add initial implementation of get-utxo - an easy way to get unspent outputs

Author: makevoid

blockchain-api/get-utxos.js

@@ -0,0 +1,39 @@
+const { get } = require('axios')
+
+const bcInfoHost = "https://blockchain.info"
+const unspentUrl = (address) => `${bcInfoHost}/unspent?active=${address}&format=json&cors=true`
+
+// convert from blockchain.info format to bitcore-lib utxo format
+const convertUTXO = (utxo) => (
+  {
+    txId: utxo.tx_hash_big_endian,
+    vout: utxo.tx_output_n,
+    script: utxo.script,
+    satoshis: utxo.value,
+  }
+)
+
+const getUnspentOutputs = async ({ address }) => {
+  const url = unspentUrl(address)
+  const resp = await get(url)
+  const data = resp.data
+  if (data == "No free outputs to spend") return []
+  if (data == "Invalid Bitcoin Address")  throw Error(`Bitcoin address is not valid - address: ${address}`)
+  return data.unspent_outputs
+}
+
+// raise an error if there are no spendable outputs
+const checkUTXOs = ({ utxos, address }) => {
+  utxos = utxos.filter(utxo => utxo.confirmations > 0)
+  utxos = utxos.filter(utxo => utxo.value > 1000)
+  if (utxos.length == 0) throw Error(`No spendable outputs were found, please fund the address or wait for transactions to confirm - address: ${address}`)
+}
+
+const getUTXOs = async ({ address }) => {
+  let utxos = await getUnspentOutputs({ address })
+  checkUTXOs({ utxos, address })
+  utxos = utxos.map(convertUTXO)
+  return utxos
+}
+
+module.exports = getUTXOs