HTTP Server in C

A basic HTTP/1.1 server implementation written in C that handles multiple concurrent connections using poll-based I/O multiplexing.

Overview

This project implements a simple HTTP server from scratch in C, demonstrating low-level network programming and HTTP protocol handling. The server can handle basic GET and POST requests, serve files, echo messages, and parse HTTP headers.

Technologies & Concepts Learned

Network Programming

• Berkeley Sockets API - Socket creation, binding, listening, and accepting connections
• TCP/IP - Understanding the transport layer protocol
• IPv4/IPv6 - Dual-stack socket addressing with sockaddr_storage
• poll() - Event-driven I/O multiplexing for handling multiple concurrent connections
• SO_REUSEADDR - Socket option to allow address reuse

HTTP Protocol

• HTTP/1.1 - Request/response structure and status codes
• HTTP Methods - Handling GET and POST requests
• HTTP Headers - Parsing headers (User-Agent, Content-Length, Content-Type)
• MIME Types - Setting appropriate content types (text/plain, application/octet-stream)

C Programming

• String manipulation - strtok(), strstr(), sscanf(), snprintf()
• Memory management - Dynamic allocation with malloc(), realloc(), strdup(), and free()
• Signal handling - Graceful shutdown with SIGINT, SIGTERM, SIGHUP, SIGQUIT
• File I/O - Reading and writing files with fopen(), fgets(), fprintf()
• Command-line arguments - Parsing arguments for directory configuration

Features

• Route handling:

  • GET / - Returns 200 OK
  • GET /echo/{message} - Echoes back the message
  • GET /user-agent - Returns the User-Agent header value
  • GET /files/{filename} - Serves files from a specified directory
  • POST /files/{filename} - Creates files in the specified directory

• Concurrent connections - Uses poll() to handle multiple clients simultaneously

• Dynamic scaling - Doubles the client capacity when max connections are reached

• Graceful shutdown - Handles termination signals to close sockets properly

Usage

# Compile
gcc -o server server.c

# Run without file serving
./server

# Run with file directory
./server --directory /path/to/files

The server listens on port 4221 by default.

Learning Outcomes

This project provided hands-on experience with:

• Low-level network programming and socket API
• HTTP protocol implementation from scratch
• Event-driven programming with poll()
• Manual memory management in C
• Parsing and handling text-based protocols
• Building a real-world server application