Wirth-style minimal SSE web framework with topic-scoped pub/sub
Project description
py_sse
A small Python web framework for real-time hypermedia apps. HTTP/1.1, one OS thread per connection, brotli-compressed SSE, topic-scoped pub/sub. No async. About 1200 lines.
Pairs with html-tags and Datastar.
Install
pip install py-sse
Hello, live page
from py_sse import serve, live, Database, signals
from html_tags import h
db = Database("app.db", schema="CREATE TABLE IF NOT EXISTS msg (text TEXT)")
@live(topic="chat")
def home(req):
msgs = db.all("SELECT text FROM msg")
return [
h.h1("chat"),
h.ul(*[h.li(t) for (t,) in msgs]),
h.input({"data-bind:text": "",
"data-on:keydown": "evt.key === 'Enter' && "
"($text && (@post('/say'), $text=''))"}),
]
def say(req):
text = (signals(req).get("text") or "").strip()
if text:
db.execute("INSERT INTO msg (text) VALUES (?)", (text,))
db.changes.notify("chat")
return (200, [], b"")
ROUTES = [("GET", "/", home), ("POST", "/say", say)]
if __name__ == "__main__":
serve(ROUTES, port=8000, changes=db.changes, head=[
h.title("chat"),
h.script(type="module", src="https://cdn.jsdelivr.net/gh/"
"starfederation/datastar@v1.0.1/bundles/datastar.js"),
])
Open two browser tabs. Type in one, watch it appear in the other.
How it works
-
One URL per live page.
@live(topic="x")makes the handler serve three transport modes from the same route, dispatched byAccept:- Live SSE while viewers are under
soft_cap. - Polling between
soft_capandhard_cap(interval ramps exponentially). - Static above
hard_cap(page stops auto-updating). - Polling clients re-upgrade to live when capacity drops.
- Live SSE while viewers are under
-
CQRS. Reads come down the long-lived SSE stream. Writes are short-lived
@post()calls that mutate state and calldb.changes.notify("topic"). All open streams re-render. -
Topic patterns. Subjects are dotted:
"game.42.score". A waiter on"game.42.*"wakes on any ofgame.42.score,game.42.players, etc.@live(topic="game.{id}.*")expands{id}from URL parameters.changes.wait([p1, p2, ...])waits on multiple patterns at once. -
Fat morph. Every frame is the whole page. idiomorph diffs in place. Brotli's cross-frame state compresses repeated HTML at ~200:1.
-
Framework owns the envelope. Pass
head=[...]toserve()once. The<html><head><body>is byte-identical on every render, so idiomorph leaves it alone and scripts stay running across morphs.
API
serve(routes, *, host, port, changes, head, capacity, on_event,
before_hooks, ui_theme, max_connections, access_log)
live(handler, topic=..., hard_cap=...) # function or @live(topic="...")
Database(path, schema) # apsw passthrough + .changes
Changes() # topic-scoped pub/sub
.notify(subject) # publish
.wait(pattern, timeout=...) # pattern: str | iterable of str
Capacity(soft_cap, hard_cap, ...) # viewer capacity
html(body), redirect(loc), error(status, msg), no_content()
signals(req) # parse Datastar signals
set_cookie(req, name, value, **opts)
Handlers return html_tags Node, Safe, or an iterable of those.
Writes return a (status, headers, body) tuple.
on_event(event_dict) is an optional callback fired on
stream_open, stream_close, and page_render. No-op by default.
Status
0.8.0. Small, opinionated, not yet hardened for hostile traffic. Pair with a reverse proxy for TLS. Compression and SSE buffering are already correct on the application side.
MIT.
Release history Release notifications | RSS feed
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