1 unstable release

Uses old Rust 2015

0.1.0 May 30, 2016

#60 in #buffer

MIT license

1.5K SLoC


A higher-level event loop built on top of mio. mai manages buffers and streams so you can focus on sending and receiving your protocol's frames.


Largely functional. APIs subject to change.

Getting Started

Using mai requires three steps:

  • Selecting a data type to be your protocol's Frame, an actionable message.
  • Defining a Codec that knows how to read and write Frames into byte buffers.
  • Specifying a Handler to react to new connections, incoming Frames and errors.

Buffer pooling, low-level reads and writes and Token management are handled by mai.

An Echo Client example


Implement the Protocol trait by specifying the family of types you'll be using.

use mai::*;

struct EchoCodec;
struct EchoClientHandler;
struct EchoClient;

impl Protocol for EchoClient {
  type ByteStream = TcpStream; // vs a UnixStream, for example
  type Frame = String;
  type Codec = EchoCodec;
  type Handler = EchoClientHandler;
  type Timeout = usize;


Define methods to encode and decode your frames. Use the return codes to indicate that you got a frame, don't have enough bytes to read a frame yet or that you encountered a protocol error.

// For a simple Echo server, we can use `String` as our Frame type.
// This codec would work for both a client and server connection.
impl Codec<String> for EchoCodec {
  // Provide a method to try to write a given frame to a byte buffer
  fn encode(&mut self, message: &String, buffer: &mut [u8]) -> EncodingResult {
    let bytes = message.as_bytes();
    // If the buffer isn't big enough, say so via the return value
    if bytes.len() > buffer.len() {
      return Err(EncodingError::InsufficientBuffer);
    // Copy the bytes of our String into the buffer
    for (index, &byte) in bytes.iter().enumerate() {
        buffer[index] = byte;
    // Tell the frame engine how many bytes we wrote

  // Provide a method to try to parse a frame from a byte buffer
  fn decode(&mut self, buffer: &[u8]) -> DecodingResult<String> {
    use std::str;
    // Validate that the buffer contains a utf-8 String
    let message: String = match str::from_utf8(buffer) {
      Ok(message) => message.to_owned(),
      // For this example, assume that an invalid message means 
      // that we just don't have enough bytes yet
      Err(error) => return Err(DecodingError::IncompleteFrame)
    Ok(DecodedFrame::new(message, BytesRead(buffer.len())))


Define callbacks to handle byte stream events: connections, frames, timeouts, errors, and disconnects.

use mai::*;

impl Handler<EchoClient> for EchoClientHandler {
  fn on_ready(&mut self, context: &mut Context<EchoClient>) {
    let stream = context.stream();
    println!("Connected to {:?}", stream.peer_addr());
    let message: String = "Supercalifragilisticexpialidocious!".to_owned();
  fn on_frame(&mut self, stream: &mut Context<EchoClient>, message: String) {
    let stream = context.stream();
    println!("Received a message from {:?}: '{}'", stream.peer_addr(), &message.trim_right());
  fn on_timeout(&mut self, timeout: usize) {
    println!("A timeout has occurred: {:?}", timeout);
  fn on_error(&mut self, context: &mut Context<EchoClient>, error: &Error) {
    let stream = context.stream();
    println!("Error. {:?}, {:?}", stream.peer_addr(), error);
  fn on_closed(&mut self, stream: &Context<EchoClient>) {
    let stream = context.stream();
    println!("Disconnected from {:?}", stream.peer_addr());

Get to work

Create a ProtocolEngine and hand it any mio type that is Evented+Read+Write. Watch it go!

fn main() {
  // Create a TcpStream connected to `nc` running as an echo server
  // nc -l -p 2000 -c 'xargs -n1 echo'
  println!("Connecting to localhost:9999...");
  let address = "".parse().unwrap();
  let socket = TcpSocket::v4().unwrap();
  let (stream, _complete) = socket.connect(&address).unwrap();
  // Hand the TcpStream off to our new `ProtocolEngine` configured to treat its
  // byte streams as Echo clients.
  let protocol_engine: ProtocolEngine<EchoClient> = mai::protocol_engine(EchoClientHandler)
  let token = protocol_engine.manage(stream);
  let _ = protocol_engine.wait();

Creating a Server

Currently mai does not have a built-in way to manage incoming connections. This is being worked on.

Running a server is conceptually a straightforward process: create a separate thread using mio to listen for incoming connections. Each time a client connection is avialable, pass the corresponding TcpStream to the ProtocolEngine running in the background. Until there is a formal API, you can get a channel to send commands to the ProtocolEngine instance by running protocol_engine.command_sender.clone() and sending a Command::Manage(P::ByteStream) message that contains the ByteStream you'd like it to manage.


~43K SLoC