Build Your Own Redis in Go (from Scratch)

A fully functional Redis clone built entirely from scratch using the Go standard library. This project explores core Redis features and systems programming concepts including RESP parsing, custom TCP servers, in-memory data storage, transactions, persistence, and PUB/SUB.

Goals

• Understand and implement the Redis protocol (RESP)
• Build a robust, concurrent TCP server from scratch
• Reproduce core Redis functionality (PING, ECHO, SET, GET, INCR, etc.)
• Implement advanced Redis data types like Lists
• Handle complex features like transactions, RDB persistence, and PUB/SUB
• Strengthen skills in concurrency, systems design, and Go internals

Implemented Features

Commands

Command	Description
PING	Returns PONG, or a custom message if provided (PING hello → hello)
ECHO <msg>	Returns the exact message sent
SET <key> <val> [EX seconds/PX milliseconds]	Stores val under key, overwrites if it exists
GET <key>	Retrieves value for key, or nil if it doesn’t exist
DEL <key> [key ...]	Deletes one or more the key-value pairs
INCR <key>	Increments an integer value (creates it if missing, starts at 0)
DECR <key>	Decrements an integer value (creates it if missing, starts at -1)
EXISTS <key> [key ...]	Returns an integer of how many of the provided keys exist
TYPE <key>	Returns the type of the value stored at key
TTL <key>	Returns remaining time-to-live in seconds (-1 if no expiry, -2 if key missing)
MULTI	Begins transaction mode, queues following commands
EXEC	Executes queued transaction commands
KEYS <pattern>	Returns all keys matching glob-style pattern (*, etc)
CONFIG GET	Returns RDB config like filename and directory
RPUSH <key> <val> [val ...]	Appends value(s) to list at key, creates list if it doesn’t exist
LPUSH <key> <val> [val ...]	Prepends value(s) to the start of the list at key (creates list if it doesn’t exist)
LRANGE <key> <start> <stop>	Returns elements in the list from index start to stop (inclusive, supports negative indices)
LLEN <key>	Returns the length of the list stored at key
LPOP <key>	Removes and returns the first element of the list at key
RPOP <key>	Removes and returns the last element of the list at key
BLPOP key timeout	Removes and returns the first element of the list at the given key, block if empty until a timeout or new data arrives.
SUBSCRIBE <channel>	registers a client as a subscriber to channel
PUBLISH <channel> <message>	delivers a message to all clients subscribed to a channel
UNSUBSCRIBE <channel>	Unsubscribes a client from a channel

Concurrency & Networking

• Manual TCP server built with net.Listen and Accept
• Goroutine-per-connection concurrency model
• Graceful client connection and disconnection
• RESP protocol parser (array, bulk strings, simple strings, errors, integers)
• Structured logging (with slog)

In-Memory Store

• Thread-safe key-value store using sync.RWMutex
• Optional TTL support via expiry timestamps
• Clean handling of expired keys

Transaction System

• Command queueing with MULTI
• Conditional execution with EXEC
• Aborting transactions via DISCARD
• Dirty flag detection for invalid commands within a transaction

Persistence

• Loads data from RDB snapshot on startup
• Configurable file location via dbfilename and dir
• Parses string keys and values from standard RDB format
• Supports optional TTL and skips expired keys
• Validates file structure and handles malformed input

PUB/SUB

• SUBSCRIBE – Subscribe to a channel
• Enter subscriber mode (only PUB/SUB commands allowed)
• PUBLISH – Send a message to all subscribers
• UNSUBSCRIBE [channel] – Unsubscribe from a channel

How to Run

1. Clone the repository

git clone git@github.com:raphico/codecrafters-redis-go.git
cd codecrafters-redis-go

2. Run the server

go run app/main.go

3. Test with redis-cli

redis-cli PING

Folder structure

├── app/main.go                # Entry point, registers commands, starts server
├── config/config.go           # Defines and validates configuration, such as RDB path
├── handlers/                  # Individual command handlers
├── persistence/
│   ├── load.go                # Handles restoring dataset from RDB file
│   └── save.go                # Handles saving dataset to RDB file
├── protocol/
│   ├── request.go             # Parses incoming RESP requests
│   └── response.go            # Serializes and formats RESP responses
├── pubsub/pubsub.go           # Defines a message broker
├── registry/registry.go       # Dispatches commands to handlers
├── server/server.go           # TCP server, handles concurrent clients
├── session/
│   ├── session.go             # Per-client connection state
│   └── transaction.go         # Handles transaction queueing and context
├── store/
│   ├── store.go               # Thread-safe key-value store
│   └── entry.go               # Defines key-value pair with optional expiry

Attribution

This project was built as part of the Codecrafters "Build Your Own HTTP Server" Challenge