Redis in Python

A toy Redis server built as part of the CodeCrafters challenge. Implemented in Python using asyncio, it speaks the Redis wire protocol (RESP2) and supports both master and replica roles.

I built this with Claude, but did most of the coding and architecture myself. I used Claude for refactoring and debugging, etc. See CLAUDE.md for more info on architecture.

Supported Commands

Command	Notes
PING	Returns +PONG
ECHO <message>	Returns the message as a bulk string
SET <key> <value> [EX seconds|PX milliseconds]	In-memory set with optional expiry
GET <key>	Returns value or null bulk string
INFO replication	Returns replication metadata
REPLCONF listening-port <port> / capa psync2	Replica handshake
REPLCONF GETACK *	Replica responds with current replication offset
PSYNC <replication_id> <offset>	Returns +FULLRESYNC <replid> 0 + RDB file
WAIT <numreplicas> <timeout>	Blocks until N replicas acknowledge all previous writes, or timeout (ms) expires

Replication

• Master propagates write commands (SET) to all connected replicas over the replication connection
• Replicas complete the full handshake (PING → REPLCONF → PSYNC), consume the RDB file, then enter a command loop
• Replicas process commands silently — only respond to REPLCONF GETACK
• Replication offset tracked on both master and replica
• WAIT returns the total number of replicas that have acknowledged all previous writes

Running

Master:

python3 -m app.main -p 6379

Replica:

python3 -m app.main -p 6380 --replicaof "localhost 6379"

Testing

sh check.sh