Difference between revisions of "NBT"
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* [https://github.com/PistonDevelopers/hematite_nbt Rust], | * [https://github.com/PistonDevelopers/hematite_nbt Rust], | ||
* [https://github.com/drXor/ScalaNBT Scala], | * [https://github.com/drXor/ScalaNBT Scala], | ||
− | * [https://gist.github.com/camdenorrb/bec73c5608267f0232bd8f5c42e0784d Kotlin (Extremely simple, | + | * [https://gist.github.com/camdenorrb/bec73c5608267f0232bd8f5c42e0784d Kotlin (Extremely simple, 300 lines, NIO, Endianness support)], |
* [https://github.com/DevSrSouza/KotlinNBT Kotlin Multiplatform], | * [https://github.com/DevSrSouza/KotlinNBT Kotlin Multiplatform], | ||
* You get the idea… | * You get the idea… |
Revision as of 05:00, 15 April 2020
The Named Binary Tag (NBT) file format is an extremely simple, albeit annoying (did we really need yet another format?)[See Discussion] structured binary format used by the Minecraft game for a variety of things. Due to this, several third-party utilities now also utilize the format. You may find example files at the bottom of this article.
Mojang has also released a reference implementation along with their Anvil conversion tool, available from https://mojang.com/2012/02/new-minecraft-map-format-anvil/
Contents
Current Uses
The NBT format is currently used in several places, chiefly:
- In the Protocol as part of Slot Data
- Multiplayer saved server list (
servers.dat
). - Player data (both single player and multiplayer, one file per player). This includes such things as inventory and location.
- Saved worlds (both single player and multiplayer).
- World index file (
level.dat
) that contains general information (spawn point, time of day, etc...) - Chunk data (see Region Files)
- World index file (
Unfortunately, the NBT files you can encounter as a developer will be stored in three different ways, just to make things interesting.
Libraries
There are many, many libraries for manipulating NBT, written in several languages, and often several per language. For example,
- C,
- C#,
- D,
- Go (New),
- Go (Old, without TagLongArray),
- Java (Old, without TagLongArray),
- Javascript,
- PHP,
- Python,
- Ruby,
- Rust,
- Scala,
- Kotlin (Extremely simple, 300 lines, NIO, Endianness support),
- Kotlin Multiplatform,
- You get the idea…
Unless you have specific goals or licence requirements, it is extremely recommended to go with one of the existing libraries.
Utilities
Almost every 3rd-party Minecraft application uses NBT on some level. There also exist several dedicated NBT editors, which will likely be useful to you if you are developing an NBT library of your own. These include:
- NBTEdit (C#, Mono-capable), one of the very first NBT editors.
- NEINedit (Obj-C), an OS X specific editor.
- nbt2yaml (Python), provides command-line editing of NBT via the YAML format, as well as a fast and minimalist NBT parsing/rendering API.
- nbted (Rust; CC0), provides command-line editing of NBT files via your $EDITOR
- nbt2json (Golang; MIT) Command-line utility for NBT to JSON/YAML conversion and back. MCPE-NBT support. Can be used as library.
Specification
The NBT file format is extremely simple, and writing a library capable of reading/writing it is a simple affair. There are 13 datatypes supported by this format, one of which is used to close compound tags. It is strongly advised to read this entire section or you may run into issues.
Type ID | Type Name | Payload Size (Bytes) | Description |
---|---|---|---|
0 | TAG_End | 0 | Signifies the end of a TAG_Compound. It is only ever used inside a TAG_Compound, and is not named despite being in a TAG_Compound |
1 | TAG_Byte | 1 | A single signed byte |
2 | TAG_Short | 2 | A single signed, big endian 16 bit integer |
3 | TAG_Int | 4 | A single signed, big endian 32 bit integer |
4 | TAG_Long | 8 | A single signed, big endian 64 bit integer |
5 | TAG_Float | 4 | A single, big endian IEEE-754 single-precision floating point number (NaN possible) |
6 | TAG_Double | 8 | A single, big endian IEEE-754 double-precision floating point number (NaN possible) |
7 | TAG_Byte_Array | ... | A length-prefixed array of signed bytes. The prefix is a signed integer (thus 4 bytes) |
8 | TAG_String | ... | A length-prefixed modified UTF-8 string. The prefix is an unsigned short (thus 2 bytes) signifying the length of the string in bytes |
9 | TAG_List | ... | A list of nameless tags, all of the same type. The list is prefixed with the Type ID of the items it contains (thus 1 byte), and the length of the list as a signed integer (a further 4 bytes). If the length of the list is 0 or negative, the type may be 0 (TAG_End) but otherwise it must be any other type. (The notchian implementation uses TAG_End in that situation, but another reference implementation by Mojang uses 1 instead; parsers should accept any type if the length is <= 0).
|
10 | TAG_Compound | ... | Effectively a list of a named tags. Order is not guaranteed. |
11 | TAG_Int_Array | ... | A length-prefixed array of signed integers. The prefix is a signed integer (thus 4 bytes) and indicates the number of 4 byte integers. |
12 | TAG_Long_Array | ... | A length-prefixed array of signed longs. The prefix is a signed integer (thus 4 bytes) and indicates the number of 8 byte longs. |
There are a couple of simple things to remember:
- The datatypes representing numbers are in big-endian in the PC version, but Pocket Version is in little-endian. Unless you're using Java, you will most likely have to swap it to little-endian. See the Wikipedia article on Endianness.
- Every NBT file will always implicitly be inside a tag compound, and also begin with a TAG_Compound
- The structure of a NBT file is defined by the TAG_List and TAG_Compound types, as such a tag itself will only contain the payload, but depending on what the tag is contained within may contain additional headers. I.e. if it's inside a Compound, then each tag will begin with the TAG_id, and then a string (the tag's name), and finally the payload. While in a list it will be only the payload, as there is no name and the tag type is given in the beginning of the list.
For example, here's the example layout of a TAG_Short
on disk:
Type ID | Length of Name | Name | Payload | |
---|---|---|---|---|
Decoded | 2 | 9 | shortTest
|
32767
|
On Disk (in hex) | 02
|
00 09
|
73 68 6F 72 74 54 65 73 74
|
7F FF
|
If this TAG_Short
had been in a TAG_List
, it would have been nothing more than the payload, since the type is implied and tags within the first level of a list are nameless.
Examples
There are two defacto example files used for testing your implementation (test.nbt
& bigtest.nbt
), originally provided by Markus. The example output provided below was generated using PyNBT's debug-nbt tool.
test.nbt
This first example is an uncompressed "Hello World" NBT example. Should you parse it correctly, you will get a structure similar to the following:
TAG_Compound('hello world'): 1 entry { TAG_String('name'): 'Bananrama' }
Here is the example explained:
(The entire thing is implicitly inside a compound) | Type ID (first element in the implicit compound) | Length of name of the root compound | Name of the root compound | Type ID of first element in root compound | Length of name of first element in root | Name of first element | Length of string | String | Tag end (of root compound) |
---|---|---|---|---|---|---|---|---|---|
Decoded | Compound | 11 | hello world | String | 4 | name | 9 | Bananrama | |
On Disk (in hex) | 0a
|
00 0b
|
68 65 6c 6c 6f 20 77 6f 72 6c 64
|
08
|
00 04
|
6e 61 6d 65
|
00 09
|
42 61 6e 61 6e 72 61 6d 61
|
00
|
bigtest.nbt
This second example is a gzip compressed test of every available tag. If your program can successfully parse this file, then you've done well. Note that the tags under TAG_List do not have a name, as mentioned above.
TAG_Compound('Level'): 11 entries { TAG_Compound('nested compound test'): 2 entries { TAG_Compound('egg'): 2 entries { TAG_String('name'): 'Eggbert' TAG_Float('value'): 0.5 } TAG_Compound('ham'): 2 entries { TAG_String('name'): 'Hampus' TAG_Float('value'): 0.75 } } TAG_Int('intTest'): 2147483647 TAG_Byte('byteTest'): 127 TAG_String('stringTest'): 'HELLO WORLD THIS IS A TEST STRING \xc3\x85\xc3\x84\xc3\x96!' TAG_List('listTest (long)'): 5 entries { TAG_Long(None): 11 TAG_Long(None): 12 TAG_Long(None): 13 TAG_Long(None): 14 TAG_Long(None): 15 } TAG_Double('doubleTest'): 0.49312871321823148 TAG_Float('floatTest'): 0.49823147058486938 TAG_Long('longTest'): 9223372036854775807L TAG_List('listTest (compound)'): 2 entries { TAG_Compound(None): 2 entries { TAG_Long('created-on'): 1264099775885L TAG_String('name'): 'Compound tag #0' } TAG_Compound(None): 2 entries { TAG_Long('created-on'): 1264099775885L TAG_String('name'): 'Compound tag #1' } } TAG_Byte_Array('byteArrayTest (the first 1000 values of (n*n*255+n*7)%100, starting with n=0 (0, 62, 34, 16, 8, ...))'): [1000 bytes] TAG_Short('shortTest'): 32767 }
servers.dat
The servers.dat file contains a list of multiplayer servers you've added to the game. To mix things up a bit, this file will always be uncompressed. Below is an example of the structure seen in servers.dat.
TAG_Compound(''): 1 entry { TAG_List('servers'): 2 entries { TAG_Compound(None): 3 entries { TAG_Byte('acceptTextures'): 1 (Automatically accept resourcepacks from this server) TAG_String('ip'): '199.167.132.229:25620' TAG_String('name'): 'Dainz1 - Creative' } TAG_Compound(None): 3 entries { TAG_String('icon'): 'iVBORw0KGgoAAAANUhEUgAAAEAAAABACA...' (The base64-encoded server icon. Trimmed here for the example's sake) TAG_String('ip'): '76.127.122.65:25565' TAG_String('name'): 'minstarmin4' } } }
level.dat
This final example is of a single player level.dat, which is compressed using gzip. Notice the player's inventory and general world details such as spawn position, world name, and the game seed.
TAG_Compound(''): 1 entry { TAG_Compound('Data'): 17 entries { TAG_Byte('raining'): 0 TAG_Long('RandomSeed'): 3142388825013346304L TAG_Int('SpawnX'): 0 TAG_Int('SpawnZ'): 0 TAG_Long('LastPlayed'): 1323133681772L TAG_Int('GameType'): 1 TAG_Int('SpawnY'): 63 TAG_Byte('MapFeatures'): 1 TAG_Compound('Player'): 24 entries { TAG_Int('XpTotal'): 0 TAG_Compound('abilities'): 4 entries { TAG_Byte('instabuild'): 1 TAG_Byte('flying'): 1 TAG_Byte('mayfly'): 1 TAG_Byte('invulnerable'): 1 } TAG_Int('XpLevel'): 0 TAG_Int('Score'): 0 TAG_Short('Health'): 20 TAG_List('Inventory'): 13 entries { TAG_Compound(None): 4 entries { TAG_Byte('Count'): 1 TAG_Byte('Slot'): 0 TAG_Short('id'): 24 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 1 TAG_Byte('Slot'): 1 TAG_Short('id'): 25 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 1 TAG_Byte('Slot'): 2 TAG_Short('id'): 326 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 1 TAG_Byte('Slot'): 3 TAG_Short('id'): 29 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 10 TAG_Byte('Slot'): 4 TAG_Short('id'): 69 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 3 TAG_Byte('Slot'): 5 TAG_Short('id'): 33 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 43 TAG_Byte('Slot'): 6 TAG_Short('id'): 356 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 64 TAG_Byte('Slot'): 7 TAG_Short('id'): 331 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 20 TAG_Byte('Slot'): 8 TAG_Short('id'): 76 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 64 TAG_Byte('Slot'): 9 TAG_Short('id'): 331 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 1 TAG_Byte('Slot'): 10 TAG_Short('id'): 323 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 16 TAG_Byte('Slot'): 11 TAG_Short('id'): 331 TAG_Short('Damage'): 0 } TAG_Compound(None): 4 entries { TAG_Byte('Count'): 1 TAG_Byte('Slot'): 12 TAG_Short('id'): 110 TAG_Short('Damage'): 0 } } TAG_Short('HurtTime'): 0 TAG_Short('Fire'): -20 TAG_Float('foodExhaustionLevel'): 0.0 TAG_Float('foodSaturationLevel'): 5.0 TAG_Int('foodTickTimer'): 0 TAG_Short('SleepTimer'): 0 TAG_Short('DeathTime'): 0 TAG_List('Rotation'): 2 entries { TAG_Float(None): 1151.9342041015625 TAG_Float(None): 32.249679565429688 } TAG_Float('XpP'): 0.0 TAG_Float('FallDistance'): 0.0 TAG_Short('Air'): 300 TAG_List('Motion'): 3 entries { TAG_Double(None): -2.9778325794951344e-11 TAG_Double(None): -0.078400001525878907 TAG_Double(None): 1.1763942772801152e-11 } TAG_Int('Dimension'): 0 TAG_Byte('OnGround'): 1 TAG_List('Pos'): 3 entries { TAG_Double(None): 256.87499499518492 TAG_Double(None): 112.62000000476837 TAG_Double(None): -34.578128612797634 } TAG_Byte('Sleeping'): 0 TAG_Short('AttackTime'): 0 TAG_Int('foodLevel'): 20 } TAG_Int('thunderTime'): 2724 TAG_Int('version'): 19132 TAG_Int('rainTime'): 5476 TAG_Long('Time'): 128763 TAG_Byte('thundering'): 1 TAG_Byte('hardcore'): 0 TAG_Long('SizeOnDisk'): 0 TAG_String('LevelName'): 'Sandstone Test World' } }
Download
- test.nbt/hello_world.nbt (uncompressed),
- bigtest.nbt (gzip compressed)
- NaN-value-double.dat (compressed, origin version unknown)