A comparison of a stupid/simple filter and its implementation as middleware.

wsgi2-filter-vs-middleware.py

# You have a simple application:

def hello(environ):
    status = b'200 OK'
    headers = [(b'Content-Type', b'text/plain')]
    body = b"Hello " + environ['wsgiorg.routing_args'][1]['name'] + b'!'
    
    headers.append((b'Content-Length', len(body).encode('ascii')))
    
    return status, headers, [result]


# Example (really crappy) filter to process GET arguments:

def get_filter(environ):
    environ['wsgiorg.routing_args'] = [[], dict()]
    args = environ['wsgiorg.routing_args'][1]
    
    for chunk in environ['QUERY_STRING'].split(b'&'):
        name, _, value = chunk.partition(b'=')
        # need to process value a bit
        args[name] = value

# Example usage

HTTPServer(None, 8080, app=hello, ingress=[get_filter]).serve()


# The same as middleware:

def get_middleware(app):
    def inner(environ):
        environ['wsgiorg.routing_args'] = [[], dict()]
        args = environ['wsgiorg.routing_args'][1]
        
        for chunk in environ['QUERY_STRING'].split(b'&'):
            name, _, value = chunk.partition(b'=')
            # need to process value a bit
            args[name] = value
        
        return app(environ)

# Example usage.

HTTPServer(None, 8080, app=get_middleware(hello)).serve()


# The problem with middleware:

HTTPServer(None, 8080, app=\
    get_middleware(
        post_middleware(
            cookie_middleware(
                session_middleware(
                    db_middleware(
                        hello
                    )
                )
            )
        )
    )
).serve()

# The only callable that -should- be middleware in that stack is db_middleware, as it needs to
# trap exceptions within the application!  Middleware stacks are often even deeper than this!