Minecraft NBT (Named Binary Tag): Lua parsing library

A structured binary format native to Minecraft for saving game data and transferring it over the network (in multiplayer), such as player data (<player>.dat; contains e.g. player's inventory and location), saved worlds (level.dat and Chunk format), list of saved multiplayer servers (servers.dat) and so on - see https://minecraft.gamepedia.com/NBT_format#Uses.

The entire file should be gzip-compressed (in accordance with the original specification NBT.txt by Notch), but can also be compressed with zlib or uncompressed.

This spec can only handle uncompressed NBT data, so be sure to first detect what type of data you are dealing with. You can use the Unix file command to do this (file-5.20 or later is required; older versions do not recognize zlib-compressed data and return application/octet-stream instead):

file --brief --mime-type input-unknown.nbt

If it says:

  • application/x-gzip or application/gzip (since file-5.37), you can decompress it by
    • gunzip -c input-gzip.nbt > output.nbt or
    • python3 -c "import sys, gzip; sys.stdout.buffer.write( gzip.decompress(sys.stdin.buffer.read()) )" < input-gzip.nbt > output.nbt
  • application/zlib, you can use
    • openssl zlib -d -in input-zlib.nbt -out output.nbt (does not work on most systems)
    • python3 -c "import sys, zlib; sys.stdout.buffer.write( zlib.decompress(sys.stdin.buffer.read()) )" < input-zlib.nbt > output.nbt
  • something else (especially image/x-pcx and application/octet-stream), it is most likely already uncompressed.

The file output.nbt generated by one of the above commands can already be processed with this Kaitai Struct specification.

This spec only implements the Java edition format. There is also a Bedrock edition NBT format, which uses little-endian encoding and has a few other differences, but it isn't as popular as the Java edition format.

Implementation note: strings in TAG_String are incorrectly decoded with standard UTF-8, while they are encoded in Modified UTF-8 (MUTF-8). That's because MUTF-8 is not supported natively by most target languages, and thus one must use external libraries to achieve a fully-compliant decoder. But decoding in standard UTF-8 is still better than nothing, and it usually works fine.

All Unicode code points with incompatible representations in MUTF-8 and UTF-8 are U+0000 (NUL), U+D800-U+DFFF (High and Low Surrogates) and U+10000-U+10FFFF (all Supplementary Planes; includes e.g. emoticons, pictograms). A MUTF-8-encoded string containing these code points cannot be successfully decoded as UTF-8. The behavior in this case depends on the target language - usually an exception is thrown, or the bytes that are not valid UTF-8 are replaced or ignored.

Sample files:

Application

Minecraft

File extension

["nbt", "dat", "schematic", "schem"]

KS implementation details

License: CC0-1.0

References

This page hosts a formal specification of Minecraft NBT (Named Binary Tag) using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Lua source code to parse Minecraft NBT (Named Binary Tag)

minecraft_nbt.lua

-- This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
--
-- This file is compatible with Lua 5.3

local class = require("class")
require("kaitaistruct")
local enum = require("enum")
local str_decode = require("string_decode")
local utils = require("utils")

-- 
-- A structured binary format native to Minecraft for saving game data and transferring
-- it over the network (in multiplayer), such as player data
-- ([`<player>.dat`](https://minecraft.gamepedia.com/Player.dat_format); contains
-- e.g. player's inventory and location), saved worlds
-- ([`level.dat`](
--   https://minecraft.gamepedia.com/Java_Edition_level_format#level.dat_format
-- ) and [Chunk format](https://minecraft.gamepedia.com/Chunk_format#NBT_structure)),
-- list of saved multiplayer servers
-- ([`servers.dat`](https://minecraft.gamepedia.com/Servers.dat_format)) and so on -
-- see <https://minecraft.gamepedia.com/NBT_format#Uses>.
-- 
-- The entire file should be _gzip_-compressed (in accordance with the original
-- specification [NBT.txt](
--   https://web.archive.org/web/20110723210920/https://www.minecraft.net/docs/NBT.txt
-- ) by Notch), but can also be compressed with _zlib_ or uncompressed.
-- 
-- This spec can only handle uncompressed NBT data, so be sure to first detect
-- what type of data you are dealing with. You can use the Unix `file` command
-- to do this (`file-5.20` or later is required; older versions do not recognize
-- _zlib_-compressed data and return `application/octet-stream` instead):
-- 
-- ```shell
-- file --brief --mime-type input-unknown.nbt
-- ```
-- 
-- If it says:
-- 
--   * `application/x-gzip` or `application/gzip` (since `file-5.37`), you can decompress it by
--     * `gunzip -c input-gzip.nbt > output.nbt` or
--     * `python3 -c "import sys, gzip; sys.stdout.buffer.write(
--       gzip.decompress(sys.stdin.buffer.read()) )" < input-gzip.nbt > output.nbt`
--   * `application/zlib`, you can use
--     * `openssl zlib -d -in input-zlib.nbt -out output.nbt` (does not work on most systems)
--     * `python3 -c "import sys, zlib; sys.stdout.buffer.write(
--       zlib.decompress(sys.stdin.buffer.read()) )" < input-zlib.nbt > output.nbt`
--   * something else (especially `image/x-pcx` and `application/octet-stream`),
--     it is most likely already uncompressed.
-- 
-- The file `output.nbt` generated by one of the above commands can already be
-- processed with this Kaitai Struct specification.
-- 
-- This spec **only** implements the Java edition format. There is also
-- a [Bedrock edition](https://wiki.vg/NBT#Bedrock_edition) NBT format,
-- which uses little-endian encoding and has a few other differences, but it isn't
-- as popular as the Java edition format.
-- 
-- **Implementation note:** strings in `TAG_String` are incorrectly decoded with
-- standard UTF-8, while they are encoded in [**Modified UTF-8**](
--   https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8
-- ) (MUTF-8). That's because MUTF-8 is not supported natively by most target
-- languages, and thus one must use external libraries to achieve a fully-compliant
-- decoder. But decoding in standard UTF-8 is still better than nothing, and
-- it usually works fine.
-- 
-- All Unicode code points with incompatible representations in MUTF-8 and UTF-8 are
-- U+0000 (_NUL_), U+D800-U+DFFF (_High_ and _Low Surrogates_) and U+10000-U+10FFFF
-- (all _Supplementary_ Planes; includes e.g. emoticons, pictograms).
-- A _MUTF-8_-encoded string containing these code points cannot be successfully
-- decoded as UTF-8. The behavior in this case depends on the target language -
-- usually an exception is thrown, or the bytes that are not valid UTF-8
-- are replaced or ignored.
-- 
-- **Sample files:**
-- 
--   * <https://wiki.vg/NBT#Download>
--   * <https://github.com/twoolie/NBT/blob/f9e892e/tests/world_test/data/scoreboard.dat>
--   * <https://github.com/chmod222/cNBT/tree/3f74b69/testdata>
--   * <https://github.com/PistonDevelopers/hematite_nbt/tree/0b85f89/tests>
-- See also: Source (https://wiki.vg/NBT)
-- See also: Source (https://web.archive.org/web/20110723210920/https://www.minecraft.net/docs/NBT.txt)
-- See also: Source (https://minecraft.gamepedia.com/NBT_format)
MinecraftNbt = class.class(KaitaiStruct)

MinecraftNbt.Tag = enum.Enum {
  end = 0,
  byte = 1,
  short = 2,
  int = 3,
  long = 4,
  float = 5,
  double = 6,
  byte_array = 7,
  string = 8,
  list = 9,
  compound = 10,
  int_array = 11,
  long_array = 12,
}

function MinecraftNbt:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt:_read()
  if  ((self.root_type == MinecraftNbt.Tag.end) and (false))  then
    self.root_check = self._io:read_bytes(0)
  end
  self.root = MinecraftNbt.NamedTag(self._io, self, self._root)
end

MinecraftNbt.property.root_type = {}
function MinecraftNbt.property.root_type:get()
  if self._m_root_type ~= nil then
    return self._m_root_type
  end

  local _pos = self._io:pos()
  self._io:seek(0)
  self._m_root_type = MinecraftNbt.Tag(self._io:read_u1())
  self._io:seek(_pos)
  if not(self.root_type == MinecraftNbt.Tag.compound) then
    error("not equal, expected " ..  MinecraftNbt.Tag.compound .. ", but got " .. self.root_type)
  end
  return self._m_root_type
end


MinecraftNbt.TagLongArray = class.class(KaitaiStruct)

function MinecraftNbt.TagLongArray:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt.TagLongArray:_read()
  self.num_tags = self._io:read_s4be()
  self.tags = {}
  for i = 0, self.num_tags - 1 do
    self.tags[i + 1] = self._io:read_s8be()
  end
end

MinecraftNbt.TagLongArray.property.tags_type = {}
function MinecraftNbt.TagLongArray.property.tags_type:get()
  if self._m_tags_type ~= nil then
    return self._m_tags_type
  end

  self._m_tags_type = MinecraftNbt.Tag.long
  return self._m_tags_type
end


MinecraftNbt.TagByteArray = class.class(KaitaiStruct)

function MinecraftNbt.TagByteArray:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt.TagByteArray:_read()
  self.len_data = self._io:read_s4be()
  self.data = self._io:read_bytes(self.len_data)
end


MinecraftNbt.TagIntArray = class.class(KaitaiStruct)

function MinecraftNbt.TagIntArray:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt.TagIntArray:_read()
  self.num_tags = self._io:read_s4be()
  self.tags = {}
  for i = 0, self.num_tags - 1 do
    self.tags[i + 1] = self._io:read_s4be()
  end
end

MinecraftNbt.TagIntArray.property.tags_type = {}
function MinecraftNbt.TagIntArray.property.tags_type:get()
  if self._m_tags_type ~= nil then
    return self._m_tags_type
  end

  self._m_tags_type = MinecraftNbt.Tag.int
  return self._m_tags_type
end


MinecraftNbt.TagList = class.class(KaitaiStruct)

function MinecraftNbt.TagList:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt.TagList:_read()
  self.tags_type = MinecraftNbt.Tag(self._io:read_u1())
  self.num_tags = self._io:read_s4be()
  self.tags = {}
  for i = 0, self.num_tags - 1 do
    local _on = self.tags_type
    if _on == MinecraftNbt.Tag.long_array then
      self.tags[i + 1] = MinecraftNbt.TagLongArray(self._io, self, self._root)
    elseif _on == MinecraftNbt.Tag.compound then
      self.tags[i + 1] = MinecraftNbt.TagCompound(self._io, self, self._root)
    elseif _on == MinecraftNbt.Tag.double then
      self.tags[i + 1] = self._io:read_f8be()
    elseif _on == MinecraftNbt.Tag.list then
      self.tags[i + 1] = MinecraftNbt.TagList(self._io, self, self._root)
    elseif _on == MinecraftNbt.Tag.float then
      self.tags[i + 1] = self._io:read_f4be()
    elseif _on == MinecraftNbt.Tag.short then
      self.tags[i + 1] = self._io:read_s2be()
    elseif _on == MinecraftNbt.Tag.int then
      self.tags[i + 1] = self._io:read_s4be()
    elseif _on == MinecraftNbt.Tag.byte_array then
      self.tags[i + 1] = MinecraftNbt.TagByteArray(self._io, self, self._root)
    elseif _on == MinecraftNbt.Tag.byte then
      self.tags[i + 1] = self._io:read_s1()
    elseif _on == MinecraftNbt.Tag.int_array then
      self.tags[i + 1] = MinecraftNbt.TagIntArray(self._io, self, self._root)
    elseif _on == MinecraftNbt.Tag.string then
      self.tags[i + 1] = MinecraftNbt.TagString(self._io, self, self._root)
    elseif _on == MinecraftNbt.Tag.long then
      self.tags[i + 1] = self._io:read_s8be()
    end
  end
end


MinecraftNbt.TagString = class.class(KaitaiStruct)

function MinecraftNbt.TagString:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt.TagString:_read()
  self.len_data = self._io:read_u2be()
  self.data = str_decode.decode(self._io:read_bytes(self.len_data), "utf-8")
end

-- 
-- unsigned according to https://wiki.vg/NBT#Specification.

MinecraftNbt.TagCompound = class.class(KaitaiStruct)

function MinecraftNbt.TagCompound:_init(io, parent, root)
  KaitaiStruct._init(self, io)
  self._parent = parent
  self._root = root or self
  self:_read()
end

function MinecraftNbt.TagCompound:_read()
  self.tags = {}
  local i = 0
  while true do
    _ = MinecraftNbt.NamedTag(self._io, self, self._root)
    self.tags[i + 1] = _
    if _.is_tag_end then
      break
    end
    i = i + 1
  end
end

MinecraftNbt.TagCompound.property.dump_num_tags = {}
function MinecraftNbt.TagCompound.property.dump_num_tags:get()
if self._m_dump_num_tags ~= nil then
  return self._m_dump_num_tags
end

self._m_dump_num_tags = (#self.tags - utils.box_unwrap(( ((#self.tags >= 1) and (self.tags[#self.tags].is_tag_end)) ) and utils.box_wrap(1) or (0)))
return self._m_dump_num_tags
end


MinecraftNbt.NamedTag = class.class(KaitaiStruct)

function MinecraftNbt.NamedTag:_init(io, parent, root)
KaitaiStruct._init(self, io)
self._parent = parent
self._root = root or self
self:_read()
end

function MinecraftNbt.NamedTag:_read()
self.type = MinecraftNbt.Tag(self._io:read_u1())
if not(self.is_tag_end) then
  self.name = MinecraftNbt.TagString(self._io, self, self._root)
end
if not(self.is_tag_end) then
  local _on = self.type
  if _on == MinecraftNbt.Tag.long_array then
    self.payload = MinecraftNbt.TagLongArray(self._io, self, self._root)
  elseif _on == MinecraftNbt.Tag.compound then
    self.payload = MinecraftNbt.TagCompound(self._io, self, self._root)
  elseif _on == MinecraftNbt.Tag.double then
    self.payload = self._io:read_f8be()
  elseif _on == MinecraftNbt.Tag.list then
    self.payload = MinecraftNbt.TagList(self._io, self, self._root)
  elseif _on == MinecraftNbt.Tag.float then
    self.payload = self._io:read_f4be()
  elseif _on == MinecraftNbt.Tag.short then
    self.payload = self._io:read_s2be()
  elseif _on == MinecraftNbt.Tag.int then
    self.payload = self._io:read_s4be()
  elseif _on == MinecraftNbt.Tag.byte_array then
    self.payload = MinecraftNbt.TagByteArray(self._io, self, self._root)
  elseif _on == MinecraftNbt.Tag.byte then
    self.payload = self._io:read_s1()
  elseif _on == MinecraftNbt.Tag.int_array then
    self.payload = MinecraftNbt.TagIntArray(self._io, self, self._root)
  elseif _on == MinecraftNbt.Tag.string then
    self.payload = MinecraftNbt.TagString(self._io, self, self._root)
  elseif _on == MinecraftNbt.Tag.long then
    self.payload = self._io:read_s8be()
  end
end
end

MinecraftNbt.NamedTag.property.is_tag_end = {}
function MinecraftNbt.NamedTag.property.is_tag_end:get()
if self._m_is_tag_end ~= nil then
  return self._m_is_tag_end
end

self._m_is_tag_end = self.type == MinecraftNbt.Tag.end
return self._m_is_tag_end
end