unrar-js/lib/ByteBuffer.js

Pure javascript unrar library. salvaged from bitjs.

/**
 * A write-only Byte buffer which uses a Uint8 Typed Array as a backing store.
 * @param {number} numBytes The number of bytes to allocate.
 * @constructor
 */
function ByteBuffer(numBytes) {
    if (typeof numBytes != typeof 1 || numBytes <= 0) {
        throw "Error! ByteBuffer initialized with '" + numBytes + "'";
    }
    this.data = new Uint8Array(numBytes);
    this.ptr = 0;
};


/**
 * @param {number} b The byte to insert.
 */
ByteBuffer.prototype.insertByte = function(b) {
    // TODO: throw if byte is invalid?
    this.data[this.ptr++] = b;
};


/**
 * @param {Array.<number>|Uint8Array|Int8Array} bytes The bytes to insert.
 */
ByteBuffer.prototype.insertBytes = function(bytes) {
    // TODO: throw if bytes is invalid?
    this.data.set(bytes, this.ptr);
    this.ptr += bytes.length;
};


/**
 * Writes an unsigned number into the next n bytes.  If the number is too large
 * to fit into n bytes or is negative, an error is thrown.
 * @param {number} num The unsigned number to write.
 * @param {number} numBytes The number of bytes to write the number into.
 */
ByteBuffer.prototype.writeNumber = function(num, numBytes) {
    if (numBytes < 1) {
        throw 'Trying to write into too few bytes: ' + numBytes;
    }
    if (num < 0) {
        throw 'Trying to write a negative number (' + num +
            ') as an unsigned number to an ArrayBuffer';
    }
    if (num > (Math.pow(2, numBytes * 8) - 1)) {
        throw 'Trying to write ' + num + ' into only ' + numBytes + ' bytes';
    }

    // Roll 8-bits at a time into an array of bytes.
    var bytes = [];
    while (numBytes-- > 0) {
        var eightBits = num & 255;
        bytes.push(eightBits);
        num >>= 8;
    }

    this.insertBytes(bytes);
};


/**
 * Writes a signed number into the next n bytes.  If the number is too large
 * to fit into n bytes, an error is thrown.
 * @param {number} num The signed number to write.
 * @param {number} numBytes The number of bytes to write the number into.
 */
ByteBuffer.prototype.writeSignedNumber = function(num, numBytes) {
    if (numBytes < 1) {
        throw 'Trying to write into too few bytes: ' + numBytes;
    }

    var HALF = Math.pow(2, (numBytes * 8) - 1);
    if (num >= HALF || num < -HALF) {
        throw 'Trying to write ' + num + ' into only ' + numBytes + ' bytes';
    }

    // Roll 8-bits at a time into an array of bytes.
    var bytes = [];
    while (numBytes-- > 0) {
        var eightBits = num & 255;
        bytes.push(eightBits);
        num >>= 8;
    }

    this.insertBytes(bytes);
};


/**
 * @param {string} str The ASCII string to write.
 */
ByteBuffer.prototype.writeASCIIString = function(str) {
    for (var i = 0; i < str.length; ++i) {
        var curByte = str.charCodeAt(i);
        if (curByte < 0 || curByte > 255) {
            throw 'Trying to write a non-ASCII string!';
        }
        this.insertByte(curByte);
    }
};

module.exports = ByteBuffer;