nbt2json

A command line utility and Go module that reads NBT data and converts it to JSON or YAML for editing and then back to NBT.

Features

nbt2json executable will auto-detect and decompress gzipped files
nbt2json executable has option to gzip output
Can read and write both Minecraft Bedrock Edition and Java Edition NBT data
- Does not auto-detect which
- nbt2json executable defaults to Bedrock Edition / little endian
Can import to other Go projects
Can use either JSON or YAML
Can include comment in JSON/YAML output (which is ignored when converting back to NBT)

Help screen

By defualt, the nbt2json executable waits for input from stdin, so you need to nbt2json -h to see the help screen.

NAME:
   NBT to JSON - Converts NBT-encoded data to JSON | https://github.com/midnightfreddie/nbt2json

USAGE:
   nbt2json.exe [global options] command [command options] [arguments...]

VERSION:
   0.4.0

AUTHOR:
   Jim Nelson <jim@jimnelson.us>

COMMANDS:
   help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --reverse, -r                  Convert JSON to NBT instead (default: false)
   --gzip, -z                     Compress output with gzip (default: false)
   --comment COMMENT, -c COMMENT  Add COMMENT to json or yaml output, use quotes if contains white space
   --big-endian, --java, -b       Use for Minecraft Java Edition (like most other NBT tools) (default: false)
   --in FILE, -i FILE             Input FILE path (default: "-")
   --out FILE, -o FILE            Output FILE path (default: "-")
   --yaml, --yml, -y              Use YAML instead of JSON (default: false)
   --long-as-string, -l           If set, nbt long values will be a string instead of uint32 pair (default: false)
   --skip NUM                     Skip NUM bytes of NBT input. For Bedrock's level.dat, use --skip 8 to bypass header (default: 0)
   --help, -h                     show help (default: false)
   --version, -v                  print the version (default: false)

COPYRIGHT:
   (c) 2018, 2019, 2020 Jim Nelson

Compiling

This repo is both a Go module and a command line utility. To build the utility:

Ensure Go v1.16 or later is installed and configured (GOPATH is set)
cd into repo root folder
go build ./cmd/nbt2json will put the executable in the current directory. Important: include the ./ at the beginning or else it will throw "package cmd/nbt2json is not in GOROOT". (I do that. Every. Time.)

JSON format notes

The JSON document should be an object with an "nbt" field which is an array. Objects in the array represent one tag and will typically have tagType, name, and value fields. A typical Minecraft NBT will have one compound tag with a number of other tags inside that one. This converter needs at least one tag.

Many JSON libraries cannot properly handle a 64-bit integer, so nbt2json handles the long tag in one of two special ways for portability and compatibility.

By default it presents valueLeast and valueMost unsigned 32-bit integers. valueMost is the most significant 32 bits, so it should be rolled bitwise to the left 32 bits in a 64-bit space and added (or bitwise 'or'ed) to valueLeast to reassemble the 64-bit long singed integer. Here is an example:

{
  "nbt": [
    {
      "tagType": 4,
      "name": "LongAsUint32PairExample",
      "value": {
        "valueLeast": 4294967295,
        "valueMost": 2147483647
      }
    }
  ]
}

Alternately it can turn the 64-bit integer into a string. This would be easier to edit by hand in a text editor. Example:

{
  "nbt": [
    {
      "tagType": 4,
      "name": "LongAsStringExample",
      "value": "9223372036854775807"
    }
  ]
}

Dev notes

Client Go code needs to import "github.com/midnightfreddie/nbt2json"
Defaults to little-endian encoding for Bedrock Edition. Call nbt2json.UseJavaEncoding() and nbt2json.UseBedrockEncoding() to change encoding mode for as long as the module is open.
The functions use byte arrays where you might expect strings. Convert as such: var myString = someByteArray[:] or var myByteArray = []byte(someStringValue)
All errors should bubble up through the error part of the result and should describe where the problem was
The Json2Nbt function uses an interface{} and encodes based on the tagType fields. I had originally hoped to Marshal and Unmarshal to and from JSON and NBT, but my goal was to export to JSON, edit and then reencode. This way the struct doesn't have to match the data schema.
My main motivation for this project is to convert to/from JSON and use any JSON editor to modify Minecraft PE data with McpeTool, and to keep the read/write primitives in Go code while letting a client browser manage any validation to avoid having to re-release the read/write tools every time Minecraft changes formats.

Exported Go functions

Nbt2Yaml converts uncompressed NBT byte array to YAML byte array
```
  func Nbt2Yaml(b []byte, comment string) ([]byte, error)
```
Nbt2Json converts uncompressed NBT byte array to JSON byte array
```
  func Nbt2Json(b []byte, comment string) ([]byte, error)
```
Yaml2Nbt converts JSON byte array to uncompressed NBT byte array (Hint: You can just use this for both JSON and YAML if you like since JSON is a valid subeset of YAML)
```
  func Yaml2Nbt(b []byte) ([]byte, error)
```
Json2Nbt converts JSON byte array to uncompressed NBT byte array
```
  func Json2Nbt(b []byte) ([]byte, error)
```
UseJavaEndoding sets any nbt encoding/decoding to big-endian to match Minecraft Java Edition
```
  func UseJavaEncoding()
```
UseBedrockEncoding sets nbt encoding/decoding to little-endian to match Minecraft Bedrock Edition (default)
```
  func UseBedrockEncoding()
```
UseLongAsString sets json output for nbt long tags to numbers in strings
```
  func UseLongAsString()
```
UseLongAsUint32Pair sets json output for nbt long tags to a uint32 pair (default, needed for json portability)
```
  func UseLongAsUint32Pair()
```

Other exports of possible interest are in common.go.