index.js

'use strict'
const ethUtil = require('ethereumjs-util')
const fees = require('ethereum-common/params')
const BN = ethUtil.BN

// secp256k1n/2
const N_DIV_2 = new BN('7fffffffffffffffffffffffffffffff5d576e7357a4501ddfe92f46681b20a0', 16)

/**
 * Creates a new transaction object
 * @class {Buffer|Array} data a transaction can be initiailized with either a buffer containing the RLP serialized transaction or an array of buffers relating to each of the tx Properties, listed in order below in the exmple. Or lastly an Object containing the Properties of the transaction like in the Usage example
 *
 * For Object and Arrays each of the elements can either be a Buffer, a hex-prefixed (0x) String , Number, or an object with a toBuffer method such as Bignum
 * @example
 * var rawTx = {
 *   nonce: '00',
 *   gasPrice: '09184e72a000',
 *   gasLimit: '2710',
 *   to: '0000000000000000000000000000000000000000',
 *   value: '00',
 *   data: '7f7465737432000000000000000000000000000000000000000000000000000000600057',
 *   v: '1c',
 *   r: '5e1d3a76fbf824220eafc8c79ad578ad2b67d01b0c2425eb1f1347e8f50882ab',
 *   s '5bd428537f05f9830e93792f90ea6a3e2d1ee84952dd96edbae9f658f831ab13'
 * };
 * var tx = new Transaction(rawTx);
 * @prop {Buffer} raw The raw rlp decoded transaction
 * @prop {Buffer} nonce
 * @prop {Buffer} to the to address
 * @prop {Buffer} value the amount of ether sent
 * @prop {Buffer} data this will contain the data of the message or the init of a contract
 * @prop {Buffer} v EC signature parameter
 * @prop {Buffer} r EC signature parameter
 * @prop {Buffer} s EC recovery ID
 */
module.exports = class Transaction {
  constructor (data) {
    // Define Properties
    const fields = [{
      name: 'nonce',
      length: 32,
      allowLess: true,
      default: new Buffer([])
    }, {
      name: 'gasPrice',
      length: 32,
      allowLess: true,
      default: new Buffer([])
    }, {
      name: 'gasLimit',
      alias: 'gas',
      length: 32,
      allowLess: true,
      default: new Buffer([])
    }, {
      name: 'to',
      allowZero: true,
      length: 20,
      default: new Buffer([])
    }, {
      name: 'value',
      length: 32,
      allowLess: true,
      default: new Buffer([])
    }, {
      name: 'data',
      alias: 'input',
      allowZero: true,
      default: new Buffer([])
    }, {
      name: 'v',
      length: 1,
      default: new Buffer([0x1c])
    }, {
      name: 'r',
      length: 32,
      allowLess: true,
      default: new Buffer([])
    }, {
      name: 's',
      length: 32,
      allowLess: true,
      default: new Buffer([])
    }]

    /**
     * Returns the rlp encoding of the transaction
     * @method serialize
     * @return {Buffer}
     */
    // attached serialize
    ethUtil.defineProperties(this, fields, data)

    /**
     * @prop {Buffer} from (read only) sender address of this transaction, mathematically derived from other parameters.
     */
    Object.defineProperty(this, 'from', {
      enumerable: true,
      configurable: true,
      get: this.getSenderAddress.bind(this)
    })

    this._homestead = true
  }

  /**
   * If the tx's `to` is to the creation address
   * @return {Boolean}
   */
  toCreationAddress () {
    return this.to.toString('hex') === ''
  }

  /**
   * Computes a sha3-256 hash of the serialized tx
   * @param {Boolean} [signature=true] whether or not to inculde the signature
   * @return {Buffer}
   */
  hash (signature) {
    let toHash

    if (typeof signature === 'undefined') {
      signature = true
    }

    toHash = signature ? this.raw : this.raw.slice(0, 6)

    // create hash
    return ethUtil.rlphash(toHash)
  }

  /**
   * returns the sender's address
   * @return {Buffer}
   */
  getSenderAddress () {
    if (this._from) {
      return this._from
    }
    const pubkey = this.getSenderPublicKey()
    this._from = ethUtil.publicToAddress(pubkey)
    return this._from
  }

  /**
   * returns the public key of the sender
   * @return {Buffer}
   */
  getSenderPublicKey () {
    if (!this._senderPubKey || !this._senderPubKey.length) {
      this.verifySignature()
    }
    return this._senderPubKey
  }

  /**
   * Determines if the signature is valid
   * @return {Boolean}
   */
  verifySignature () {
    const msgHash = this.hash(false)

    // All transaction signatures whose s-value is greater than secp256k1n/2 are considered invalid.
    if (this._homestead && new BN(this.s).cmp(N_DIV_2) === 1) {
      return false
    }

    try {
      this._senderPubKey = ethUtil.ecrecover(msgHash, this.v, this.r, this.s)
    } catch (e) {
      return false
    }

    return !!this._senderPubKey
  }

  /**
   * sign a transaction with a given a private key
   * @param {Buffer} privateKey
   */
  sign (privateKey) {
    const msgHash = this.hash(false)
    const sig = ethUtil.ecsign(msgHash, privateKey)
    Object.assign(this, sig)
  }

  /**
   * The amount of gas paid for the data in this tx
   * @return {BN}
   */
  getDataFee () {
    const data = this.raw[5]
    const cost = new BN(0)
    for (var i = 0; i < data.length; i++) {
      data[i] === 0 ? cost.iaddn(fees.txDataZeroGas.v) : cost.iaddn(fees.txDataNonZeroGas.v)
    }
    return cost
  }

  /**
   * the minimum amount of gas the tx must have (DataFee + TxFee + Creation Fee)
   * @return {BN}
   */
  getBaseFee () {
    const fee = this.getDataFee().iaddn(fees.txGas.v)
    if (this._homestead && this.toCreationAddress()) {
      fee.iaddn(fees.txCreation.v)
    }
    return fee
  }

  /**
   * the up front amount that an account must have for this transaction to be valid
   * @return {BN}
   */
  getUpfrontCost () {
    return new BN(this.gasLimit)
      .imul(new BN(this.gasPrice))
      .iadd(new BN(this.value))
  }

  /**
   * validates the signature and checks to see if it has enough gas
   * @param {Boolean} [stringError=false] whether to return a string with a dscription of why the validation failed or return a Bloolean
   * @return {Boolean|String}
   */
  validate (stringError) {
    const errors = []
    if (!this.verifySignature()) {
      errors.push('Invalid Signature')
    }

    if (this.getBaseFee().cmp(new BN(this.gasLimit)) > 0) {
      errors.push([`gas limit is to low. Need at least ${this.getBaseFee()}`])
    }

    if (stringError === undefined || stringError === false) {
      return errors.length === 0
    } else {
      return errors.join(' ')
    }
  }
}