Streaming

Streaming envelopes over Server-Sent Events and WebSocket.

Envelopes stream with the same JSON as a fetch response: Envelope.to_json(), compact UTF-8 with v first, byte-identical to the Rust and TypeScript engines.

• format_event() frames an envelope as one SSE event (event: template).

• format_packet() returns the JSON for one WebSocket text message.

• Stream(template, slot, params).run(engine) renders and frames an SSE event in one call.

Server-Sent Events (FastAPI)

import asyncio
from fastapi.responses import StreamingResponse
from anza import Fragment, format_event

@app.get("/feed/stream")
async def stream_feed():
    async def events():
        while True:
            envelope = Fragment("feed/card.html", "feed", {"title": "Push"}).run(engine)
            yield format_event(envelope)   # 'event: template\ndata: {"v":2,...}\n\n'
            await asyncio.sleep(2)
    return StreamingResponse(events(), media_type="text/event-stream")

WebSocket (Starlette / FastAPI)

from anza import Fragment, format_packet

@app.websocket("/feed/ws")
async def feed_ws(ws):
    await ws.accept()
    envelope = Fragment("feed/card.html", "feed", {"title": "Push"}).run(engine)
    await ws.send_text(format_packet(envelope))

Receivers verify streamed envelopes like any other, with verify_envelope().