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import logging
import os
import sys
from base64 import urlsafe_b64encode
from pprint import pformat
import tornado.escape
import tornado.ioloop
import tornado.options
import tornado.web
import tornado.websocket
from bson import json_util # Installed with PyMongo.
from tornado.options import define, options
from motor.motor_tornado import MotorClient
define("port", default=8888, help="run on the given port", type=int)
define("debug", default=False, help="reload on source changes")
define("mongo", default="mongodb://localhost", help="MongoDB URI")
define("ns", default="test.test", help="database and collection name")
class Application(tornado.web.Application):
def __init__(self):
handlers = [(r"/", MainHandler), (r"/socket", ChangesHandler)]
templates = os.path.join(os.path.dirname(__file__), "tornado_change_stream_templates")
super().__init__(
handlers, template_path=templates, template_whitespace="all", debug=options.debug
)
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.render("index.html", changes=ChangesHandler.cache)
class ChangesHandler(tornado.websocket.WebSocketHandler):
waiters = set()
cache = []
cache_size = 5
def open(self):
ChangesHandler.waiters.add(self)
def on_close(self):
ChangesHandler.waiters.remove(self)
@classmethod
def update_cache(cls, change):
cls.cache.append(change)
if len(cls.cache) > cls.cache_size:
cls.cache = cls.cache[-cls.cache_size :]
@classmethod
def send_change(cls, change):
change_json = json_util.dumps(change)
for waiter in cls.waiters:
try:
waiter.write_message(change_json)
except Exception as exc:
logging.exception(exc)
@classmethod
def on_change(cls, change):
logging.info("got change of type '%s'", change.get("operationType"))
# Each change notification has a binary _id. Use it to make an HTML
# element id, then remove it.
data = change["_id"]["_data"]
if not isinstance(data, bytes):
data = data.encode("utf-8")
html_id = urlsafe_b64encode(data).decode().rstrip("=")
change.pop("_id")
change_pre = tornado.escape.xhtml_escape(pformat(change))
change["html"] = f'<div id="change-{html_id}"><pre>{change_pre}</pre></div>'
change["html_id"] = html_id
ChangesHandler.send_change(change)
ChangesHandler.update_cache(change)
change_stream = None
async def watch(collection):
global change_stream
async with collection.watch() as change_stream:
async for change in change_stream:
ChangesHandler.on_change(change)
def main():
tornado.options.parse_command_line()
if "." not in options.ns:
sys.stderr.write(f'Invalid ns "{options.ns}", must contain a "."')
sys.exit(1)
db_name, collection_name = options.ns.split(".", 1)
client = MotorClient(options.mongo)
collection = client[db_name][collection_name]
app = Application()
app.listen(options.port)
loop = tornado.ioloop.IOLoop.current()
# Start watching collection for changes.
try:
loop.run_sync(lambda: watch(collection))
except KeyboardInterrupt:
if change_stream:
loop.run_sync(change_stream.close)
if __name__ == "__main__":
main()
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