Educational HTTP Server in C

A simple HTTP server implementation for educational purposes demonstrating:

• Basic socket programming
• HTTP protocol handling
• Concurrent connection management using forking
• Signal handling

Features

• Handles multiple concurrent connections using process forking
• Responds to GET requests with basic HTML page
• Displays requested path and method
• Proper signal handling for zombie processes
• Port reuse capability (SO_REUSEADDR)

Prerequisites

• C compiler (gcc recommended)
• POSIX-compliant operating system (Linux/macOS)
• Basic understanding of networking concepts

Building

make
./http_server

Phase 1: Protocol Compliance

1. Proper HTTP Header Parsing ✅

   • Parse full request headers into key-value pairs
   • Handle Host, User-Agent, and Content-Length headers
   • Example structure:

   typedefstruct {
   charmethod[8];
   charpath[1024];
   charheaders[32][2][256]; // [header_count][key/value]intheader_count;
   } HTTPRequest;

2. HTTP Error Handling ✅

   • Implement 400 (Bad Request), 404 (Not Found), 501 (Not Implemented)
   • Create error template HTML responses
   • Handle malformed requests gracefully

3. HTTP/1.1 Keep-Alive Support ✅

   • Add Connection: keep-alive header
   • Implement request pipelining
   • Use content-length for proper message delimitation

---

Phase 2: Concurrency Improvements

4. Thread Pool Implementation ✅

   • Replace fork() with POSIX threads (pthread)
   • Create worker thread pool with task queue
   • Use mutexes and condition variables for synchronization

5. Event-Driven Architecture

   • Implement using epoll (Linux) or kqueue (BSD)
   • Non-blocking I/O with state machines
   • Compare performance against process/thread models

---

Phase 3: Performance Optimization

6. Zero-Copy File Transfer ✅ Implement using sendfile() system call:

   intfile_fd=open(filename, O_RDONLY);
   off_toffset=0;
   sendfile(client_socket, file_fd, &offset, file_size);

7. Buffer Management

   • Create ring buffer for request/response handling ✅
   • Implement dynamic buffer resizing ✅
   • Add read/write timeout protection

8. HTTP Compression ✅

   • Add gzip compression using zlib
   • Handle Accept-Encoding header
   • Compress responses on-the-fly

---

Phase 4: Security Enhancements

9. TLS Support

   • Integrate OpenSSL library
   • Implement HTTPS on port 443
   • Handle SSL handshake and encryption

10. Request Validation

    • Add maximum request size limit
    • Sanitize file paths to prevent directory traversal
    • Implement basic rate limiting

---

Phase 5: Advanced Features

11. Static File Serving

    • Serve files from document root directory
    • Handle MIME types (Content-Type header)
    • Add directory listing support

12. CGI Support

    • Execute external programs via fork/exec
    • Handle environment variables:

    setenv("REQUEST_METHOD", method, 1);
    setenv("QUERY_STRING", query, 1);

13. Reverse Proxy

    • Forward requests to backend servers
    • Handle load balancing between multiple backends
    • Add caching layer

---

Phase 6: Production Readiness

14. Configuration System

    • Read config file (JSON/INI format)
    • Support virtual hosts
    • Hot reload without restart

15. Logging & Monitoring

    • Implement access logs (Common Log Format)
    • Add metrics collection (requests/sec, latency)
    • Create health check endpoint

16. Benchmarking

    • Compare with nginx using wrk:

    wrk -t12 -c400 -d30s http://localhost:8080/

    • Profile with perf/valgrind

---

Learning Milestones

1. Networking Foundations

   • Complete Phases 1-3 → Understand HTTP/TCP stack

2. Systems Programming

   • Complete Phase 2 & 5 → Master concurrency/I/O

3. Production Engineering

   • Complete Phase 6 → Learn deployment concerns