Add caching and updating of Sapling note nullifier.

src/wallet/wallet.cpp

@@ -474,8 +474,10 @@ void CWallet::ChainTip(const CBlockIndex *pindex,
 {
     if (added) {
         IncrementNoteWitnesses(pindex, pblock, sproutTree, saplingTree);
+        UpdateSaplingNullifierNoteMapForBlock(pblock);
     } else {
         DecrementNoteWitnesses(pindex);
+        UpdateSaplingNullifierNoteMapForBlock(pblock);
     }
 }
 
@@ -1169,6 +1171,10 @@ bool CWallet::UpdateNullifierNoteMap()
                     }
                 }
             }
+
+            // TODO: Sapling.  This method is only called from RPC walletpassphrase, which is currently unsupported
+            // as RPC encryptwallet is hidden behind two flags: -developerencryptwallet -experimentalfeatures
+
             UpdateNullifierNoteMapWithTx(wtxItem.second);
         }
     }
@@ -1176,7 +1182,8 @@ bool CWallet::UpdateNullifierNoteMap()
 }
 
 /**
- * Update mapSproutNullifiersToNotes with the cached nullifiers in this tx.
+ * Update mapSproutNullifiersToNotes and mapSaplingNullifiersToNotes
+ * with the cached nullifiers in this tx.
  */
 void CWallet::UpdateNullifierNoteMapWithTx(const CWalletTx& wtx)
 {
@@ -1187,6 +1194,71 @@ void CWallet::UpdateNullifierNoteMapWithTx(const CWalletTx& wtx)
                 mapSproutNullifiersToNotes[*item.second.nullifier] = item.first;
             }
         }
+
+        for (const mapSaplingNoteData_t::value_type& item : wtx.mapSaplingNoteData) {
+            if (item.second.nullifier) {
+                mapSaplingNullifiersToNotes[*item.second.nullifier] = item.first;
+            }
+        }
+    }
+}
+
+/**
+ * Update mapSaplingNullifiersToNotes, computing the nullifier from a cached witness if necessary.
+ */
+void CWallet::UpdateSaplingNullifierNoteMapWithTx(CWalletTx& wtx) {
+    LOCK(cs_wallet);
+
+    for (mapSaplingNoteData_t::value_type &item : wtx.mapSaplingNoteData) {
+        SaplingOutPoint op = item.first;
+        SaplingNoteData nd = item.second;
+
+        if (nd.witnesses.size() == 0) {
+            // If there are no witnesses, erase the nullifier and associated mapping.
+            if (item.second.nullifier) {
+                mapSaplingNullifiersToNotes.erase(item.second.nullifier.get());
+            }
+            item.second.nullifier = boost::none;
+        }
+        else if (nd.witnesses.size() > 0) {
+            uint64_t position = nd.witnesses.front().position();
+            SaplingFullViewingKey fvk = mapSaplingFullViewingKeys.at(nd.ivk);
+            OutputDescription output = wtx.vShieldedOutput[op.n];
+            auto optPlaintext = SaplingNotePlaintext::decrypt(output.encCiphertext, nd.ivk, output.ephemeralKey, output.cm);
+            if (!optPlaintext) {
+                // An item in mapSaplingNoteData must have already been successfully decrypted,
+                // otherwise the item would not exist in the first place.
+                assert(false);
+            }
+            auto optNote = optPlaintext.get().note(nd.ivk);
+            if (!optNote) {
+                assert(false);
+            }
+            auto optNullifier = optNote.get().nullifier(fvk, position);
+            if (!optNullifier) {
+                // This should not happen.  If it does, maybe the position has been corrupted or miscalculated?
+                assert(false);
+            }
+            uint256 nullifier = optNullifier.get();
+            mapSaplingNullifiersToNotes[nullifier] = op;
+            item.second.nullifier = nullifier;
+        }
+    }
+}
+
+/**
+ * Iterate over transactions in a block and update the cached Sapling nullifiers
+ * for transactions which belong to the wallet.
+ */
+void CWallet::UpdateSaplingNullifierNoteMapForBlock(const CBlock *pblock) {
+    LOCK(cs_wallet);
+
+    for (const CTransaction& tx : pblock->vtx) {
+        auto hash = tx.GetHash();
+        bool txIsOurs = mapWallet.count(hash);
+        if (txIsOurs) {
+            UpdateSaplingNullifierNoteMapWithTx(mapWallet[hash]);
+        }
     }
 }