feat(sdk-coin-ada): add dummy witness in legacy build for sponsored tx

Ticket: WIN-8764

Author: Ranjna-G

modules/sdk-coin-ada/src/lib/transaction.ts

@@ -450,4 +450,5 @@ export class Transaction extends BaseTransaction {
 export interface SponsorshipInfo {
   feeAddress: string;
   feeAddressInputBalance: string;
+  isRebuild?: boolean; // hack to redirect the flow to the legacy build
 }

modules/sdk-coin-ada/src/lib/transactionBuilder.ts

@@ -476,7 +476,14 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
 
   /** @inheritdoc */
   protected async buildImplementation(): Promise<Transaction> {
-    if (this._isTokenTransaction || (this._sponsorshipInfo && this._type === TransactionType.Send)) {
+    /**
+     * Fee address utxo reservation builds a new transaction that goes through legacy build
+     * rebuild flag is just a hack to redirect the flow to the legacy build
+     */
+    if (
+      this._isTokenTransaction ||
+      (this._sponsorshipInfo && !this._sponsorshipInfo.isRebuild && this._type === TransactionType.Send)
+    ) {
       return this.processTokenBuild();
     }
     const inputs = CardanoWasm.TransactionInputs.new();
@@ -598,6 +605,11 @@ export abstract class TransactionBuilder extends BaseTransactionBuilder {
         if (this._type !== TransactionType.Send) {
           vkeyWitnesses.add(vkeyWitness);
         }
+        if (this._sponsorshipInfo?.isRebuild) {
+          const sponsorPrv = CardanoWasm.PrivateKey.generate_ed25519();
+          const sponsorVkeyWitness = CardanoWasm.make_vkey_witness(txHash, sponsorPrv);
+          vkeyWitnesses.add(sponsorVkeyWitness);
+        }
       }
       witnessSet.set_vkeys(vkeyWitnesses);
 

modules/sdk-coin-ada/test/unit/tokenWithdrawal.ts

@@ -403,6 +403,78 @@ describe('ADA Token Operations', async () => {
     tx.getFee.should.equal('182485'); // Fee with two witnesses
   });
 
+  it(`should rebuild a sponsored transaction from hex with isRebuild flag`, async () => {
+    const feeAddress =
+      'addr_test1qz2fxv2umyhttkxyxp8x0dlpdt3k6cwng5pxj3jhsydzer3jcu5d8ps7zex2k2xt3uqxgjqnnj83ws8lhrn648jjxtwq2ytjqp';
+    const quantity = '20';
+    const senderInputBalance = 5000000;
+    const feeAddressInputBalance = 20000000;
+    const totalAssetList = {
+      [fingerprint]: {
+        quantity: '100',
+        policy_id: policyId,
+        asset_name: asciiEncodedName,
+      },
+    };
+
+    // Step 1: Build the initial sponsored transaction
+    const txBuilder = factory.getTransferBuilder();
+    txBuilder.input({
+      transaction_id: '3677e75c7ba699bfdc6cd57d42f246f86f63aefd76025006ac78313fad2bba21',
+      transaction_index: 1,
+    });
+    txBuilder.input({
+      transaction_id: '3677e75c7ba699bfdc6cd57d42f246f86f63aefd76025006ac78313fad2bba22',
+      transaction_index: 0,
+    });
+
+    txBuilder.output({
+      address: receiverAddress,
+      amount: '0',
+      multiAssets: {
+        asset_name: asciiEncodedName,
+        policy_id: policyId,
+        quantity,
+        fingerprint,
+      },
+    });
+
+    txBuilder.changeAddress(senderAddress, senderInputBalance.toString(), totalAssetList);
+    txBuilder.sponsorshipInfo({
+      feeAddress: feeAddress,
+      feeAddressInputBalance: feeAddressInputBalance.toString(),
+    });
+    txBuilder.ttl(800000000);
+    txBuilder.isTokenTransaction();
+    const initialTx = (await txBuilder.build()) as Transaction;
+    const initialTxHex = initialTx.toBroadcastFormat();
+    const initialFee = initialTx.getFee;
+
+    // Step 2: Rebuild from hex with isRebuild = true
+    const rebuildTxBuilder = factory.from(initialTxHex);
+    rebuildTxBuilder.changeAddress(senderAddress, senderInputBalance.toString(), totalAssetList);
+    rebuildTxBuilder.sponsorshipInfo({
+      feeAddress: feeAddress,
+      feeAddressInputBalance: feeAddressInputBalance.toString(),
+      isRebuild: true,
+    });
+
+    const rebuiltTx = (await rebuildTxBuilder.build()) as Transaction;
+    const rebuiltTxData = rebuiltTx.toJson();
+
+    // Verify the rebuilt transaction has same structure
+    rebuiltTxData.inputs.length.should.equal(2);
+    rebuiltTxData.outputs.length.should.equal(4);
+
+    // The fee should remain the same since isRebuild adds dummy witness for fee calculation
+    rebuiltTx.getFee.should.equal(initialFee);
+
+    // Verify receiver output is preserved
+    const receiverOutput = rebuiltTxData.outputs.filter((output) => output.address === receiverAddress);
+    receiverOutput.length.should.equal(1);
+    receiverOutput[0].amount.should.equal('1500000');
+  });
+
   describe('AdaToken verifyTransaction', () => {
     let bitgo: TestBitGoAPI;
     let adaToken;