Smallchat: A Beginner‑Friendly Open‑Source C Chat Server by Redis Founder

Smallchat is a minimal chat server written entirely in C. The source code is hosted on GitHub at https://github.com/antirez/smallchat.

The program is intended as an educational example for developers to explore system‑level concepts such as single‑process multiplexed I/O, client state tracking, and rapid access to newly arrived data.

The codebase consists of roughly 300 lines; after removing blank lines and comments it is just over 200 lines.

Core data structures

struct chatState *Chat

– global variable that stores all server state. struct client *clients[MAX_CLIENTS] – array that records each client’s file descriptor and nickname.

Execution flow

1. initChat initializes global variables and creates the listening socket, storing it in Chat->serversock.
2. Enter an infinite while loop.
3. Initialize an fd_set collection.
4. Add the listening socket and client sockets to the fd_set.
5. Call select() to monitor the fd_set for events, storing results back into the set.
6. Test whether the listening socket or any client socket has an event.
7. Dispatch the appropriate business logic for each ready descriptor.

The architecture mirrors the network I/O handling found in Redis’s source code, making the example a clear, hands‑on reference for beginners learning C network programming.

Future revisions may add symmetric encryption and more advanced networking models.