coinselect



An unspent transaction output (UTXO) selection module for bitcoin.

WARNING: Value units are in satoshis, not Bitcoin.

Algorithms

Module | Algorithm | Re-orders UTXOs?
-|-|-
require('coinselect') | Blackjack, with Accumulative fallback | By Descending Value
require('coinselect/accumulative') | Accumulative - accumulates inputs until the target value (+fees) is reached, skipping detrimental inputs | -
require('coinselect/blackjack') | Blackjack - accumulates inputs until the target value (+fees) is matched, does not accumulate inputs that go over the target value (within a threshold) | -
require('coinselect/break') | Break - breaks the input values into equal denominations of output (as provided) | -
require('coinselect/split') | Split - splits the input values evenly between all outputs, any provided output with .value remains unchanged | -

Note: Each algorithm will add a change output if the input - output - fee value difference is over a dust threshold.
This is calculated independently by utils.finalize, irrespective of the algorithm chosen, for the purposes of safety.

Pro-tip: if you want to send-all inputs to an output address, coinselect/split with a partial output (.address defined, no .value) can be used to send-all, while leaving an appropriate amount for the fee.

Example

`` javascript
let coinSelect = require('coinselect')
let feeRate = 55 // satoshis per byte
let utxos = [
...,
{
txId: '...',
vout: 0,
...,
value: 10000,
// For use with PSBT:
// not needed for coinSelect, but will be passed on to inputs later
nonWitnessUtxo: Buffer.from('...full raw hex of txId tx...', 'hex'),
// OR
// if your utxo is a segwit output, you can use witnessUtxo instead
witnessUtxo: {
script: Buffer.from('... scriptPubkey hex...', 'hex'),
value: 10000 // 0.0001 BTC and is the exact same as the value above
}
}
]
let targets = [
...,
{
address: '1EHNa6Q4Jz2uvNExL497mE43ikXhwF6kZm',
value: 5000
}
]

// ...
let { inputs, outputs, fee } = coinSelect(utxos, targets, feeRate)

// the accumulated fee is always returned for analysis
console.log(fee)

// .inputs and .outputs will be undefined if no solution was found
if (!inputs || !outputs) return

let psbt = new bitcoin.Psbt()

inputs.forEach(input =>
psbt.addInput({
hash: input.txId,
index: input.vout,
nonWitnessUtxo: input.nonWitnessUtxo,
// OR (not both)
witnessUtxo: input.witnessUtxo,
})
)
outputs.forEach(output => {
// watch out, outputs may have been added that you need to provide
// an output address/script for
if (!output.address) {
output.address = wallet.getChangeAddress()
wallet.nextChangeAddress()
}

psbt.addOutput({
address: output.address,
value: output.value,
})
})
``

License MIT