Build Your Own Redis (Java)

A lightweight, concurrent Redis server implementation written in pure Java (JDK 17+) adhering strictly to the Redis Serialization Protocol (RESP) specification and CodeCrafters challenge requirements.

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🚀 Features & Stages Implemented

• Pure Java Standard Library: Zero external third-party dependencies (java.net, java.io, java.util.concurrent).
• Stage 1 & 2 (Server Initialization & PING):
  • Binds to port 6379 with setReuseAddress(true).
  • Responds to PING with simple string +PONG\r\n or custom arguments as bulk strings.
• Stage 3 & 4 (Concurrent Clients & ECHO):
  • Multi-threaded client handling using virtual threads (Executors.newVirtualThreadPerTaskExecutor()) with fallback to cached thread pool.
  • Implements ECHO <message> command returning Bulk String format ($<length>\r\n<arg>\r\n).
• Stage 5 (SET & GET Commands):
  • Thread-safe storage with ConcurrentHashMap<String, ValueEntry>.
  • Implements SET <key> <value> replying with +OK\r\n.
  • Implements GET <key> replying with Bulk String or Null Bulk String ($-1\r\n) if key is absent.
• Stage 6 (Key Expiry with PX):
  • Supports SET <key> <value> [PX <expiry_in_millis>] and [EX <expiry_in_seconds>].
  • Passive eviction: On GET, evaluates if TTL has expired and evicts atomically.
  • Active eviction: Background daemon executor periodically cleans expired keys.
• Robust RESP Protocol Engine:
  • Handles streaming TCP input, fragmented packets, and pipelining.
  • Supports RESP Arrays (*), Bulk Strings ($), Simple Strings (+), Integers (:), and Errors (-).
  • Supports raw inline command input from telnet / netcat.

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📁 Project Structure

redis-java-clone/
├── src/
│   ├── main/
│   │   └── java/
│   │       ├── Main.java                                # CodeCrafters entry point
│   │       └── com/codecrafters/redis/
│   │           ├── Server.java                          # TCP Server & connection accept loop
│   │           ├── ClientHandler.java                   # Per-connection read/eval/write loop
│   │           ├── protocol/
│   │           │   ├── RespType.java                    # RESP type definitions
│   │           │   ├── RespValue.java                   # Immutable RESP value model & encoder
│   │           │   ├── RespReader.java                  # Streaming RESP parser
│   │           │   └── RespWriter.java                  # Low-overhead RESP output writer
│   │           ├── storage/
│   │           │   ├── ValueEntry.java                  # Key value + TTL metadata
│   │           │   └── RedisStore.java                  # Thread-safe in-memory store
│   │           └── command/
│   │               ├── Command.java                     # Parsed command representation
│   │               └── CommandHandler.java              # Command dispatcher & executor
│   └── test/
│       └── java/
│           └── com/codecrafters/redis/
│               └── RedisServerTest.java                 # Comprehensive test suite (37+ tests)
├── spawn_redis_server.sh                                # CodeCrafters runner script
└── pom.xml                                              # Standard Maven POM

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🛠️ Building and Running

Using the CodeCrafters runner script:

./spawn_redis_server.sh [--port <port>]

Running the built-in test suite:

mkdir -p /tmp/test-classes
javac -d /tmp/test-classes $(find src -name "*.java")
java -cp /tmp/test-classes com.codecrafters.redis.RedisServerTest

Connecting with redis-cli:

redis-cli -p 6379 PING
redis-cli -p 6379 ECHO "Hello World"
redis-cli -p 6379 SET mykey myvalue PX 5000
redis-cli -p 6379 GET mykey