go 31 lines · 7 steps

Streaming server-sent events in Gin

A Gin handler pushes a metrics snapshot to the browser every second over an SSE connection until the client disconnects.

Explained by highlit
Gin Intermediate server-sent-events streaming channels context-cancellation tickers
1func StreamMetrics(c *gin.Context) {
2 clientGone := c.Request.Context().Done()
3 ticker := time.NewTicker(time.Second)
4 defer ticker.Stop()
5 
6 c.Writer.Header().Set("Content-Type", "text/event-stream")
7 c.Writer.Header().Set("Cache-Control", "no-cache")
8 c.Writer.Header().Set("Connection", "keep-alive")
9 
10 c.Stream(func(w io.Writer) bool {
11 select {
12 case <-clientGone:
13 return false
14 case t := <-ticker.C:
15 snapshot, err := collectSnapshot()
16 if err != nil {
17 c.SSEvent("error", gin.H{"message": err.Error()})
18 return true
19 }
20 
21 c.SSEvent("metrics", gin.H{
22 "timestamp": t.UTC().Format(time.RFC3339),
23 "cpu": snapshot.CPUPercent,
24 "memory": snapshot.MemoryBytes,
25 "goroutines": snapshot.Goroutines,
26 "connections": snapshot.ActiveConns,
27 })
28 return true
29 }
30 })
31}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Watching the request context's Done channel lets a streaming handler stop cleanly the moment the client disconnects.
  2. 2A ticker plus a select loop turns a single HTTP response into a steady stream of timed updates.
  3. 3Returning true keeps Gin's Stream loop alive while false ends it, so the boolean is your exit switch.

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