ethernet-ip/src/enip/cip/epath/segments/data/index.js

A simple node interface for Ethernet/IP.

const Types = {
    Simple: 0x80,
    ANSI_EXTD: 0x91
};

const ElementTypes = {
    UINT8: 0x28,
    UINT16: 0x29,
    UINT32: 0x2a
};

/**
 * Builds EPATH Data Segment
 *
 * @param {string|buffer} data
 * @param {boolean} [ANSI=true] Declare if ANSI Extended or Simple
 * @returns {buffer}
 */
const build = (data, ANSI = true) => {
    if (!(typeof data === "string" || Buffer.isBuffer(data)))
        throw new Error("Data Segment Data Must be a String or Buffer");

    // Build Element Segment If Int
    if (data % 1 === 0) return elementBuild(parseInt(data));

    // Build symbolic segment by default
    return symbolicBuild(data, ANSI);
};

/**
 * Builds EPATH Symbolic Segment
 *
 * @param {string|buffer} data
 * @param {boolean} [ANSI=true] Declare if ANSI Extended or Simple
 * @returns {buffer}
 */
const symbolicBuild = (data, ANSI = true) => {
    // Initialize Buffer
    let buf = Buffer.alloc(2);

    // Write Appropriate Segment Byte
    buf.writeUInt8(ANSI ? Types.ANSI_EXTD : Types.Simple, 0);

    // Write Appropriate Length
    buf.writeUInt8(ANSI ? data.length : Math.ceil(data.length / 2), 1);

    // Append Data
    buf = Buffer.concat([buf, Buffer.from(data)]);

    // Add Pad Byte if Odd Length
    if (buf.length % 2 === 1) buf = Buffer.concat([buf, Buffer.alloc(1)]); // Pad Odd Length Strings

    return buf;
};

/**
 * Builds EPATH Element Segment
 *
 * @param {string} data
 * @returns {buffer}
 */
const elementBuild = data => {
    // Get Element Length - Data Access 2 - IOI Segments - Element Segments
    let type;
    let dataBuf;

    if (data < 256) {
        type = ElementTypes.UINT8; // UNIT8 x28 xx
        dataBuf = Buffer.alloc(1);
        dataBuf.writeUInt8(data);
    } else if (data < 65536) {
        type = ElementTypes.UINT16; // UINT16 x29 00 xx xx
        dataBuf = Buffer.alloc(3);
        dataBuf.writeUInt16LE(data, 1);
    } else {
        type = ElementTypes.UINT32; // UINT32 x2a 00 xx xx xx xx
        dataBuf = Buffer.alloc(5);
        dataBuf.writeUInt32LE(data, 1);
    }

    // Initialize Buffer
    let buf = Buffer.alloc(1);

    // Write Appropriate Segment Byte
    buf.writeUInt8(type, 0);

    // Append Data
    buf = Buffer.concat([buf, dataBuf]);

    return buf;
};

module.exports = { Types, build };