doc: add copy/paste keyUtils example

Author: coolaj86

examples/key-utils.js

@@ -0,0 +1,72 @@
+"use strict";
+
+let Secp256k1 = require("@dashincubator/secp256k1");
+
+/** @typedef {Required<import('dashtx').TxKeyUtils>} TxKeyUtils */
+/**
+ * @typedef KeyUtilsPartial
+ * @prop {KeySet} set
+ */
+/** @typedef {TxKeyUtils & KeyUtilsPartial} KeyUtils */
+
+/**
+ * @callback KeySet
+ * @param {String} id
+ * @param {KeyInfo} keyInfo
+ */
+
+/** @type {KeyUtils} */
+let KeyUtils = module.exports;
+
+/**
+ * @typedef KeyInfo
+ * @prop {String} [walletId] - from DashHd.toId(walletKey)
+ * @prop {String} [hdpath] - ex: m/44'/5'/0'/0/0
+ * @prop {String} address - generally convenient
+ * @prop {Uint8Array} privateKey - for signing
+ * @prop {Uint8Array} publicKey - for TxInput
+ * @prop {String} pubKeyHash - for TxOutput
+ */
+
+/** @type Object.<String, KeyInfo> */
+let keysMap = {};
+
+KeyUtils.set = function (id, keyInfo) {
+  if (!id) {
+    throw new Error(`key identifier is not defined)`);
+  }
+  keysMap[id] = keyInfo;
+};
+
+KeyUtils.sign = async function (privKeyBytes, hashBytes) {
+  let sigOpts = { canonical: true, extraEntropy: true };
+  let sigBytes = await Secp256k1.sign(hashBytes, privKeyBytes, sigOpts);
+  return sigBytes;
+};
+KeyUtils.getPrivateKey = async function (input) {
+  if (!input.address) {
+    //throw new Error('should put the address on the input there buddy...');
+    console.warn("missing address:", input.txid, input.outputIndex);
+    return null;
+  }
+
+  let keyInfo = keysMap[input.address];
+  return keyInfo.privateKey;
+};
+
+KeyUtils.getPublicKey = async function (txInput, i) {
+  let privKeyBytes = await KeyUtils.getPrivateKey(txInput, i);
+  if (!privKeyBytes) {
+    return null;
+  }
+  let pubKeyBytes = await KeyUtils.toPublicKey(privKeyBytes);
+
+  return pubKeyBytes;
+};
+
+KeyUtils.toPublicKey = async function (privKeyBytes) {
+  let isCompressed = true;
+  let pubKeyBytes = Secp256k1.getPublicKey(privKeyBytes, isCompressed);
+
+  return pubKeyBytes;
+};