pg-sse

Live updates from the Postgres you already run. No Redis, no broker, no WebSocket service: a table trigger sends NOTIFY, one listener per process wakes the open streams, and each stream re-reads from its cursor and sends server-sent events. Works with Starlette and FastAPI out of the box, and with any other framework through hub.stream.

pip install "pg-sse[starlette]"   # or "pg-sse[fastapi]"; plain "pg-sse" is enough for hub.stream
pip install "psycopg[binary]"     # on a machine without libpq; see the psycopg install docs for the alternatives

The one rule

A notification carries only a key (a room id, a conversation id) and means "something changed here, re-read from your cursor". It never carries the data. So a lost notification costs a delay, never an event, and there's no 8000-byte payload limit to hit.

Why not X

• Polling. Every client hits the database on a timer, so load grows with clients times frequency, and latency is half the interval. Here an idle stream costs one read a minute, and a write reaches clients within milliseconds.
• WebSockets. You usually end up running a second service and writing your own reconnect and catch-up logic. EventSource reconnects by itself and sends Last-Event-ID, and one-way updates are all most pages need.
• Redis pub/sub. It is another system to run, secure and keep consistent with your database, and a message missed during a disconnect is gone. Here the database is the source of truth and a missed wake-up costs a delay.
• Supabase Realtime. It ties you to one vendor's platform and its protocol. This runs against any Postgres 14+ you can open a direct connection to.

Use it

1. Once, in a migration: wire the table to a channel.

from pg_sse import trigger_sql

conn.execute(trigger_sql("messages", key_column="room", channel="room_change", order_column="id"))

That creates two triggers:

Trigger	Why
pg_notify('room_change', room) after every insert, update and delete (or only the writes you pick with on)	No writer can forget it: not a cron job, not a psql session. Delivered on commit; a rollback announces nothing.
With order_column (a serial, bigserial or identity column): ids follow commit order within a key	Without it, a reader at cursor 11 can skip id 10 committing late. An insert locks its key until it commits, then draws the next id (see Limits for the cost).

2. The app:

from typing import Annotated
from fastapi import FastAPI, Header
from fastapi.responses import StreamingResponse
from pg_sse import Event, Hub, IntCursor, event_stream_responses

hub = Hub(DIRECT_DATABASE_URL, channel="room_change")  # a direct connection, not a pooled one
app = FastAPI(lifespan=hub.lifespan)
cursors = IntCursor()  # a Last-Event-ID is client input: only digits get through


def read_after(room: str, after: int) -> list[Event]:
    rows = db.fetch("SELECT id, body FROM messages WHERE room = %s AND id > %s ORDER BY id LIMIT 500", (room, after))
    return [Event({"id": id, "body": body}, id=id) for id, body in rows]


def latest_id(room: str) -> int:
    return db.fetchval("SELECT coalesce(max(id), 0) FROM messages WHERE room = %s", (room,))


@app.get("/rooms/{room}/stream", responses=event_stream_responses(), response_class=StreamingResponse)
async def stream(room: str, last_event_id: Annotated[str | None, Header()] = None):
    cursor = cursors.parse_one(last_event_id)  # None for no header or one that is not a cursor: start from now
    return hub.sse(room, read=lambda after: read_after(room, after), cursor=cursor, start=lambda: latest_id(room))

FastAPI cannot see what hub.sse returns, so without the responses= and response_class= in the decorator the route is missing from the OpenAPI document as an event stream. event_stream_responses() declares text/event-stream and the Cache-Control and X-Accel-Buffering headers. Without response_class, FastAPI lists application/json for the route too. It returns a new dict, so you can add responses to it ({**event_stream_responses(), 404: {...}}), and takes the status_code of a route that does not return 200.

3. The browser:

const source = new EventSource("/rooms/lobby/stream");
source.onmessage = (e) => render(JSON.parse(e.data));

EventSource reconnects by itself and sends Last-Event-ID; the stream catches up from there. The header is client input, so IntCursor lets only digits through, and the route starts anything else from now, as if there were no header. Not a 422: EventSource stops for good on any response that is not a 200, so one stale or malformed id (an old cursor format after a deploy) would end live updates in that tab. Do not hand-roll the check with str.isdigit(): it is true for ², which int() then rejects, so a client could turn the route into a 500.

When EventSource is not enough (to send an Authorization header, to see why a request was refused, or to retry a 503 after its Retry-After instead of stopping for good), use pg-sse-client: npm install pg-sse-client. The pg-sse package on npm is unrelated.

A full runnable app, with async reads on a connection pool and a browser page: examples/chat.py.

Notify only for the writes a reader can see. By default every insert, update and delete notifies. A cursor-based read only finds new rows, so on a table with edits, read receipts or soft deletes, each update would wake every reader of that key for a read that returns nothing. Say which writes matter:

trigger_sql("messages", key_column="room", channel="room_change", order_column="id", on=("insert",))
# Inserts, deletes, and edits of body (the key column is watched too):
trigger_sql("messages", key_column="room", channel="room_change", update_of=("body",))

on takes any of "insert", "update" and "delete". update_of narrows updates to those whose SET list names one of the columns; the key column is always added, so a row that moves to another key still notifies. Run the SQL again with different options to change an installed trigger.

SQLAlchemy and Alembic

trigger_sql returns plain SQL, so it goes through whatever runs your migrations. With Alembic, install the trigger after the table exists in upgrade, and remove it before the table goes in downgrade (dropping a table drops its triggers but leaves the functions behind):

# alembic/versions/0001_messages.py
import sqlalchemy as sa
from alembic import op
from pg_sse import drop_trigger_sql, trigger_sql


def upgrade() -> None:
    op.create_table(
        "messages",
        sa.Column("id", sa.BigInteger, primary_key=True, autoincrement=True),
        sa.Column("room_id", sa.Integer, nullable=False),
        sa.Column("body", sa.Text, nullable=False),
    )
    op.execute(trigger_sql("messages", key_column="room_id", channel="room_change", order_column="id", on=("insert",)))


def downgrade() -> None:
    op.execute(drop_trigger_sql("messages", key_column="room_id", order_column="id"))
    op.drop_table("messages")

The SQL is several statements in one string. psycopg runs that; asyncpg refuses it ("cannot insert multiple commands into a prepared statement"). If your app uses asyncpg, point Alembic at postgresql+psycopg:// (psycopg 3 is already a dependency; the async migration template works with it too). Your app's own engine can stay on asyncpg.

read and start on an AsyncSession, wired the same way as the chat example. The room id is an integer here, and a key is always text, so the route passes str(room_id):

from functools import partial
from typing import Annotated

from fastapi import FastAPI, Header
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine

from pg_sse import Event, Hub, IntCursor

engine = create_async_engine("postgresql+asyncpg://...")  # the app's own connection, pooled however you like
Session = async_sessionmaker(engine, expire_on_commit=False)
hub = Hub(DIRECT_DATABASE_URL, channel="room_change")  # psycopg; a direct connection, not a pooled one
app = FastAPI(lifespan=hub.lifespan)
cursors = IntCursor()


async def read_after(room_id: int, after: int) -> list[Event]:
    async with Session() as session:
        query = select(Message).where(Message.room_id == room_id, Message.id > after).order_by(Message.id).limit(500)
        return [Event({"id": m.id, "body": m.body}, id=m.id) for m in await session.scalars(query)]


async def latest_id(room_id: int) -> int:
    async with Session() as session:
        return (
            await session.scalar(select(func.coalesce(func.max(Message.id), 0)).where(Message.room_id == room_id)) or 0
        )


@app.get("/rooms/{room_id}/stream")
async def stream(room_id: int, last_event_id: Annotated[str | None, Header()] = None):
    return hub.sse(
        str(room_id),  # not room_id: an int subscribes fine, never wakes, and pg_sse raises a TypeError for it
        read=partial(read_after, room_id),
        cursor=cursors.parse_one(last_event_id),
        start=partial(latest_id, room_id),
    )

Both blocks were run against a real database (an Alembic upgrade and downgrade, and a live stream on the psycopg and asyncpg drivers) but are not part of the test suite, so treat them as illustrative.

Other frameworks

hub.sse is a thin wrapper over hub.stream, which yields encoded SSE frames (str) and knows nothing about Starlette. It raises TooManySubscribers at the call, before any response exists, so turn that into your framework's 503. The Django and Litestar snippets below are illustrative, not tested in CI.

# Django (ASGI; run the hub's lifespan from your ASGI app or a lifespan wrapper)
from django.http import HttpResponse, StreamingHttpResponse
from pg_sse import TooManySubscribers


async def stream(request, room):
    try:
        frames = hub.stream(room, read=lambda after: read_after(room, after), start=lambda: latest_id(room))
    except TooManySubscribers:
        return HttpResponse(status=503, headers={"Retry-After": "30"})
    return StreamingHttpResponse(frames, content_type="text/event-stream", headers={"Cache-Control": "no-cache"})

# Litestar
from litestar import get
from litestar.response import Stream


@get("/rooms/{room:str}/stream")
async def stream(room: str) -> Stream:
    frames = hub.stream(room, read=lambda after: read_after(room, after), start=lambda: latest_id(room))
    return Stream(
        frames, media_type="text/event-stream", headers={"Cache-Control": "no-cache", "X-Accel-Buffering": "no"}
    )

Aiohttp and Quart work the same way: write each frame to the response as it arrives.

Signal streams

A stream doesn't have to carry data. It can tell the page what to refetch: "this list changed", "only the typing indicator changed", "you may have missed something, refetch everything". For that, give read a second parameter named wake (or a required second parameter). It receives a Wake that says why the read is running; several causes can arrive together, since a burst is one read.

Field	Meaning
start	The stream's first read.
keys	Keys with a database notification since the last read.
signals	Labels from hub.wake(key, signal=...) since the last read.
signal_keys	For each of those labels, the keys it was sent for: a per-key stream sees its own key, an all-keys stream sees which keys signalled. Not part of equality, so Wake(signals=...) in a test still equals what the hub passes.
resync	The listener connected or reconnected: anything may have changed.
reread	Nothing woke the stream for reread_seconds.

wake.data_may_have_changed is True unless the only causes are hub.wake signals.

When several causes arrive together, answer them in this order: start, then resync or reread, then keys, then signals. The first two already tell the page to refetch everything, so anything after them would repeat it. read may be async def: it then runs on the event loop with no thread hop, which suits a read that only looks at wake.

from pg_sse import Event, Wake


async def signals(cursor, wake: Wake) -> list[Event]:
    if wake.start:
        return [Event({}, event="ready")]  # the page loads everything once
    if wake.resync or wake.reread:
        return [Event({}, event="resync")]  # anything may have changed
    events = []  # a write and a signal can arrive together: answer both
    if wake.keys:
        events.append(Event({"keys": sorted(wake.keys)}, event="change"))
    if "typing" in wake.signals:
        events.append(Event({}, event="typing"))  # refetch only the typing indicator
    return events


@app.get("/inbox/stream")
async def inbox(user: User = Depends(current_user)):
    return hub.sse(None, read=signals, owner=str(user.id))  # every key on the channel; an int would also do


typing = hub.ephemeral("typing", ttl=8)  # at import time, next to the hub
# elsewhere, from any thread, on every keystroke:
typing.set(room_id, user_id)

signal_read builds that function for you, with the same order of causes:

from pg_sse import signal_read

read = signal_read(change="messages", signals={"typing": "typing"})
hub.sse(room, read=read)
# sends: "ready" first; "resync" after a reconnect or a quiet re-read; "messages" for a write; "typing" for that signal

A runnable version, with a typing indicator that lapses on its own and an inbox that watches every room: examples/inbox.py.

A one-parameter read(cursor) works too, and so does one whose second parameter has a default under another name (read(after, limit=500)): only a parameter named wake, or a required one, receives the Wake. hub.wake(key) reaches the streams for key and the all-keys streams (key=None); all_keys=False keeps it on its key, which is right for ephemeral per-key state (typing, presence, a cursor position) that an all-keys view has nothing to show for. Database notifications always reach the all-keys streams: they report real writes.

Frames you will see

What hub.stream yields, and what EventSource does with each:

Frame	Looks like	Meaning
Id only	id: 42	The first frame when you pass a cursor, so the browser records it as its Last-Event-ID. Dispatches nothing.
Ping	: ping	A comment, sent when nothing else was. Dispatches nothing.
Event	id: 43, event: change, data: {...}	Your Event. The id becomes the browser's Last-Event-ID.
Goodbye	retry: 1000, or with end_event, retry: 1000, event: end, data: {"reason":"max_age"}	The last frame before a planned close. No id, so Last-Event-ID stays at the last event.

Ephemeral state

Typing and presence are true only while a client keeps saying so. hub.ephemeral keeps them for you: a signal per key and person that lapses unless renewed, and wakes the key's streams when it starts, is removed or lapses, so a closed tab never leaves a stale "typing" on another screen.

typing = hub.ephemeral("typing", ttl=8)

typing.set(room_id, user_id)  # a keystroke: wakes the room's streams the first time, then only renews
typing.set(room_id, user_id, on=False)  # they sent the message: removed, wakes
typing.live(room_id)  # ["ann", "bo"]: who has not lapsed, for the GET the page refetches

What hub.sse does for you

• Subscribes before the catch-up read, so a write between the two is a queued wake-up, not a gap.
• Calls start() after subscribing when there's no cursor, and sends that cursor as the first frame's id, so a reconnect resumes from it even if no event arrived.
• Re-reads on every wake-up, and a burst of notifications costs one read.
• Pings every 15–25 s (ping_seconds) with an SSE comment, so proxies do not time an idle stream out. A ping costs no database read.
• Re-reads after 60 s of quiet (reread_seconds) even when nothing woke it. This is the safety net under every lost notification: the worst case is a one-minute delay.
• Wakes every stream after the listener connects or reconnects, since anything committed before its LISTEN existed (at startup, or while it was down) was missed. Each stream re-reads after its own random delay of up to resync_spread (2 s), so the reads do not arrive together. Reconnects with backoff; a SELECT 1 every minute and TCP keepalives catch a half-open connection.
• Bounded queue per stream (64). Identical wake-ups are queued once, so a hot key costs one slot, not one per write. A stream ends, rather than buffers, when more than queue_size distinct keys or signals arrive during one read (only an all-keys stream on a wide channel gets there). It still sends what that read found, so its cursor moves on, then says behind; the browser reconnects and catches up.
• Caps open streams per process (500) and, when you pass owner (a user id, session, or client address, as text), per key and owner (5). Past a cap, hub.sse raises a 503 with Retry-After: 30. The per-owner cap counts one key at a time: an owner may hold 5 streams on every key it can name, up to the process cap. To bound one client's total, set max_total_per_owner (off by default). Without owner, a client is not counted at all and can hold every slot in a worker, so pass owner on public endpoints, and size the caps on the total rather than on the per-key number.
• Ends streams after 15 minutes. A stream is authenticated once, when it opens; this bounds how long a revoked session keeps one. To end it sooner, call hub.close(owner=...) when you revoke, or pass revalidate= to hub.sse and the stream asks about every revalidate_seconds (15) whether it may go on.
• Ends every stream on SIGTERM, so a deploy doesn't wait out uvicorn's graceful-shutdown timeout. It chains onto the server's handler; with no handler installed (a plain script) the default action is left alone and ends the process as usual.
• Says goodbye before a planned close. The last frame carries retry:, which EventSource applies by itself, and, with end_event set, a named event with the reason:

Reason	When	retry (ms)	What the client should do
max_age	The stream reached max_stream_seconds.	1000	Reconnect now, with its cursor.
shutdown	SIGTERM, or the lifespan ending.	1000–5000, random	Reconnect after the delay. The jitter spreads a deploy's reconnects out.
behind	The stream's queue filled.	1000	Reconnect and catch up from its cursor.
recheck	Its revalidate failed revalidate_failures times in a row.	1000–5000, random	Reconnect after the delay; the route's own auth check decides.
revoked	hub.close ended it (an owner or key was revoked), or its revalidate said no.	1000	Reconnect; the route's own auth check decides whether it is let in.

There is no goodbye after Event(final=True), since the application already said what it meant, or when read or start raised, since the stream's state is unknown and an abrupt close is the honest signal.

// EventSource: nothing to write. `retry` is applied automatically; the reason is there if you want it.
source.addEventListener("end", (e) => console.debug("stream ended:", JSON.parse(e.data).reason));

// A fetch-based reader decides for itself.
if (event.event === "end") {
  const { reason } = JSON.parse(event.data);
  scheduleReconnect(event.retry ?? 1_000);
}

pg-sse-client does this for you: it reconnects after the retry: and passes the reason to onEnd.

API

Everything is importable from pg_sse. Each name below has a short description; the docstrings carry the rest.

Hub

Hub(conninfo, channel, *, max_subscribers=500, max_per_owner=5, max_total_per_owner=None, queue_size=64,
    max_stream_seconds=900, ping_seconds=(15, 25), reread_seconds=60, json_default=None, end_event=None,
    handle_signals=True, listen_timeout=5.0, resync_spread=2.0, application_name="pg-sse-listener",
    read_executor=None, on_error=None, log_owner=False, revalidate_seconds=15, revalidate_failures=3,
    revalidate_timeout=10, listen_poll_seconds=1.0)

One per channel per process.

• conninfo: a DSN, or a function returning one. A function is called on every connect, so a rotating password or settings that are only readable at startup need no rebuilt hub.
• max_subscribers: open streams per process.
• max_per_owner: open streams per key and owner, so several tabs on one room are one client. It does not limit how many keys an owner opens streams on.
• max_total_per_owner: open streams per owner across all keys; None (the default) sets no total. This is the cap that keeps one client from filling max_subscribers.
• Both owner caps apply only to streams opened with an owner; anonymous streams are limited by max_subscribers alone. A refused stream is a TooManySubscribers, a 503 from hub.sse.
• queue_size: wake-ups queued per stream before it is ended as too far behind. At least 1. A resync takes no slot.
• max_stream_seconds: how long a stream lives before a planned close. math.inf turns the limit off.
• The durations here and in Ephemeral take any real number (int, float, Decimal, a numpy scalar) and are kept as float; a bool, a string or NaN raises ValueError.
• ping_seconds: the (low, high) range, jittered, between pings on an idle stream.
• reread_seconds: how long a stream may sit quiet before it re-reads anyway.
• json_default: json.dumps's default for Event data that is not JSON-native. json_default=str is the common choice for datetimes, UUIDs and Decimals.
• end_event: names the event sent with the reason before a planned close. Checked when it is given: an empty name, or one with a line break or NUL, raises ValueError (here and in stream/sse). Off by default; the retry: alone is always sent.
• handle_signals: chain onto SIGTERM and SIGINT so streams end at once on a deploy. Pass False in tests.
• listen_timeout: seconds lifespan waits for the first LISTEN before the app starts (None: do not wait). A finite number, 0 or more. It never fails startup.
• listen_poll_seconds: how long a quiet listener waits before it checks its stop flag and runs its keepalive query. Leaving lifespan wakes it at once, so this is only the fallback; a test can shorten it. A finite number above 0.
• resync_spread: after the listener connects or reconnects, every stream re-reads. Each waits a random 0 to this many seconds first, so a database that has just come back is not hit by every open stream at once (up to max_subscribers reads queued behind your thread pool or connection pool). A notification for the stream's key during the wait starts the resync early (an all-keys stream keeps its time: every notification reaches it, so on a busy channel the first one would end all their waits at once). Any read in the meantime that re-reads everything counts as the resync: every read of a read(cursor), and a quiet re-read. A read(cursor, wake) woken by a hub.wake signal alone reads at once and still gets its resync at its time. A resync takes no queue slot, so it never ends a busy stream as behind. 0 reads at once. Pings and the periodic re-read are already jittered; this closes the one synchronised burst.
• read_executor: a thread pool (concurrent.futures.ThreadPoolExecutor; a ProcessPoolExecutor or InterpreterPoolExecutor raises ValueError, since a read runs with the caller's context variables) for plain (not async) read and start functions. By default they share asyncio's thread pool (at most 32 threads, also used by everything else that calls asyncio.to_thread), so a burst of stream re-reads can starve other work. Give the streams their own bounded pool: ThreadPoolExecutor(8, thread_name_prefix="sse-read"). Async reads do not use it, and the hub never shuts it down.
• on_error: on_error(key, exc), or on_error(key, exc, info) (a third positional parameter named info, or with no default) to also get the stream's StreamInfo: its owner and age_seconds, to tell whose stream failed. A function that takes neither raises TypeError when the hub is made. The signature is what inspect.signature reports, which follows functools.wraps, so a decorated three-argument handler gets three. Called when a stream fails, after the failure is logged: read or start raised, or revalidate failed revalidate_failures times in a row, or read returned something the hub could not send (not an Event, data json.dumps refuses, a tuple id). Use it to report to an error tracker. A plain function runs in asyncio's default pool (not read_executor, where in an outage it would wait behind the failing reads), and an async def one on the loop, each as its own task, so a slow tracker never holds the failed response open, its slot taken, or the loop; leaving lifespan waits up to 5 seconds for those still running, then cancels them. An exception either raises is logged and ignored. A failed read or start ends the stream without a goodbye. A revalidate that failed revalidate_failures times in a row ends it with the goodbye recheck.
• log_owner: whether the log line for a failed stream names its owner (default False: an owner may be a session token or an address; True or False only, TypeError otherwise). on_error receives it in info either way.
• revalidate_seconds: about how long a stream waits between two runs of its revalidate (see hub.stream; jittered by a quarter either way, like the pings), and so, with the time the check takes, how long a revoked session can keep a stream that hub.close did not end. Greater than 0 and finite.
• revalidate_timeout: how long one run may take before it counts as a failure (default 10 seconds). Greater than 0 and finite.
• revalidate_failures: how many runs of a stream's revalidate in a row must fail (raise, or run over revalidate_timeout) to end the stream with recheck (default 3; 1 ends it at the first failure; None never ends it, so a failing check only warns and is counted in revalidate_errors_total). Fail-closed is the default because a check that raises exactly when a session is gone (a lookup that finds nothing) would otherwise leave a revoked session its stream, with a warning as the only sign. The cost: an outage of the session store ends every stream after about three intervals, and the route that has to let each client back in probably needs the same store and fails. A bare EventSource does not retry a non-200 and stops until the page reloads; a client that retries on its own comes back once the store does. If you cannot have that, pass None and let max_stream_seconds bound the rest. The runs before the last warn at most once a minute for the hub.
• application_name: what pg_stat_activity shows for the listener's connection, to tell several services' listeners apart.

hub.lifespan

FastAPI(lifespan=hub.lifespan), or async with hub.lifespan(): inside your own lifespan. Chains onto an existing SIGTERM/SIGINT handler (a default action is left alone) and restores it when it exits. Starts without a database: the listener keeps retrying and listener_connected says whether it is live. On exit every stream says goodbye with reason shutdown, including one created but not read yet, even if it is first read after the hub has started again. After it, hub.stream and hub.sse refuse new streams as during shutdown (a 503 from hub.sse).

hub.stream

hub.stream(key, read, *, cursor=None, start=None, owner=None, end_event=None, max_stream_seconds=None,
           revalidate=None) -> AsyncIterator[str]

The primary API: an async iterator of encoded SSE frames, for any framework. Raises TooManySubscribers when it is called, before any response exists: the stream takes its slot then, not when its first frame is read, and gives it back when it ends, or, for a response that was never sent (the route raised after making it, or the client left before the body started), when it is garbage-collected (at once on CPython) and 30 seconds after it was made at the latest. A server reads a stream the moment it sends the response, so one read after that ends at once, with no goodbye.

• key: what the stream watches, or None for every key on the channel. It must be a str, the text form of the key column (str(room_id) for an integer column): the notification payload is key::text, a NULL key notifies "", and any other type raises a TypeError.
• read: takes (cursor) or (cursor, wake) and returns a list of Event, not a generator, which would run its queries on the event loop. A plain function runs in a thread; an async one runs on the loop. Its type is pg_sse.Read.
• cursor: where to start, already parsed from the client (Last-Event-ID, a query parameter). IntCursor parses and checks an integer one. Text with a line break or NUL cannot be an SSE id: the stream then starts from now, with a warning at most once a minute, rather than answering the client with a 500. A cursor of the wrong type (a row, bytes, a bool) raises TypeError.
• start: gives the current cursor when cursor is None, so the stream starts from now. Plain or async. Its type is pg_sse.Start.
• owner: a user id or session, for the per-owner caps and hub.close(owner=...). A str, or an int, which is turned into text, so hub.close(owner=7) and hub.close(owner="7") find the same streams. Any other type (a UUID, a bool) raises TypeError: pass str(owner).
• end_event: overrides the hub's.
• max_stream_seconds: overrides the hub's age limit for this stream, so a visitor's stream can expire sooner than a dashboard session's. Must be greater than 0; math.inf for no limit.
• revalidate: await revalidate() says whether the stream may go on, so a removed member or a signed-out session loses its stream without a hub.close at every place that revokes. A falsy answer, None too, ends it with the goodbye revoked, as hub.close does: return False for a session that is gone, and raise only when the check itself could not be made. An auth helper that raises to deny (an HTTPException(403)) is a failure, not a no: catch it and return False. (An async def that forgot its return ends every stream with revoked about every 15 seconds, which shows at once.) It must be async, an async def or a functools.partial of one (use partial(is_member, user_id) where you would write a lambda), not a plain function or a lambda: it runs on the event loop for every open stream, where a blocking call would stall them all and nothing could interrupt it. It is checked when the stream is made, with whether it takes arguments: TypeError otherwise. It runs about every revalidate_seconds (15 by default, jittered), on a clock of its own: the first time about that long after the stream is first read, since the route has just checked, and not tied to pings or reads, so a stream in a long read, or stuck in start, is ended too. It runs in a task of its own, with the context variables of the task that reads the stream, so make it a cached lookup, and close over the session or user id: it is not given the request. If it raises or runs over revalidate_timeout (10 seconds), that is a failure: it warns, at most once a minute for the hub, and is counted in HubStats.revalidate_errors_total; alert on that, since a check that always fails leaves the stream unchecked until revalidate_failures (3) in a row end it with the goodbye recheck. That end is counted in ended_total.recheck, given to on_error and, at most once a minute for the hub, logged; the client reconnects after a jittered 1 to 5 seconds and the route's own check decides. Its type is pg_sse.Revalidate.

A revalidate on a sync driver. revalidate must be async, and a plain function is a TypeError: it runs on the event loop for every open stream, and a blocking call in it would stall them all. If your session lookup is a plain database call, wrap it in a thread yourself and hand hub.sse a partial:

from functools import partial
from starlette.concurrency import run_in_threadpool


async def session_is_valid(token: str) -> bool:
    return await run_in_threadpool(db.session_is_valid, token)  # False for a session that is gone


hub.sse(room, read=..., owner=str(user_id), revalidate=partial(session_is_valid, token))

A thread cannot be interrupted, so revalidate_timeout stops waiting for it but not the thread: a database that hangs holds one thread per stream in Starlette's pool (40 by default), shared with every sync route. Prefer an async driver, or a lookup answered from a cache, so the check is quick.

hub.sse

hub.sse(key, read, *, cursor=None, start=None, owner=None, end_event=None, max_stream_seconds=None,
        revalidate=None, headers=None, refuse_with=None)

stream as a Starlette/FastAPI response (needs the starlette extra). Past a cap it raises a 503 with Retry-After: 30; refuse_with(err) returns your own exception to raise instead, e.g. one your error tracker ignores. headers are added to the response. For FastAPI's OpenAPI document pass responses=pg_sse.event_stream_responses() and response_class=StreamingResponse to the route.

Event

Event(data, id=None, event=None, final=False)

• data: a str as is, anything else as JSON.
• id: the cursor after this event, handed back to read unchanged.
• event: the SSE event name; None means the browser's message.
• final: end the stream after this event (a closed conversation).

Wake

Wake(start=False, keys=frozenset(), signals=frozenset(), resync=False, reread=False, signal_keys={})

Why read runs, for a read(cursor, wake). See Signal streams for the fields. wake.data_may_have_changed is True unless the only causes are hub.wake signals.

hub.close

hub.close(*, owner=None, key=None)

Ends this process's streams opened with owner and/or on key, so a removed operator, a blocked visitor or a revoked session does not keep a stream for up to max_stream_seconds. That includes a stream that hub.sse has created but whose first frame has not been read yet, a stream whose read is running (an async def read is cancelled, so the goodbye goes out at once; a plain one runs on in its thread and what it found is not sent), and a stream partway through sending a batch (the rest is not sent). Each stream sends a goodbye with reason revoked and ends. A stream given revalidate ends the same way without a call here, once the check says no. At least one argument is required; hub.close_all() ends every stream. owner is a str or an int, as for stream; any other type raises TypeError.

• When it acts. Safe from any thread. Called on the event loop it takes effect before it returns; from another thread it is handed to the loop. It does nothing, silently, while the hub is not running, when there are no streams to end.
• Who it reaches. A stream opened after the call (the user signed in again) is not ended with the old ones, even when the call came from another thread and reaches the loop later. A route that checked the session before the revoke but opens its stream after the call is not reached; max_stream_seconds bounds that window.
• Slots. An ended stream's slot is free once it has said goodbye, or 10 seconds after it ended, whichever comes first. Until then it still holds a connection and counts against the caps and in open_streams, so a client that stops reading cannot open one stream after another, while a half-open connection (whose send blocks until TCP gives up) holds it no longer than that. A reconnect within that time can be refused with a 503. The same holds for a stream dropped for falling behind or ended by shutdown.
• A dropped stream past the grace. Once its slot is free the hub forgets it. A dropped stream whose read is still running then is out of reach of a shutdown that starts later: it says behind, not shutdown, and reconnects a little sooner.
• Not for one tab per user. Do not call it from the stream route to keep one tab per user: the closed tab reconnects a second later and its route closes the other, back and forth for as long as both are open.

await db.revoke_session(session_id)  # first: the reconnect below must be refused
hub.close(owner=str(user_id))

• Revoke in the database first. The client reconnects after the goodbye, and the route must refuse it; EventSource stops for good on a 401 or 403.
• With both arguments, only streams matching both end. A stream watching every key (key=None) matches by owner only.
• Only streams opened with owner= can be found by owner. Pass owner on every authenticated stream.
• It reaches this process only. With several workers, call it in each one; nothing is broadcast.

hub.wake

hub.wake(key, signal="wake", *, all_keys=True)

Wakes one key's streams for a change that is not a database write (someone is typing). Safe from any thread, and reaches only this process's streams. signal shows up in wake.signals; all_keys=False leaves the all-keys streams alone. key and signal must be str: a signal is matched against text labels, so an Enum would never match.

hub.call_later

hub.call_later(seconds, callback, *args)

Runs callback(*args) on the hub's event loop after seconds, for follow-up work on ephemeral state (check that a typing signal lapsed, then hub.wake). Safe from any thread; does nothing while the hub has no running loop.

signal_read

signal_read(*, start="ready", resync="resync", change="change", change_data=None, signals=None) -> Read

An async read(cursor, wake) for streams that tell the page what to refetch instead of sending rows. It runs on the event loop with no thread hop. An empty event name raises ValueError (the browser would dispatch it as a plain message) and a name that is not a str raises TypeError; pass None to send nothing. With resync=None, a resync that arrives with notified keys or signals still sends their events. Every event's data is {}, except change when change_data is given and a signal mapped to (event_name, data_fn).

Argument	Meaning
start	Event name for the stream's first read. None sends nothing.
resync	Event name for "anything may have changed": the listener (re)connected, or reread_seconds of quiet passed. None sends nothing.
change	Event name when a database notification reached the stream's key. None disables it.
change_data	fn(keys) -> payload for the change event, given the keys notified since the last read. Default payload {}. A per-key stream might pass lambda keys: {"conversationId": ...}; an all-keys one lambda keys: {"rooms": sorted(keys)}. With change=None it raises TypeError, since no event would carry it.
signals	{signal_label: event_name} for hub.wake and Ephemeral signals, such as {"presence": "presence"}; the event's data is {}. A value may be (event_name, data_fn) instead: data_fn(keys) gets the keys the signal was sent for and returns the data, e.g. {"presence": ("presence", lambda keys: {"conversationIds": sorted(keys)})}: a per-key stream gets its own key, an all-keys stream every key that signalled. keys is empty for a Wake built by hand without signal_keys, so do not index into it. One signal_read still serves every stream, because the keys come from the wake, not from a closure. Any other value raises TypeError when signal_read is called.

Causes are answered in this order, because the first two tell the page to refetch everything and anything after them would repeat it:

1. start: only the start event.
2. resync or reread: only the resync event.
3. Otherwise the change event if keys were notified, then one event per mapped signal that arrived, in the order of signals (so the result is deterministic). A write that coincides with a signal sends both.

A cause with no mapping, or mapped to None, contributes nothing, so the result may be [].

IntCursor

IntCursor(parts=1, *, sep=".", max_digits=15)

Parses and formats a cursor of parts non-negative integers joined by sep: 42, or 12.3 for a feed that spans two tables.

Member	Behaviour
parse_one(text)	For parts=1, what a stream route wants: the integer, or None for no cursor and for anything that is not one, so the stream starts from now (not a 422: EventSource gives up for good on a non-200). Takes the header as text or as raw bytes (read as Latin-1, as HTTP does). Never raises for client input; ValueError if parts is not 1, and TypeError for an int, which the code parsed already. An all-digit header longer than max_digits logs a warning (at most once a minute, and only when a larger max_digits would read it), since it is likely an id this app sent and catching up would be lost: pass a larger max_digits.
parse(text)	None or "" gives None: no cursor, so the stream starts from start=. Anything else must be exactly parts groups of 1 to max_digits ASCII digits (leading zeros aside) joined by sep, and gives a tuple of ints (also for parts=1). Otherwise ValueError("cursor must look like 1.2"); a stream route should then start from now. Pass format(*parsed) as cursor for several parts: the hub raises TypeError for a tuple cursor or Event id, which it could not send as an id parse accepts back.
format(*values)	The text for Event(id=...). ValueError unless there are exactly parts values, each a non-negative int (a bool or a float is refused) that parse would accept back.

max_digits=15 is exact in a JavaScript number. For longer ids (snowflake ids; a bigint has up to 19 digits) pass max_digits=19; format raises ValueError for a value with more digits than max_digits. Both parse and format raise ValueError for a part above the bigint maximum (9223372036854775807), so a 19-digit cursor never reaches the query out of range.

The constructor raises ValueError for parts or max_digits that is not an int (a bool included), parts < 1, max_digits outside 1 to 19, or a sep that is not a str, is empty, or holds a digit, a line break or NUL.

distinct

distinct(read, key)  # -> a read

Wraps read so a snapshot is sent only when it changed. key(event) summarises what the event shows, as a hashable value; an event whose key equals the key of the last one sent is dropped. None means "always send" (the next event is then compared with nothing, so it is sent too), and a final event is always sent. read may be read(cursor) or read(cursor, wake), sync or async; the wrapper takes the same arguments and is always async. A sync read runs in the hub's read_executor inside a stream, and in asyncio's default pool when you call the wrapper yourself (from a hub.subscribe loop, say), so it never blocks the loop. key runs on the event loop either way, once the events are back from read, so keep it cheap.

@app.get("/rooms/{room}/stream")
async def stream(room: str):
    # a read that returns a snapshot every time it runs; the page is told only when it differs
    return hub.sse(room, read=distinct(partial(snapshot, room), key=lambda e: e.data["unread"]))

Three things to get right:

• The state is per stream. Call distinct inside the route, once per request. Built once at import time, one wrapper would be shared by every stream, and a stream that has never been sent a snapshot would be told nothing.
• A dropped event's id is never applied. The hub advances the cursor only on events it yields, and the browser records only ids it receives. Drop only events whose id would not have advanced the cursor: a snapshot with no id, or one that repeats the last. Never drop an event that carries a new row, or a reconnect would replay from before it: make key change with every new row (next point), or, failing that, return None for any event that carries rows.
• None forgets the last key. After an event that is always sent, the next snapshot is sent again even if it is unchanged. Where you can, make key cover everything the client is shown, including the newest message or row id: a new row then changes the key by itself and None is not needed.

hub.ephemeral and Ephemeral

hub.ephemeral(name, *, ttl, signal=None, grace=0.25, all_keys=False, clock=time.monotonic) -> Ephemeral

Signals per key that lapse unless renewed (typing, presence), announced with hub.wake. hub.ephemeral(...) is Ephemeral(hub, name, ...).

Argument	Meaning
ttl	Seconds a signal lasts without renewal.
signal	The label hub.wake carries, so wake.signals contains it. Defaults to name. Two instances may share one: a typing (8 s) and a viewing (45 s) can both wake one presence frame.
grace	The lapse check runs this long after expiry, so it never finds a signal a hair from expiring.
all_keys	Passed to hub.wake. False by default: ephemeral state is per key, and a view of every key has nothing to show for it.
clock	Seconds, monotonic. Replace it in tests.

Method	Behaviour
set(key, who, on=True)	Renews or starts (on) or removes (not on) who's signal on key. Returns whether what a reader sees changed, and wakes the key's streams only then. A renewal returns False. Removing returns True if there was an entry, even one that lapsed a moment ago: someone may have read it before it lapsed.
clear(key, who=None)	Removes one who, or everyone on key. Returns and wakes as set(..., on=False) does.
live(key)	Who has not lapsed right now, in the order they started. Never lists an expired entry, even if its lapse check has not run.
reset()	Forgets every key and signal, and wakes no stream. For a test fixture's clean slate.

set and clear are safe from any thread; key must be a str. Each renewal schedules one lapse check with hub.call_later; a check that finds the signal renewed leaves it alone, and the renewal's own check handles it later. State lives in this process only, so with several workers a signal set on one is invisible to the streams on the others, and it is lost on restart. While the hub is stopped nothing checks, so entries linger until the next set or clear for their key (live still skips them).

hub.stats

A frozen HubStats: open_streams, refused_total, dropped_total, listener_connected, listener_reconnects_total, last_notification_at (Unix time or None), read_errors_total (streams that failed: read or start raised, or read returned something that could not be sent) and revalidate_errors_total (runs of a revalidate that raised or timed out; streams that revalidate_failures ended are in ended_total.recheck) and ended_total, a frozen EndedTotals of goodbyes sent by reason: max_age, shutdown, revoked, behind and recheck. "Streams dropped for being slow" is dropped_total; ended_total.behind counts the ones that then said so, which leaves out a dropped stream that a close or shutdown reached first, or whose client left. A goodbye is counted once the client took it, so a stream whose client left, or that ended with a final event or a failed read or start, is in none of them. dataclasses.asdict(hub.stats()) gives all of it as a dict, ended_total as a nested one. The _total fields only grow, so a metrics exporter can read them on a timer and publish them as counters. They are per process and start at zero. pg-sse ships no exporter code, since people use different ones.

hub.streams

hub.streams() -> list[StreamInfo]

Every subscription still holding a slot, oldest first, as StreamInfo(key, owner, age_seconds, ended) (key is None for an all-keys stream, owner is None for one opened without it, and ended is true for one closed or dropped that is still saying goodbye: it counts against the caps until it has). For an admin view or a debug endpoint; this process only. It copies a set the event loop changes: safe from another thread under CPython's GIL, but on a free-threaded build call it on the event loop.

hub.listening

A threading.Event, set while the listener holds its LISTEN. hub.stats().listener_connected says the same.

hub.subscribe and hub.unsubscribe

hub.subscribe(key, owner=None) -> Subscription
hub.unsubscribe(subscription)

The low-level queue under stream, for a custom stream loop. key and owner are checked like stream's. Unsubscribe in a finally.

await subscription.wait(timeout) returns everything queued once there is anything, or None on timeout. An item is ("notify", key) for a database notification, ("wake", key, signal) for a hub.wake, or ("marker", name), which means re-read everything. Once subscription.ended is true the stream is over: it fell behind, the hub is shutting down (hub.closing), or hub.close ended it. After a listener connect or reconnect the resync marker arrives at once: resync_spread applies only to hub.stream and hub.sse, so a custom loop that serves many streams should add its own jitter.

Read, Start, Revalidate and ErrorHandler

The types of read, start, revalidate and on_error: Read is Callable[..., Iterable[Event] | Awaitable[Iterable[Event]]], and Start is Callable[[], Any], Revalidate is Callable[[], Awaitable[Any]], and ErrorHandler is a function of (key, exc) or (key, exc, info). Use them to annotate a helper that wraps hub.sse:

from pg_sse import Hub, Read, Start


def room_stream(hub: Hub, room_id: int, read: Read, start: Start):
    return hub.sse(str(room_id), read=read, start=start)

event_stream_responses

event_stream_responses(status_code=200, description=None) -> dict

FastAPI's responses= for a route that returns hub.sse(...): text/event-stream and its Cache-Control and X-Accel-Buffering headers, under status_code for a route that sets another one, and with description if given (otherwise the route's response_description applies to its own status code). Pass response_class=StreamingResponse too, or FastAPI also lists application/json. It returns a new dict each time, so add to it freely.

trigger_sql

trigger_sql(table, key_column, channel, *, order_column=None, on=("insert", "update", "delete"), update_of=None)

The SQL that wires a table to a channel, to run once in a migration. Postgres 14+.

• Names are plain lower-case identifiers; table may be schema.table.
• order_column must be a serial, bigserial or identity column; installing fails with a clear error otherwise.
• on limits which writes notify: any of "insert", "update", "delete".
• update_of limits updates to those whose SET list names one of the columns (plus the key column). Needs "update" in on.
• It creates a function and a trigger named "pg_sse$notify$<table>$<key>" (and "pg_sse$order$<table>$<order_column>"), which is what you will see in \d. Running it again replaces them.
• The order trigger looks up the column's sequence once, when the SQL runs, and writes its name into the function, so an insert does no catalog search while it holds the key's lock. Dropping and recreating the sequence under the same name is fine; if you rename it or move it to another schema, run trigger_sql again.

drop_trigger_sql

drop_trigger_sql(table, key_column, *, order_column=None)

The SQL that removes what trigger_sql created, for a downgrade migration. It does not need channel, on or update_of.

Health check

import dataclasses

from fastapi.responses import JSONResponse


@app.get("/healthz")
async def healthz():
    stats = hub.stats()
    return JSONResponse(dataclasses.asdict(stats), status_code=200 if stats.listener_connected else 503)

Testing your app

The hub needs a real Postgres; there is nothing to mock, because the database is the source of truth. Point the tests at a scratch database and enter the hub's lifespan. Starlette's TestClient runs the lifespan off the main thread, where the signal hook is skipped anyway, but pass handle_signals=False in tests so a test never touches the process's signal handlers.

hub = Hub(TEST_DSN, channel="room_change", handle_signals=False)
with TestClient(app) as client:  # runs the lifespan
    ...

A fixture keeps that in one place. It needs an async plugin: anyio, with the tests marked @pytest.mark.anyio, or pytest-asyncio with asyncio_mode = "auto" (in its default strict mode, decorate it with @pytest_asyncio.fixture instead):

@pytest.fixture
async def running_hub():
    async with hub.lifespan():
        yield hub

To read a stream without a server, run the hub on the test's event loop with async with hub.lifespan(): (leaving it forgets every subscription, so the next test starts clean) and read frames with pg_sse.testing:

from pg_sse.testing import goodbye, next_event


async def test_a_new_message_arrives():
    async with hub.lifespan():
        frames = hub.stream("lobby", read=read_after_lobby, cursor=0)
        insert_message("lobby", "hi")
        assert (await next_event(frames)).json() == {"id": 1, "body": "hi"}

The timings are plain attributes, so a test can shorten them after building the hub and its signals: hub.ping_seconds = (0.2, 0.2), hub.reread_seconds = 0.2, and typing.ttl = 0.2 on an Ephemeral. Set them before the first stream opens; the constructor's checks do not run on assignment, so keep ping_seconds a (low, high) tuple with 0 < low <= high. Call typing.reset() between tests that share an Ephemeral. Set resync_spread=0 if a test expects the re-read after a listener reconnect to come at once.

next_event skips pings and the id-only frame that opens a stream with a cursor. Keep that: a ping comes before any frame a re-read produces, because every idle timeout pings, even the one that leads to the re-read, and before a goodbye when the age limit and the ping timeout coincide. A test that expects the very next frame to be the event is flaky without it. Use next_frame when the ping or the id is what you are testing.

pg_sse.testing

Reading a stream in tests, with no test framework and no database: the helpers take any async iterator of frames (what hub.stream returns, or a response's body_iterator). See Testing your app.

Name	Behaviour
next_frame(frames, timeout=5.0)	The next frame, whatever it is.
next_event(frames, timeout=5.0, *, event=None)	The next event: skips pings and id-only frames, and with event= frames of any other name.
goodbye(frames, timeout=5.0)	The retry: frame before a planned close. Skips pings; any other frame fails.
ended(frames, timeout=5.0)	Fails unless the stream is over.
until(predicate, timeout=5.0)	Waits, yielding to the event loop, until predicate() is true.
decode(frame)	Parses one frame into a Frame: id, event, data (lines joined with \n; None without one), retry, comment, raw, json(), and is_ping, is_cursor, is_goodbye.

Waiting past timeout raises TimeoutError naming the frames seen so far; a stream that ends early fails with an AssertionError that does the same. A timed-out read cancels the generator, so the stream is over afterwards.

Multiple workers

Each process (each uvicorn or gunicorn worker) holds one LISTEN connection and its own caps and counters. Nothing is shared between workers and nothing needs to be: Postgres delivers every notification to every listener, and each worker wakes its own streams. Budget one connection per worker.

The exception is hub.wake: it reaches only the streams of the process that calls it, since nothing is written to the database. State that lives in one worker's memory, which includes everything in hub.ephemeral (the typing indicator in the inbox example), is invisible to readers on the other workers; keep it where every worker can see it before you run more than one.

Logging

pg-sse logs to the standard-library logger named pg_sse and adds no handlers, so configure it like any other. At WARNING it logs a stream refused at a cap or during shutdown (back-pressure, not a fault), the listener losing its connection (with the traceback and the retry delay), and, at most once a minute per hub, a revalidate that failed without ending its stream. It also warns, at most once a minute, about a client cursor with a line break or NUL (the stream starts from now) and about an id longer than an IntCursor's max_digits. At ERROR it logs, with a traceback, a stream whose read or start raised or returned something other than Event items (that stream ends and the client reconnects), naming its key, its owner (if log_owner=True) and age; one that a failing revalidate ended is logged the same way at most once a minute per hub, and a failed run that ends nothing is a WARNING. It also logs an on_error callback that failed.

Limits

• LISTEN needs a direct connection. Behind a transaction-mode pooler (PgBouncer in transaction mode, the pooled connection strings Supabase and Neon give out) LISTEN succeeds and nothing ever arrives; streams then update only on the re-read. Give the hub the direct URL; your queries can still use the pooler.
• The cursor sees new rows, not updates. If a stream must show edits, have read return the current state alongside new rows, or use a cursor that moves on update (a version column with order_column). If it does not need to show them, stop them from notifying: trigger_sql(..., on=("insert",)), or update_of=(...) to wake only for edits of the columns a reader shows. Otherwise every update wakes every reader of that key for a read that returns nothing. A write the trigger leaves out never wakes a stream; the stream finds it on its next re-read.
• A key is text. hub.stream, hub.sse, hub.subscribe and hub.wake raise a TypeError for a key that is not a str, because a notification carries the key column as text and an int would subscribe and never wake. Pass str(room_id).
• Sync reads run in a thread pool. A plain-function read or start runs in asyncio's default executor (min(32, cpu + 4) threads) unless you pass read_executor, and under Starlette other sync routes share anyio's pool of 40. Hundreds of streams re-reading at once queue behind it. Prefer async read and start on an psycopg_pool.AsyncConnectionPool; see examples/chat.py. Use functools.partial(read_after, room) rather than a lambda to keep an async function off the pool.
• order_column serialises inserts per key. The ordering trigger takes pg_advisory_xact_lock on the key and holds it until the transaction ends, so every other insert to that key waits for the whole transaction. Two transactions inserting into keys in opposite order can deadlock, and Postgres aborts one of them. Keep the transaction that inserts short, or skip order_column and tolerate a late id arriving on the next re-read. The lock is pg_advisory_xact_lock(hashtext(channel), hashtext(key)); advisory locks share one namespace per database, so an application taking the same two-int lock would serialise against these inserts, and since hashtext is 32-bit two different keys can collide and briefly wait on each other (a delay, never wrong ids).
• Ephemeral state is per process. hub.ephemeral keeps its signals in memory: with several workers a signal set on one is invisible to the streams on the others, and a restart loses it. That costs nothing for typing or presence; anything that must be seen everywhere belongs in a table with a trigger.
• Per process. Each worker runs its own listener, which works, but the caps are per process.
• The database may be down at startup. lifespan waits up to listen_timeout for the first LISTEN and then starts anyway; until the listener connects, streams update on their re-read and listener_connected is false.
• Disconnect detection depends on the server. Starlette 1.7 under an ASGI server that advertises spec_version 2.4 does not listen for http.disconnect during a streaming response: a dead client is noticed at the next write, at most ping_seconds[1] later, and its slot is held until then. uvicorn 0.54 advertises 2.3 and frees the slot at once.
• psycopg 3 for the listener; your own queries can use any driver.
• A framework for the response. hub.sse needs Starlette or FastAPI; any other framework uses hub.stream.

For AI coding agents

llms.txt has the rules for generating code with this library, in a form meant to be fed to an agent. Runnable examples are in examples/: a chat room with async reads on a connection pool, and an inbox with a typing indicator built on signal streams.

Development

See CONTRIBUTING.md. In short:

uv sync
PG_SSE_TEST_DSN=postgresql://sse:sse@127.0.0.1:55432/pg_sse_test uv run pytest --cov
uv run ruff check . && uv run mypy

The tests create and drop a schema per test in the database you point them at; use a scratch database.

License

MIT