fix: add op_return value size when calculating fee

package.json

@@ -1,6 +1,6 @@
 {
   "name": "btc-staking-ts",
-  "version": "0.2.7",
+  "version": "0.2.8",
   "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",
@@ -60,4 +60,4 @@
     "@bitcoin-js/tiny-secp256k1-asmjs": "^2.2.3",
     "bitcoinjs-lib": "^6.1.5"
   }
-}
+}

src/constants/fee.ts

@@ -14,3 +14,8 @@ export const MAX_NON_LEGACY_OUTPUT_SIZE = 43;
 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;
+// Estimated size of the OP_RETURN output value in bytes
+export const OP_RETURN_OUTPUT_VALUE_SIZE = 8;
+// Because our OP_RETURN data will always be less than 80 bytes, which is less than 0xfd (253),
+// the value serialization size will always be 1 byte.
+export const OP_RETURN_VALUE_SERIALIZE_SIZE = 1;

src/utils/fee/index.ts

@@ -3,6 +3,8 @@ import { BTC_DUST_SAT } from "../../constants/dustSat";
 import {
   LOW_RATE_ESTIMATION_ACCURACY_BUFFER,
   MAX_NON_LEGACY_OUTPUT_SIZE,
+  OP_RETURN_OUTPUT_VALUE_SIZE,
+  OP_RETURN_VALUE_SERIALIZE_SIZE,
   P2TR_INPUT_SIZE,
   TX_BUFFER_SIZE_OVERHEAD,
   WALLET_RELAY_FEE_RATE_THRESHOLD,
@@ -141,7 +143,7 @@ const getEstimatedSize = (
       ? address.toOutputScript(output.address, network)
       : output.script;
     if (isOP_RETURN(script)) {
-      return acc + script.length;
+      return acc + script.length + OP_RETURN_OUTPUT_VALUE_SIZE + OP_RETURN_VALUE_SERIALIZE_SIZE;
     }
     return acc + MAX_NON_LEGACY_OUTPUT_SIZE;
   }, 0);

tests/utils/fee/stakingtxFee.test.ts

@@ -96,7 +96,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
         1,
         outputs,
       );
-      expect(result.fee).toBe(316); // This number is calculated manually
+      expect(result.fee).toBe(325); // This number is calculated manually
       expect(result.selectedUTXOs.length).toEqual(2);
 
       result = getStakingTxInputUTXOsAndFees(
@@ -106,7 +106,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
         2,
         outputs,
       );
-      expect(result.fee).toBe(516); // This number is calculated manually
+      expect(result.fee).toBe(534); // This number is calculated manually
       expect(result.selectedUTXOs.length).toEqual(2);
 
       // Once fee rate is set to 3, the fee will be calculated with addition of TX_BUFFER_SIZE_OVERHEAD * feeRate
@@ -117,7 +117,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
         3,
         outputs,
       );
-      expect(result.fee).toBe(729); // This number is calculated manually
+      expect(result.fee).toBe(756); // This number is calculated manually
       expect(result.selectedUTXOs.length).toEqual(2);
     });
 
@@ -149,7 +149,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
         1,
         outputs,
       );
-      expect(result.fee).toBe(336); // This number is calculated manually
+      expect(result.fee).toBe(345); // This number is calculated manually
       expect(result.selectedUTXOs.length).toEqual(2);
     });
 
@@ -163,7 +163,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
           txid: dataGenerator.generateRandomTxId(),
           vout: Math.floor(Math.random() * 10),
           scriptPubKey: nativeSegwit.scriptPubKey,
-          value: 1000,
+          value: 1009,
         },
         {
           txid: dataGenerator.generateRandomTxId(),
@@ -181,7 +181,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
         1,
         outputs,
       );
-      expect(result.fee).toBe(293); // This is the fee for 2 inputs and 2 outputs without change
+      expect(result.fee).toBe(302); // This is the fee for 2 inputs and 2 outputs without change
       expect(result.selectedUTXOs.length).toEqual(2);
     });
 
@@ -213,7 +213,7 @@ testingNetworks.forEach(({ networkName, network, dataGenerator }) => {
         1,
         outputs,
       );
-      expect(result.fee).toBe(225);
+      expect(result.fee).toBe(234);
       expect(result.selectedUTXOs.length).toEqual(1);
     });
   });