutDuplicateNullifier,
+    SproutUnknownAnchor,
+    SaplingDuplicateNullifier,
+    SaplingUnknownAnchor,
+};
+
 /** CCoinsView that adds a memory cache for transactions to another CCoinsView */
 class CCoinsViewCache : public CCoinsViewBacked
 {
@@ -566,7 +574,7 @@ public:
     bool HaveInputs(const CTransaction& tx) const;
 
     //! Check whether all joinsplit and sapling spend requirements (anchors/nullifiers) are satisfied
-    bool HaveShieldedRequirements(const CTransaction& tx) const;
+    std::optional<UnsatisfiedShieldedReq> HaveShieldedRequirements(const CTransaction& tx) const;
 
     //! Return priority of tx at height nHeight
     double GetPriority(const CTransaction &tx, int nHeight) const;

src/main.cpp

@@ -115,6 +115,28 @@ const string strMessageMagic = "Zcash Signed Message:\n";
 // Internal stuff
 namespace {
 
+    unsigned char ShieldedReqRejectCode(UnsatisfiedShieldedReq shieldedReq)
+    {
+        switch (shieldedReq) {
+            case UnsatisfiedShieldedReq::SproutDuplicateNullifier:
+            case UnsatisfiedShieldedReq::SaplingDuplicateNullifier:
+                return REJECT_DUPLICATE;
+            case UnsatisfiedShieldedReq::SproutUnknownAnchor:
+            case UnsatisfiedShieldedReq::SaplingUnknownAnchor:
+                return REJECT_INVALID;
+        }
+    }
+
+    std::string ShieldedReqRejectReason(UnsatisfiedShieldedReq shieldedReq)
+    {
+        switch (shieldedReq) {
+            case UnsatisfiedShieldedReq::SproutDuplicateNullifier:  return "bad-txns-sprout-duplicate-nullifier";
+            case UnsatisfiedShieldedReq::SproutUnknownAnchor:       return "bad-txns-sprout-unknown-anchor";
+            case UnsatisfiedShieldedReq::SaplingDuplicateNullifier: return "bad-txns-sapling-duplicate-nullifier";
+            case UnsatisfiedShieldedReq::SaplingUnknownAnchor:      return "bad-txns-sapling-unknown-anchor";
+        }
+    }
+
     /** Abort with a message */
     bool AbortNode(const std::string& strMessage, const std::string& userMessage="")
     {
@@ -1540,10 +1562,18 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
             return state.Invalid(error("AcceptToMemoryPool: inputs already spent"),
                                  REJECT_DUPLICATE, "bad-txns-inputs-spent");
 
-        // are the joinsplits' and sapling spends' requirements met in tx(valid anchors/nullifiers)?
+        // Are the shielded spends' requirements met?
-        if (!view.HaveShieldedRequirements(tx))
+        auto unmetShieldedReq = view.HaveShieldedRequirements(tx);
-            return state.Invalid(error("AcceptToMemoryPool: shielded requirements not met"),
+        if (unmetShieldedReq) {
-                                 REJECT_DUPLICATE, "bad-txns-shielded-requirements-not-met");
+            auto txid = tx.GetHash().ToString();
+            auto rejectCode = ShieldedReqRejectCode(*unmetShieldedReq);
+            auto rejectReason = ShieldedReqRejectReason(*unmetShieldedReq);
+            TracingError(
+                "main", "AcceptToMemoryPool(): shielded requirements not met",
+                "txid", txid.c_str(),
+                "reason", rejectReason.c_str());
+            return state.Invalid(false, rejectCode, rejectReason);
+        }
 
         // Bring the best block into scope
         view.GetBestBlock();
@@ -2174,9 +2204,18 @@ bool CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoins
         if (!inputs.HaveInputs(tx))
             return state.Invalid(error("CheckInputs(): %s inputs unavailable", tx.GetHash().ToString()));
 
-        // are the JoinSplit's requirements met?
+        // Are the shielded spends' requirements met?
-        if (!inputs.HaveShieldedRequirements(tx))
+        auto unmetShieldedReq = inputs.HaveShieldedRequirements(tx);
-            return state.Invalid(error("CheckInputs(): %s JoinSplit requirements not met", tx.GetHash().ToString()));
+        if (unmetShieldedReq) {
+            auto txid = tx.GetHash().ToString();
+            auto rejectCode = ShieldedReqRejectCode(*unmetShieldedReq);
+            auto rejectReason = ShieldedReqRejectReason(*unmetShieldedReq);
+            TracingError(
+                "main", "CheckInputs(): shielded requirements not met",
+                "txid", txid.c_str(),
+                "reason", rejectReason.c_str());
+            return state.Invalid(false, rejectCode, rejectReason);
+        }
 
         CAmount nValueIn = 0;
         CAmount nFees = 0;
@@ -2859,10 +2898,18 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
                 return state.DoS(100, error("ConnectBlock(): inputs missing/spent"),
                                  REJECT_INVALID, "bad-txns-inputs-missingorspent");
 
-            // are the JoinSplit's requirements met?
+            // Are the shielded spends' requirements met?
-            if (!view.HaveShieldedRequirements(tx))
+            auto unmetShieldedReq = view.HaveShieldedRequirements(tx);
-                return state.DoS(100, error("ConnectBlock(): JoinSplit requirements not met"),
+            if (unmetShieldedReq) {
-                                 REJECT_INVALID, "bad-txns-joinsplit-requirements-not-met");
+                auto txid = tx.GetHash().ToString();
+                auto rejectCode = ShieldedReqRejectCode(*unmetShieldedReq);
+                auto rejectReason = ShieldedReqRejectReason(*unmetShieldedReq);
+                TracingError(
+                    "main", "ConnectBlock(): shielded requirements not met",
+                    "txid", txid.c_str(),
+                    "reason", rejectReason.c_str());
+                return state.DoS(100, false, rejectCode, rejectReason);
+            }
 
             // insightexplorer
             // https://github.com/bitpay/bitcoin/commit/017f548ea6d89423ef568117447e61dd5707ec42#diff-7ec3c68a81efff79b6ca22ac1f1eabbaR2597

src/test/coins_tests.cpp

@@ -644,7 +644,7 @@ BOOST_AUTO_TEST_CASE(chained_joinsplits)
         CMutableTransaction mtx;
         mtx.vJoinSplit.push_back(js2);
 
-        BOOST_CHECK(!cache.HaveShieldedRequirements(mtx));
+        BOOST_CHECK(cache.HaveShieldedRequirements(mtx) == std::optional(UnsatisfiedShieldedReq::SproutUnknownAnchor));
     }
 
     {
@@ -654,7 +654,7 @@ BOOST_AUTO_TEST_CASE(chained_joinsplits)
         mtx.vJoinSplit.push_back(js2);
         mtx.vJoinSplit.push_back(js1);
 
-        BOOST_CHECK(!cache.HaveShieldedRequirements(mtx));
+        BOOST_CHECK(cache.HaveShieldedRequirements(mtx) == std::optional(UnsatisfiedShieldedReq::SproutUnknownAnchor));
     }
 
     {
@@ -662,7 +662,7 @@ BOOST_AUTO_TEST_CASE(chained_joinsplits)
         mtx.vJoinSplit.push_back(js1);
         mtx.vJoinSplit.push_back(js2);
 
-        BOOST_CHECK(cache.HaveShieldedRequirements(mtx));
+        BOOST_CHECK(cache.HaveShieldedRequirements(mtx) == std::nullopt);
     }
 
     {
@@ -671,7 +671,7 @@ BOOST_AUTO_TEST_CASE(chained_joinsplits)
         mtx.vJoinSplit.push_back(js2);
         mtx.vJoinSplit.push_back(js3);
 
-        BOOST_CHECK(cache.HaveShieldedRequirements(mtx));
+        BOOST_CHECK(cache.HaveShieldedRequirements(mtx) == std::nullopt);
     }
 
     {
@@ -681,7 +681,7 @@ BOOST_AUTO_TEST_CASE(chained_joinsplits)
         mtx.vJoinSplit.push_back(js2);
         mtx.vJoinSplit.push_back(js3);
 
-        BOOST_CHECK(cache.HaveShieldedRequirements(mtx));
+        BOOST_CHECK(cache.HaveShieldedRequirements(mtx) == std::nullopt);
     }
 }