wse-server 2.4.1

Rust-powered WebSocket engine for Python. Up to 5M fan-out del/s. Zero-GIL JWT.

WSE - WebSocket Engine

High-performance WebSocket server built in Rust with native clustering, E2E encryption, message recovery, presence tracking, and real-time fan-out. Exposed to Python via PyO3 with zero GIL overhead on the data path. Ships with Rust-accelerated utilities for application code: priority queues, rate limiters, event sequencing, compression, cryptography, and JWT.

Features

Server

Feature	Details
Rust core	tokio async runtime, tungstenite WebSocket transport, dedicated thread pool, zero GIL on the data path
JWT authentication	HS256, RS256, ES256 algorithms via jsonwebtoken crate. Validated during handshake (0.01ms), cookie + Authorization header extraction, key rotation, kid validation
Protocol negotiation	client_hello/server_hello handshake with feature discovery, capability advertisement, version agreement
Topic subscriptions	Per-connection topic subscriptions with automatic cleanup on disconnect
Pre-framed broadcast	WebSocket frame built once, shared via Arc across all connections, single allocation per broadcast
Vectored writes	write_vectored (writev syscall) batches multiple frames per connection in a single kernel call
Write coalescing	Write task drains up to 256 pending frames per iteration via recv_many
DashMap state	Lock-free sharded concurrent hash maps for topics, rates, formats, activity tracking
mimalloc allocator	Global allocator optimized for multi-threaded workloads with frequent small allocations
Deduplication	50,000-entry AHashSet with FIFO eviction per send_event() call
Rate limiting	Per-connection token bucket: 100K capacity, 10K/s refill, client warning at 20% remaining
Zombie detection	Server pings every 25s, force-closes connections with no activity for 60s
Drain mode	Lock-free crossbeam bounded channel, Python acquires GIL once per batch (not per event)
Compression	zlib for client-facing messages above threshold (default 1024 bytes)
MessagePack	Opt-in binary transport via ?format=msgpack, roughly 2x faster serialization, 30% smaller
Message signing	Selective HMAC-SHA256 signing for critical operations, nonce-based replay prevention
Queue groups	Round-robin dispatch within named groups for load-balanced worker pools
Topic ACL	Per-connection allow/deny glob patterns for topic access control
Graceful drain	drain() sends Close frame to all clients, rejects new connections, notifies cluster peers

End-to-End Encryption

Feature	Details
Key exchange	ECDH P-256 (per-connection keypair, automatic during handshake)
Encryption	AES-GCM-256 with unique 12-byte IV per message
Key derivation	HKDF-SHA256 (no salt, info: wse-encryption/aes-gcm-key)
Wire format	E: prefix + 12-byte IV + AES-GCM ciphertext + 16-byte auth tag
Key rotation	Configurable rotation interval (default 1 hour), automatic renegotiation
Replay prevention	Nonce cache (10K entries, 5-minute TTL) on the client side

Cluster Protocol

Feature	Details
Topology	Full TCP mesh, direct peer-to-peer connections
Wire format	Custom binary frames: 8-byte header + topic + payload, 12 message types
Interest routing	SUB/UNSUB/RESYNC frames, messages forwarded only to peers with matching subscribers
Gossip discovery	PeerAnnounce/PeerList frames, new nodes need one seed address to join
mTLS	rustls + tokio-rustls, P-256 certificates, WebPkiClientVerifier for both sides
Compression	zstd level 1 for payloads above 256 bytes, capability-negotiated, output capped at 1 MB
Heartbeat	5s ping interval, 15s timeout, dead peer detection
Circuit breaker	10 failures to open, 60s reset, 3 half-open probe calls
Dead letter queue	1000-entry ring buffer for failed cluster sends
Presence sync	PresenceUpdate/PresenceFull frames, CRDT last-write-wins conflict resolution
Topology API	cluster_info() returns connected peer list with address, instance_id, status

Presence Tracking

Feature	Details
Per-topic tracking	Which users are active in each topic, with custom metadata (status, avatar, etc.)
User-level grouping	Multiple connections from same JWT sub share one presence entry
Join/leave lifecycle	presence_join on first connection, presence_leave on last disconnect
O(1) stats	presence_stats() returns member/connection counts without iteration
Data updates	update_presence() broadcasts to all topics where the user is present
Cluster sync	Synchronized across all nodes, CRDT last-write-wins resolution
TTL sweep	Background task every 30s removes entries from dead connections

Message Recovery

Feature	Details
Ring buffers	Per-topic, power-of-2 capacity, bitmask indexing (single AND instruction)
Epoch+offset tracking	Precise recovery positioning, epoch changes on buffer recreation
Memory management	Global budget (default 256 MB), TTL eviction, LRU eviction when over budget
Zero-copy storage	Recovery entries share Bytes (Arc) with the broadcast path
Recovery on reconnect	subscribe_with_recovery() replays missed messages automatically
Per-message stamp	When recovery is enabled, every topic broadcast carries tp/e/o (topic, epoch, offset) so clients dedup idempotently and detect gaps from the messages themselves

Client SDKs (Python + TypeScript/React)

Feature	Details
Auto-reconnection	4 strategies: exponential, linear, fibonacci, adaptive backoff with jitter
Connection pool	Multi-endpoint with health scoring, 3 load balancing strategies, automatic failover
Circuit breaker	CLOSED/OPEN/HALF_OPEN state machine, prevents connection storms
Rate limiting	Client-side token bucket, coordinates with server feedback
E2E encryption	Wire-compatible AES-GCM-256 + ECDH P-256 (both clients speak the same protocol)
Event sequencing	Duplicate detection (sliding window) + per-topic (epoch, offset) idempotent dedup with automatic gap recovery
Network monitor	Real-time latency, jitter, and connection-quality scoring (Python client also estimates packet loss)
Priority queues	5 levels from CRITICAL to BACKGROUND
Offline queue	IndexedDB persistence (TypeScript), replayed on reconnect
Compression	Automatic zlib for messages above threshold
MessagePack	Binary encoding for smaller payloads and faster serialization
Message signing	HMAC-SHA256 integrity verification

Transport Security

Feature	Details
Origin validation	Configure in reverse proxy (nginx/Caddy) to prevent CSWSH
Cookie auth	access_token HTTP-only cookie with Secure + SameSite=Lax (OWASP recommended for browsers)
Frame protection	1 MB max frame size, serde_json parsing (no eval), escaped user IDs in server_ready; inbound msgpack rejected beyond 64 nesting levels
Cluster frame protection	zstd decompression output capped at 1 MB (MAX_FRAME_SIZE), protocol version validation
Slowloris protection	At most 512 concurrent pre-handshake connections; sockets that never complete the WS upgrade are bounded and dropped
Bounded callback dispatch	Callback mode caps in-flight on_message callbacks at 256 per connection; excess inbound work is shed and counted as rate-limited
Fail-closed recovery ACL	Recovery replay applies the connection's topic ACL — unauthorized topics are never replayed or position-probed

---

Quick Start

pip install wse-server

from wse_server import RustWSEServer, rust_jwt_encode
import time, threading

server = RustWSEServer(
    "0.0.0.0", 5007,
    max_connections=10_000,
    jwt_secret=b"replace-with-a-strong-secret-key!",
    jwt_issuer="my-app",
    jwt_audience="my-api",
)
server.enable_drain_mode()
server.start()

def handle_events(srv):
    while True:
        for ev in srv.drain_inbound(256, 50):
            if ev[0] == "auth_connect":
                srv.subscribe_connection(ev[1], ["updates"])
            elif ev[0] == "msg":
                print(f"Message from {ev[1]}: {ev[2]}")
            elif ev[0] == "disconnect":
                print(f"Disconnected: {ev[1]}")

threading.Thread(target=handle_events, args=(server,), daemon=True).start()

while server.is_running():
    time.sleep(1)

Generate a test token:

token = rust_jwt_encode(
    {"sub": "user-1", "iss": "my-app", "aud": "my-api",
     "exp": int(time.time()) + 3600, "iat": int(time.time())},
    b"replace-with-a-strong-secret-key!",
)

---

Server Configuration

RustWSEServer constructor parameters:

Parameter	Default	Description
host	required	Bind address
port	required	Bind port
max_connections	1000	Maximum concurrent WebSocket connections
jwt_secret	None	JWT key for validation. HS256: shared secret (bytes, min 32). RS256/ES256: PEM public key. None disables auth
jwt_issuer	None	Expected iss claim. Skipped if None
jwt_audience	None	Expected aud claim. Skipped if None
jwt_cookie_name	"access_token"	Cookie name for JWT token extraction
jwt_previous_secret	None	Previous key for zero-downtime rotation. HS256: previous secret. RS256/ES256: previous public key PEM
jwt_key_id	None	Expected kid header claim. Rejects tokens with mismatched key ID
jwt_algorithm	None	JWT algorithm: "HS256" (default), "RS256", or "ES256"
jwt_private_key	None	PEM private key for RS256/ES256 token encoding. Not needed for HS256
max_inbound_queue_size	131072	Drain mode bounded queue capacity
recovery_enabled	False	Enable per-topic message recovery buffers
recovery_buffer_size	128	Ring buffer slots per topic (rounded to power-of-2)
recovery_ttl	300	Buffer TTL in seconds before eviction
recovery_max_messages	500	Max messages returned per recovery response
recovery_memory_budget	268435456	Global memory limit for all recovery buffers (bytes, default 256 MB)
presence_enabled	False	Enable per-topic presence tracking
presence_max_data_size	4096	Max bytes for a user's presence metadata
presence_max_members	0	Max tracked members per topic (0 = unlimited)
max_outbound_queue_bytes	16777216	Per-connection outbound buffer limit (bytes, default 16 MB). Messages dropped when exceeded
max_subscriptions_per_connection	0	Max topics per connection (0 = unlimited). Prevents topic explosion DoS
rate_limit_capacity	100000.0	Token bucket capacity per connection
rate_limit_refill	10000.0	Token bucket refill rate per second
max_message_size	1048576	Maximum WebSocket frame size in bytes (default 1 MB)
ping_interval	25	Server-initiated ping interval in seconds
idle_timeout	60	Force-close connections idle for this many seconds

---

API Reference

Lifecycle

server.start()                          # Start the server
server.stop()                           # Graceful shutdown
server.is_running()                     # Check server status (bool)

Event Handling

Drain mode (recommended) - events are queued in a lock-free crossbeam channel. Python polls in batches, acquiring the GIL once per batch.

server.enable_drain_mode()              # Switch to batch-polling mode (call before start)
events = server.drain_inbound(256, 50)  # Poll up to 256 events, wait up to 50ms

Each event is a tuple: (event_type, conn_id, payload)

Event Type	Trigger	Payload
"auth_connect"	JWT-validated connection	user_id (string)
"connect"	Connection without JWT	cookies (string)
"msg"	Client sent WSE-prefixed JSON	parsed dict
"raw"	Client sent plain text	raw string
"bin"	Client sent binary frame	bytes
"disconnect"	Connection closed	None
"presence_join"	User's first connection joined a topic	dict with user_id, topic, data
"presence_leave"	User's last connection left a topic	dict with user_id, topic, data

Callback mode - alternative to drain mode. Callbacks are invoked via spawn_blocking per event.

server.set_callbacks(on_connect, on_message, on_disconnect)

Sending Messages

server.send(conn_id, text)                      # Send text to one connection
server.send_bytes(conn_id, data)                 # Send binary to one connection
server.send_event(conn_id, event_dict)           # Send structured event (auto-serialized, deduped, rate-checked)

server.broadcast_all(text)                       # Send to every connected client (text)
server.broadcast_all_bytes(data)                 # Send to every connected client (binary)
server.broadcast_local(topic, text)              # Fan-out to topic subscribers on this instance
server.broadcast(topic, text)                    # Fan-out to topic subscribers across all cluster nodes

Method	Scope	Notes
send	Single connection	Raw text frame
send_bytes	Single connection	Raw binary frame
send_event	Single connection	JSON-serialized, compressed if above threshold, deduplication via 50K-entry FIFO window
broadcast_all	All connections	Pre-framed, single frame build shared via Arc
broadcast_local	Topic (local)	Pre-framed, DashMap subscriber lookup, stored in recovery buffer if enabled
broadcast	Topic (all nodes)	Local fan-out + forwarded to cluster peers with matching interest

Topic Subscriptions

server.subscribe_connection(conn_id, ["prices", "news"])              # Subscribe to topics
server.subscribe_connection(conn_id, ["chat"], {"status": "online"})  # Subscribe with presence data
server.subscribe_connection(conn_id, ["tasks"], queue_group="workers") # Subscribe with queue group (round-robin)
server.unsubscribe_connection(conn_id, ["news"])                      # Unsubscribe from specific topics
server.unsubscribe_connection(conn_id, None)                          # Unsubscribe from all topics
server.get_topic_subscriber_count("prices")                           # Subscriber count for a topic

Subscriptions are cleaned up automatically on disconnect. In cluster mode, interest changes are propagated to peers via SUB/UNSUB frames.

Queue groups: connections in the same queue_group receive messages round-robin instead of fanout. Normal subscribers (no queue group) still receive all messages. Useful for distributing work across a pool of consumers.

Topic ACL

Per-connection topic access control with glob pattern matching.

# Allow only "user:*" topics, deny everything else
server.set_topic_acl(conn_id, allow=["user:*"])

# Allow "data:*" but deny "data:internal:*"
server.set_topic_acl(conn_id, allow=["data:*"], deny=["data:internal:*"])

# Must be called before subscribe_connection
server.subscribe_connection(conn_id, ["data:prices"])   # allowed
server.subscribe_connection(conn_id, ["data:internal:audit"])  # denied

Deny patterns take precedence over allow patterns. Supports * (any characters) and ? (single character) wildcards. Applied at subscribe time.

Presence Tracking

Requires presence_enabled=True in the constructor.

# Query members in a topic
members = server.presence("chat-room")
# {"alice": {"data": {"status": "online"}, "connections": 2},
#  "bob":   {"data": {"status": "away"},   "connections": 1}}

# Lightweight counts (O(1), no iteration)
stats = server.presence_stats("chat-room")
# {"num_users": 2, "num_connections": 3}

# Update a user's presence data across all their subscribed topics
server.update_presence(conn_id, {"status": "away"})

Presence is tracked at the user level (JWT sub claim). Multiple connections from the same user share a single presence entry. presence_join fires on first connection, presence_leave on last disconnect. In cluster mode, presence state is synchronized across all nodes using CRDT last-write-wins resolution.

Message Recovery

Requires recovery_enabled=True in the constructor.

result = server.subscribe_with_recovery(
    conn_id, ["prices"],
    recover=True,
    epoch=client_epoch,       # From previous session
    offset=client_offset,     # From previous session
)
# {"topics": {"prices": {"epoch": "0000007b", "offset": 456, "recovered": True, "count": 12}}}

The server maintains per-topic ring buffers (power-of-2 capacity, bitmask indexing). When recovery is enabled, every topic broadcast is stamped with tp/e/o (topic, epoch, offset) fields, so clients track their per-topic position from the messages themselves, drop duplicates idempotently by (epoch, offset), and automatically request recovery when they detect an offset gap. On reconnect, the server replays missed messages from the ring buffer. If the gap is too large or the epoch has changed, the client receives a NotRecovered status and should re-subscribe from scratch.

Memory is managed with a global budget (default 256 MB), TTL eviction for idle buffers, and LRU eviction when over budget.

Cluster

# Join a cluster mesh with mTLS
server.connect_cluster(
    peers=["10.0.0.2:9999", "10.0.0.3:9999"],
    tls_ca="/etc/wse/ca.pem",
    tls_cert="/etc/wse/node.pem",
    tls_key="/etc/wse/node.key",
    cluster_port=9999,
)

# With gossip discovery (only seed addresses needed)
server.connect_cluster(
    peers=[],
    seeds=["10.0.0.2:9999"],
    cluster_addr="10.0.0.1:9999",
    cluster_port=9999,
)

server.cluster_connected()       # True if connected to at least one peer
server.cluster_peers_count()     # Number of active peer connections
server.cluster_info()            # List of connected peers (address, instance_id, connected)

Nodes form a full TCP mesh automatically. The cluster protocol uses a custom binary frame format with an 8-byte header, 12 message types, and capability negotiation during handshake. Features:

• Interest-based routing - SUB/UNSUB/RESYNC frames. Messages are only forwarded to peers with matching subscribers.
• Gossip discovery - PeerAnnounce/PeerList frames. New nodes need one seed address to join.
• mTLS - mutual TLS via rustls with P-256 certificates and WebPkiClientVerifier.
• zstd compression - payloads above 256 bytes compressed at level 1, capability-negotiated.
• Circuit breaker - 10 failures to open, 60s reset, 3 half-open probe calls.
• Heartbeat - 5s interval, 15s timeout, dead peer detection.
• Dead letter queue - 1000-entry ring buffer for failed cluster sends.
• Presence sync - PresenceUpdate/PresenceFull frames with CRDT conflict resolution.

Health Monitoring

health = server.health_snapshot()
# {
#     "connections": 150,
#     "inbound_queue_depth": 0,
#     "inbound_dropped": 0,
#     "uptime_secs": 3600.5,
#     "recovery_enabled": True,
#     "recovery_topic_count": 5,
#     "recovery_total_bytes": 1048576,
#     "cluster_connected": True,
#     "cluster_peer_count": 2,
#     "cluster_messages_sent": 50000,
#     "cluster_messages_delivered": 49950,
#     "cluster_messages_dropped": 0,
#     "cluster_bytes_sent": 1048576,
#     "cluster_bytes_received": 1024000,
#     "cluster_reconnect_count": 0,
#     "cluster_unknown_message_types": 0,
#     "cluster_dlq_size": 0,
#     "presence_enabled": True,
#     "presence_topics": 3,
#     "presence_total_users": 25,
# }

Connection Management

server.get_connection_count()        # Lock-free AtomicUsize read
server.get_connections()             # List all connection IDs (snapshot)
server.disconnect(conn_id)           # Force-disconnect a connection
server.drain(close_code=4300, close_reason="shutting down", timeout=10)  # Graceful drain
server.inbound_queue_depth()         # Events waiting to be drained
server.inbound_dropped_count()       # Events dropped due to full queue
server.get_cluster_dlq_entries()     # Retrieve failed cluster messages from dead letter queue

drain() sends a WebSocket Close frame to all connected clients and rejects new connections. The drain wait runs as a separate task, so the command processor stays responsive. Use for zero-downtime deployments and rolling restarts.

---

Security

JWT Authentication

Rust-native HS256 validation during the WebSocket handshake. Zero GIL acquisition, 0.01ms per decode.

Token delivery:

• Browser clients: access_token HTTP-only cookie (set by your login endpoint, attached automatically by the browser)
• Backend clients: Authorization: Bearer <token> header and/or access_token cookie
• API clients: Authorization: Bearer <token> header

Required claims: sub (user ID), exp (expiration). Recommended: iat (issued at). Optional: iss, aud (validated if configured).

End-to-End Encryption

Per-connection session keys via ECDH P-256 key exchange, AES-GCM-256 encryption, HKDF-SHA256 key derivation.

Wire format: E: prefix + 12-byte IV + AES-GCM ciphertext + 16-byte auth tag.

Enable on the client side - the server handles key exchange automatically during the handshake.

Rate Limiting

Per-connection token bucket: 100,000 token capacity, 10,000 tokens/second refill. Clients receive a rate_limit_warning at 20% remaining capacity, and RATE_LIMITED error when exceeded.

Deduplication

send_event() maintains a 50,000-entry AHashSet with FIFO eviction. Duplicate message IDs are dropped before serialization.

Zombie Detection

Server pings every connected client every 25 seconds. Connections with no activity for 60 seconds are force-closed.

Full security documentation: docs/SECURITY.md

---

Wire Protocol

WSE uses a custom wire protocol with categorized JSON messages:

Text frames: JSON with c field for category: "WSE" (system), "S" (snapshot), "U" (update)

Binary frames: C: (zlib compressed), M: (MessagePack), E: (AES-GCM encrypted), raw zlib (0x78 magic byte)

MessagePack transport: opt-in per connection via ?format=msgpack query parameter. Roughly 2x faster serialization and 30% smaller payloads.

Protocol negotiation: client_hello/server_hello handshake with feature discovery, capability advertisement, and version agreement.

Full protocol specification: docs/PROTOCOL.md

---

Compression

Two compression layers:

• Client-facing: zlib for messages above the configurable threshold (default 1024 bytes). Applied automatically by send_event().
• Inter-peer (cluster): zstd level 1 for payloads above 256 bytes. Capability-negotiated during handshake. Decompression output capped at 1 MB (MAX_FRAME_SIZE).

---

Client SDKs

Python

pip install wse-client

Full-featured async and sync client with connection pool, circuit breaker, auto-reconnect, E2E encryption, and msgpack binary transport.

from wse_client import connect

async with connect("ws://localhost:5007/wse", token="<jwt>") as client:
    await client.subscribe(["updates"])
    async for event in client:
        print(event.type, event.payload)

Sync interface:

from wse_client import SyncWSEClient

client = SyncWSEClient("ws://localhost:5007/wse", token="<jwt>")
client.connect()
client.subscribe(["updates"])

@client.on("updates")
def handle(event):
    print(event.payload)

client.run_forever()

Key features: 4 reconnect strategies (exponential, linear, fibonacci, adaptive), connection pool with health scoring and 3 load balancing strategies, circuit breaker, token bucket rate limiter, event sequencer with id dedup plus per-topic (epoch, offset) idempotent dedup and gap recovery, network quality monitoring (latency/jitter/packet loss).

See python-client/ for full source and examples.

TypeScript / React

npm install wse-client

Single React hook (useWSE) for connection lifecycle, subscriptions, and message dispatch.

import { useWSE } from 'wse-client';

function App() {
  const { sendMessage, connectionHealth } = useWSE(
    '<jwt-token>',
    ['updates'],
    { endpoints: ['ws://localhost:5007/wse'] },
  );

  return <div>Status: {connectionHealth}</div>;
}

Key features: offline queue with IndexedDB persistence, adaptive quality management, connection pool with health scoring, E2E encryption (Web Crypto API), message batching, 5 priority levels, Zustand store for external state access.

See ts-client/ for full source and examples.

---

Performance

Benchmarked on AMD EPYC 7502P (32 cores / 64 threads, 128 GB RAM), Ubuntu 24.04.

Mode	Peak Throughput	Connections	Message Loss
Standalone (fan-out)	4.7M deliveries/s	100K	0%
Standalone (inbound JSON)	14.7M msg/s	500K	0%
Standalone (inbound msgpack)	30M msg/s	500K	0%
Cluster (2 nodes, 50/50)	6.6M deliveries/s	500 per node	0%

Sub-millisecond latency. Median 0.38ms with JWT authentication. Connection handshake: 0.53ms median (Rust JWT path).

Detailed results: Benchmarks | Fan-out | Rust Client | Python Client | TS Client

---

Examples

Working examples in the examples/ directory:

Example	Description
standalone_basic.py	Basic server with JWT auth and echo
standalone_broadcast.py	Topic-based pub/sub with broadcasting
standalone_presence.py	Per-topic presence tracking with join/leave events
standalone_recovery.py	Message recovery on reconnect with epoch+offset

---

Documentation

• Architecture - server internals, PyO3 bridge, concurrency model
• Integration Guide - complete setup and API reference
• Wire Protocol - message format specification
• Cluster Protocol - TCP mesh, frame format, gossip, interest routing
• Rust Utilities - priority queues, rate limiters, sequencing, compression, crypto, JWT
• Security - JWT, encryption, mTLS, rate limiting, circuit breaker
• Deployment - production setup, Docker, Kubernetes, cluster configuration
• Migration Guide - upgrading from v1.x to v2.x
• Contributing - development setup and coding standards
• Changelog - version history

---

License

MIT