fix: create multiple outputs if balance exceeds maxValueSize (#169)

.changeset/thirty-years-cough.md

@@ -0,0 +1,5 @@
+---
+"@blaze-cardano/tx": patch
+---
+
+Add balanceMultiAssetChange to avoid exceeding the max value size for an output

packages/blaze-tx/src/tx.ts

@@ -1320,6 +1320,54 @@ export class TxBuilder {
     this.body.setCollateralReturn(ret);
   }
 
+  /**
+   * Adjusts the balance of the transaction by creating or updating a change output.
+   * This method takes only the native assets from excess value from the transaction, removes any zero-valued
+   * tokens from the multiasset map, and then creates change outputs that don't exceed the minValueSize.
+   *
+   * Updates the changeOutputIndex to the index of the last change output.
+   *
+   * @param {Value} excessValue - The excess value that needs to be returned as change.
+   * returns {Value} The remaining excess value after creating change outputs. (Which should only be ADA)
+   */
+  private balanceMultiAssetChange(excessValue: Value): Value {
+    const tokenMap = excessValue.multiasset();
+    if (tokenMap) {
+      for (const key of tokenMap.keys()) {
+        if (tokenMap.get(key) == 0n) {
+          tokenMap.delete(key);
+        }
+      }
+      excessValue.setMultiasset(tokenMap);
+    }
+    let changeExcess = excessValue;
+    const multiAsset = excessValue.multiasset();
+    if (!multiAsset || multiAsset.size == 0) return excessValue;
+    let output = new TransactionOutput(this.changeAddress!, value.zero());
+    for (const [asset, qty] of Array.from(multiAsset.entries())) {
+      const newOutputValue = value.merge(
+        output.amount(),
+        value.makeValue(0n, [asset, qty]),
+      );
+      const newOutputValueByteLength = newOutputValue.toCbor().length / 2;
+      //We need to check if the new output value is too large
+      //We leave a small buffer for the change ADA. Also we don't need such a big output so 10% is fine
+      if (newOutputValueByteLength > this.params.maxValueSize * 0.9) {
+        this.addOutput(output);
+        changeExcess = value.sub(changeExcess, output.amount());
+        output = new TransactionOutput(
+          this.changeAddress!,
+          value.makeValue(0n, [asset, qty]),
+        );
+      } else {
+        output = new TransactionOutput(this.changeAddress!, newOutputValue);
+      }
+    }
+    this.addOutput(output);
+    changeExcess = value.sub(changeExcess, output.amount());
+    return changeExcess;
+  }
+
   /**
    * Balances the collateral change by creating a transaction output that returns the excess collateral.
    * Throws an error if the change address is not set.
@@ -1457,6 +1505,8 @@ export class TxBuilder {
       );
     }
 
+    // We first balance the native assets  to avoid issues with the max value size being exceeded
+    excessValue = this.balanceMultiAssetChange(excessValue);
     // Balance the change output with the updated excess value.
     this.balanceChange(excessValue);
     // Ensure a change output index has been set after balancing.

packages/blaze-tx/test/tx.test.ts

@@ -22,12 +22,17 @@ function flatten<U>(iterator: IterableIterator<U> | undefined): U[] {
   return result;
 }
 
-const ASSET_NAME_1 = "ab".repeat(56 / 2);
-const ASSET_NAME_2 = "cd".repeat(56 / 2);
-// const ASSET_NAME_3 = "ef".repeat(56/2)
+const ASSETS = Array.from({ length: 1200 }, (_, i) =>
+  i
+    .toString(16)
+    .padStart(2, "0")
+    .concat("ef".repeat(56 / 2)),
+);
 
 describe("Transaction Building", () => {
   it("A complex transaction should balance correctly", async () => {
+    const ASSET_NAME_1 = ASSETS[0]!;
+    const ASSET_NAME_2 = ASSETS[1]!;
     // $hosky
     const testAddress = Address.fromBech32(
       "addr1q86ylp637q7hv7a9r387nz8d9zdhem2v06pjyg75fvcmen3rg8t4q3f80r56p93xqzhcup0w7e5heq7lnayjzqau3dfs7yrls5",
@@ -88,4 +93,80 @@ describe("Transaction Building", () => {
     // console.dir(tx.toCore(), {depth: null})
     expect(inputValue.toCbor()).toEqual(outputValue.toCbor());
   });
+  it("Should correctly balance change for a really big output change", async () => {
+    // $hosky
+    const testAddress = Address.fromBech32(
+      "addr1q86ylp637q7hv7a9r387nz8d9zdhem2v06pjyg75fvcmen3rg8t4q3f80r56p93xqzhcup0w7e5heq7lnayjzqau3dfs7yrls5",
+    );
+    const utxo1Assets: [string, bigint][] = ASSETS.slice(
+      0,
+      ASSETS.length / 2,
+    ).map((x) => [x, 1n]);
+    const utxo2Assets: [string, bigint][] = ASSETS.slice(ASSETS.length / 2).map(
+      (x) => [x, 1n],
+    );
+    const utxos = [
+      new TransactionUnspentOutput(
+        new TransactionInput(TransactionId("0".repeat(64)), 0n),
+        new TransactionOutput(
+          testAddress,
+          value.makeValue(10_000_000_000n, ...utxo1Assets),
+        ),
+      ),
+      new TransactionUnspentOutput(
+        new TransactionInput(TransactionId("1".padStart(64, "0")), 0n),
+        new TransactionOutput(
+          testAddress,
+          value.makeValue(10_000_000_000n, ...utxo2Assets),
+        ),
+      ),
+    ];
+    const tx = await new TxBuilder(hardCodedProtocolParams)
+      .addUnspentOutputs(utxos)
+      .setNetworkId(NetworkId.Testnet)
+      .setChangeAddress(testAddress)
+      .payAssets(
+        testAddress,
+        value.makeValue(10_001_000_000n, [ASSETS[0]!, 1n]),
+      )
+      .complete();
+
+    const inputValue =
+      // value.merge(
+      tx
+        .body()
+        .inputs()
+        .values()
+        .map((x) =>
+          utxos
+            .find((y) => {
+              return y.input().toCbor() == x.toCbor();
+            })!
+            .output()
+            .amount(),
+        )
+        .reduce(value.merge, value.zero());
+    //   ,new Value(
+    //     flatten(tx.body().withdrawals()?.values()).reduce((x, y) => x + y, 0n),
+    //   ),
+    // )
+    //
+
+    const outputValue = value.merge(
+      Array.from(tx.body().outputs().values())
+        .map((x) => x.amount())
+        .reduce(value.merge, value.zero()),
+      new Value(tx.body().fee()),
+    );
+
+    console.log("Change: ", tx.body().outputs().at(1)?.amount().coin());
+
+    console.dir(inputValue.toCore(), { depth: null });
+    console.dir(outputValue.toCore(), { depth: null });
+
+    expect(inputValue.multiasset()?.size).toEqual(
+      outputValue.multiasset()?.size,
+    );
+    expect(inputValue.toCbor()).toEqual(outputValue.toCbor());
+  });
 });