Roblox Mesh to OBJ

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-- @CloneTrooper1019, 2017
-- Mesh2obj.lua
-- This script converts Roblox's mesh format into a .obj file
-- Written for Dawgra, with the intent of recovering the meshes stored in this model:
-- https://www.roblox.com/library/12468931/Reason-2-Die-Meshpack-2
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--[[

~ CONTEXT OF CREATION ~

In 2009, Roblox used to have a "feature" (hack) where you could store a content file directly inside of their .rbxm format if you
encoded the content into a base64 string, and put it inside of <binary></binary> tags. This was probably intended to be for
debugging purposes, but some clever users at the time discovered this feature and utilized it to inject meshes into Roblox long before
uploading meshes was even a feature. The problem here was that you could inject basically any arbitrary data into Roblox, which in turn
allowed users to bypass moderation. Thus Roblox removed the feature and user meshes were no more (until mid 2016).

To recover those meshes with this script:
01: Save the model that contains the mesh binary data as a .rbxmx file
02: In a text editor, strip out all the XML text until you're just left with the base64 encoded string
03: Paste the base64 content onto a website that decodes base64 data into it's raw binary data
04: Copy the decoded file and paste it onto pastebin
05: Get the raw url for that paste and replace the meshDataUrl with that url.
06: Copy this code into a Script in Roblox Studio
07: Run the game and copy the contents of the output. Make sure you get rid of extra prints, such as the Auto-Save print.
08: Paste that into a new file and save it as a .obj file
09: Import the mesh into Blender or whatever mesh editing tool you use.
10: Save the mesh as a .FBX file
11: Add a MeshPart to the Workspace, and upload the .FBX mesh

Congratulations, you have recovered the mesh!

]]--
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local HttpService = game:GetService("HttpService")
local meshDataUrl = "https://pastebin.com/raw/dH43Yvn7"

local meshData = HttpService:GetAsync(meshDataUrl)
local readLine = meshData:gmatch("[^\r\n]+")

-- Read mesh file
local version = readLine()
assert(version:sub(1,9) == "version 1","Unsupported version " .. version)

local meshScale = 0.5
if version == "version 1.01" then
    meshScale = 1
end

local numFaces = tonumber(readLine())
assert(numFaces,"number of faces not specified!")

local data = readLine()
local readChar = data:gmatch(".")
local meshFaces = {}

local function seek(token)
    local read = ""
    while true do
        local char = readChar()
        if char == token then
            break
        elseif char == nil then
            error("Reached end of data stream prematurely while seeking token: " .. token)
        end
        read = read .. char
    end
    return tonumber(read)
end

local function readVector3(scale)
    local scale = scale or 1
    local x,y,z
    seek("[")
    x = seek(",")
    y = seek(",")
    z = seek("]")
    return Vector3.new(x,y,z) * scale
end

for faceId = 1,numFaces do
    local face = {}
    face.Vertices = {}
    face.Normals = {}
    face.UVs = {}
    for i = 1,3 do
        face.Vertices[i] = readVector3(meshScale)
        face.Normals[i] = readVector3()
        face.UVs[i] = readVector3()
    end
    meshFaces[faceId] = face
end

-- Dump as .obj

local v3Format = "%s %s %s %s"
local faceFormat = "\nf %s/%s/%s %s/%s/%s %s/%s/%s"

local function writeVector3(v3,tag)
    print(v3Format:format(tag,v3.X,v3.Y,v3.Z))
end

local function writeFace(faceIndex)
    local r = (faceIndex-1)*3
    local a,b,c = r+1,r+2,r+3
    print(faceFormat:format(a,a,a,b,b,b,c,c,c))
end

print("g Mesh")

for faceIndex,face in ipairs(meshFaces) do
    for i = 1,3 do
        print()
        local v = face.Vertices[i]
        writeVector3(v,"v")
        local n = face.Normals[i]
        writeVector3(n,"vn")
        local t = face.UVs[i]
        writeVector3(t,"vt")
    end
    writeFace(faceIndex)
end