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

Uses delaneyj/toolbelt/embeddednats to run NATS inside the same binary - 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.

How Embedded NATS Works

// Start embedded NATS server (JetStream enabled by default)
ns, err := embeddednats.New(ctx,
    embeddednats.WithDirectory("./data/nats"),
)
ns.WaitForServer()

// Get client connection to embedded server
nc, err := ns.Client()

Data is persisted to ./data/nats/ for JetStream durability.

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:

js.AddStream(&nats.StreamConfig{
    Name:      "CHAT",
    Subjects:  []string{"chat.>"},
    MaxMsgs:   1000,  // Keep last 1000 messages
    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:

embeddednats.New() starts the server
nc.Subscribe(subject, handler) for receiving
nc.Publish(subject, data) for sending
NATS handles delivery, no polling

Next Steps

If this pattern proves useful, it could be promoted to a Via plugin:

// Hypothetical future API
v.Config(via.WithEmbeddedNATS("./data/nats"))

// In page init
c.Subscribe("events.user.*", func(data []byte) {
    c.Sync()
})

c.Publish("events.user.login", userData)