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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 eventlet.wsgi.server with
it:
from eventlet import wsgi
import eventlet
def hello_world(env, start_response):
start_response('200 OK', [('Content-Type', 'text/plain')])
return ['Hello, World!\r\n']
wsgi.server(eventlet.listen(('', 8090)), hello_world)You can find a slightly more elaborate version of this code in the
file examples/wsgi.py.
eventlet.wsgi
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 ~eventlet.wsgi.server
method:
wsgi.server(eventlet.wrap_ssl(eventlet.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
Eventlet's WSGI server supports a non-standard extension to the WSGI
specification where env['eventlet.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 eventlet import wsgi
import eventlet
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['eventlet.posthooks'].append(
(hook, ('arg1', 'arg2'), {'kwarg3': 3, 'kwarg4': 4}))
start_response('200 OK', [('Content-Type', 'text/plain')])
return ['Hello, World!\r\n']
wsgi.server(eventlet.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.
"100 Continue" Response Headers
Eventlet's WSGI server supports sending (optional) headers with HTTP "100 Continue" provisional responses. This is useful in such cases where a WSGI server expects to complete a PUT request as a single HTTP request/response pair, and also wants to communicate back to client as part of the same HTTP transaction. An example is where the HTTP server wants to pass hints back to the client about characteristics of data payload it can accept. As an example, an HTTP server may pass a hint in a header the accompanying "100 Continue" response to the client indicating it can or cannot accept encrypted data payloads, and thus client can make the encrypted vs unencrypted decision before starting to send the data).
This works well for WSGI servers as the WSGI specification mandates HTTP expect/continue mechanism (PEP333).
To define the "100 Continue" response headers, one may call set_hundred_continue_response_header on env['wsgi.input'] as shown
in the following example:
from eventlet import wsgi
import eventlet
def wsgi_app(env, start_response):
# Define "100 Continue" response headers
env['wsgi.input'].set_hundred_continue_response_headers(
[('Hundred-Continue-Header-1', 'H1'),
('Hundred-Continue-Header-k', 'Hk')])
# The following read() causes "100 Continue" response to
# the client. Headers 'Hundred-Continue-Header-1' and
# 'Hundred-Continue-Header-K' are sent with the response
# following the "HTTP/1.1 100 Continue\r\n" status line
text = env['wsgi.input'].read()
start_response('200 OK', [('Content-Length', str(len(text)))])
return [text]You can find a more elaborate example in the file:
tests/wsgi_test.py, test_024a_expect_100_continue_with_headers.