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.

toml [dependencies] fastnbt = "0.13"

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.

```rust 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, // 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.

| Feature | fastnbt | Hematite nbt | note | | ------- | --------- | -------------- | ---- | | Benchmark world render* | 23.8+-0.7s | 31.6+-0.9s | making fastnbt 33% faster in this test | | Deserialization | yes | yes | | | Serialization | no | yes | | | Value-like type | yes | yes | | | Long Array (MC 1.12+) | yes | yes | | | Minecraft specialized unicode | no** | yes | | | Deserialize from reader | no | yes | | | WASM compatible | yes | unknown | |

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

**intended feature