Borsh in Rust  

borsh-rs is Rust implementation of the Borsh binary serialization format.

Borsh stands for Binary Object Representation Serializer for Hashing. It is meant to be used in security-critical projects as it prioritizes consistency, safety, speed, and comes with a strict specification.

Example

use borsh::{BorshSerialize, BorshDeserialize, from_slice, to_vec};

#[derive(BorshSerialize, BorshDeserialize, PartialEq, Debug)]
struct A {
    x: u64,
    y: String,
}

#[test]
fn test_simple_struct() {
    let a = A {
        x: 3301,
        y: "liber primus".to_string(),
    };
    let encoded_a = to_vec(&a).unwrap();
    let decoded_a = from_slice::<A>(&encoded_a).unwrap();
    assert_eq!(a, decoded_a);
}

Features

Opting out from Serde allows borsh to have some features that currently are not available for serde-compatible serializers. Currently we support two features: borsh(init=<your initialization method name> and borsh(skip) (the former one not available in Serde).

borsh(init=...) allows to automatically run an initialization function right after deserialization. This adds a lot of convenience for objects that are architectured to be used as strictly immutable. Usage example:

#[derive(BorshSerialize, BorshDeserialize)]
#[borsh(init=init)]
struct Message {
    message: String,
    timestamp: u64,
    public_key: CryptoKey,
    signature: CryptoSignature
    hash: CryptoHash
}

impl Message {
    pub fn init(&mut self) {
        self.hash = CryptoHash::new().write_string(self.message).write_u64(self.timestamp);
        self.signature.verify(self.hash, self.public_key);
    }
}

borsh(skip) allows to skip serializing/deserializing fields, assuming they implement Default trait, similarly to #[serde(skip)].

#[derive(BorshSerialize, BorshDeserialize)]
struct A {
    x: u64,
    #[borsh(skip)]
    y: f32,
}

Enum with explicit discriminant

#[borsh(use_discriminant=false|true]) is required if you have an enum with explicit discriminant. This setting affects BorshSerialize and BorshDeserialize behaviour at the same time.

In the future, borsh will drop the requirement to explicitly use #[borsh(use_discriminant=false|true)], and will default to true, but to make sure that the transition from the older versions of borsh (before 0.11 release) does not cause silent breaking changes in de-/serialization, borsh 1.0 will require to specify if the explicit enum discriminant should be used as a de-/serialization tag value.

If you don't specify use_discriminant option for enum with explicit discriminant, you will get an error:

error: You have to specify `#[borsh(use_discriminant=true)]` or `#[borsh(use_discriminant=false)]` for all enums with explicit discriminant

In order to preserve the behaviour of borsh versions before 0.11, which did not respect explicit enum discriminants for de-/serialization, use #[borsh(use_discriminant=false)], otherwise, use true:

#[derive(BorshDeserialize, BorshSerialize)]
#[borsh(use_discriminant=false)]
enum A {
    X,
    Y = 10,
}

Advanced examples

Some of the less trivial examples are present in examples folder:

• implementing BorshSerialize/BorshDeserialize for third-party serde_json::Value

Testing

Integration tests should generally be preferred to unit ones. Root module of integration tests of borsh crate is linked here.

Releasing

The versions of all public crates in this repository are collectively managed by a single version in the workspace manifest.

So, to publish a new version of all the crates, you can do so by simply bumping that to the next "patch" version and submit a PR.

We have CI Infrastructure put in place to automate the process of publishing all crates once a version change has merged into master.

However, before you release, make sure the CHANGELOG is up to date and that the [Unreleased] section is present but empty.

License

This repository is distributed under the terms of both the MIT license and the Apache License (Version 2.0). See LICENSE-MIT and LICENSE-APACHE for details.