Merge pull request #46 from babylonchain/accurate-fee-calculation

hotfix: Accurate fee calculation

.husky/pre-commit

@@ -1 +1,2 @@
 npm test
+npm run build

jest.config.js

@@ -2,6 +2,7 @@
 export default {
   preset: 'ts-jest',
   testEnvironment: 'node',
+  setupFilesAfterEnv: ['./jest.setup.js'],
   testMatch: ['**/tests/**/*.test.ts', '**/?(*.)+(spec|test).ts'],
   moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
   transform: {

jest.setup.js

@@ -0,0 +1,16 @@
+const originalTest = global.test;
+const NUM_ITERATIONS = 10;
+
+global.test = (name, fn, timeout) => {
+  for (let i = 0; i < NUM_ITERATIONS; i++) {
+    originalTest(`${name} (iteration ${i + 1})`, fn, timeout);
+  }
+};
+
+const originalIt = global.it;
+
+global.it = (name, fn, timeout) => {
+  for (let i = 0; i < NUM_ITERATIONS; i++) {
+    originalIt(`${name} (iteration ${i + 1})`, fn, timeout);
+  }
+};

package.json

@@ -1,6 +1,6 @@
 {
   "name": "btc-staking-ts",
-  "version": "0.2.4",
+  "version": "0.2.5",
   "description": "Library exposing methods for the creation and consumption of Bitcoin transactions pertaining to Babylon's Bitcoin Staking protocol. Experimental version, should not be used for production purposes or with real funds.",
   "module": "dist/index.js",
   "main": "dist/index.cjs",
@@ -9,8 +9,8 @@
   "scripts": {
     "generate-types": "dts-bundle-generator -o ./dist/index.d.ts ./src/index.ts",
     "build": "node build.js && npm run generate-types",
-    "format": "prettier --check \"src/**/*.ts\"",
-    "format:fix": "prettier --write \"src/**/*.ts\"",
+    "format": "prettier --check \"src/**/*.ts\" \"tests/**/*.ts\"",
+    "format:fix": "prettier --write \"src/**/*.ts\" \"tests/**/*.ts\"",
     "lint": "eslint ./src --fix",
     "prepare": "husky",
     "prepublishOnly": "npm run build",

src/constants/fee.ts

@@ -0,0 +1,16 @@
+// Estimated size of a non-SegWit input in bytes
+export const DEFAULT_INPUT_SIZE = 180;
+// Estimated size of a P2WPKH input in bytes
+export const P2WPKH_INPUT_SIZE = 68;
+// Estimated size of a P2TR input in bytes
+export const P2TR_INPUT_SIZE = 58;
+// Estimated size of a transaction buffer in bytes
+export const TX_BUFFER_SIZE_OVERHEAD = 11;
+// Buffer for estimation accuracy when fee rate <= 2 sat/byte
+export const LOW_RATE_ESTIMATION_ACCURACY_BUFFER = 30;
+// Size of a Taproot output, the largest non-legacy output type
+export const MAX_NON_LEGACY_OUTPUT_SIZE = 43;
+// Buffer size for withdraw transaction fee calculation
+export const WITHDRAW_TX_BUFFER_SIZE = 17;
+// Threshold for wallet relay fee rate. Different buffer fees are used based on this threshold
+export const WALLET_RELAY_FEE_RATE_THRESHOLD = 2;

src/index.ts

@@ -7,11 +7,9 @@ import { UTXO } from "./types/UTXO";
 import { PsbtTransactionResult } from "./types/transaction";
 import { isValidBitcoinAddress } from "./utils/address";
 import { initBTCCurve } from "./utils/curve";
-import {
-  getEstimatedFee,
-  getStakingTxInputUTXOsAndFees,
-  inputValueSum,
-} from "./utils/fee";
+import { getStakingTxInputUTXOsAndFees, getWithdrawTxFee } from "./utils/fee";
+import { inputValueSum } from "./utils/fee/utils";
+import { buildStakingOutput } from "./utils/staking";
 import { PK_LENGTH, StakingScriptData } from "./utils/stakingScript";
 
 export { StakingScriptData, initBTCCurve };
@@ -84,14 +82,14 @@ export function stakingTransaction(
     throw new Error("Invalid public key");
   }
 
-  // Calculate the number of outputs based on the presence of the data embed script
-  // We have 2 outputs by default: staking output and change output
-  const numOutputs = scripts.dataEmbedScript ? 3 : 2;
+  // Build outputs and estimate the fee
+  const psbtOutputs = buildStakingOutput(scripts, network, amount);
   const { selectedUTXOs, fee } = getStakingTxInputUTXOsAndFees(
+    network,
     inputUTXOs,
     amount,
     feeRate,
-    numOutputs,
+    psbtOutputs,
   );
 
   // Create a partially signed transaction
@@ -112,33 +110,8 @@ export function stakingTransaction(
     });
   }
 
-  const scriptTree: Taptree = [
-    {
-      output: scripts.slashingScript,
-    },
-    [{ output: scripts.unbondingScript }, { output: scripts.timelockScript }],
-  ];
-
-  // Create an pay-2-taproot (p2tr) output using the staking script
-  const stakingOutput = payments.p2tr({
-    internalPubkey,
-    scriptTree,
-    network,
-  });
-
   // Add the staking output to the transaction
-  psbt.addOutput({
-    address: stakingOutput.address!,
-    value: amount,
-  });
-
-  if (scripts.dataEmbedScript) {
-    // Add the data embed output to the transaction
-    psbt.addOutput({
-      script: scripts.dataEmbedScript,
-      value: 0,
-    });
-  }
+  psbt.addOutputs(psbtOutputs);
 
   // Add a change output only if there's any amount leftover from the inputs
   const inputsSum = inputValueSum(selectedUTXOs);
@@ -362,8 +335,7 @@ function withdrawalTransaction(
   if (outputValue < BTC_DUST_SAT) {
     throw new Error("Output value is less than dust limit");
   }
-  // withdraw tx always has 1 output only
-  const estimatedFee = getEstimatedFee(feeRate, psbt.txInputs.length, 1);
+  const estimatedFee = getWithdrawTxFee(feeRate);
   const value = tx.outs[outputIndex].value - estimatedFee;
   if (!value) {
     throw new Error(

src/types/psbtOutputs.ts

@@ -0,0 +1,21 @@
+import { PsbtOutput } from "bip174/src/lib/interfaces";
+
+export type PsbtOutputExtended =
+  | PsbtOutputExtendedAddress
+  | PsbtOutputExtendedScript;
+
+interface PsbtOutputExtendedAddress extends PsbtOutput {
+  address: string;
+  value: number;
+}
+
+interface PsbtOutputExtendedScript extends PsbtOutput {
+  script: Buffer;
+  value: number;
+}
+
+export const isPsbtOutputExtendedAddress = (
+  output: PsbtOutputExtended,
+): output is PsbtOutputExtendedAddress => {
+  return (output as PsbtOutputExtendedAddress).address !== undefined;
+};