Host default login background images in Navidrome's own website

server/backgrounds/handler.go

@@ -0,0 +1,88 @@
+package backgrounds
+
+import (
+	"context"
+	"encoding/base64"
+	"io"
+	"math/rand"
+	"net/http"
+	"net/url"
+	"path"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/navidrome/navidrome/consts"
+	"github.com/navidrome/navidrome/log"
+)
+
+type Handler struct {
+	list []string
+	lock sync.RWMutex
+}
+
+func NewHandler() *Handler {
+	h := &Handler{}
+	go func() {
+		_, _ = h.getImageList(context.Background())
+	}()
+	return h
+}
+
+const ndImageServiceURL = "https://www.navidrome.org"
+
+func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	image, err := h.getRandomImage(r.Context())
+	if err != nil {
+		defaultImage, _ := base64.StdEncoding.DecodeString(consts.DefaultUILoginBackgroundOffline)
+		w.Header().Set("content-type", "image/png")
+		_, _ = w.Write(defaultImage)
+		return
+	}
+
+	http.Redirect(w, r, buildPath(ndImageServiceURL, "backgrounds", image+".jpg"), http.StatusFound)
+}
+
+func (h *Handler) getRandomImage(ctx context.Context) (string, error) {
+	list, err := h.getImageList(ctx)
+	if err != nil {
+		return "", err
+	}
+	return list[rand.Intn(len(list))], nil
+}
+
+func (h *Handler) getImageList(ctx context.Context) ([]string, error) {
+	h.lock.RLock()
+	if len(h.list) > 0 {
+		defer h.lock.RUnlock()
+		return h.list, nil
+	}
+
+	h.lock.RUnlock()
+	h.lock.Lock()
+	defer h.lock.Unlock()
+	start := time.Now()
+
+	c := http.Client{
+		Timeout: 5 * time.Second,
+	}
+
+	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, buildPath(ndImageServiceURL, "images"), nil)
+	resp, err := c.Do(req)
+	if err != nil {
+		log.Warn(ctx, "Could not get list from image service", err)
+		return nil, err
+	}
+	defer resp.Body.Close()
+	body, err := io.ReadAll(resp.Body)
+	h.list = strings.Split(string(body), "\n")
+	log.Debug(ctx, "Loaded images from image service", "total", len(h.list), "elapsed", time.Since(start))
+	return h.list, err
+}
+
+func buildPath(baseURL string, endpoint ...string) string {
+	u, _ := url.Parse(baseURL)
+	p := path.Join(endpoint...)
+	u.Path = path.Join(u.Path, p)
+	return u.String()
+}