A lightweight WebSocket gateway for delivering real-time messages to players, with server-side publishing, offline queueing, rate limiting, and Prometheus metrics.

• WebSocket connections per player (multiple connections supported)
• Token-based authentication (players & servers)
• Offline message queue with TTL
• Per-server-token rate limiting
• Broadcast and targeted messaging
• Automatic token revalidation
• Prometheus metrics endpoint
• Graceful shutdown

• Players connect via WebSocket (/ws) using player tokens
• Servers publish messages via HTTP (/publish, /broadcast) using server tokens
• Tokens are validated against a SQL database
• Messages are delivered immediately or queued if the player is offline

• GET /ws?token=PLAYER_TOKEN

• POST /publish
• Header: Authorization: Bearer SERVER_TOKEN
• Body:

{
  "player_id": "player123",
  "event": "event_name",
  "payload": { "any": "json" }
}

• POST /broadcast
• Header: Authorization: Bearer SERVER_TOKEN
• Body (all players):

{
  "event": "event_name",
  "payload": { "any": "json" }
}

• Body (single player):

{
  "player_id": "player123",
  "event": "event_name",
  "payload": { "any": "json" }
}

• GET /metrics (Prometheus format)

• -addr – HTTP server address (default :8080)
• -db – Database driver (sqlite or mysql)
• -dsn – Database DSN
• -origins – Comma-separated allowed WS origins
• -max-conns – Max WS connections per player
• -max-queued – Max offline queued messages per player
• -offline-ttl – Offline message TTL
• -rate-limit – Messages per rate period per server token
• -rate-period – Rate limit window
• -revalidate-period – Token revalidation interval

Required table:

CREATE TABLE IF NOT EXISTS ws_token (
    token       VARBINARY(32) NOT NULL PRIMARY KEY,
    player_id   INTEGER(10) UNSIGNED DEFAULT NULL,
    subject_id  VARBINARY(32) NOT NULL,
    is_server   BOOLEAN NOT NULL,
    expires_at  DATETIME(6) NOT NULL
);
CREATE INDEX idx_ws_token_server_exp ON ws_token (is_server, expires_at);

• player_id is used for player tokens
• subject_id is used for server tokens

• ws_active_connections
• ws_messages_published_total
• ws_messages_delivered_total

go build
./ws-gateway \
  -db sqlite \
  -dsn file:ws_tokens.db?cache=shared

./ws-gateway \
  -db mysql \
  -dsn "root@/echoCTF"

• Designed to be stateless except for in-memory queues
• Offline messages are best-effort (not persisted)
• Suitable for game backends, notification systems, and real-time apps