Rooms in FastAPI

A room is a name pages join to get its events. Your server declares your rooms once, by pattern, with what they keep and allow, and answers for each user who asks to join.

Declaring rooms

# app.py
# The updates of an order: its customer and the staff, the last 20 kept.
def may_follow_order(user, p):
    if user is None:
        return False
    order = find_order(p["id"])
    return order is not None and (order.customer_id == user or is_staff(user))

realtime.room("order:{id}", may_follow_order, history=20)

# A chat between two people, chat:34:42: those two only. They send messages and typing to it, and the messages are kept.
realtime.room("chat:{a}:{b}", lambda user, p: str(user) in (p["a"], p["b"]), history=50, emit=["message", "typing"])

# The page of a product: anyone, signed in or not, with a live count of who is looking.
realtime.room("product:{id}", public=True, count=True)

• user is what your current_user(request) gave: the request user id, or None.
• The parts of the pattern come as strings: {"a": "34", "b": "42"}. A rule may take only user, or user, params, room.
• The answer: False (or None) for no, True for yes, or {"info": …} for yes with what the others see of them in a presence room.
• For one user, the answer may narrow the room: {"emit": ["typing"]} lets them send only that, {"readOnly": True} nothing.

Names and patterns

• Room names: up to 200 characters of A-Z a-z 0-9 _ - = @ , . ; :.
• {name} matches one or more characters other than : and ..
• The most specific rule wins: the pattern with the most fixed characters, and on a tie the one declared first. A room no pattern matches is refused (no_rule).
• When the rule runs: when a page joins, and when its token is renewed (every 6 hours by default). A page asks for every room it joins in the same moment in one request, and keeps the tokens across reconnects and moves.

What a room keeps and allows

Option	Default
history	none	Events kept for pages that reconnect: a number (50), up to 1,000, for 30 minutes. Or {"last": 50, "days": 0.01} for less (0.01 of a day is about 15 minutes)
emit	none	Events pages may send to the room: names, or "*" for any (events from the page)
presence	off	Its members are listed, with their info, and join and leave tell the others (presence)
count	off	A live count of who is in it, at any size, without a list
webhook	none	Which of the page events your server gets too (sending from your server)
public	off	Anyone may join, signed in or not. Its grant names no user, so it may sit in a page a CDN caches
seal	on	Its events, its member info and its history are sealed with the room key (encryption)

The options travel in the room token, signed by your server, so WordPlus Cloud enforces them and nothing is set in two places.

Joining

const order = rt.join( 'order:1042' );
order.on( 'updated', ( data, meta ) => showStatus( data.status ) );   // meta: { from, id, at }
order.on( 'joined', () => showLive() );
order.on( 'error', ( e ) => console.warn( e.code ) );   // forbidden, no_rule, full …

rt.leave( 'order:1042' );

• join() gives the same room for the same name. The tabs of a user ride one connection (the worker), each with its own rooms.
• Events reach a listener opened: you never handle sealed values.
• meta.from is the user who sent it from a page, or nothing for your server. meta.id and meta.at are the kept event id and time.
• Reserved names: joined, join, leave, count and error are kept for the room itself. Your server and pages cannot send them.

History, and nothing lost

A room keeps its events for 30 minutes at most, for recovery. Your app keeps its own records, such as the messages of a chat, from the webhook.

A room that keeps history gives a page that comes back what it missed: a reconnect within the history span gets the missed events first, in order, with meta.replayed, then the new ones.

const { events, more } = await order.history( { limit: 50 } );          // the newest 50, oldest first
const older = await order.history( { before: events[ 0 ].id, limit: 50 } );

Events over 64 KB are sent but not kept. volatile ones are never kept. Your server reads and erases history too: realtime.in_room("order:1042").history() and .forget() (sending from your server).

More, with Node and PHP side by side: rooms in depth.