Multi-threaded HTTP Server

A fully-featured HTTP server implementation using low-level socket programming in Python.

Project Structure

cn_assignment/
├── server.py              # Main server implementation
├── resources/             # Static files directory
│   └── uploads/          # Directory for POST uploads
└── README.md

Requirements

• Python 3.7 or higher
• No external dependencies required (uses standard library only)

Usage

Basic Usage

python server.py

Custom Configuration

python server.py [port] [host] [thread_pool_size]

Examples:

python server.py 8000                    # Run on port 8000
python server.py 8000 0.0.0.0           # Run on all interfaces
python server.py 8000 0.0.0.0 20        # With 20 threads

Features Summary

✅ Core HTTP Server

• TCP socket programming with proper lifecycle management
• HTTP/1.0 and HTTP/1.1 protocol support
• Request parsing and response generation
• Support for GET and POST methods

✅ Multi-threading

• Fixed-size thread pool (configurable, default: 10)
• Connection queue for overflow handling
• Thread-safe operations with mutex locks
• Worker thread lifecycle management

✅ File Serving

• HTML files rendered in browser
• Binary file downloads (images, text files)
• Proper Content-Type and Content-Disposition headers
• Support for .html, .txt, .png, .jpg, .jpeg files

✅ JSON Upload

• POST request handling with JSON validation
• Content-Type validation
• Timestamped unique filenames
• Automatic uploads directory creation

✅ Security

• Path traversal protection
• Host header validation
• Input sanitization
• Request size limits

✅ Connection Management

• Keep-Alive support (persistent connections)
• 30-second timeout for idle connections
• Maximum 100 requests per connection
• Proper connection closure

✅ Error Handling

• Comprehensive HTTP status codes (200, 201, 400, 403, 404, 405, 415, 500)
• Graceful error recovery
• Detailed error logging

Testing

Using a Web Browser

• Navigate to http://localhost:8080/ to view index.html
• Try http://localhost:8080/about.html for other pages
• Download files by clicking links on the pages

Using curl

GET HTML file:

curl http://localhost:8080/

Download binary file:

curl -O http://localhost:8080/sample.txt

POST JSON data:

curl -X POST http://localhost:8080/upload -H "Content-Type: application/json" -H "Host: localhost:8080" -d @test_upload.json

Test security (should return 403):

curl http://localhost:8080/../etc/passwd

Test error handling (should return 404):

curl http://localhost:8080/nonexistent.html

Automated Testing

Run the comprehensive test suite:

python test_server.py

This will test:

• GET requests (HTML and binary files)
• POST requests (JSON uploads)
• Security features (path traversal, host validation)
• Error handling (404, 403, 405, 415)
• Keep-Alive connections

Project Structure

cn_assignment/
├── server.py              # Main server implementation
├── test_server.py         # Automated test suite
├── test_upload.json       # Sample JSON for POST testing
├── README.md              # Project overview and usage
├── TECHNICAL_DOCS.md      # Detailed technical documentation
└── resources/             # Static files directory
    ├── index.html         # Home page
    ├── about.html         # About page
    ├── contact.html       # Contact page
    ├── sample.txt         # Test text file
    ├── document.txt       # Test document
    └── uploads/           # Directory for POST uploads

Technical Details

Thread Pool Architecture

• Pre-spawned worker threads
• Connection queue for overflow handling
• Mutex-based synchronization
• Configurable pool size

Binary File Transfer

• Files read in binary mode
• Content sent as application/octet-stream
• Content-Disposition header triggers downloads
• Supports large files (tested >1MB)

Security Measures

• Path Traversal: Validates all paths stay within resources directory
• Host Validation: Ensures requests are intended for this server
• Input Validation: Checks request format, JSON validity, Content-Type

Performance

• Concurrent connections: Limited by thread pool size (default: 10)
• Requests per connection: Up to 100 (Keep-Alive)
• Connection timeout: 30 seconds
• Request size limit: 8192 bytes

For detailed technical documentation, see TECHNICAL_DOCS.md

HTTP Status Codes

Code	Meaning	When Used
200	OK	Successful GET request
201	Created	Successful POST request
400	Bad Request	Malformed request, missing Host, invalid JSON
403	Forbidden	Path traversal attempt, Host mismatch
404	Not Found	Requested file doesn't exist
405	Method Not Allowed	Unsupported HTTP method (PUT, DELETE, etc.)
415	Unsupported Media Type	Wrong Content-Type or unsupported file type
500	Internal Server Error	Unexpected server error

Known Limitations

• No HTTPS/SSL support
• No response compression
• No caching mechanisms
• Limited to GET and POST methods
• Single-process (cannot scale across CPU cores)
• Python GIL limitations for CPU-bound tasks