Expose less information about Sapling outputs to change calculation.

zcash_client_backend/src/fees.rs

@@ -82,7 +82,7 @@ pub trait ChangeStrategy {
         transparent_inputs: &[impl TransparentInput],
         transparent_outputs: &[TxOut],
         sapling_inputs: &[impl SaplingInput],
-        sapling_outputs: &[SaplingOutput],
+        sapling_outputs: &[impl SaplingOutput],
     ) -> Result<TransactionBalance, ChangeError<Self::Error>>;
 }
 
@@ -115,7 +115,7 @@ impl ChangeStrategy for BasicFixedFeeChangeStrategy {
         transparent_inputs: &[impl TransparentInput],
         transparent_outputs: &[TxOut],
         sapling_inputs: &[impl SaplingInput],
-        sapling_outputs: &[SaplingOutput],
+        sapling_outputs: &[impl SaplingOutput],
     ) -> Result<TransactionBalance, ChangeError<Self::Error>> {
         let overflow = || ChangeError::StrategyError(BalanceError::Overflow);
         let underflow = || ChangeError::StrategyError(BalanceError::Underflow);

zcash_primitives/CHANGELOG.md

@@ -21,15 +21,15 @@ and this library adheres to Rust's notion of
     - `Builder::sapling_inputs()`
     - `Builder::sapling_outputs()`
 - `zcash_primitives::transaction::fees` a new module containing abstractions
-  and types related to fee calculations. 
+  and types related to fee calculations.
   - `FeeRule` a trait that describes how to compute the fee required for a
     transaction given inputs and outputs to the transaction.
 - Added to `zcash_primitives::transaction::components::sapling::builder`
   - `SaplingInput` a trait that provides a minimized view of a Sapling input suitable
-    for use in fee computation.
-  - The `SaplingOutput` type has been made public, so that it can now be used in fee
-    computation.
-  - `SaplingBuilder::inputs` and `SaplingBuilder::outputs`: accessors for Sapling 
+    for use in change and fee computation.
+  - `SaplingOutput` a trait that provides a minimized view of a Sapling output suitable
+    for use in change and fee computation.
+  - `SaplingBuilder::inputs` and `SaplingBuilder::outputs`: accessors for Sapling
     builder state.
 - Added to `zcash_primitives::transaction::components::transparent::builder`
   - `TransparentInput` a trait that provides a minimized view of a transparent input suitable
@@ -74,9 +74,9 @@ and this library adheres to Rust's notion of
   - `ChainCode::as_bytes`
   - `DiversifierIndex::{as_bytes}`
   - Implementations of `From<u32>` and `From<u64>` for `DiversifierIndex`
-- `zcash_primitives::zip32::sapling` has been added and now contains 
+- `zcash_primitives::zip32::sapling` has been added and now contains
   all of the Sapling zip32 key types that were previously located in
-  `zcash_primitives::zip32` directly. The base `zip32` module reexports 
+  `zcash_primitives::zip32` directly. The base `zip32` module reexports
   the moved types for backwards compatibility.
   - `DiversifierKey::{from_bytes, as_bytes}`
   - `ExtendedSpendingKey::{from_bytes, to_bytes}`

zcash_primitives/src/transaction/builder.rs

@@ -177,7 +177,7 @@ impl<'a, P, R> Builder<'a, P, R> {
 
     /// Returns the set of Sapling outputs currently set to be produced by
     /// the transaction.
-    pub fn sapling_outputs(&self) -> &[SaplingOutput] {
+    pub fn sapling_outputs(&self) -> &[impl SaplingOutput] {
         self.sapling_builder.outputs()
     }
 }

zcash_primitives/src/transaction/components/sapling/builder.rs

@@ -67,6 +67,13 @@ pub trait SaplingInput {
     fn value(&self) -> Amount;
 }
 
+/// A trait that provides a minimized view of a Sapling output suitable for use in
+/// fee and change calculation.
+pub trait SaplingOutput {
+    /// The value of the output being produced.
+    fn value(&self) -> Amount;
+}
+
 #[derive(Debug, Clone)]
 pub struct SpendDescriptionInfo {
     extsk: ExtendedSpendingKey,
@@ -87,7 +94,7 @@ impl SaplingInput for SpendDescriptionInfo {
 /// A struct containing the information required in order to construct a
 /// Sapling output to a transaction.
 #[derive(Clone)]
-pub struct SaplingOutput {
+struct SaplingOutputInfo {
     /// `None` represents the `ovk = ⊥` case.
     ovk: Option<OutgoingViewingKey>,
     to: PaymentAddress,
@@ -95,7 +102,7 @@ pub struct SaplingOutput {
     memo: MemoBytes,
 }
 
-impl SaplingOutput {
+impl SaplingOutputInfo {
     fn new_internal<P: consensus::Parameters, R: RngCore>(
         params: &P,
         rng: &mut R,
@@ -119,7 +126,7 @@ impl SaplingOutput {
             rseed,
         };
 
-        Ok(SaplingOutput {
+        Ok(SaplingOutputInfo {
             ovk,
             to,
             note,
@@ -127,12 +134,6 @@ impl SaplingOutput {
         })
     }
 
-    pub fn value(&self) -> Amount {
-        // this unwrap is safe because the note's value was initially
-        // constructed from an `Amount`.
-        Amount::from_u64(self.note.value).unwrap()
-    }
-
     fn build<P: consensus::Parameters, Pr: TxProver, R: RngCore>(
         self,
         prover: &Pr,
@@ -173,6 +174,12 @@ impl SaplingOutput {
     }
 }
 
+impl SaplingOutput for SaplingOutputInfo {
+    fn value(&self) -> Amount {
+        Amount::from_u64(self.note.value).expect("Note values should be checked at construction.")
+    }
+}
+
 /// Metadata about a transaction created by a [`SaplingBuilder`].
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct SaplingMetadata {
@@ -217,7 +224,7 @@ pub struct SaplingBuilder<P> {
     target_height: BlockHeight,
     value_balance: Amount,
     spends: Vec<SpendDescriptionInfo>,
-    outputs: Vec<SaplingOutput>,
+    outputs: Vec<SaplingOutputInfo>,
 }
 
 #[derive(Clone)]
@@ -255,7 +262,7 @@ impl<P> SaplingBuilder<P> {
     }
 
     /// Returns the Sapling outputs that will be produced by the transaction being constructed
-    pub fn outputs(&self) -> &[SaplingOutput] {
+    pub fn outputs(&self) -> &[impl SaplingOutput] {
         &self.outputs
     }
 
@@ -314,7 +321,7 @@ impl<P: consensus::Parameters> SaplingBuilder<P> {
         value: Amount,
         memo: MemoBytes,
     ) -> Result<(), Error> {
-        let output = SaplingOutput::new_internal(
+        let output = SaplingOutputInfo::new_internal(
             &self.params,
             &mut rng,
             self.target_height,

zcash_primitives/src/transaction/fees.rs

@@ -29,7 +29,7 @@ pub trait FeeRule {
         transparent_inputs: &[impl TransparentInput],
         transparent_outputs: &[TxOut],
         sapling_inputs: &[impl SaplingInput],
-        sapling_outputs: &[SaplingOutput],
+        sapling_outputs: &[impl SaplingOutput],
     ) -> Result<Amount, Self::Error>;
 }
 
@@ -50,7 +50,7 @@ pub trait FutureFeeRule: FeeRule {
         transparent_inputs: &[impl TransparentInput],
         transparent_outputs: &[TxOut],
         sapling_inputs: &[impl SaplingInput],
-        sapling_outputs: &[SaplingOutput],
+        sapling_outputs: &[impl SaplingOutput],
         tze_inputs: &[impl TzeInput],
         tze_outputs: &[TzeOut],
     ) -> Result<Amount, Self::Error>;
@@ -79,7 +79,7 @@ impl FeeRule for FixedFeeRule {
         _transparent_inputs: &[impl TransparentInput],
         _transparent_outputs: &[TxOut],
         _sapling_inputs: &[impl SaplingInput],
-        _sapling_outputs: &[SaplingOutput],
+        _sapling_outputs: &[impl SaplingOutput],
     ) -> Result<Amount, Self::Error> {
         Ok(self.fixed_fee)
     }
@@ -94,7 +94,7 @@ impl FutureFeeRule for FixedFeeRule {
         _transparent_inputs: &[impl TransparentInput],
         _transparent_outputs: &[TxOut],
         _sapling_inputs: &[impl SaplingInput],
-        _sapling_outputs: &[SaplingOutput],
+        _sapling_outputs: &[impl SaplingOutput],
         _tze_inputs: &[impl TzeInput],
         _tze_outputs: &[TzeOut],
     ) -> Result<Amount, Self::Error> {