Parsing the Request - Post¶

When the request method is POST the query string will be sent in the HTTP request body in instead of in the URL. The request body is in the WSGI server supplied wsgi.input file like environment variable.

It is necessary to know the response body size as an integer to read it from wsgi.input. The PEP 3333 says that the CONTENT_LENGTH variable, which holds the body size, may be empty or missing so read it in a try/except block.

The HTML’s form tag in this script instructs the browser to do a POST request (method="post"):

#!/usr/bin/env python

from wsgiref.simple_server import make_server
from cgi import parse_qs, escape

html = """
<html>
<body>
   <form method="post" action="">
        <p>
           Age: <input type="text" name="age" value="%(age)s">
        </p>
        <p>
            Hobbies:
            <input
                name="hobbies" type="checkbox" value="software"
                %(checked-software)s
            > Software
            <input
                name="hobbies" type="checkbox" value="tunning"
                %(checked-tunning)s
            > Auto Tunning
        </p>
        <p>
            <input type="submit" value="Submit">
        </p>
    </form>
    <p>
        Age: %(age)s<br>
        Hobbies: %(hobbies)s
    </p>
</body>
</html>
"""

def application(environ, start_response):

    # the environment variable CONTENT_LENGTH may be empty or missing
    try:
        request_body_size = int(environ.get('CONTENT_LENGTH', 0))
    except (ValueError):
        request_body_size = 0

    # When the method is POST the variable will be sent
    # in the HTTP request body which is passed by the WSGI server
    # in the file like wsgi.input environment variable.
    request_body = environ['wsgi.input'].read(request_body_size)
    d = parse_qs(request_body)

    age = d.get('age', [''])[0] # Returns the first age value.
    hobbies = d.get('hobbies', []) # Returns a list of hobbies.

    # Always escape user input to avoid script injection
    age = escape(age)
    hobbies = [escape(hobby) for hobby in hobbies]

    response_body = html % { # Fill the above html template in
        'checked-software': ('', 'checked')['software' in hobbies],
        'checked-tunning': ('', 'checked')['tunning' in hobbies],
        'age': age or 'Empty',
        'hobbies': ', '.join(hobbies or ['No Hobbies?'])
    }

    status = '200 OK'

    response_headers = [
        ('Content-Type', 'text/html'),
        ('Content-Length', str(len(response_body)))
    ]

    start_response(status, response_headers)
    return [response_body]

httpd = make_server('localhost', 8051, application)
httpd.serve_forever()