wsgi – WSGI server

The wsgi module provides a simple and easy way to start an event-driven WSGI server. This can serve as an embedded web server in an application, or as the basis for a more full-featured web server package. One such package is Spawning.

To launch a wsgi server, simply create a socket and call evy.wsgi.server() with it:

from evy.web import wsgi
import evy

def hello_world(env, start_response):
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return ['Hello, World!\r\n']

wsgi.server(evy.listen(('', 8090)), hello_world)

You can find a slightly more elaborate version of this code in the file examples/wsgi.py.

SSL

Creating a secure server is only slightly more involved than the base example. All that’s needed is to pass an SSL-wrapped socket to the server() method:

wsgi.server(evy.wrap_ssl(evy.listen(('', 8090)),
                              certfile='cert.crt',
                              keyfile='private.key',
                              server_side=True),
            hello_world)

Applications can detect whether they are inside a secure server by the value of the env['wsgi.url_scheme'] environment variable.

Non-Standard Extension to Support Post Hooks

Evy’s WSGI server supports a non-standard extension to the WSGI specification where env['evy.posthooks'] contains an array of post hooks that will be called after fully sending a response. Each post hook is a tuple of (func, args, kwargs) and the func will be called with the WSGI environment dictionary, followed by the args and then the kwargs in the post hook.

For example:

from evy.web import wsgi
import evy

def hook(env, arg1, arg2, kwarg3=None, kwarg4=None):
    print 'Hook called: %s %s %s %s %s' % (env, arg1, arg2, kwarg3, kwarg4)

def hello_world(env, start_response):
    env['evy.posthooks'].append(
        (hook, ('arg1', 'arg2'), {'kwarg3': 3, 'kwarg4': 4}))
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return ['Hello, World!\r\n']

wsgi.server(evy.listen(('', 8090)), hello_world)

The above code will print the WSGI environment and the other passed function arguments for every request processed.

Post hooks are useful when code needs to be executed after a response has been fully sent to the client (or when the client disconnects early). One example is for more accurate logging of bandwidth used, as client disconnects use less bandwidth than the actual Content-Length.