Implement a Simple Redis Client That Speaks RESP

Topic Overview

RESP Data Types

Redis speaks RESP over TCP port 6379. Every value starts with a type prefix character:

• +OK\r\n simple string
• -ERR unknown command\r\n error
• :42\r\n integer
• $6\r\nfoobar\r\n bulk string (length-prefixed)
• *2\r\n... array of nested values

Encoding a Command

The GET mykey command encodes as:

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That is: array of 2 elements, bulk string "GET" (3 bytes), bulk string "mykey" (5 bytes). Bulk strings use $-1\r\n for NULL; arrays use *-1\r\n for NULL.

Parsing Strategy

A simple state machine reads the prefix byte, parses the length for bulk strings, then consumes exactly that many bytes plus \r\n. No formal grammar needed. Arrays nest arbitrarily: a MULTI/EXEC transaction wraps multiple commands in an outer array, and pipelining sends several encoded commands back-to-back on one TCP connection to 127.0.0.1:6379.

Why This Exercise

This task asks you to encode a Redis command and decode a RESP response. redis-cli is nothing more than a RESP encoder wrapped around stdin/stdout, and every client library (redis-py, Jedis) uses this same wire format on TCP port 6379. Redis chose RESP because a simple state machine can parse it without a formal grammar, which keeps the server implementation small and fast.

Write a C program that encodes a Redis command into RESP format and decodes a RESP response.

Requirements:

• Implement a function to encode a Redis command as a RESP array of bulk strings
• Support commands like PING, GET key, and SET key value
• Implement a function to decode a RESP response and print its type and value
• Handle simple strings (+), errors (-), integers (:), bulk strings ($), and arrays (*)
• Print the encoded RESP bytes for a sample command
• Print the decoded result for a sample response
• Show the breakdown of each RESP element with printf
• Do not use any Redis client libraries