go-sseutil

Server-Sent Events (SSE) utilities for Go. Server broker and client, zero dependencies

Installation

go get github.com/philiprehberger/go-sseutil

Usage

Server (Broker)

package main

import (
	"net/http"
	"time"

	"github.com/philiprehberger/go-sseutil"
)

func main() {
	broker := sseutil.NewBroker(sseutil.WithKeepAlive(15 * time.Second))

	http.Handle("/events", broker.Handler())

	go func() {
		for {
			broker.Broadcast(sseutil.Event{
				Event: "tick",
				Data:  "hello",
			})
			time.Sleep(1 * time.Second)
		}
	}()

	http.ListenAndServe(":8080", nil)
}

Client

package main

import (
	"context"
	"fmt"

	"github.com/philiprehberger/go-sseutil"
)

func main() {
	ctx := context.Background()
	stream, err := sseutil.Connect(ctx, "http://localhost:8080/events")
	if err != nil {
		panic(err)
	}
	defer stream.Close()

	for event := range stream.Events() {
		fmt.Printf("Event: %s, Data: %s\n", event.Event, event.Data)
	}
}

JSON Events

// Send JSON to a specific client.
type Message struct {
	Text string `json:"text"`
	From string `json:"from"`
}

err := broker.SendJSON("client-1", "chat", Message{Text: "hi", From: "alice"})
// Sends: event: chat\ndata: {"text":"hi","from":"alice"}\n\n

// Broadcast JSON to all clients.
err = broker.BroadcastJSON("update", map[string]any{"status": "ok"})

Topics

// Subscribe a client to topics.
broker.Subscribe("client-1", "sports", "news")

// Publish to a topic — only subscribed clients receive the event.
broker.PublishTopic("sports", sseutil.Event{Event: "score", Data: "3-2"})

Lifecycle Hooks

broker.OnConnect(func(clientID string) {
	log.Printf("client connected: %s", clientID)
})

broker.OnDisconnect(func(clientID string) {
	log.Printf("client disconnected: %s", clientID)
})

Event Builder

event := sseutil.Event{
	ID:    "1",
	Event: "update",
	Data:  "payload data",
	Retry: 5000,
}

fmt.Print(event.String())
// Output:
// id: 1
// event: update
// data: payload data
// retry: 5000

API

Type / Function	Description
Event	SSE event with ID, Event, Data, and Retry fields
Event.Bytes()	Encode event to SSE wire format
Event.String()	String representation of SSE event
Broker	Manages SSE client connections
NewBroker(opts...)	Create a new broker with options
WithKeepAlive(d)	Set keep-alive interval (default 30s)
Broker.Handler()	HTTP handler for SSE endpoint
Broker.Broadcast(e)	Send event to all clients
Broker.Send(id, e)	Send event to a specific client
Broker.SendJSON(id, event, data)	Marshal data to JSON and send to a client
Broker.BroadcastJSON(event, data)	Marshal data to JSON and broadcast to all
Broker.Subscribe(id, topics...)	Subscribe a client to named topics
Broker.PublishTopic(topic, e)	Send event to all clients subscribed to topic
Broker.OnConnect(fn)	Set callback for client connections
Broker.OnDisconnect(fn)	Set callback for client disconnections
Broker.ClientCount()	Number of connected clients
Connect(ctx, url)	Connect to an SSE endpoint
Stream.Events()	Channel of received events
Stream.Close()	Close the connection
Stream.LastEventID()	Last received event ID

Development

go test ./...
go vet ./...

Support

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License

MIT