/*!
* framer.js - packet framer for bcoin
* Copyright (c) 2014-2015, Fedor Indutny (MIT License)
* Copyright (c) 2014-2017, Christopher Jeffrey (MIT License).
* https://github.com/bcoin-org/bcoin
*/
'use strict';
const assert = require('bsert');
const Network = require('../protocol/network');
const hash256 = require('bcrypto/lib/hash256');
/**
* Protocol Message Framer
* @alias module:net.Framer
*/
class Framer {
/**
* Create a framer.
* @constructor
* @param {Network} network
*/
constructor(network) {
this.network = Network.get(network);
}
/**
* Frame a payload with a header.
* @param {String} cmd - Packet type.
* @param {Buffer} payload
* @param {Buffer?} checksum - Precomputed checksum.
* @returns {Buffer} Payload with header prepended.
*/
packet(cmd, payload, checksum) {
assert(payload, 'No payload.');
assert(cmd.length < 12);
assert(payload.length <= 0xffffffff);
const msg = Buffer.allocUnsafe(24 + payload.length);
// Magic value
msg.writeUInt32LE(this.network.magic, 0, true);
// Command
msg.write(cmd, 4, 'ascii');
for (let i = 4 + cmd.length; i < 16; i++)
msg[i] = 0;
// Payload length
msg.writeUInt32LE(payload.length, 16, true);
if (!checksum)
checksum = hash256.digest(payload);
// Checksum
checksum.copy(msg, 20, 0, 4);
payload.copy(msg, 24);
return msg;
}
}
/*
* Expose
*/
module.exports = Framer;