Server-Sent Events

package main

import (
  "log"
  "net/http"
  "strconv"
  "time"

  "github.com/0mjs/zinc"
)

func main() {
  app := zinc.New()

  app.Get("/events", func(c *zinc.Context) error {
    flusher, ok := c.Writer().(http.Flusher)
    if !ok {
      return zinc.ErrInternalServerError.WithMessage("streaming is not supported")
    }

    ticker := time.NewTicker(time.Second)
    defer ticker.Stop()

    for {
      select {
      case now := <-ticker.C:
        if err := c.SSE(zinc.SSEvent{
          Event: "clock",
          ID:    strconv.FormatInt(now.Unix(), 10),
          Data:  zinc.Map{"time": now.UTC()},
        }); err != nil {
          return err
        }
        flusher.Flush()
      case <-c.Context().Done():
        return nil
      }
    }
  })

  log.Fatal(app.Listen(":8080"))
}

Browser client:

const events = new EventSource("/events");
events.addEventListener("clock", (event) => {
  console.log(JSON.parse(event.data));
});

c.SSE sets the event-stream headers and writes one event. Flush after every event so it reaches the client immediately. The handler exits when the client disconnects and the request context is cancelled.