Bitcoin: Transferring BTC using Node js code fails with error “No signed inputs”
Error Handling in Bitcoin Node.js Code: “No Inputs Signed”
As a developer working with Bitcoin, you’ve probably encountered the infamous “Inputs Not Signed” error. This issue can be frustrating, especially when building a system that requires transferring funds from one user’s wallet to another. In this article, we’ll explore why this error occurs and provide instructions on how to resolve it using Node.js.
Understanding the Error
When a request is made in your code to transfer Bitcoin (BTC), the bitcoinjs-rs library (a popular choice for developing Bitcoin-based applications) attempts to create a new transaction. However, if the signature of the recipient’s wallet is not properly signed, the bitcoinjs-rs library will throw an error.
Unsigned Input Error
This error occurs when the sender and recipient wallets do not have matching private keys or their signatures are incorrect. The Bitcoinjs-rs library expects both parties to provide a valid signature for each transaction input (e.g., transferred UTXO).
When you try to create a new transaction without signed inputs, the library throws an error stating “Unsigned input”.
Node.js code example
Let’s take a closer look at how specific Node.js code might cause this problem:
const bitcoin = require('bitcoinjs-rs');
// Load a wallet (UTXO) from disk
const utxos = loadWallet();
// Create a new transaction without signed inputs
const tx = {
sender: 'Spendable', // sender address
receiver: 'Spendable', // recipient address
};
tx.inputs = [
bitcoin.TransactionInput.new({
address: "Spendable",
scriptSig: [bitcoin.SigType.HMAC, '0x1234567890abcdef'],
scriptPubKey: [bitcoin.ScriptPubKey.new([bitcoin.ScriptPubKey.ASSIGN_SCRIPT pubkey, '0x1234567890abcdef'])],
}),
];
// Sign the transaction inputs
tx.inputs.forEach((input) => {
bitcoin.signTransaction(input);
});
// Attempt to create a new transaction without signed inputs
const result = bitcoin.createTransaction(tx);
Solution
To resolve this issue, you must ensure that both parties provide a valid signature for each transaction input. Here are some steps to follow:
- Load and Verify UTXO
: Load the wallet UTXO from disk and verify its validity by checking its balance and ownership.
- Sign Input: Use bitcoin.signTransaction() to sign each input with the sender’s private key. You can use a library like BitcoinJS-Wallet-Node, or you can create your own implementation of this step.
- Create New Transaction: Create a new transaction using bitcoin.createTransaction(), passing in the signed inputs.
Here is an updated example code snippet:
“javascript
const bitcoin = require('bitcoinjs-rs');
// Load and Verify UTXO
const utxos = loadWallet();
utxos.forEach((txo) => {
if (!bitcoin.verifyTxHash(txo.hash, txo.outpoint)) {
console.error(Invalid transaction hash: ${txo.hash}`);
return;
}
});
// Enter signature
const sender = bitcoin.createAddress(‘Spendable’);
const receiver = bitcoin.createAddress(‘Received’);
const senderSign = bitcoin.signTransaction({
sender,
input: utxos.map((txo) => {
return bitcoin.TransactionInput.new({
address: txo.address,
scriptSig: bitcoin.SigType.HMAC, // Sign with sender’s private key
scriptPubKey: bitcoin.ScriptPubKey.new([bitcoin.ScriptPubKey.ASSIGN_SCRIPT.pubkey, ‘0x1234567890abcdef’])],
});
}),
});
// Create a new transaction
const result = bitcoin.createTransaction({
input: utxos.map((txo) => {
return bitcoin.TransactionInput.new({
address: txo.address,
scriptSig: bitcoin.SigType.HMAC, // Sign with sender’s private key
scriptPubKey: bitcoin.ScriptPubKey.new([bitcoin.ScriptPubKey.ASSIGN_SCRIPT.
