web3-provider-engine/dist/es5/subproviders/gasprice.js

A JavaScript library for composing Ethereum provider objects using middleware modules

"use strict";

/*
 * Calculate gasPrice based on last blocks.
 * @author github.com/axic
 *
 * FIXME: support minimum suggested gas and perhaps other options from geth:
 * https://github.com/ethereum/go-ethereum/blob/master/eth/gasprice.go
 * https://github.com/ethereum/go-ethereum/wiki/Gas-Price-Oracle
 */

var map = require('async/map');
var inherits = require('util').inherits;
var Subprovider = require('./subprovider.js');
module.exports = GaspriceProvider;
inherits(GaspriceProvider, Subprovider);
function GaspriceProvider(opts) {
  opts = opts || {};
  this.numberOfBlocks = opts.numberOfBlocks || 10;
  this.delayInBlocks = opts.delayInBlocks || 5;
}
GaspriceProvider.prototype.handleRequest = function (payload, next, end) {
  if (payload.method !== 'eth_gasPrice') return next();
  var self = this;
  self.emitPayload({
    method: 'eth_blockNumber'
  }, function (err, res) {
    // FIXME: convert number using a bignum library
    var lastBlock = parseInt(res.result, 16) - self.delayInBlocks;
    var blockNumbers = [];
    for (var i = 0; i < self.numberOfBlocks; i++) {
      blockNumbers.push('0x' + lastBlock.toString(16));
      lastBlock--;
    }
    function getBlock(item, end) {
      self.emitPayload({
        method: 'eth_getBlockByNumber',
        params: [item, true]
      }, function (err, res) {
        if (err) return end(err);
        if (!res.result) return end(new Error("GaspriceProvider - No block for \"".concat(item, "\"")));
        end(null, res.result.transactions);
      });
    }

    // FIXME: this could be made much faster
    function calcPrice(err, transactions) {
      // flatten array
      transactions = transactions.reduce(function (a, b) {
        return a.concat(b);
      }, []);

      // leave only the gasprice
      // FIXME: convert number using a bignum library
      transactions = transactions.map(function (a) {
        return parseInt(a.gasPrice, 16);
      }, []);

      // order ascending
      transactions.sort(function (a, b) {
        return a - b;
      });

      // ze median
      var half = Math.floor(transactions.length / 2);
      var median;
      if (transactions.length % 2) median = transactions[half];else median = Math.floor((transactions[half - 1] + transactions[half]) / 2.0);
      end(null, median);
    }
    map(blockNumbers, getBlock, calcPrice);
  });
};