fix(input-selection): greedy input selector now produces a correct selection under all conditions

Author: AngelCastilloB

Diff for: packages/input-selection/src/GreedySelection/GreedyInputSelector.ts

@@ -50,7 +50,7 @@ const adjustOutputsForFee = async (
   outputs: Set<Cardano.TxOut>,
   changeOutputs: Array<Cardano.TxOut>,
   currentFee: bigint
-): Promise<{ fee: bigint; change: Array<Cardano.TxOut> }> => {
+): Promise<{ fee: bigint; change: Array<Cardano.TxOut>; feeAccountedFor: boolean }> => {
   const totalOutputs = new Set([...outputs, ...changeOutputs]);
   const fee = await constraints.computeMinimumCost({
     change: [],
@@ -59,7 +59,7 @@ const adjustOutputsForFee = async (
     outputs: totalOutputs
   });
 
-  if (fee === changeLovelace) return { change: [], fee };
+  if (fee === changeLovelace) return { change: [], fee, feeAccountedFor: true };
 
   if (changeLovelace < fee) throw new InputSelectionError(InputSelectionFailure.UtxoBalanceInsufficient);
 
@@ -78,11 +78,7 @@ const adjustOutputsForFee = async (
     }
   }
 
-  if (!feeAccountedFor) {
-    throw new InputSelectionError(InputSelectionFailure.UtxoFullyDepleted);
-  }
-
-  return { change: [...updatedOutputs], fee };
+  return { change: [...updatedOutputs], fee, feeAccountedFor };
 };
 
 /**
@@ -104,7 +100,7 @@ const splitChangeAndComputeFee = async (
   constraints: SelectionConstraints,
   getChangeAddresses: () => Promise<Map<Cardano.PaymentAddress, number>>,
   fee: bigint
-): Promise<{ fee: bigint; change: Array<Cardano.TxOut> }> => {
+): Promise<{ fee: bigint; change: Array<Cardano.TxOut>; feeAccountedFor: boolean }> => {
   const changeOutputs = await splitChange(
     getChangeAddresses,
     changeLovelace,
@@ -114,7 +110,7 @@ const splitChangeAndComputeFee = async (
     fee
   );
 
-  const adjustedChangeOutputs = await adjustOutputsForFee(
+  let adjustedChangeOutputs = await adjustOutputsForFee(
     changeLovelace,
     constraints,
     inputs,
@@ -126,7 +122,7 @@ const splitChangeAndComputeFee = async (
   // If the newly computed fee is higher than tha available balance for change,
   // but there are unallocated native assets, return the assets as change with 0n coins.
   if (adjustedChangeOutputs.fee >= changeLovelace) {
-    return {
+    const result = {
       change: [
         {
           address: stubMaxSizeAddress,
@@ -136,12 +132,18 @@ const splitChangeAndComputeFee = async (
           }
         }
       ],
-      fee: adjustedChangeOutputs.fee
+      fee: adjustedChangeOutputs.fee,
+      feeAccountedFor: true
     };
+
+    if (result.change[0].value.coins < constraints.computeMinimumCoinQuantity(result.change[0]))
+      throw new InputSelectionError(InputSelectionFailure.UtxoFullyDepleted);
+
+    return result;
   }
 
   if (fee < adjustedChangeOutputs.fee) {
-    return splitChangeAndComputeFee(
+    adjustedChangeOutputs = await splitChangeAndComputeFee(
       inputs,
       outputs,
       changeLovelace,
@@ -150,8 +152,18 @@ const splitChangeAndComputeFee = async (
       getChangeAddresses,
       adjustedChangeOutputs.fee
     );
+
+    if (adjustedChangeOutputs.change.length === 0)
+      throw new InputSelectionError(InputSelectionFailure.UtxoFullyDepleted);
+  }
+
+  for (const out of adjustedChangeOutputs.change) {
+    if (out.value.coins < constraints.computeMinimumCoinQuantity(out))
+      throw new InputSelectionError(InputSelectionFailure.UtxoFullyDepleted);
   }
 
+  if (!adjustedChangeOutputs.feeAccountedFor) throw new InputSelectionError(InputSelectionFailure.UtxoFullyDepleted);
+
   return adjustedChangeOutputs;
 };
 

Diff for: packages/input-selection/src/GreedySelection/util.ts

@@ -102,10 +102,12 @@ const getMinUtxoAmount = (amount: bigint): bigint => {
  *
  * @param output The output to be split.
  * @param computeMinimumCoinQuantity ComputeMinimumCoinQuantity.
+ * @param fee current expected fee.
  */
 const splitChangeOutput = (
   output: Cardano.TxOut,
-  computeMinimumCoinQuantity: ComputeMinimumCoinQuantity
+  computeMinimumCoinQuantity: ComputeMinimumCoinQuantity,
+  fee: bigint
 ): Array<Cardano.TxOut> => {
   const amount = output.value.coins;
   const minUtxoAdaAmount = getMinUtxoAmount(amount);
@@ -115,7 +117,7 @@ const splitChangeOutput = (
   const amounts = new Array<bigint>();
   const divisor = new BigNumber(2);
 
-  while (remaining > minUtxoAdaAmount) {
+  while (remaining >= minUtxoAdaAmount) {
     const val = BigInt(new BigNumber(remaining.toString()).dividedBy(divisor).toFixed(0, 0));
 
     const updatedRemaining = remaining - val;
@@ -125,7 +127,8 @@ const splitChangeOutput = (
         computeMinimumCoinQuantity({
           address: output.address,
           value: { assets: output.value.assets, coins: amount - runningAmount }
-        })
+        }) +
+          fee
     ) {
       amounts.push(amount - runningAmount); // Add all that remains to account for rounding errors
       break;
@@ -207,7 +210,7 @@ export const splitChange = async (
     changeOutputs[changeOutputs.length - 1].value.coins += missingAllocation;
   }
 
-  const splitOutputs = changeOutputs.flatMap((output) => splitChangeOutput(output, computeMinimumCoinQuantity));
+  const splitOutputs = changeOutputs.flatMap((output) => splitChangeOutput(output, computeMinimumCoinQuantity, fee));
   const sortedOutputs = splitOutputs.sort(sortByCoins).filter((out) => out.value.coins > 0n);
 
   if (sortedOutputs && sortedOutputs.length > 0) sortedOutputs[0].value.assets = totalChangeAssets; // Add all assets to the 'biggest' output.

Diff for: packages/input-selection/test/GreedySelection/util.test.ts

@@ -16,7 +16,7 @@ describe('splitChange', () => {
       undefined,
       () => 10n,
       () => false,
-      2_000_000n
+      0n
     );
 
     expect(getCoinValueForAddress('A', change)).toEqual(50n);
@@ -46,7 +46,7 @@ describe('splitChange', () => {
       undefined,
       () => 10n,
       () => false,
-      2_000_000n
+      0n
     );
 
     expect(getCoinValueForAddress('A', change)).toEqual(34n);