ranges

    RANGE_REGEX = /^bytes=(\d+)?-(\d+)?$/;
    function parseRange (str) {
        if (!RANGE_REGEX.test(str)) {
            throw new Error("Incorrect format.");
        }
        var match = RANGE_REGEX.exec(str);
        var ranges = {};
        var start = match[1] ? parseInt(match[1], 10) : 0;
        var end = match[2] ? parseInt(match[2], 10) : Infinity;
        ranges.start = Math.min(start, end);
        ranges.end = Math.max(start, end);
        if (ranges.start === 0) {
            ranges.start = null;
        }
        if (ranges.end === Infinity) {
            ranges.end = null;
        }
        return ranges;
    };

    function stringifyRange(obj) {
        var start = obj.start;
        var end = obj.end;
        if (start === null || end === null) {
            if (start === null) {
                start = "";
            }
            if (end === null) {
                end = "";
            }
        } else {
            if (start > end) {
                var temp = start;
                start = end;
                end = temp;
            }
        }
        return "bytes=" + start + "-" + end;
    };