Test app for printing http headers

Save this as app.py:

from flask import Flask, request, jsonify
import logging
 
app = Flask(__name__)
 
# Configure logging to print to stdout (visible in docker logs)
logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(levelname)s - %(message)s'
)
logger = logging.getLogger(__name__)
 
@app.route('/')
def index():
    """Main route that logs headers and returns HTML."""
    x_forwarded_for = request.headers.get('X-Forwarded-For', 'Not set')
    x_real_ip = request.headers.get('X-Real-IP', 'Not set')
 
    # Log to console
    logger.info(f"--- Request to / ---")
    logger.info(f"X-Forwarded-For: {x_forwarded_for}")
    logger.info(f"X-Real-IP: {x_real_ip}")
 
    return f"""
    <html>
    <head><title>Header Test</title></head>
    <body>
        <h1>Headers Received</h1>
        <p><strong>X-Forwarded-For:</strong> {x_forwarded_for}</p>
        <p><strong>X-Real-IP:</strong> {x_real_ip}</p>
        <p><a href="/testheaders">/testheaders</a> - JSON output</p>
        <p><a href="/allheaders">/allheaders</a> - All headers</p>
        <p><em>Check docker logs for detailed output.</em></p>
    </body>
    </html>
    """
 
@app.route('/testheaders')
def testheaders():
    """
    Dedicated route for testing header propagation.
    Returns all headers as JSON for easy programmatic verification.
    """
    # Capture all headers
    all_headers = dict(request.headers)
 
    # Specifically extract the ones we care about
    x_forwarded_for = request.headers.get('X-Forwarded-For', 'MISSING')
    x_real_ip = request.headers.get('X-Real-IP', 'MISSING')
 
    # Log the specific values
    logger.info(f"--- Request to /testheaders ---")
    logger.info(f"X-Forwarded-For: {x_forwarded_for}")
    logger.info(f"X-Real-IP: {x_real_ip}")
 
    # Return JSON response
    return jsonify({
        "status": "success",
        "headers_received": {
            "X-Forwarded-For": x_forwarded_for,
            "X-Real-IP": x_real_ip,
            "Host": request.headers.get('Host'),
            "User-Agent": request.headers.get('User-Agent')
        },
        "all_headers": all_headers
    }), 200
 
@app.route('/allheaders')
def allheaders():
    """
    Route that displays ALL headers received.
    Useful for debugging what Nginx is actually forwarding.
    """
    # Get all headers as a dictionary
    all_headers = dict(request.headers)
 
    # Log each header for debugging
    logger.info("--- Request to /allheaders ---")
    for key, value in all_headers.items():
        logger.info(f"{key}: {value}")
 
    # Create HTML table for readability
    header_rows = ''.join([
        f'<tr><td><strong>{key}</strong></td><td>{value}</td></tr>'
        for key, value in sorted(all_headers.items())
    ])
 
    return f"""
    <!DOCTYPE html>
    <html>
    <head>
        <title>All Headers</title>
        <style>
            body {{ font-family: monospace; margin: 20px; }}
            table {{ border-collapse: collapse; width: 100%; }}
            th, td {{ border: 1px solid #ddd; padding: 8px; text-align: left; }}
            th {{ background-color: #4CAF50; color: white; }}
            tr:nth-child(even) {{ background-color: #f2f2f2; }}
        </style>
    </head>
    <body>
        <h1>All Headers Received</h1>
        <p><strong>Total Headers:</strong> {len(all_headers)}</p>
        <table>
            <tr><th>Header Name</th><th>Value</th></tr>
            {header_rows}
        </table>
        <p><a href="/">← Back to Home</a></p>
        <p><em>Check docker logs for timestamped output.</em></p>
    </body>
    </html>
    """
 
if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8080)

Add Dockerfile:

| download

FROM python:3.11-slim
 
WORKDIR /app
 
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
ENV TZ=Europe/Malta
 
COPY app.py .
 
EXPOSE 8080
 
CMD ["python", "app.py"]

Build the image and run:

docker build -t header-test-app .
docker run -d --name app-container -p 8080:8080 --network <your_network> header-test-app

Change ports and network if necessary.

antisaWiki

Table of Contents

Test app for printing http headers

Tested on

See also

References