Add on_open option in WebSocketWSGI

[fukuchidaisuke]

This pull request adds flexibility on accepting websocket connections as follows.

import base64
import eventlet
from eventlet import wsgi, websocket
import six
import time


def handle(ws):
    while True:
        message = ws.wait()
        if message is None:
            break
        print("received {0}".format(message))
        ws.send(message)


def on_open(environ):
    if "HTTP_COOKIE" in environ:
        cookie = six.moves.http_cookies.SimpleCookie()
        cookie.load(environ["HTTP_COOKIE"])
        if ("SID" in cookie) and cookie["SID"].value == "validSession":
            return []

    print("not authenticated")

    if "QUERY_STRING" not in environ:
        raise websocket.BadRequest(status="403 Forbidden")

    queries = six.moves.urllib.parse.parse_qs(environ["QUERY_STRING"])
    if "authorization_basic" not in queries:
        raise websocket.BadRequest(status="403 Forbidden")

    if queries["authorization_basic"][0] != base64.b64encode("username:password".encode()).decode():
        raise websocket.BadRequest(status="403 Forbidden")

    expires = time.strftime("%a, %d-%b-%Y %T GMT", time.gmtime(time.time() + 3600))
    return [("Set-Cookie", "SID=validSession; Path=/; Expires={0}".format(expires))]


if __name__ == "__main__":
    wsgi.server(eventlet.listen(("", 8080)), websocket.WebSocketWSGI(handle, on_open=on_open))