Bincode

A compact encoder / decoder pair that uses a binary zero-fluff encoding scheme. The size of the encoded object will be the same or smaller than the size that the object takes up in memory in a running Rust program.

In addition to exposing two simple functions (one that encodes to Vec<u8>, and one that decodes from &[u8]), binary-encode exposes a Reader/Writer API that makes it work perfectly with other stream-based APIs such as Rust files, network streams, and the flate2-rs compression library.

API Documentation

Bincode in the wild

• google/tarpc: Bincode is used to serialize and deserialize networked RPC messages.
• servo/webrender: Bincode records webrender API calls for record/replay-style graphics debugging.
• servo/ipc-channel: IPC-Channel uses Bincode to send structs between processes using a channel-like API.

Example

use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, PartialEq, Debug)]
struct Entity {
    x: f32,
    y: f32,
}

#[derive(Serialize, Deserialize, PartialEq, Debug)]
struct World(Vec<Entity>);

fn main() {
    let world = World(vec![Entity { x: 0.0, y: 4.0 }, Entity { x: 10.0, y: 20.5 }]);

    let encoded: Vec<u8> = bincode::serialize(&world).unwrap();

    // 8 bytes for the length of the vector, 4 bytes per float.
    assert_eq!(encoded.len(), 8 + 4 * 4);

    let decoded: World = bincode::deserialize(&encoded[..]).unwrap();

    assert_eq!(world, decoded);
}

Details

The encoding (and thus decoding) proceeds unsurprisingly -- primitive types are encoded according to the underlying Writer, tuples and structs are encoded by encoding their fields one-by-one, and enums are encoded by first writing out the tag representing the variant and then the contents.

However, there are some implementation details to be aware of:

• isize/usize are encoded as i64/u64, for portability.
• enums variants are encoded as a u32 instead of a usize. u32 is enough for all practical uses.
• str is encoded as (u64, &[u8]), where the u64 is the number of bytes contained in the encoded string.