fix: should throw if funds can not cover the fee in withdraw and unbo…

…nding (#33)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "btc-staking-ts",
-  "version": "0.2.2",
+  "version": "0.2.3",
   "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",
@@ -45,4 +45,4 @@
     "@bitcoin-js/tiny-secp256k1-asmjs": "^2.2.3",
     "bitcoinjs-lib": "^6.1.5"
   }
-}
+}

src/index.ts

@@ -363,9 +363,13 @@ function withdrawalTransaction(
   }
   // withdraw tx always has 1 output only
   const estimatedFee = getEstimatedFee(feeRate, psbt.txInputs.length, 1);
+  const value = tx.outs[outputIndex].value - estimatedFee;
+  if (!value) {
+    throw new Error("Not enough funds to cover the fee for withdrawal transaction");
+  }
   psbt.addOutput({
     address: withdrawalAddress,
-    value: tx.outs[outputIndex].value - estimatedFee,
+    value,
   });
 
   return {
@@ -699,7 +703,10 @@ export function unbondingTransaction(
     scriptTree: outputScriptTree,
     network,
   });
-
+  const value = stakingTx.outs[outputIndex].value - transactionFee;
+  if (!value) {
+    throw new Error("Not enough funds to cover the fee for unbonding transaction");
+  }
   // Add the unbonding output
   psbt.addOutput({
     address: unbondingOutput.address!,