Lua telegram unpack util

telegram_unpack.lua

--[[
BSD 2-Clause License

Copyright (c) 2020, Giuseppe Marino
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
--]]
local b = require 'base64'
local unpack = string.unpack
local byte = string.byte
local char = string.char

local WEB_LOCATION_FLAG = 1 << 24
local FILE_REFERENCE_FLAG = 1 << 25

local THUMBNAIL = 0x00;
local PROFILE_PHOTO = 0x01;
local PHOTO = 0x02;
local VOICE = 0x03;
local VIDEO = 0x04;
local DOCUMENT = 0x05;
local ENCRYPTED = 0x06;
local TEMP = 0x07;
local STICKER = 0x08;
local AUDIO = 0x09;
local GIF = 0x0A;
local ENCRYPTED_THUMBNAIL = 0x0B;
local WALLPAPER = 0x0C;
local VIDEO_NOTE = 0x0D;
local SECURE_RAW = 0x0F;
local SECURE = 0x10;
local BACKGROUND = 0x11;
local SIZE = 0x12;

local function rleDecode(input)
    local new = '';
    local last = '';
    local null = string.char(0);
    local len = #input
    for i = 1, len do
        local cur = input:sub(i, i)
        if (last == null) then
            new = new .. string.rep(last, string.byte(cur));
            last = '';
        else
            new =  new ..last;
            last = cur;
        end
    end
    return new .. last;
end

local function posmod(a, b)
    local resto = a % b;

    return resto < 0 and (resto + math.abs(b)) or resto;
end

local function decodeFileID(file_id)
    local file_info = rleDecode(b.from_b64(file_id))

    local file_type = unpack('<b', file_info:sub(1, 1))
    local file_flags = unpack('<i', char(0) .. file_info:sub(2, 4))

    local version = byte(file_info:sub(-1))
    local subVersion = version == 4 and byte(file_info:sub(-2, -1)) or 0
    local dc_id = unpack('<i', file_info:sub(5,8))

    file_info = file_info:sub(9,-1)
    local file_reference = nil

    if not ((file_flags & FILE_REFERENCE_FLAG) == 0) then
        local frlen = byte(file_info:sub(1,1))
        local pad = 0
        file_info = char(0) .. file_info:sub(2, -1)
        if frlen == 254 then
            frlen = unpack('<i', file_info)
            pad = math.abs(-frlen % 4)
        else
            pad = math.abs(frlen % -4)
        end

        file_reference = file_info:sub(1, frlen)
        file_info = file_info:sub(frlen+pad+1, -1)
    end

    local infos = {
        type = file_type,
        dc = dc_id,
        version = version..'.'..subVersion,
        flags = file_flags,
    }

    if file_reference then
        infos.file_reference = b.to_b64(file_reference)
    end

    if file_type == TYPE_THUMBNAIL or file_type == TYPE_PROFILE_PHOTO or file_type == TYPE_PHOTO then
        local id, access_hash, volume_id, secret, robastrana, local_id = unpack('<llllii', file_info)
        infos.id = id
        infos.access_hash = access_hash
        infos.volume_id = volume_id
        infos.secret = secret
        infos.robastrana = robastrana
        infos.local_id = local_id
    else
        local id, access_hash = unpack('<ll', file_info)
        infos.id = id
        infos.access_hash = access_hash
    end

    if file_type == TYPE_STICKER then
        infos.creator_id = infos.id >> 32
    end

    return infos
end

local function decodeInlineMessageId(inline_message_id)
    local decoded = b.from_b64url(inline_message_id)

    local dc_id, message_id, chat_id, access_hash = unpack('<iiil', decoded)
    return {
        dc = dc_id,
        message_id = message_id,
        chat_id = chat_id,
        access_hash = access_hash
    }
end