s101.js

const EventEmitter = require('events').EventEmitter;
const util = require('util');
const SmartBuffer = require('smart-buffer').SmartBuffer;
const winston = require('winston');

const S101_BOF = 0xFE;
const S101_EOF = 0xFF;
const S101_CE  = 0xFD;
const S101_XOR = 0x20;
const S101_INV = 0xF8;

const SLOT = 0x00;

const MSG_EMBER = 0x0E;

const CMD_EMBER = 0x00;
const CMD_KEEPALIVE_REQ = 0x01;
const CMD_KEEPALIVE_RESP = 0x02;

const VERSION = 0x01;

const FLAG_SINGLE_PACKET = 0xC0;
const FLAG_FIRST_MULTI_PACKET = 0x80;
const FLAG_LAST_MULTI_PACKET = 0x40;
const FLAG_EMPTY_PACKET = 0x20;
const FLAG_MULTI_PACKET = 0x00;

const DTD_GLOW = 0x01;
const DTD_VERSION_MAJOR = 0x02;
const DTD_VERSION_MINOR = 0x1F;

const CRC_TABLE = [
    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
    0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
    0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
    0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
    0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
    0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
    0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
    0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
    0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
    0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
    0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
    0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
    0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
    0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
    0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
    0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
    0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
    0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
    0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
    0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
    0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
    0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
];

function S101Codec() {
    var self = this;
    S101Codec.super_.call(this);
    self.inbuf = new SmartBuffer();
    self.emberbuf = new SmartBuffer();
    self.escaped = false;
}

util.inherits(S101Codec, EventEmitter);

S101Codec.prototype.dataIn = function(buf) {
    var self = this;
    for(var i=0; i<buf.length; i++) {
        var b = buf.readUInt8(i);
        if(self.escaped) {
            self.inbuf.writeUInt8(b ^ S101_XOR);
            self.escaped = false;
        } else if(b == S101_CE) {
            self.escaped = true;
        } else if(b == S101_BOF) {
            self.inbuf.clear();
            self.escaped = false;
        } else if(b == S101_EOF) {
            self.inbuf.moveTo(0);
            self.handleFrame(self.inbuf);
            self.inbuf.clear();
        } else {
            self.inbuf.writeUInt8(b);
        }
    }
}

S101Codec.prototype.handleFrame = function(frame) {
    var self = this;
    if(!validateFrame(frame.toBuffer())) {
        /*winston.error('dropping frame of length %d with invalid CRC',
            frame.length);*/
        return;
    }

    var slot = frame.readUInt8();
    var message = frame.readUInt8();
    if(slot != SLOT || message != MSG_EMBER) {
        winston.error('dropping frame of length %d (not an ember frame; slot=%d, msg=%d)',
            frame.length, slot, message);
        return;
    }

    var command = frame.readUInt8();
    if(command == CMD_KEEPALIVE_REQ) {
        winston.debug('received keepalive request');
        self.emit('keepaliveReq');
    } else if(command == CMD_KEEPALIVE_RESP) {
        winston.debug('received keepalive response');
        self.emit('keepaliveResp');
    } else if(command == CMD_EMBER) {
        self.handleEmberFrame(frame);
    } else {
        winston.error('dropping frame of length %d with unknown command %d',
            frame.length, command);
        return;
    }
}

S101Codec.prototype.handleEmberFrame = function(frame) {
    var self = this;
    var version = frame.readUInt8();
    var flags = frame.readUInt8();
    var dtd = frame.readUInt8();
    var appBytes = frame.readUInt8();

    if(version != VERSION) {
        winston.warn('Unknown ember frame version %d', version);
    }

    if(dtd != DTD_GLOW) {
        winston.error('Dropping frame with non-Glow DTD');
        return;
    }

    var glowMinor = 0;
    var glowMajor = 0;

    if(appBytes < 2) {
        winston.warn('Frame missing Glow DTD version');
        frame.skip(appBytes);
    } else {
        glowMinor = frame.readUInt8();
        glowMajor = frame.readUInt8();
        appBytes -= 2;
        if(appBytes > 0) {
            frame.skip(appBytes);
            winston.warn('App bytes with unknown meaning left over');
        }
    }


    var payload = frame.readBuffer();
    payload = payload.slice(0, payload.length - 2);
    if(flags & FLAG_FIRST_MULTI_PACKET) {
        winston.debug('multi ember packet start');
        self.emberbuf.clear();
    }
    if ((flags & FLAG_EMPTY_PACKET) === 0) {
        // not empty, save the payload
        self.emberbuf.writeBuffer(payload);
    }
    if(flags & FLAG_LAST_MULTI_PACKET) {
        winston.debug('multi ember packet end');
        self.emberbuf.moveTo(0);
        self.handleEmberPacket(self.emberbuf);
        self.emberbuf.clear();
    }
}

S101Codec.prototype.handleEmberPacket = function(packet) {
    var self = this;

    winston.debug('ember packet');
    self.emit('emberPacket', packet.toBuffer());
}

var makeBERFrame = function(flags, data) {
    var frame = new SmartBuffer();
    frame.writeUInt8(S101_BOF);
    frame.writeUInt8(SLOT);
    frame.writeUInt8(MSG_EMBER);
    frame.writeUInt8(CMD_EMBER);
    frame.writeUInt8(VERSION);
    frame.writeUInt8(flags);
    frame.writeUInt8(DTD_GLOW);
    frame.writeUInt8(2); // number of app bytes
    frame.writeUInt8(DTD_VERSION_MINOR);
    frame.writeUInt8(DTD_VERSION_MAJOR);
    frame.writeBuffer(data);
    return finalizeBuffer(frame);
}

S101Codec.prototype.encodeBER = function(data) {
    var frames = [];
    var encbuf = new SmartBuffer();
    for(var i=0; i<data.length; i++) {
        var b = data.readUInt8(i);
        if(b < S101_INV) {
            encbuf.writeUInt8(b);
        } else {
            encbuf.writeUInt8(S101_CE);
            encbuf.writeUInt8(b ^ S101_XOR);
        }

        if(encbuf.length >= 1024 && i < data.length-1) {
            if(frames.length == 0) {
                frames.push(makeBERFrame(FLAG_FIRST_MULTI_PACKET, encbuf.toBuffer()));
            } else {
                frames.push(makeBERFrame(FLAG_MULTI_PACKET, encbuf.toBuffer()));
            }
            encbuf.clear();
        }
    }

    if(frames.length == 0) {
        frames.push(makeBERFrame(FLAG_SINGLE_PACKET, encbuf.toBuffer()));
    } else {
        frames.push(makeBERFrame(FLAG_LAST_MULTI_PACKET, encbuf.toBuffer()));
    }

    return frames;
};

S101Codec.prototype.keepAliveRequest = function() {
    var packet = new SmartBuffer();
    packet.writeUInt8(S101_BOF);
    packet.writeUInt8(SLOT);
    packet.writeUInt8(MSG_EMBER);
    packet.writeUInt8(CMD_KEEPALIVE_REQ);
    packet.writeUInt8(VERSION);
    return finalizeBuffer(packet);
}

S101Codec.prototype.keepAliveResponse = function() {
    var packet = new SmartBuffer();
    packet.writeUInt8(S101_BOF);
    packet.writeUInt8(SLOT);
    packet.writeUInt8(MSG_EMBER);
    packet.writeUInt8(CMD_KEEPALIVE_RESP);
    packet.writeUInt8(VERSION);
    return finalizeBuffer(packet);
}

var finalizeBuffer = function(smartbuf) {
    var crc = (~calculateCRCCE(smartbuf.toBuffer().slice(1, smartbuf.length))) & 0xFFFF;
    var crc_hi = crc >> 8;
    var crc_lo = crc & 0xFF;

    if(crc_lo < S101_INV) {
        smartbuf.writeUInt8(crc_lo);
    } else {
        smartbuf.writeUInt8(S101_CE);
        smartbuf.writeUInt8(crc_lo ^ S101_XOR);
    }

    if(crc_hi < S101_INV) {
        smartbuf.writeUInt8(crc_hi);
    } else {
        smartbuf.writeUInt8(S101_CE);
        smartbuf.writeUInt8(crc_hi ^ S101_XOR);
    }

    smartbuf.writeUInt8(S101_EOF);
    return smartbuf.toBuffer();
}

var calculateCRC = function(buf) {
    var crc = 0xFFFF;
    for(var i=0; i < buf.length; i++) {
        var b = buf.readUInt8(i);
        crc = ((crc >> 8) ^ CRC_TABLE[(crc ^ b) & 0xFF]) & 0xFFFF;
    }
    return crc;
}

var calculateCRCCE = function(buf) {
    var crc = 0xFFFF;
    for(var i=0; i < buf.length; i++) {
        var b = buf.readUInt8(i);
        if(b == S101_CE) {
            b = S101_XOR ^ buf.readUInt8(++i);
        }
        crc = ((crc >> 8) ^ CRC_TABLE[(crc ^ b) & 0xFF]) & 0xFFFF;
    }
    return crc;
}

var validateFrame = function(buf) {
    return calculateCRC(buf) == 0xF0B8;
}

S101Codec.prototype.validateFrame = validateFrame;

module.exports = S101Codec;