refactor(sdk-coin-flrp): enhance fee calculation for import transactions

modules/sdk-coin-flrp/src/lib/ImportInCTxBuilder.ts

@@ -11,7 +11,6 @@ import {
   TransferableInput,
   Address,
   utils as FlareUtils,
-  avmSerial,
 } from '@flarenetwork/flarejs';
 import utils from './utils';
 import { DecodedUtxoObj, FlareTransactionType, SECP256K1_Transfer_Output, Tx } from './iface';
@@ -63,16 +62,6 @@ export class ImportInCTxBuilder extends AtomicInCTransactionBuilder {
 
     // Calculate fee based on input/output difference
     const fee = totalInputAmount - totalOutputAmount;
-    // Calculate cost units using the same method as buildFlareTransaction
-    const feeSize = this.calculateImportCost(baseTx);
-    // Use integer division to ensure feeRate can be converted back to BigInt
-    const feeRate = Math.floor(Number(fee) / feeSize);
-
-    this.transaction._fee = {
-      fee: fee.toString(),
-      feeRate: feeRate,
-      size: feeSize,
-    };
 
     // Use credentials passed from TransactionBuilderFactory (properly extracted using codec)
     const credentials = parsedCredentials || [];
@@ -88,6 +77,30 @@ export class ImportInCTxBuilder extends AtomicInCTransactionBuilder {
     const inputThreshold = firstInput.sigIndicies().length || this.transaction._threshold;
     this.transaction._threshold = inputThreshold;
 
+    // Create a temporary UnsignedTx for accurate fee size calculation
+    // This includes the full structure (ImportTx, AddressMaps, Credentials)
+    const tempAddressMap = new FlareUtils.AddressMap();
+    for (let i = 0; i < inputThreshold; i++) {
+      if (this.transaction._fromAddresses && this.transaction._fromAddresses[i]) {
+        tempAddressMap.set(new Address(this.transaction._fromAddresses[i]), i);
+      }
+    }
+    const tempAddressMaps = new FlareUtils.AddressMaps([tempAddressMap]);
+    const tempCredentials =
+      credentials.length > 0 ? credentials : [new Credential(Array(inputThreshold).fill(utils.createNewSig('')))];
+    const tempUnsignedTx = new UnsignedTx(baseTx, [], tempAddressMaps, tempCredentials);
+
+    // Calculate cost units using the full UnsignedTx structure
+    const feeSize = this.calculateImportCost(tempUnsignedTx);
+    // Use integer division to ensure feeRate can be converted back to BigInt
+    const feeRate = Math.floor(Number(fee) / feeSize);
+
+    this.transaction._fee = {
+      fee: fee.toString(),
+      feeRate: feeRate,
+      size: feeSize,
+    };
+
     // Create AddressMaps based on signature slot order (matching credential order), not sorted addresses
     // This matches the approach used in credentials: addressesIndex determines signature order
     // AddressMaps should map addresses to signature slots in the same order as credentials
@@ -166,7 +179,8 @@ export class ImportInCTxBuilder extends AtomicInCTransactionBuilder {
     const { inputs, amount, credentials } = this.createInputs();
 
     // Calculate import cost units (matching AVAXP's costImportTx approach)
-    // Create a temporary transaction with full amount to calculate fee size
+    // Create a temporary UnsignedTx with full amount to calculate fee size
+    // This includes the full structure (ImportTx, AddressMaps, Credentials) for accurate size calculation
     const tempOutput = new evmSerial.Output(
       new Address(this.transaction._to[0]),
       new BigIntPr(amount),
@@ -180,8 +194,18 @@ export class ImportInCTxBuilder extends AtomicInCTransactionBuilder {
       [tempOutput]
     );
 
-    // Calculate feeSize once using full amount (matching AVAXP approach)
-    const feeSize = this.calculateImportCost(tempImportTx);
+    // Create AddressMaps for fee calculation (same as final transaction)
+    const firstUtxo = this.transaction._utxos[0];
+    const tempAddressMap = firstUtxo
+      ? this.createAddressMapForUtxo(firstUtxo, this.transaction._threshold)
+      : new FlareUtils.AddressMap();
+    const tempAddressMaps = new FlareUtils.AddressMaps([tempAddressMap]);
+
+    // Create temporary UnsignedTx with full structure for accurate fee calculation
+    const tempUnsignedTx = new UnsignedTx(tempImportTx, [], tempAddressMaps, credentials);
+
+    // Calculate feeSize once using full UnsignedTx (matching AVAXP approach)
+    const feeSize = this.calculateImportCost(tempUnsignedTx);
     const feeRate = BigInt(this.transaction._fee.feeRate);
     const fee = feeRate * BigInt(feeSize);
 
@@ -211,21 +235,11 @@ export class ImportInCTxBuilder extends AtomicInCTransactionBuilder {
       [output]
     );
 
-    // Create AddressMaps based on signature slot order (matching credential order), not sorted addresses
-    // This matches the approach used in credentials: addressesIndex determines signature order
-    // AddressMaps should map addresses to signature slots in the same order as credentials
-    // For C-chain imports, we typically have one input, so use the first UTXO
-    // Use centralized method for AddressMap creation
-    const firstUtxo = this.transaction._utxos[0];
-    const addressMap = firstUtxo
-      ? this.createAddressMapForUtxo(firstUtxo, this.transaction._threshold)
-      : new FlareUtils.AddressMap();
-    const addressMaps = new FlareUtils.AddressMaps([addressMap]);
-
+    // Reuse the AddressMaps already calculated for fee calculation
     const unsignedTx = new UnsignedTx(
       importTx,
       [], // Empty UTXOs array, will be filled during processing
-      addressMaps,
+      tempAddressMaps,
       credentials
     );
 
@@ -298,39 +312,21 @@ export class ImportInCTxBuilder extends AtomicInCTransactionBuilder {
   }
 
   /**
-   * Calculate the import cost for C-chain import transactions
-   * Matches AVAXP's costImportTx formula:
-   * - Base byte cost: transactionSize * txBytesGas (1 gas per byte)
-   * - Per-input cost: numInputs * costPerSignature (1000 per signature) * threshold
-   * - Fixed fee: 10000
-   *
-   * This returns cost "units" to be multiplied by feeRate, matching AVAXP's approach:
-   * AVAXP: fee = feeRate.muln(costImportTx(tx))
-   * FLRP:  fee = feeRate * calculateImportCost(tx)
-   *
-   * @param tx The ImportTx to calculate the cost for
+   * @param unsignedTx The UnsignedTx to calculate the cost for (includes ImportTx, AddressMaps, and Credentials)
    * @returns The total cost units
    */
-  private calculateImportCost(tx: evmSerial.ImportTx): number {
-    const codec = avmSerial.getAVMManager().getDefaultCodec();
-    const txBytes = tx.toBytes(codec);
-
-    // Base byte cost: 1 gas per byte (matching AVAX txBytesGas)
+  private calculateImportCost(unsignedTx: UnsignedTx): number {
+    const signedTxBytes = unsignedTx.getSignedTx().toBytes();
     const txBytesGas = 1;
-    let bytesCost = txBytes.length * txBytesGas;
-
-    // Per-input cost: costPerSignature (1000) per signature
+    let bytesCost = signedTxBytes.length * txBytesGas;
     const costPerSignature = 1000;
-    const numInputs = tx.importedInputs.length;
-    const numSignatures = this.transaction._threshold; // Each input requires threshold signatures
-    const inputCost = numInputs * costPerSignature * numSignatures;
-    bytesCost += inputCost;
-
-    // Fixed fee component
+    const importTx = unsignedTx.getTx() as evmSerial.ImportTx;
+    importTx.importedInputs.forEach((input: TransferableInput) => {
+      const inCost = costPerSignature * input.sigIndicies().length;
+      bytesCost += inCost;
+    });
     const fixedFee = 10000;
-    const totalCost = bytesCost + fixedFee;
-
-    return totalCost;
+    return bytesCost + fixedFee;
   }
 
   /**

modules/sdk-coin-flrp/test/resources/transactionData/importInC.ts

@@ -1,13 +1,13 @@
 export const IMPORT_IN_C = {
-  txhash: '2Q5RkxF2eRK3KCzDaijoScyunahbEvt6ai6YZipmShQTPryfky',
+  txhash: '5wgxtB8tSyS2MNroAQgs8fA9sDUWCwrGJG88b77xUm1po685Q',
   unsignedHex:
-    '0x0000000000000000007278db5c30bed04c05ce209179812850bbb3fe6d46d7eef3744d814c0da5552479000000000000000000000000000000000000000000000000000000000000000000000001fcea1c0e2cb7e3d77c993eb74ee05d98c24325ded1918e8a0595c96a789e2f790000000158734f94af871c3d131b56131b6fb7a0291eacadd261e69dfb42a9cdf6f7fddd00000005000000001dcd65000000000200000000000000010000000117dbd11b9dd1c9be337353db7c14f9fb3662e5b5000000001d8114dc58734f94af871c3d131b56131b6fb7a0291eacadd261e69dfb42a9cdf6f7fddd0000000100000009000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000000000003329be7d01cd3ebaae6654d7327dd9f17a2e15810000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000576b6e21',
+    '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',
   halfSignedSignature:
     '0xd365ef7ce45aebc4e81bc03f600867f515cebb25c4a0e8e1f06d9fe0a00d41fd2efac6c6df392e5f92e271c57486e39425537da7cafbb085cd1bd21aff06955d00',
   halfSigntxHex:
-    '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',
+    '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',
   fullSigntxHex:
-    '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',
+    '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',
   fullSignedSignature:
     '0x70d2ca9711622142610ddd347e482cbe5dc45aeafe66876bb82bfd57581300045b8457d804cc1b8f2efc10401367e5919b1912ee26d2d48c06cf82dc3f146acd00',
 
@@ -39,7 +39,7 @@ export const IMPORT_IN_C = {
   to: '0x17Dbd11B9dD1c9bE337353db7C14f9fb3662E5B5',
   sourceChainId: 'vE8M98mEQH6wk56sStD1ML8HApTgSqfJZLk9gQ3Fsd4i6m3Bi',
   threshold: 2,
-  fee: '409', // feeRate multiplier: 5,000,000 (desired fee) ÷ ~12,228 (cost units) ≈ 409
+  fee: '550',
   locktime: 0,
   INVALID_CHAIN_ID: 'wrong chain id',
   VALID_C_CHAIN_ID: 'yH8D7ThNJkxmtkuv2jgBa4P1Rn3Qpr4pPr7QYNfcdoS6k6HWp',