initial implementation

main.go

@@ -1,4 +1,88 @@
 package main
 
-func main() {
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"image"
+	"image/color"
+	"image/png"
+	"log"
+	"net/http"
+	"os"
+	"sync"
+	"time"
+)
+
+var port = flag.Int("port", 8000, "port")
+
+type Now struct {
+	lastUpdated time.Time
+	cacheWindow time.Duration
+	buffer      *bytes.Buffer
+	lock        sync.RWMutex
+}
+
+func NewNow(d time.Duration) *Now {
+	return &Now{
+		cacheWindow: d,
+		buffer:      &bytes.Buffer{},
+	}
+}
+
+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()
+}
+
+func (n *Now) Update() {
+	resp, err := http.Get("http://imgs.xkcd.com/comics/now.png")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer resp.Body.Close()
+	src, err := png.Decode(resp.Body)
+	if err != nil {
+		log.Fatal(err)
+	}
+	bounds := src.Bounds()
+	dest := image.NewNRGBA(bounds)
+	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+		for x := bounds.Min.X; x < bounds.Max.X; x++ {
+			r, g, b, _ := src.At(x, y).RGBA()
+			if r == 0xFFFF && g == 0xFFFF && b == 0xFFFF {
+				dest.Set(x, y, color.NRGBA{0, 0, 0, 0})
+			} else {
+				dest.Set(x, y, src.At(x, y))
+			}
+		}
+	}
+	n.lock.Lock()
+	png.Encode(n.buffer, dest)
+	n.lock.Unlock()
+}
+
+func main() {
+	flag.Parse()
+
+	hostname, err := os.Hostname()
+	if err != nil {
+		log.Fatal("problem getting hostname:", err)
+	}
+	log.Printf("serving on: http://%s:%d/", hostname, *port)
+	addr := fmt.Sprintf(":%d", *port)
+
+	http.Handle("/", NewNow(15*time.Minute))
+
+	err = http.ListenAndServe(addr, nil)
+	if err != nil {
+		log.Fatal(err)
+	}
 }