fastnbt crate

Documentation: docs.rs

Fast (or trying to be!) deserializer and parser for Minecraft: Java Edition's NBT format.

Includes

• a serde based deserializer for NBT for deserialization.
• a lower level parser using the Read trait.

The derserializer allows you to avoid allocations where possible. Strings can be deserialized to &'a str where 'a is the lifetime of the data being deserialized. This can also be done for lists of any integral type into &'a [u8]. The same applies to the Array types in NBT.

You can then parse the &[u8] only when you need it. The fastanvil crate has a PackedBits type that can do this for you.

fastnbt::Value can be used to deserialize any NBT value.

See the examples directory for more examples.

[dependencies]
fastnbt = "0.12"

Serde derserialize example

This example shows retrieving a players inventory from the palyer.dat file found in the world/playerdata directory.

Some points:

• we are avoiding allocating a new string for every inventory slot by instead having a &str with a lifetime tied to the input data.
• we are deserializing the tag structure which is very dynamic using Value.
• we rename fields using serde. NBT structures tend to mix case a lot.

use fastnbt::error::Result;
use fastnbt::{de::from_bytes, Value};
use flate2::read::GzDecoder;
use serde::Deserialize;
use std::io::Read;

// This example show retrieving a players inventory from the palyer.dat file
// found in the world/playerdata directory.
//
// In particular we are avoiding allocating a new string for every inventory
// slot by instead having a &str with a lifetime tied to the input data.

#[derive(Deserialize, Debug)]
#[serde(rename_all = "PascalCase")]
struct PlayerDat<'a> {
    data_version: i32,

    #[serde(borrow)]
    inventory: Vec<InventorySlot<'a>>,
    ender_items: Vec<InventorySlot<'a>>,
}

#[derive(Deserialize, Debug)]
struct InventorySlot<'a> {
    id: &'a str,        // We avoid allocating a string here.
    tag: Option<Value>, // Also get the less structured properties of the object.

    // We need to rename fields a lot.
    #[serde(rename = "Count")]
    count: i8,
}

fn main() {
    let args: Vec<_> = std::env::args().skip(1).collect();
    let file = std::fs::File::open(args[0].clone()).unwrap();

    // Player dat files are compressed with GZip.
    let mut decoder = GzDecoder::new(file);
    let mut data = vec![];
    decoder.read_to_end(&mut data).unwrap();

    let player: Result<PlayerDat> = from_bytes(data.as_slice());

    println!("{:#?}", player);
}

Comparison to other NBT crates

There are other crates for NBT out there, this tries to give an honest comparison to them.

*see 01-11-2020.md in benchmarks directory

**intended feature