fastapi-stream-lease

One user. One stream. Two tabs.

This demo holds a Redis lease for each SSE stream. Both panels share one HttpOnly session cookie, so the second stream is rejected with 429 until the first one finishes or disconnects.

Active streams

0 / 20

Per user

Backend

checking...

Tab A

Synthetic SSE stream

idle

Tokens received 0 / 0 Last token —

Ready.

Tab B

Same cookie, same user

idle

Tokens received 0 / 0 Last token —

Ready.

What you are seeing

Each stream is a synthetic 20-second SSE response. No LLM calls or API keys are involved.
The lease lives in Redis with a 25-second TTL and is renewed while the response is open.
The public limits are 1 concurrent stream per session and 20 globally.
If Redis is unavailable, the API returns 503 instead of silently allowing streams.