coinselect

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

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