Key-Value Storage System (C, Socket Programming)

A simple client-server key-value store implemented in C using TCP sockets.
The server maintains key-value pairs in memory, and the client provides both interactive and batch modes to manipulate stored data via a custom binary protocol.

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Features

• Supports Create, Read, Update, Delete (CRUD) operations
• Keys are integers, values are arbitrary-length byte strings
• Custom binary protocol for reliable transmission over TCP
• Client supports:
  • Interactive mode: run commands with a prompt
  • Batch mode: execute commands from a file
• In-memory hash-table–based store with persistence across client sessions
• Handles TCP packet-splitting via exact-length read_n/write_n helpers
• Human-readable error responses
• Single-client server (simple to extend for concurrency)

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Protocol

Client → Server (Request)

A fixed 9-byte header followed by an optional value:

• byte 0 : op (ASCII) – 'C' = create, 'R' = read, 'U' = update, 'D' = delete
• bytes 1-4 : int32_t key (network byte order)
• bytes 5-8 : int32_t value_size (network byte order; 0 if no value follows)
• bytes 9.. : value (raw bytes, length = value_size)

Server → Client (Response)

A fixed 5-byte header followed by payload:

• byte 0 : status – 'O' (OK) or 'E' (Error)
• bytes 1-4 : int32_t payload_size (network byte order)
• bytes 5.. : payload
• On successful READ: payload = value bytes
• On other successes: payload = "OK"
• On errors: payload = ASCII error message

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Build Instructions

Compile the server and client using gcc:

gcc -o kv-server kv-server.c
gcc -o kv-client kv-client.c

Running the server

./kv-server <bind-ip> <port>

Running the Client

Interactive mode

./kv-client interactive

Batch Mode

./kv-client batch commands.txt

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Supported Client Commands

• connect <server-ip> <server-port>
• disconnect
• create <key> <value-size> <value>
• read <key>
• update <key> <value-size> <value>
• delete <key>

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Implementation Notes

• Server stores key-value pairs in a chained hash table
• Memory dynamically allocated for values and freed on deletion
• Server ignores SIGPIPE so broken pipes return errors instead of crashing
• Client enforces active connection before running operations
• Values may be multi-line in batch/interactive mode: if fewer bytes than are provided on one line, the client reads additional input until the full value is collected
• No authentication, no concurrency — can be extended
• Errors returned as ASCII strings for easier debugging