bencode.js

exports.encode = function encode(s){
    var type = typeof s, result, i, sLen, prop, props;
    if (type === 'number') {
        return 'i' + s + 'e';
    }
    else 
        if (type === 'string') {
            return s.length + ':' + s;
        }
        else 
            if (type === 'object') {
                if (s) {
                    if (s instanceof Array) {
                        result = 'l';
                        for (i = 0, sLen = s.length; i < sLen; i += 1) {
                            result += encode(s[i]);
                        }
                        return result + 'e';
                    }
                    else {
                        result = 'd';
                        props = [];
                        for (prop in s) {
                            if (s.hasOwnProperty(prop)) {
                                props.push(prop);
                            }
                        }
                        props.sort();
                        for (i = 0, sLen = props.length; i < sLen; i += 1) {
                            prop = props[i];
                            result += encode(prop) + encode(s[prop]);
                        }
                        return result + 'e';
                    }
                }
                throw "unexpected null";
            }
            else {
                throw "unexpected type " + type;
            }
};

function checkedIndexOf(s, c){
    var result = s.indexOf(c);
    if (result < 0) {
        throw "expected a " + c;
    }
    return result;
}

function decodeInt(s){
    s = s.substring(1);
    var e = checkedIndexOf(s, 'e');
    return [parseInt(s.substring(0, e), 10), s.substring(e + 1)];
}

function decodeString(s){
    var e = checkedIndexOf(s, ':'), len = parseInt(s.substring(0, e), 10), startOfString = e + 1, endOfString = startOfString + len;
    return [s.substring(startOfString, endOfString), s.substring(endOfString)];
}

// Predeclaration to make jslint happy.
var decode2;

function decodeList(s){
    s = s.substring(1);
    var a = [], s2;
    while (true) {
        if (s.length === 0) {
            throw "end of input while looking for 'e'";
        }
        if (s.charAt(0) === 'e') {
            return [a, s.substring(1)];
        }
        else {
            s2 = decode2(s);
            a.push(s2[0]);
            s = s2[1];
        }
    }
}

function decodeDictionary(s){
    s = s.substring(1);
    var a = {}, s2, k;
    while (true) {
        if (s.length === 0) {
            throw "end of input while looking for 'e'";
        }
        if (s.charAt(0) === 'e') {
            return [a, s.substring(1)];
        }
        else {
            s2 = decode2(s);
            k = s2[0];
            s = s2[1];
            s2 = decode2(s);
            a[k] = s2[0];
            s = s2[1];
        }
    }
}

function decode2(s){
    if ('string' !== typeof s || s.length < 1) {
        throw "expected a non-empty string";
    }
    var c = s.charAt(0);
    if (c === 'i') {
        return decodeInt(s);
    }
    else 
        if (c >= '0' && c <= '9') {
            return decodeString(s);
        }
        else 
            if (c === 'l') {
                return decodeList(s);
            }
            else 
                if (c === 'd') {
                    return decodeDictionary(s);
                }
                else {
                    throw "unexpected character " + c;
                }
}

exports.decode2 = decode2;

exports.decode = function decode(s){
    var result = decode2(s), leftOver = result[1];
    if (leftOver !== '') {
        throw "'characters left over at end of decode: '" + leftOver + "'";
    }
    return result[0];
};