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A toy chat server spec and some sample implementations, to help you choose among the many ways to write code to perform concurrent I/O.


The server is an executable with a single command-line argument indicating an IP address on which to listen. The server runs forever, accepting and handling TCP connections arriving on that address.

When the server is ready to receive connections, it prints a single line to stdout, of the form "listening on [address]".

The purpose of the server is to forward messages to all connected clients. There can be any number of connected clients active at a time. Each message received from any client should be sent to all clients, including the sender.

A message is a sequence of bytes consisting of a 1-byte header and a variable-length body. The body's length is equal to the value of the header byte interpreted as an unsigned 8-bit integer.

Clients must receive messages in an order that is sequentially consistent with the order that they were sent.

The server is allowed to drop messages -- i.e. to not send them to some senders. Doing so may be necessary to prevent unbounded buffering in the case where the server receives messages faster than it can send them out. However, dropping too many messages may cause the server to receive lower scores in benchmark tests.


Implementations live in the impls directory. Please submit a pull request to add your own!


This repo includes some tools to allow you to test implementations and to compare their performance.

$ cargo build --release
$ cd impls/gjio && cargo build --release && cd ../..
$ ./target/release/stresstest -a ./impls/gjio/target/release/server
cargo run --release --bin commandline-client

wish list

Our goal is to collect many different implementations of the server spec to illustrate a wide variety of concurrency styles. Below are listed some libraries that might be particularly interesting to try.


toy chat server spec and example implementations




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