server.go

package main

import (
	"encoding/json"
	"fmt"
	"math/rand"
	"net/http"
	"strconv"
	"time"
)

type datapoint struct {
	Series    int   `json:"series"`
	Timestamp int64 `json:"timestamp"`
	Value     int   `json:"value"`
}

func main() {
	http.HandleFunc("/", handler)
	if err := http.ListenAndServe(":8080", nil); err != nil {
		panic(err)
	}

}

func handler(w http.ResponseWriter, r *http.Request) {
	flusher, ok := w.(http.Flusher)
	if !ok {
		panic("expected http.ResponseWriter to be an http.Flusher")
	}

	// How many different metrics to generate
	numSeries := 1
	numSeriesParam := r.URL.Query().Get("numSeries")
	if numSeriesParam != "" {
		numSeries, _ = strconv.Atoi(numSeriesParam)
	}

	ticker := time.NewTicker(50 * time.Millisecond)
	for {
		select {
		case t := <-ticker.C:
			for i := 0; i < numSeries; i++ {
				currentPoint := &datapoint{
					Series:    i,
					Timestamp: t.UnixNano() / 1000000, // JS likes ms timestamps
					Value:     rand.Intn(10) + 10*i,
				}
				j, _ := json.Marshal(currentPoint)
				fmt.Fprintf(w, "%s\n", j)
				flusher.Flush() // Trigger "chunked" encoding and send a chunk...
			}
		}
	}

}