ryan/via

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Ryan Hamamura 60009124c9

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feat: add declarative Options.Streams for automatic JetStream stream creation

Streams listed in Options.Streams are created by Start() when the
embedded NATS server initializes, replacing manual EnsureStream calls
during setup. Migrates nats-chatroom and pubsub-crud examples.

2026-02-19 12:24:44 -10:00

3.3 KiB

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NATS Chatroom Example (Embedded)

A chatroom built with Via and an embedded NATS server, demonstrating pub/sub messaging as an alternative to the custom Rooms implementation in ../chatroom.

Via includes an embedded NATS server that starts automatically — no external server required.

Key Differences from Original Chatroom

Aspect	Original (`../chatroom`)	This Example
Pub/sub	Custom `Rooms` struct (~160 lines)	NATS subjects
Member tracking	Manual `map[TU]Syncable`	NATS handles subscribers
Publish timing	Ticker every 100ms + dirty flag	Instant delivery
Durability	None (in-memory)	JetStream persists to disk
Multi-instance	Not supported	Works across server instances
External deps	None	None (NATS embedded in binary)

Run the Example

go run ./internal/examples/nats-chatroom

That's it. No separate NATS server needed.

Open multiple browser tabs at http://localhost:7331 to see messages broadcast across all clients.

Architecture

┌─────────────────────────────────────────────────────────┐
│                    Single Binary                         │
│                                                          │
│  Browser A          Embedded NATS         Browser B      │
│      │                   │                    │          │
│      │-- Via Action ---> │                    │          │
│      │   (Send msg)      │                    │          │
│      │                   │                    │          │
│      │              nc.Publish()              │          │
│      │              "chat.room.Go"            │          │
│      │                   │                    │          │
│      │<-- Subscribe -----|---- Subscribe --->│          │
│      │    callback       │    callback        │          │
│      │                   │                    │          │
│      │-- c.Sync() ------>│<--- c.Sync() -----|          │
│      │   (SSE)           │     (SSE)          │          │
│                                                          │
└─────────────────────────────────────────────────────────┘

JetStream Durability

Messages persist to disk via JetStream. Streams are declared in Options.Streams and created automatically when v.Start() initializes the embedded NATS server:

v.Config(via.Options{
    Streams: []via.StreamConfig{{
        Name:     "CHAT",
        Subjects: []string{"chat.>"},
        MaxMsgs:  1000,
        MaxAge:   24 * time.Hour,
    }},
})

Stop and restart the app - chat history survives.

Code Comparison

Original chatroom - 160+ lines of custom pub/sub:

Rooms struct with named rooms
Room with member tracking, mutex, dirty flag
Ticker-based publish loop
Manual join/leave channels

This example - ~60 lines of NATS integration:

via.Subscribe(c, subject, handler) for receiving
via.Publish(c, subject, data) for sending
Streams declared in Options — NATS handles delivery, no polling

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