bencodec/lib/BencodeDecoder.js

Library for decoding and encoding bencode data

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.BencodeDecoder = void 0;
const types_1 = require("./types");
const node_buffer_1 = require("node:buffer");
class BencodeDecoder {
    /**
     * Check if character in integer
     */
    static _isInteger(char) {
        return char >= 0x30 && char <= 0x39;
    }
    /**
     * Constructor
     */
    constructor(data, options) {
        if (!data) {
            throw new Error('Nothing to decode');
        }
        this._index = 0;
        this._options = options || {};
        this._buffer = typeof data === 'string'
            ? node_buffer_1.Buffer.from(data)
            : data;
    }
    /**
     * Decode bencoded data
     */
    decode() {
        if (BencodeDecoder._isInteger(this._currentChar())) {
            return this._decodeString();
        }
        if (this._currentChar() === types_1.FLAG.INTEGER) {
            return this._decodeInteger();
        }
        if (this._currentChar() === types_1.FLAG.LIST) {
            return this._decodeList();
        }
        if (this._currentChar() === types_1.FLAG.DICTIONARY) {
            return this._decodeDictionary();
        }
        throw new Error('Invalid bencode data');
    }
    /**
     * Get character by current index
     */
    _currentChar() {
        return this._buffer[this._index];
    }
    /**
     * Get character by current index and increment
     */
    _next() {
        return this._buffer[this._index++];
    }
    /**
     * Decode bencoded string
     */
    _decodeString() {
        const length = this._decodeInteger();
        const acc = [];
        for (let i = 0; i < length; i++) {
            acc.push(this._next());
        }
        return this._options.stringify
            ? node_buffer_1.Buffer.from(acc).toString('utf8')
            : node_buffer_1.Buffer.from(acc);
    }
    /**
     * Decode bencoded integer
     */
    _decodeInteger() {
        let sign = 1;
        let isFloat = false;
        let integer = 0;
        if (this._currentChar() === types_1.FLAG.INTEGER) {
            this._index++;
        }
        if (this._currentChar() === types_1.FLAG.PLUS) {
            this._index++;
        }
        if (this._currentChar() === types_1.FLAG.MINUS) {
            this._index++;
            sign = -1;
        }
        while (BencodeDecoder._isInteger(this._currentChar()) || this._currentChar() === types_1.FLAG.DOT) {
            if (this._currentChar() === types_1.FLAG.DOT) {
                isFloat = true;
            }
            isFloat === false
                ? integer = integer * 10 + (this._next() - 0x30)
                : this._index++;
        }
        if (this._currentChar() === types_1.FLAG.END) {
            this._index++;
        }
        if (this._currentChar() === types_1.FLAG.STR_DELIMITER) {
            this._index++;
        }
        return integer * sign;
    }
    /**
     * Decode bencoded list
     */
    _decodeList() {
        const acc = [];
        // skip LIST flag
        this._next();
        while (this._currentChar() !== types_1.FLAG.END) {
            acc.push(this.decode());
        }
        // skip END flag
        this._next();
        return acc;
    }
    /**
     * Decode bencoded dictionary
     */
    _decodeDictionary() {
        const acc = {};
        // skip DICTIONARY flag
        this._next();
        while (this._currentChar() !== types_1.FLAG.END) {
            const key = this._decodeString();
            acc[key.toString()] = this.decode();
        }
        // skip END flag
        this._next();
        return acc;
    }
}
exports.BencodeDecoder = BencodeDecoder;