fix(jellyfin): let net/http sniff image Content-Type instead of forcing jpeg

server/jellyfin/images.go

@@ -2,11 +2,13 @@ package jellyfin
 
 import (
 	"context"
+	"errors"
 	"io"
 	"net/http"
 	"strconv"
 
 	"github.com/go-chi/chi/v5"
+	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
 )
 
@@ -17,12 +19,17 @@ func (api *Router) getItemImage(w http.ResponseWriter, r *http.Request) {
 
 	artID := api.resolveArtworkID(ctx, itemId)
 	reader, _, err := api.artwork.GetOrPlaceholder(ctx, artID, size, false)
-	if err != nil {
+	switch {
+	case errors.Is(err, context.Canceled):
+		return
+	case err != nil:
+		log.Warn(ctx, "Error retrieving artwork", "id", itemId, err)
 		http.Error(w, "Not Found", http.StatusNotFound)
 		return
 	}
 	defer reader.Close()
-	w.Header().Set("Content-Type", "image/jpeg")
+	// Content-Type is left unset so net/http sniffs it from the first bytes written
+	// (placeholders are WebP; unresized covers can be PNG/WebP/etc, not always JPEG).
 	_, _ = io.Copy(w, reader)
 }
 

server/jellyfin/images_test.go

@@ -1,11 +1,11 @@
 package jellyfin
 
 import (
+	"bytes"
 	"context"
 	"io"
 	"net/http"
 	"net/http/httptest"
-	"strings"
 	"time"
 
 	"github.com/go-chi/chi/v5"
@@ -19,11 +19,26 @@ import (
 type fakeArtwork struct {
 	artwork.Artwork
 	recvId string
+	data   []byte
 }
 
 func (f *fakeArtwork) GetOrPlaceholder(ctx context.Context, id string, size int, square bool) (io.ReadCloser, time.Time, error) {
 	f.recvId = id
-	return io.NopCloser(strings.NewReader("IMG")), time.Now(), nil
+	data := f.data
+	if data == nil {
+		data = []byte("IMG")
+	}
+	return io.NopCloser(bytes.NewReader(data)), time.Now(), nil
+}
+
+func newImageRequest(itemId string) (*httptest.ResponseRecorder, *http.Request) {
+	w := httptest.NewRecorder()
+	r := httptest.NewRequest("GET", "/Items/"+itemId+"/Images/Primary", nil)
+	rctx := chi.NewRouteContext()
+	rctx.URLParams.Add("itemId", itemId)
+	rctx.URLParams.Add("type", "Primary")
+	r = r.WithContext(context.WithValue(r.Context(), chi.RouteCtxKey, rctx))
+	return w, r
 }
 
 var _ = Describe("Images", func() {
@@ -33,16 +48,26 @@ var _ = Describe("Images", func() {
 		fa := &fakeArtwork{}
 		api := &Router{ds: ds, artwork: fa}
 
-		w := httptest.NewRecorder()
-		r := httptest.NewRequest("GET", "/Items/a1/Images/Primary", nil)
-		rctx := chi.NewRouteContext()
-		rctx.URLParams.Add("itemId", "a1")
-		rctx.URLParams.Add("type", "Primary")
-		r = r.WithContext(context.WithValue(r.Context(), chi.RouteCtxKey, rctx))
+		w, r := newImageRequest("a1")
 		api.getItemImage(w, r)
 
 		Expect(w.Code).To(Equal(http.StatusOK))
 		Expect(w.Body.String()).To(Equal("IMG"))
 		Expect(fa.recvId).To(ContainSubstring("a1"))
 	})
+
+	It("sniffs the Content-Type instead of hardcoding it", func() {
+		ds := &tests.MockDataStore{}
+		ds.Album(context.Background()).(*tests.MockAlbumRepo).SetData(model.Albums{{ID: "a1", Name: "One"}})
+
+		png := append([]byte{0x89, 'P', 'N', 'G', '\r', '\n', 0x1a, '\n'}, make([]byte, 512)...)
+		fa := &fakeArtwork{data: png}
+		api := &Router{ds: ds, artwork: fa}
+
+		w, r := newImageRequest("a1")
+		api.getItemImage(w, r)
+
+		Expect(w.Code).To(Equal(http.StatusOK))
+		Expect(w.Header().Get("Content-Type")).To(Equal("image/png"))
+	})
 })