moves change notes construction inside of build function of `Propos…

…edTransaction`. Makes it so no new method is required for build layer (#4572)

ironfish-rust-nodejs/index.d.ts

@@ -223,7 +223,7 @@ export class Transaction {
    * aka: self.value_balance - intended_transaction_fee - change = 0
    */
   post(spenderHexKey: string, changeGoesTo: string | undefined | null, intendedTransactionFee: bigint): Buffer
-  build(proofGenerationKeyStr: string, viewKeyStr: string, outgoingViewKeyStr: string, publicAddressStr: string, intendedTransactionFee: bigint): Buffer
+  build(proofGenerationKeyStr: string, viewKeyStr: string, outgoingViewKeyStr: string, publicAddressStr: string, intendedTransactionFee: bigint, changeGoesTo?: string | undefined | null): Buffer
   setExpiration(sequence: number): void
 }
 export class FoundBlockResult {

ironfish-rust-nodejs/src/structs/transaction.rs

@@ -321,13 +321,18 @@ impl NativeTransaction {
         outgoing_view_key_str: String,
         public_address_str: String,
         intended_transaction_fee: BigInt,
+        change_goes_to: Option<String>,
     ) -> Result<Buffer> {
         let view_key = ViewKey::from_hex(&view_key_str).map_err(to_napi_err)?;
         let outgoing_view_key =
             OutgoingViewKey::from_hex(&outgoing_view_key_str).map_err(to_napi_err)?;
         let public_address = PublicAddress::from_hex(&public_address_str).map_err(to_napi_err)?;
         let proof_generation_key = ProofGenerationKey::from_hex(&proof_generation_key_str)
             .map_err(|_| to_napi_err("PublicKeyPackage hex to bytes failed"))?;
+        let change_address = match change_goes_to {
+            Some(address) => Some(PublicAddress::from_hex(&address).map_err(to_napi_err)?),
+            None => None,
+        };
         let unsigned_transaction = self
             .transaction
             .build(
@@ -336,6 +341,7 @@ impl NativeTransaction {
                 outgoing_view_key,
                 public_address,
                 intended_transaction_fee.get_i64().0,
+                change_address,
             )
             .map_err(to_napi_err)?;
 

ironfish-rust/src/transaction/mod.rs

@@ -191,7 +191,7 @@ impl ProposedTransaction {
         Ok(())
     }
 
-    pub fn add_change_notes(
+    fn add_change_notes(
         &mut self,
         change_goes_to: Option<PublicAddress>,
         public_address: PublicAddress,
@@ -223,7 +223,6 @@ impl ProposedTransaction {
                 change_notes.push(change_note);
             }
         }
-
         for change_note in change_notes {
             self.add_output(change_note)?;
         }
@@ -237,7 +236,14 @@ impl ProposedTransaction {
         outgoing_view_key: OutgoingViewKey,
         public_address: PublicAddress,
         intended_transaction_fee: i64,
+        change_goes_to: Option<PublicAddress>,
     ) -> Result<UnsignedTransaction, IronfishError> {
+        // skip adding change notes if this is special case of a miners fee transaction
+        let is_miners_fee = self.outputs.iter().any(|output| output.get_is_miners_fee());
+        if !is_miners_fee {
+            self.add_change_notes(change_goes_to, public_address, intended_transaction_fee)?;
+        }
+
         // The public key after randomization has been applied. This is used
         // during signature verification. Referred to as `rk` in the literature
         // Calculated from the authorizing key and the public_key_randomness.
@@ -330,14 +336,14 @@ impl ProposedTransaction {
         let public_address = spender_key.public_address();
 
         let i64_fee = i64::try_from(intended_transaction_fee)?;
-        self.add_change_notes(change_goes_to, public_address, i64_fee)?;
 
         let unsigned = self.build(
             spender_key.sapling_proof_generation_key(),
             spender_key.view_key().clone(),
             spender_key.outgoing_view_key().clone(),
             public_address,
             i64_fee,
+            change_goes_to,
         )?;
         unsigned.sign(spender_key)
     }
@@ -378,6 +384,7 @@ impl ProposedTransaction {
             spender_key.outgoing_view_key().clone(),
             spender_key.public_address(),
             *self.value_balances.fee(),
+            None,
         )?;
         unsigned.sign(spender_key)
     }

ironfish-rust/src/transaction/outputs.rs

@@ -60,6 +60,10 @@ impl OutputBuilder {
         self.is_miners_fee = true;
     }
 
+    pub(crate) fn get_is_miners_fee(&self) -> bool {
+        self.is_miners_fee
+    }
+
     /// Get the value_commitment from this proof as an edwards Point.
     ///
     /// This integrates the value and randomness into a single point, using an

ironfish-rust/src/transaction/tests.rs

@@ -227,11 +227,8 @@ fn test_proposed_transaction_build() {
     transaction.add_output(out_note).unwrap();
     assert_eq!(transaction.outputs.len(), 1);
 
-    let public_address = spender_key.public_address();
+    let public_address: crate::PublicAddress = spender_key.public_address();
     let intended_fee = 1;
-    transaction
-        .add_change_notes(Some(public_address), public_address, intended_fee)
-        .expect("should be able to add change notes");
 
     let unsigned_transaction = transaction
         .build(
@@ -240,6 +237,7 @@ fn test_proposed_transaction_build() {
             spender_key.outgoing_view_key().clone(),
             spender_key.public_address(),
             intended_fee,
+            Some(public_address),
         )
         .expect("should be able to build unsigned transaction");