Browse Source

just fetch periodically

master
Stephen McQuay 4 years ago
parent
commit
ae974083aa
Signed by: sm
GPG Key ID: 4E4B72F479BA3CE5
  1. 64
      main.go

64
main.go

@ -2,6 +2,7 @@ package main
import (
"bytes"
"context"
"flag"
"fmt"
"image"
@ -12,45 +13,55 @@ import (
"os"
"sync"
"time"
"github.com/pkg/errors"
)
var port = flag.Int("port", 8000, "port")
var freq = flag.Duration("d", 15*time.Second, "refresh interval")
type Now struct {
lastUpdated time.Time
cacheWindow time.Duration
buffer *bytes.Buffer
lock sync.RWMutex
sync.RWMutex
cache *bytes.Buffer
}
func NewNow(d time.Duration) *Now {
return &Now{
cacheWindow: d,
buffer: &bytes.Buffer{},
func NewNow(ctx context.Context, d time.Duration) *Now {
n := &Now{
cache: &bytes.Buffer{},
}
n.Update()
go func() {
t := time.NewTicker(d)
for {
select {
case <-t.C:
n.Update()
case <-ctx.Done():
return
}
}
}()
return n
}
func (n *Now) ServeHTTP(w http.ResponseWriter, req *http.Request) {
log.Printf("%+v", req.RemoteAddr)
if time.Now().After(n.lastUpdated.Add(n.cacheWindow)) {
log.Println("updating image")
n.Update()
n.lastUpdated = time.Now()
}
n.lock.RLock()
w.Write(n.buffer.Bytes())
n.lock.RUnlock()
n.RLock()
w.Write(n.cache.Bytes())
n.RUnlock()
}
func (n *Now) Update() {
func (n *Now) Update() error {
resp, err := http.Get("http://imgs.xkcd.com/comics/now.png")
if err != nil {
log.Fatal(err)
return errors.Wrap(err, "get")
}
defer resp.Body.Close()
src, err := png.Decode(resp.Body)
if err != nil {
log.Fatal(err)
return errors.Wrap(err, "png decode")
}
bounds := src.Bounds()
dest := image.NewNRGBA(bounds)
@ -64,9 +75,12 @@ func (n *Now) Update() {
}
}
}
n.lock.Lock()
png.Encode(n.buffer, dest)
n.lock.Unlock()
n.Lock()
png.Encode(n.cache, dest)
n.Unlock()
return nil
}
func main() {
@ -79,7 +93,9 @@ func main() {
log.Printf("serving on: http://%s:%d/", hostname, *port)
addr := fmt.Sprintf(":%d", *port)
http.Handle("/", NewNow(15*time.Minute))
n := NewNow(context.Background(), *freq)
http.Handle("/", n)
err = http.ListenAndServe(addr, nil)
if err != nil {

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