wallet: Alter `OrchardWallet::GetSpendInfo` to return the spending key

In the context of `z_sendmany`, we will need both the spending key and
note spendInfo as a pair, so it makes sense to fetch those together.

src/rust/include/rust/orchard/wallet.h

@@ -189,6 +189,17 @@ bool orchard_wallet_add_raw_address(
         const OrchardRawAddressPtr* addr,
         const OrchardIncomingViewingKeyPtr* ivk);
 
+/**
+ * Returns a pointer to the Orchard spending key corresponding to the specified raw
+ * address, if it is known to the wallet, or `nullptr` otherwise.
+ *
+ * Memory is allocated by Rust and must be manually freed using
+ * `orchard_spending_key_free`.
+ */
+OrchardSpendingKeyPtr* orchard_wallet_get_spending_key_for_address(
+        const OrchardWalletPtr* wallet,
+        const OrchardRawAddressPtr* addr);
+
 /**
  * Returns a pointer to the Orchard incoming viewing key corresponding to the specified
  * raw address, if it is known to the wallet, or `nullptr` otherwise.

src/rust/src/wallet.rs

@@ -805,6 +805,22 @@ pub extern "C" fn orchard_wallet_add_raw_address(
     wallet.key_store.add_raw_address(*addr, ivk.clone())
 }
 
+#[no_mangle]
+pub extern "C" fn orchard_wallet_get_spending_key_for_address(
+    wallet: *const Wallet,
+    addr: *const Address,
+) -> *mut SpendingKey {
+    let wallet = unsafe { wallet.as_ref() }.expect("Wallet pointer may not be null.");
+    let addr = unsafe { addr.as_ref() }.expect("Address may not be null.");
+
+    wallet
+        .key_store
+        .ivk_for_address(addr)
+        .and_then(|ivk| wallet.key_store.spending_key_for_ivk(ivk))
+        .map(|sk| Box::into_raw(Box::new(*sk)))
+        .unwrap_or(std::ptr::null_mut())
+}
+
 #[no_mangle]
 pub extern "C" fn orchard_wallet_get_ivk_for_address(
     wallet: *const Wallet,

src/wallet/gtest/test_orchard_wallet.cpp

@@ -120,7 +120,7 @@ TEST(TransactionBuilder, OrchardToOrchard) {
 
     // Now we can get spend info for the note.
     auto spendInfo = wallet.GetSpendInfo(notes);
-    EXPECT_EQ(spendInfo[0].Value(), 40000);
+    EXPECT_EQ(spendInfo[0].second.Value(), 40000);
 
     // Get the root of the commitment tree.
     OrchardMerkleFrontier tree;
@@ -130,7 +130,7 @@ TEST(TransactionBuilder, OrchardToOrchard) {
     // Create an Orchard-only transaction
     // 0.0004 z-ZEC in, 0.00025 z-ZEC out, default fee, 0.00005 z-ZEC change
     auto builder = TransactionBuilder(consensusParams, 2, orchardAnchor);
-    EXPECT_TRUE(builder.AddOrchardSpend(sk, std::move(spendInfo[0])));
+    EXPECT_TRUE(builder.AddOrchardSpend(sk, std::move(spendInfo[0].second)));
     builder.AddOrchardOutput(std::nullopt, recipient, 25000, std::nullopt);
     auto maybeTx = builder.Build();
     EXPECT_TRUE(maybeTx.IsTx());

src/wallet/orchard.cpp

@@ -4,10 +4,18 @@
 
 #include "wallet/orchard.h"
 
-std::vector<orchard::SpendInfo> OrchardWallet::GetSpendInfo(
+std::optional<libzcash::OrchardSpendingKey> OrchardWallet::GetSpendingKeyForAddress(
+    const libzcash::OrchardRawAddress& addr) const
+{
+    auto skPtr = orchard_wallet_get_spending_key_for_address(inner.get(), addr.inner.get());
+    if (skPtr == nullptr) return std::nullopt;
+    return libzcash::OrchardSpendingKey(skPtr);
+}
+
+std::vector<std::pair<libzcash::OrchardSpendingKey, orchard::SpendInfo>> OrchardWallet::GetSpendInfo(
     const std::vector<OrchardNoteMetadata>& noteMetadata) const
 {
-    std::vector<orchard::SpendInfo> result;
+    std::vector<std::pair<libzcash::OrchardSpendingKey, orchard::SpendInfo>> result;
     for (const auto& note : noteMetadata) {
         auto pSpendInfo = orchard_wallet_get_spend_info(
             inner.get(),
@@ -21,7 +29,12 @@ std::vector<orchard::SpendInfo> OrchardWallet::GetSpendInfo(
                 note.GetAddress(),
                 note.GetNoteValue());
 
-            result.push_back(std::move(spendInfo));
+            auto sk = GetSpendingKeyForAddress(note.GetAddress());
+            if (sk.has_value()) {
+                result.push_back(std::pair(std::move(sk.value()), std::move(spendInfo)));
+            } else {
+                throw std::logic_error("Unknown spending key for given outpoint");
+            }
         }
     }
     return result;

src/wallet/orchard.h

@@ -204,6 +204,9 @@ public:
         orchard_wallet_add_full_viewing_key(inner.get(), fvk.inner.get());
     }
 
+    std::optional<libzcash::OrchardSpendingKey> GetSpendingKeyForAddress(
+            const libzcash::OrchardRawAddress& addr) const;
+
     std::optional<libzcash::OrchardIncomingViewingKey> GetIncomingViewingKeyForAddress(
             const libzcash::OrchardRawAddress& addr) const {
         auto ivkPtr = orchard_wallet_get_ivk_for_address(inner.get(), addr.inner.get());
@@ -271,7 +274,7 @@ public:
         return result;
     }
 
-    std::vector<orchard::SpendInfo> GetSpendInfo(
+    std::vector<std::pair<libzcash::OrchardSpendingKey, orchard::SpendInfo>> GetSpendInfo(
         const std::vector<OrchardNoteMetadata>& noteMetadata) const;
 };
 

src/wallet/wallet.cpp

@@ -3237,7 +3237,7 @@ void CWallet::GetSaplingNoteWitnesses(const std::vector<SaplingOutPoint>& notes,
     }
 }
 
-std::vector<orchard::SpendInfo> CWallet::GetOrchardSpendInfo(
+std::vector<std::pair<libzcash::OrchardSpendingKey, orchard::SpendInfo>> CWallet::GetOrchardSpendInfo(
     const std::vector<OrchardNoteMetadata>& orchardNoteMetadata) const
 {
     AssertLockHeld(cs_wallet);

src/wallet/wallet.h

@@ -1690,7 +1690,7 @@ public:
          const std::vector<SaplingOutPoint>& notes,
          std::vector<std::optional<SaplingWitness>>& witnesses,
          uint256 &final_anchor);
-    std::vector<orchard::SpendInfo> GetOrchardSpendInfo(
+    std::vector<std::pair<libzcash::OrchardSpendingKey, orchard::SpendInfo>> GetOrchardSpendInfo(
         const std::vector<OrchardNoteMetadata>& orchardNoteMetadata) const;
 
     isminetype IsMine(const CTxIn& txin) const;