WhatsNewIn22: middleware_demo.py

"""
This is an example of a way to use WSGI middleware with
CherryPy 2.2.

This example requires EvalException from Paste.
"""

import sys

import cherrypy
from cherrypy._cpwsgi import wsgiApp, CPHTTPRequest
from cherrypy._cpwsgiserver import CherryPyWSGIServer

from paste.evalexception.middleware import EvalException

# we need a WSGI server class that accepts a WSGI application
# as a parameter to its constructor - here is an example

class SimpleWSGIServer(CherryPyWSGIServer):
    """A WSGI server that accepts a WSGI application as a parameter."""
    RequestHandlerClass = CPHTTPRequest
    
    def __init__(self, wsgi_app):
        conf = cherrypy.config.get
        bind_addr = (conf("server.socket_host"), conf("server.socket_port"))
        CherryPyWSGIServer.__init__(self, bind_addr, wsgi_app,
                                    conf("server.thread_pool"),
                                    conf("server.socket_host"),
                                    request_queue_size = conf("server.socket_queue_size"),
                                    )


# here is a sample CherryPy root class
# we are using exception catching middleware in this example,
# so the "problem" page handler purposely generates an error
# to demonstrate the middleware

class Root(object):
    @cherrypy.expose
    def index(self):
        yield "Get in <a href='/problem'>trouble</a><br>"
        yield cherrypy.request.browser_url + '<br>'
        yield cherrypy.request.path + '<br>'
        yield cherrypy.request.object_path + '<br>'

    @cherrypy.expose
    def problem(self):
        "error on purpose to show off EvalException"
        assert 0, "Houston, we have a problem."

# we need this so that errors trickle down to the middleware
cherrypy.config.update({'server.throw_errors':True})

# mount our CherryPy
cherrypy.root = Root()

# wrap the CP wsgiApp in the middleware
app = EvalException(wsgiApp, global_conf={})

# init the custom server with the middleware
mw_server = SimpleWSGIServer(app)

# start CherryPy with the custom server
cherrypy.server.start(server=mw_server)