bitmessage-js/docs/pow.js.html
Kagami Hiiragi 034f611a98 Publish docs
2015-02-12 13:44:15 +03:00

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<h1 class="page-title">Source: pow.js</h1>
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<pre class="prettyprint source linenums"><code>/**
* Implements proof of work.
* @see {@link https://bitmessage.org/wiki/Proof_of_work}
* @module bitmessage/pow
*/
"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
* @param {number} opts.ttl - Time to live of the message in seconds
* @param {number} opts.payloadLength - Length of the message payload
* (with nonce)
* @param {Buffer} opts.payload - ...or payload itself
* @param {number=} opts.nonceTrialsPerByte - This number is the average
* number of nonce trials a node will have to perform to meet the Proof
* of Work requirement. 1000 is the network minimum so any lower values
* will be automatically raised to 1000.
* @param {number=} opts.payloadLengthExtraBytes - This number is added
* to the data length to make sending small messages more difficult.
* 1000 is the network minimum so any lower values will be automatically
* raised to 1000.
* @return {number} Target.
* @function
* @static
*/
// Just a wrapper around platform-specific implementation.
var getTarget = 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
* @param {number} opts.target - Proof of work target or pass
* [getTarget]{@link module:bitmessage/pow.getTarget} options to `opts`
* to compute it
* @param {Buffer} opts.payload - Message payload (with nonce)
* @param {(number|Buffer)} opts.nonce - ...or already derived nonce
* @param {Buffer} opts.initialHash - ...and initial hash
* @return {boolean} Is the proof of work sufficient.
*/
exports.check = function(opts) {
var initialHash;
var nonce;
var target = opts.target;
if (target === undefined) {
target = getTarget(opts);
}
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(target / 4294967296);
var targetLo = 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 &lt; targetHi) {
return true;
} else {
var trialLo = resultHash.readUInt32BE(4, true);
return trialLo &lt;= targetLo;
}
};
/**
* Do a POW.
* @param {Object} opts - Proof of work options
* @param {Buffer} opts.data - Object message payload without nonce to
* get the initial hash from
* @param {Buffer} opts.initialHash - ...or already computed initial
* hash
* @param {number} opts.target - POW target
* @param {number=} opts.poolSize - POW calculation pool size (by
* default equals to number of cores)
* @return {Promise.&lt;number>} A promise that contains computed nonce for
* the given target when fulfilled.
*/
exports.doAsync = function(opts) {
var initialHash;
if (opts.data) {
initialHash = bmcrypto.sha512(opts.data);
} else {
initialHash = opts.initialHash;
}
opts = objectAssign({}, opts, {initialHash: initialHash});
return platform.pow(opts);
};
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