🖥️ HTTP Server

Building web servers with Python's built-in http.server module

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What is http.server?

The http.server module is Python's built-in library for creating HTTP servers. It provides:

• HTTPServer class - The server that listens for connections
• BaseHTTPRequestHandler class - Handles incoming HTTP requests
• Zero dependencies - Part of Python's standard library

Think of it like a small restaurant that: - Opens its doors (binds to a port) - Waits for customers (listens for requests) - Takes orders (reads HTTP requests) - Serves food (sends HTTP responses)

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Basic Server Structure

from http.server import HTTPServer, BaseHTTPRequestHandler

class MyHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        # Handle GET requests
        self.send_response(200)  # OK status
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        self.wfile.write(b'Hello, World!')

# Create and start server
server = HTTPServer(('localhost', 8000), MyHandler)
print('Server running on http://localhost:8000')
server.serve_forever()

Key Components:

Component	Purpose
HTTPServer	The actual server that listens for connections
BaseHTTPRequestHandler	Base class for handling requests
do_GET()	Method called for GET requests
send_response(code)	Sets HTTP status code
send_header(name, value)	Adds HTTP headers
end_headers()	Finishes header section
wfile.write(data)	Sends response body

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Understanding Request Handlers

The Handler Class

class MyHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        # Called when browser requests a page
        pass

    def do_POST(self):
        # Called when form is submitted
        pass

    def log_message(self, format, *args):
        # Override to customize logging
        print(f"[{self.date_time_string()}] {args[0]}")

Request Information Available

def do_GET(self):
    # The requested path (e.g., "/about")
    path = self.path

    # HTTP method used (GET, POST, etc.)
    method = self.command

    # Request headers (dictionary-like)
    user_agent = self.headers.get('User-Agent')

    # Client address
    client_ip = self.client_address[0]

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HTTP Status Codes

Always send appropriate status codes:

Code	Meaning	When to Use
200	OK	Request succeeded
301	Moved Permanently	Resource moved to new URL
302	Found	Temporary redirect
400	Bad Request	Request was malformed
404	Not Found	Resource doesn't exist
405	Method Not Allowed	Wrong HTTP method
500	Internal Server Error	Server error occurred

def do_GET(self):
    if self.path == '/':
        self.send_response(200)
    elif self.path == '/old-page':
        self.send_response(301)
        self.send_header('Location', '/new-page')
    else:
        self.send_response(404)

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Serving Different Content Types

def do_GET(self):
    self.send_response(200)

    # Set content type based on what's being served
    if self.path.endswith('.html'):
        self.send_header('Content-type', 'text/html')
    elif self.path.endswith('.css'):
        self.send_header('Content-type', 'text/css')
    elif self.path.endswith('.js'):
        self.send_header('Content-type', 'application/javascript')
    elif self.path.endswith('.json'):
        self.send_header('Content-type', 'application/json')
    elif self.path.endswith('.png'):
        self.send_header('Content-type', 'image/png')
    else:
        self.send_header('Content-type', 'text/plain')

    self.end_headers()

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Serving Static Files

import os
from http.server import HTTPServer, BaseHTTPRequestHandler

class StaticFileHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        # Map URL path to file path
        if self.path == '/':
            filepath = 'index.html'
        else:
            # Remove leading slash
            filepath = self.path.lstrip('/')

        # Security: prevent directory traversal
        filepath = os.path.normpath(filepath)
        if filepath.startswith('..'):
            self.send_error(403, "Access denied")
            return

        # Check if file exists
        if not os.path.exists(filepath):
            self.send_error(404, "File not found")
            return

        # Read and serve file
        try:
            with open(filepath, 'rb') as f:
                content = f.read()

            self.send_response(200)
            self.send_header('Content-Length', len(content))
            self.end_headers()
            self.wfile.write(content)

        except IOError:
            self.send_error(500, "Server error")

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Complete Example: Simple Web Server

"""
simple_server.py - A basic HTTP server with multiple routes
"""
from http.server import HTTPServer, BaseHTTPRequestHandler
import json

class SimpleHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        # Route based on path
        if self.path == '/':
            self.serve_home()
        elif self.path == '/about':
            self.serve_about()
        elif self.path == '/api/data':
            self.serve_api_data()
        else:
            self.serve_404()

    def serve_home(self):
        html = """<!DOCTYPE html>
<html>
<head><title>Home</title></head>
<body>
    <h1>Welcome!</h1>
    <nav>
        <a href="/">Home</a> |
        <a href="/about">About</a> |
        <a href="/api/data">API Data</a>
    </nav>
</body>
</html>"""
        self.send_response(200)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        self.wfile.write(html.encode())

    def serve_about(self):
        html = """<!DOCTYPE html>
<html>
<head><title>About</title></head>
<body>
    <h1>About This Server</h1>
    <p>Built with Python's http.server module!</p>
    <a href="/">← Back Home</a>
</body>
</html>"""
        self.send_response(200)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        self.wfile.write(html.encode())

    def serve_api_data(self):
        data = {'message': 'Hello from API', 'status': 'ok'}
        self.send_response(200)
        self.send_header('Content-type', 'application/json')
        self.end_headers()
        self.wfile.write(json.dumps(data).encode())

    def serve_404(self):
        self.send_response(404)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        self.wfile.write(b'<h1>404 - Page Not Found</h1>')

    def log_message(self, format, *args):
        # Custom logging
        print(f"[{self.date_time_string()}] {self.client_address[0]} - {args[0]}")

# Start server
if __name__ == '__main__':
    server = HTTPServer(('localhost', 8000), SimpleHandler)
    print('Server running at http://localhost:8000')
    print('Press Ctrl+C to stop')
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        print('\nShutting down...')
        server.shutdown()

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Handling POST Requests

def do_POST(self):
    # Get content length from headers
    content_length = int(self.headers.get('Content-Length', 0))

    # Read the request body
    post_data = self.rfile.read(content_length)

    # Parse form data (application/x-www-form-urlencoded)
    from urllib.parse import parse_qs
    form_data = parse_qs(post_data.decode())

    # Handle the data
    username = form_data.get('username', [''])[0]

    # Send response
    self.send_response(200)
    self.send_header('Content-type', 'text/html')
    self.end_headers()
    self.wfile.write(f'Hello, {username}!'.encode())

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Common Mistakes

Mistake	Why It's Wrong	Correct Approach
Not calling end_headers()	Browser won't receive response	Always call after sending headers
Writing strings to wfile	wfile expects bytes	Use .encode() or b'...'
Not checking file paths	Security vulnerability	Use os.path.normpath() and validation
Blocking serve_forever()	Can't stop server cleanly	Use threads or signal handlers
Forgetting content length	May cause connection issues	Set Content-Length header

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Quick Reference

from http.server import HTTPServer, BaseHTTPRequestHandler
import json

class QuickHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.send_header('Content-type', 'text/html')
        self.end_headers()
        self.wfile.write(b'<h1>Hello!</h1>')

    def do_POST(self):
        length = int(self.headers.get('Content-Length', 0))
        data = self.rfile.read(length)
        # Process data...
        self.send_response(200)
        self.end_headers()

# Run server
server = HTTPServer(('localhost', 8000), QuickHandler)
server.serve_forever()

Start server in one line (for development only):

python -m http.server 8000

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Next Steps

Now that you can build a basic server, let's learn how to route different URLs!

→ Continue to 03: Simple Routing