PubNub MCP Server

# Understanding PubNub's Publish/Subscribe (Pub/Sub) Model Publish/Subscribe, often abbreviated as Pub/Sub, is the fundamental messaging pattern that powers PubNub's real-time communication. It's a highly scalable and decoupled way for different parts of an application (clients, servers, devices) to exchange messages. ## Core Concepts 1. **Publisher:** * A client or server process that **sends (publishes)** messages. * Publishers are not concerned with who, if anyone, is currently listening. 2. **Subscriber:** * A client or server process that expresses interest in messages by **subscribing** to one or more named "channels." * Subscribers receive messages that are published to the channels they are subscribed to. * Subscribers don't need to know who the publishers are. 3. **Channel:** * A named conduit or topic through which messages are routed. Publishers send messages *to* a channel, and subscribers listen *on* a channel. * Channels are created dynamically by simply using their names. 4. **Message:** * The actual data being transmitted. In PubNub, messages are typically JSON objects, but can also be strings or other serializable data. The maximum size is 32KB. 5. **PubNub Network (The "Broker"):** * PubNub's global Data Stream Network acts as the intermediary or "broker." * It receives messages from publishers and fans them out in real-time to all active subscribers on the relevant channels. * It handles the complexities of connection management, scalability, reliability, and security. ## Key Characteristics of PubNub's Pub/Sub * **Decoupling:** * **Space Decoupling:** Publishers and subscribers do not need to know each other's network location or identity. They only need to agree on the channel name. * **Time Decoupling:** Publishers can send messages even if no subscribers are currently online. Subscribers can join a channel at any time and start receiving new messages. (With Message Persistence, they can also retrieve past messages). * **Synchronization Decoupling:** Publishers and subscribers can operate asynchronously. Publishers don't block waiting for subscribers to receive messages. * **Scalability:** The Pub/Sub model is inherently scalable. PubNub's network can handle millions of concurrent publishers and subscribers across countless channels. * **Real-Time Delivery:** PubNub is optimized for low-latency message delivery, typically aiming for sub-100ms worldwide. * **Many-to-Many Communication:** * One publisher can send messages to many subscribers (fan-out/broadcast). * Many publishers can send messages to a single channel (fan-in). * Many publishers can send to many subscribers. ## How PubNub's Publish/Subscribe Works (Simplified Flow) 1. **Publish Request:** * Client B (Publisher) uses the PubNub SDK to send a publish request with the message payload to a specific channel (e.g., "Channel_X"). 2. **Broker Ingestion & Acknowledgement:** * The PubNub network receives the publish request from Client B, authenticates and authorizes it. * It stores the message in its in-memory buffer (and persists it if Message Persistence is enabled). * The network returns a success or error response to Client B's SDK. 3. **Message Routing & Delivery:** * The PubNub network receives the message from Client B. * It identifies all currently active subscribers for "Channel_X" (including Client A). * The PubNub network pushes the message down the open persistent connection to Client A (and any other subscribers). * Client A's SDK receives the message and triggers a callback or event in Client A's application code. ## What Happens to Messages Published When No One is Listening? * **No Different from Active Listeners:** The act of publishing is independent of whether subscribers are present. The message is sent to the PubNub network regardless. * **Short-Term Cache:** PubNub caches the most recent messages (e.g., last 100, or up to ~20 minutes) in a channel's in-memory buffer. If a client subscribes (or reconnects) within this window and is configured to "catch up" (often the default SDK behavior using timetokens), it will receive these cached messages. * **Message Persistence (Add-on):** If the Message Persistence feature is enabled for your keyset, all messages published to channels are stored for your configured retention period (e.g., 1 day, 30 days, unlimited). Clients can then use the History API to retrieve messages published while they were offline, even for extended periods.