Easy protocol definitions in Rust
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Build Status Crates.io MIT licensed


Easy protocol definitions in Rust.

This crate adds a custom derive that can be added to types, allowing structured data to be sent and received from any IO stream.

Networking is built-in, with special support for TCP and UDP.

The protocol you define can be used outside of networking too - see the Parcel::from_raw_bytes and Parcel::raw_bytes methods.

This crate also provides:

  • TCP and UDP modules for easy sending and receiving of Parcels
  • A generic middleware library for automatic transformation of sent/received data
    • Middleware has already been written to support compression
    • Custom middleware can be implemented via a trait with two methods

Checkout the examples folder for usage.


Add this to your Cargo.toml:

protocol = "1.0"
protocol-derive = "1.0"

Under the hood

The most interesting part here is the protocol::Parcel trait. Any type that implements this trait can then be serialized to and from a byte stream. All primitive types, standard collections, tuples, and arrays implement this trait.

This crate becomes particularly useful when you define your own Parcel types. You can use #[derive(Protocol)] to do this. Note that in order for a type to implement Parcel, it must also implement Clone, Debug, and PartialEq.

#[derive(Parcel, Clone, Debug, PartialEq]
pub struct Health(f32);

#[derive(Parcel, Clone, Debug, PartialEq]
pub struct SetPlayerPosition {
    pub position: (f32, f32),
    pub health: Health,
    pub values: Vec<String>,

Custom derive

Any user-defined type can have the Parcel trait automatically derived.


#[macro_use] extern crate protocol_derive;
#[macro_use] extern crate protocol;

#[derive(Protocol, Clone, Debug, PartialEq)]
pub struct Handshake;

#[derive(Protocol, Clone, Debug, PartialEq)]
pub struct Hello {
    id: i64,
    data: Vec<u8>,

#[derive(Protocol, Clone, Debug, PartialEq)]
pub struct Goodbye {
    id: i64,
    reason: String,

#[derive(Protocol, Clone, Debug, PartialEq)]
pub struct Node {
    name: String,
    enabled: bool

#[protocol(discriminant = "integer")]
#[derive(Protocol, Clone, Debug, PartialEq)]
pub enum PacketKind {

fn main() {
    use std::net::TcpStream;

    let stream = TcpStream::connect("").unwrap();
    let mut connection = protocol::wire::stream::Connection::new(stream, protocol::wire::middleware::pipeline::default());

    connection.send_packet(&Packet::Hello(Hello { id: 0, data: vec![ 55 ]})).unwrap();
    connection.send_packet(&Packet::Goodbye(Goodbye { id: 0, reason: "leaving".to_string() })).unwrap();

    loop {
        if let Some(response) = connection.receive_packet().unwrap() {
            println!("{:?}", response);



Enum values can be transmitted either by their 1-based variant index, or by transmitting the string name of each variant.

NOTE: The default behaviour is to use the variant name as a string (string).

This behaviour can be changed by the #[protocol(discriminant = "<type>")] attribute.

Supported discriminant types:

  • string (default)
    • This transmits the enum variant name as the over-the-wire discriminant
    • This uses more bytes per message, but it very flexible
  • integer
    • This transmits the 1-based variant number as the over-the-wire discriminant
    • If enum variants have explicit discriminators, the
    • Enum variants cannot be reordered in the source without breaking the protocol
#[derive(Protocol, Clone, Debug, PartialEq)]
#[protocol(discriminant = "string")]
pub enum PlayerState {
  Flying { velocity: (f32,f32,f32) },
  // Discriminators can be explicitly specified.
  Jumping { height: f32 },


You can rename the variant for their serialisation.

#[derive(Protocol, Clone, Debug, PartialEq)]
#[protocol(discriminant = "string")]
pub enum Foo {
  #[protocol(name = "Biz")] // the Bing variant will be send/received as 'Biz'.