Simple Multi-user, Multi-room Asynchronous Chat Server

Built upon Tokio's example

• Uses Tokio for multi-threaded, concurrent async IO for massive scalability
• Rooms hold Peers in a HalfBrown container for fast size-dependent lookup & search. It starts as a Vector & switches to rust-lang's Hashbrown after 32 users because Vectors are much faster to iterate through thanks to contiguous memory allowing spacial locality, making it better for broadcasting a message to each user. However, searching for a specific Peer is takes O(n) time. This means that as the number of Peers in a Room grows, it will take longer to add and remove peers. This is where Hashbrown's average O(1) lookup time is utilized.
• Uses reader-writer lock for more concurrent accesses to the state*
• Leak-free thanks to 0 cycles in Arc<Rwlock>
• Kicks Peers who send inputs over 20,000 bytes long
• Gracefully exits on SIGINT or SIGTERM, allowing Tokio to close ports
• Users shouldn't be able to crash the program

Further Optimizations + Scaling

The scalability of this architecture could be improved by moving away the reader-writer lock from the entire Shared Memory, and instead using a reader-writer lock on each Room. This change would require a statically-allocated container (like an array) whose indices would represent the name of the Room hashed with the max room count. However, the specification does not mention mention a maximum number of users or rooms, so the architecture goes instead for flexibility of user count and room count at the cost of performance by using dynamically-allocated rooms & users structures.

Building

cargo build --release

Running

Without logging to stdout:

cargo run <port_id>

With logging to stdout:

cargo run <port_id> -v

Joining

If joining on your machine, you can use localhost as your address:

telnet <address> <port_id>

Tested on Ubuntu 20.04