sync-state-bridge

A deterministic, race‑safe state synchronisation bridge for real‑time applications, with built‑in QoS, backpressure handling, and network resilience.

• Versioned, per‑type sync – each entity type has its own version history.
• Segmented deltas – send only what changed, with a manifest first.
• FSM lifecycle – correct handling of add→update→delete sequences.
• Resilient reconnection – out‑of‑order drop, monotonicity guards, schema mismatch handling.
• Quality of Service (QoS) – three priority levels (CRITICAL, CONFLATABLE, BEST_EFFORT).
• Adaptive backpressure – the Governor monitors queue depth and recommends throttling.
• Pure Python + JS – no binary dependencies.
• Pluggable transports – IPC, HTTP/SSE, and more.

Quick Start

Install the server package:

pip install sync-state-bridge

For optional features (faster JSON, serial transport):

pip install sync-state-bridge[fast,serial]

Basic Usage (Simple Server with StateSync)

from sync_state import StateSync, Presets

sync = StateSync()

# Register a snapshot provider with a QoS profile
sync.register_snapshot_provider(
    "vehicles",
    get_vehicles,
    qos=Presets.low_bandwidth()   # optimised for slow links
)

# After changes:
sync.mark_dirty("vehicles")
await sync.commit()

# Stream deltas over HTTP (SSE)
from fastapi import FastAPI, StreamingResponse
app = FastAPI()

@app.get("/stream")
async def stream(versions: str = "{}"):
    return StreamingResponse(
        sync.stream_deltas(json.loads(versions)),
        media_type="text/event-stream"
    )

Advanced Full‑Stack Example (Gateway + Worker)

For a production‑grade setup with separate gateway and worker processes, see the advanced_game example. It demonstrates:

• Router – pure frame forwarder.
• SynchronisationKernel – priority queue and backpressure.
• Governor – adaptive health monitoring.
• HTTPSSETransport – web interface.
• IPCTransport – communication between gateway and worker.

Gateway (game_server.py)

from sync_state.core.sync_bridge import SyncStateBridge
from sync_state.core.ipc_transport import IPCTransport
from sync_state.web import HTTPSSETransport

bridge = SyncStateBridge()
ipc = IPCTransport(listen_on="127.0.0.1:8766")
http = HTTPSSETransport(host="127.0.0.1", port=8000, static_dir="static")

bridge.register_transport(ipc, type_list=["player"], direction="in")
bridge.register_transport(http, type_list=["player"], direction="out", qos_map={"player": 3})

bridge.start()
http.start()

Worker (game_worker.py)

from sync_state.core import StateSync
from sync_state.core.ipc_transport import IPCTransport

state_sync = StateSync()
# register snapshot providers...
ipc = IPCTransport(connect_to="127.0.0.1:8766")
# read frames, update state, commit, send deltas.

Socket Server (for low‑level IPC)

from sync_state.reliability import StateSyncSocketClient

client = StateSyncSocketClient(
    host="127.0.0.1",
    port=8765,
    on_delta_callback=handle_delta
)
await client.connect_and_listen()

Quality of Service (QoS)

Each entity type can have a QoS profile:

Policy	Behaviour
CRITICAL	Never dropped; queued until delivered.
CONFLATABLE	Intermediate deltas dropped; only the latest is sent.
BEST_EFFORT	Discarded immediately under queue pressure.

Pre‑configured profiles (Presets.conservative(), Presets.low_bandwidth(), Presets.high_throughput()) are provided.

Advanced Features

QoS‑Aware Priority Queue

The PriorityQoSQueue provides three tiers with automatic eviction.

Adaptive Governor

The Governor monitors queue depth and drop rates, providing recommendations to the application (e.g., max_particles, max_asteroids).

Snapshot Chunking

Large snapshots are split into 64 KB chunks for reliable transmission.

from sync_state.reliability import chunk_snapshot, SnapshotReassembler

chunks = chunk_snapshot(state, "snap_123")
reassembler = SnapshotReassembler()
for chunk in chunks:
    reassembler.ingest_chunk(chunk)

Testing

Run the unit tests:

pytest tests/

The test suite covers:

• Deterministic hashing (canonical_hash)
• Commit & delta generation
• Version‑gap full‑snapshot recovery
• Router, Kernel, and QoS logic

Demos

Run the demos:

• Chat – real‑time message broadcast with shared history.

cd examples/chat && python server.py

• Simple Game – turn‑based game using StateSync.

cd examples/simple-game && python server.py

• Advanced Game – spaceship game with adaptive QoS and monitoring (the most comprehensive demo).

cd examples/advanced-game && python game_start.py

These run on a local server, displayed in the web browser (at http:0.0.0.0:8000 by default). Proof of this is that you can refresh or close+reopen the browser window and it is still running.

Protocol

See PROTOCOL.md for the full SSE‑based delta protocol and the router/kernel design.

License

MIT