bitmessage-js/lib/pow.js
2015-01-30 20:13:09 +03:00

85 lines
2.3 KiB
JavaScript

/**
* Implements proof of work.
* @see {@link https://bitmessage.org/wiki/Proof_of_work}
* @module bitmessage/pow
*/
// TODO(Kagami): Find a way how to document object params properly.
"use strict";
var objectAssign = Object.assign || require("object-assign");
var bmcrypto = require("./crypto");
var platform = require("./platform");
var util = require("./_util");
/**
* Calculate target
* @param {Object} opts - Target options
* @return {number} Target.
*/
// Just a wrapper around platform-specific implementation.
exports.getTarget = function(opts) {
var payloadLength = opts.payloadLength || opts.payload.length;
return platform.getTarget({
ttl: opts.ttl,
payloadLength: payloadLength,
nonceTrialsPerByte: util.getTrials(opts),
payloadLengthExtraBytes: util.getExtraBytes(opts),
});
};
/**
* Check a POW.
* @param {Object} opts - Proof of work options
* @return {boolean} Is the proof of work sufficient.
*/
exports.check = function(opts) {
var initialHash;
var nonce;
if (opts.payload) {
nonce = opts.payload.slice(0, 8);
initialHash = bmcrypto.sha512(opts.payload.slice(8));
} else {
if (typeof opts.nonce === "number") {
nonce = new Buffer(8);
// High 32 bits.
nonce.writeUInt32BE(Math.floor(opts.nonce / 4294967296), 0, true);
// Low 32 bits.
nonce.writeUInt32BE(opts.nonce % 4294967296, 4, true);
} else {
nonce = opts.nonce;
}
initialHash = opts.initialHash;
}
var targetHi = Math.floor(opts.target / 4294967296);
var targetLo = opts.target % 4294967296;
var dataToHash = Buffer.concat([nonce, initialHash]);
var resultHash = bmcrypto.sha512(bmcrypto.sha512(dataToHash));
var trialHi = resultHash.readUInt32BE(0, true);
if (trialHi > targetHi) {
return false;
} else if (trialHi < targetHi) {
return true;
} else {
var trialLo = resultHash.readUInt32BE(4, true);
return trialLo <= targetLo;
}
};
/**
* Do a POW.
* @param {Object} opts - Proof of work options
* @return {Promise.<Buffer>} A promise that contains computed nonce for
* the given target when fulfilled.
*/
exports.doAsync = function(opts) {
var initialHash;
if (opts.payload) {
initialHash = bmcrypto.sha512(opts.payload);
} else {
initialHash = opts.initialHash;
}
opts = objectAssign({}, opts, {initialHash: initialHash});
return platform.pow(opts);
};