Return optional for Sapling commitments and nullifiers.

Unlike Sprout, they are not always computable in Sapling.

src/gtest/test_sapling_note.cpp

@@ -45,7 +45,7 @@ TEST(SaplingNote, TestVectors)
 
     // Test commitment
     SaplingNote note = SaplingNote(diversifier, pk_d, v, r);
-    ASSERT_EQ(note.cm(), cm);
+    ASSERT_EQ(note.cm().get(), cm);
 
     // Test nullifier
     SaplingSpendingKey spendingKey(sk);

src/zcash/Note.cpp

@@ -9,7 +9,7 @@
 #include "zcash/util.h"
 #include "librustzcash.h"
 
-namespace libzcash {
+using namespace libzcash;
 
 SproutNote::SproutNote() {
     a_pk = random_uint256();
@@ -48,7 +48,7 @@ SaplingNote::SaplingNote(const SaplingPaymentAddress& address, const uint64_t va
 }
 
 // Call librustzcash to compute the commitment
-uint256 SaplingNote::cm() const {
+boost::optional<uint256> SaplingNote::cm() const {
     uint256 result;
     if (!librustzcash_sapling_compute_cm(
             d.data(),
@@ -58,14 +58,14 @@ uint256 SaplingNote::cm() const {
             result.begin()
         ))
     {
-        throw std::runtime_error("librustzcash_sapling_compute_cm returned false");
+        return boost::none;
     }
 
     return result;
 }
 
 // Call librustzcash to compute the nullifier
-uint256 SaplingNote::nullifier(const SaplingSpendingKey& sk, const uint64_t position) const
+boost::optional<uint256> SaplingNote::nullifier(const SaplingSpendingKey& sk, const uint64_t position) const
 {
     auto vk = sk.full_viewing_key();
     auto ak = vk.ak;
@@ -83,7 +83,7 @@ uint256 SaplingNote::nullifier(const SaplingSpendingKey& sk, const uint64_t posi
             result.begin()
     ))
     {
-        throw std::runtime_error("librustzcash_sapling_compute_nf returned false");
+        return boost::none;
     }
 
     return result;
@@ -137,5 +137,3 @@ ZCNoteEncryption::Ciphertext SproutNotePlaintext::encrypt(ZCNoteEncryption& encr
 
     return encryptor.encrypt(pk_enc, pt);
 }
-
-}

src/zcash/Note.hpp

@@ -7,6 +7,7 @@
 #include "NoteEncryption.hpp"
 
 #include <array>
+#include <boost/optional.hpp>
 
 namespace libzcash {
 
@@ -18,7 +19,6 @@ public:
     BaseNote(uint64_t value) : value_(value) {};
     virtual ~BaseNote() {};
 
-    virtual uint256 cm() const = 0;
     inline uint64_t value() const { return value_; };
 };
 
@@ -35,7 +35,7 @@ public:
 
     virtual ~SproutNote() {};
 
-    virtual uint256 cm() const override;
+    uint256 cm() const;
 
     uint256 nullifier(const SproutSpendingKey& a_sk) const;
 };
@@ -56,9 +56,8 @@ public:
 
     virtual ~SaplingNote() {};
 
-    virtual uint256 cm() const override;
-
-    uint256 nullifier(const SaplingSpendingKey &sk, const uint64_t position) const;
+    boost::optional<uint256> cm() const;
+    boost::optional<uint256> nullifier(const SaplingSpendingKey &sk, const uint64_t position) const;
 };
 
 class BaseNotePlaintext {