Add discTitles to OpenSubsonic responses

server/subsonic/browsing.go

@@ -423,7 +423,8 @@ func (api *Router) buildAlbum(ctx context.Context, album *model.Album, mfs model
 	}
 	dir.Year = int32(album.MaxYear)
 	dir.Genre = album.Genre
-	dir.Genres = itemGenresFromGenres(album.Genres)
+	dir.Genres = buildItemGenres(album.Genres)
+	dir.DiscTitles = buildDiscSubtitles(ctx, *album)
 	dir.UserRating = int32(album.Rating)
 	if !album.CreatedAt.IsZero() {
 		dir.Created = &album.CreatedAt

server/subsonic/helpers.go

@@ -5,9 +5,12 @@ import (
 	"fmt"
 	"mime"
 	"net/http"
+	"sort"
+	"strconv"
 	"strings"
 
 	"github.com/navidrome/navidrome/consts"
+	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/model/request"
 	"github.com/navidrome/navidrome/server/public"
@@ -153,7 +156,7 @@ func childFromMediaFile(ctx context.Context, mf model.MediaFile) responses.Child
 	child.Year = int32(mf.Year)
 	child.Artist = mf.Artist
 	child.Genre = mf.Genre
-	child.Genres = itemGenresFromGenres(mf.Genres)
+	child.Genres = buildItemGenres(mf.Genres)
 	child.Track = int32(mf.TrackNumber)
 	child.Duration = int32(mf.Duration)
 	child.Size = mf.Size
@@ -231,7 +234,7 @@ func childFromAlbum(_ context.Context, al model.Album) responses.Child {
 	child.Artist = al.AlbumArtist
 	child.Year = int32(al.MaxYear)
 	child.Genre = al.Genre
-	child.Genres = itemGenresFromGenres(al.Genres)
+	child.Genres = buildItemGenres(al.Genres)
 	child.CoverArt = al.CoverArtID().String()
 	child.Created = &al.CreatedAt
 	child.Parent = al.AlbumArtistID
@@ -260,10 +263,29 @@ func childrenFromAlbums(ctx context.Context, als model.Albums) []responses.Child
 	return children
 }
 
-func itemGenresFromGenres(genres model.Genres) []responses.ItemGenre {
+func buildItemGenres(genres model.Genres) []responses.ItemGenre {
 	itemGenres := make([]responses.ItemGenre, len(genres))
 	for i, g := range genres {
 		itemGenres[i] = responses.ItemGenre{Name: g.Name}
 	}
 	return itemGenres
 }
+
+func buildDiscSubtitles(ctx context.Context, a model.Album) responses.DiscTitles {
+	if len(a.Discs) == 0 {
+		return nil
+	}
+	discTitles := responses.DiscTitles{}
+	for num, title := range a.Discs {
+		n, err := strconv.Atoi(num)
+		if err != nil {
+			log.Warn(ctx, "Invalid disc number", "num", num, "title", title, "album", a.Name, "artist", a.AlbumArtist, err)
+			continue
+		}
+		discTitles = append(discTitles, responses.DiscTitle{Disc: n, Title: title})
+	}
+	sort.Slice(discTitles, func(i, j int) bool {
+		return discTitles[i].Disc < discTitles[j].Disc
+	})
+	return discTitles
+}

server/subsonic/helpers_test.go

@@ -1,7 +1,10 @@
 package subsonic
 
 import (
+	"context"
+
 	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/server/subsonic/responses"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -33,4 +36,38 @@ var _ = Describe("helpers", func() {
 			Expect(mapSlashToDash("AC/DC")).To(Equal("AC_DC"))
 		})
 	})
+
+	Describe("buildDiscTitles", func() {
+		It("should return nil when album has no discs", func() {
+			album := model.Album{}
+			Expect(buildDiscSubtitles(context.Background(), album)).To(BeNil())
+		})
+
+		It("should return correct disc titles when album has discs with valid disc numbers", func() {
+			album := model.Album{
+				Discs: map[string]string{
+					"1": "Disc 1",
+					"2": "Disc 2",
+				},
+			}
+			expected := responses.DiscTitles{
+				{Disc: 1, Title: "Disc 1"},
+				{Disc: 2, Title: "Disc 2"},
+			}
+			Expect(buildDiscSubtitles(context.Background(), album)).To(Equal(expected))
+		})
+
+		It("should skip discs with invalid disc numbers", func() {
+			album := model.Album{
+				Discs: map[string]string{
+					"1":   "Disc 1",
+					"two": "Disc 2",
+				},
+			}
+			expected := responses.DiscTitles{
+				{Disc: 1, Title: "Disc 1"},
+			}
+			Expect(buildDiscSubtitles(context.Background(), album)).To(Equal(expected))
+		})
+	})
 })

server/subsonic/responses/.snapshots/Responses AlbumWithSongsID3 with data should match .JSON

@@ -21,6 +21,16 @@
     "musicBrainzId": "1234",
     "isCompilation": true,
     "sortName": "sorted album",
+    "discTitles": [
+      {
+        "disc": 1,
+        "title": "disc 1"
+      },
+      {
+        "disc": 2,
+        "title": "disc 2"
+      }
+    ],
     "song": [
       {
         "id": "1",

server/subsonic/responses/.snapshots/Responses AlbumWithSongsID3 with data should match .XML

@@ -2,6 +2,8 @@
   <album id="1" name="album" artist="artist" genre="rock" userRating="0" musicBrainzId="1234" isCompilation="true" sortName="sorted album">
     <genres name="rock"></genres>
     <genres name="progressive"></genres>
+    <discTitles disc="1" title="disc 1"></discTitles>
+    <discTitles disc="2" title="disc 2"></discTitles>
     <song id="1" isDir="true" title="title" album="album" artist="artist" track="1" year="1985" genre="Rock" coverArt="1" size="8421341" contentType="audio/flac" suffix="flac" starred="2016-03-02T20:30:00Z" transcodedContentType="audio/mpeg" transcodedSuffix="mp3" duration="146" bitRate="320" isVideo="false" bpm="127" comment="a comment" sortName="sorted song" mediaType="song" musicBrainzId="4321">
       <genres name="rock"></genres>
       <genres name="progressive"></genres>

server/subsonic/responses/.snapshots/Responses AlbumWithSongsID3 without data should match .JSON

@@ -11,6 +11,7 @@
     "genres": [],
     "musicBrainzId": "",
     "isCompilation": false,
-    "sortName": ""
+    "sortName": "",
+    "discTitles": []
   }
 }

server/subsonic/responses/responses.go

@@ -224,6 +224,7 @@ type AlbumID3 struct {
 	MusicBrainzId string     `xml:"musicBrainzId,attr"    json:"musicBrainzId"`
 	IsCompilation bool       `xml:"isCompilation,attr"    json:"isCompilation"`
 	SortName      string     `xml:"sortName,attr"         json:"sortName"`
+	DiscTitles    DiscTitles `xml:"discTitles"            json:"discTitles"`
 }
 
 type ArtistWithAlbumsID3 struct {
@@ -459,12 +460,7 @@ type ItemGenre struct {
 type ItemGenres []ItemGenre
 
 func (i ItemGenres) MarshalJSON() ([]byte, error) {
-	if len(i) == 0 {
-		return json.Marshal([]ItemGenre{})
-	}
-	type Alias []ItemGenre
-	a := (Alias)(i)
-	return json.Marshal(a)
+	return marshalJSONArray(i)
 }
 
 type ReplayGain struct {
@@ -475,3 +471,24 @@ type ReplayGain struct {
 	BaseGain     float64 `xml:"baseGain,omitempty,attr"     json:"baseGain,omitempty"`
 	FallbackGain float64 `xml:"fallbackGain,omitempty,attr" json:"fallbackGain,omitempty"`
 }
+
+type DiscTitle struct {
+	Disc  int    `xml:"disc,attr,omitempty" json:"disc,omitempty"`
+	Title string `xml:"title,attr,omitempty" json:"title,omitempty"`
+}
+
+type DiscTitles []DiscTitle
+
+func (d DiscTitles) MarshalJSON() ([]byte, error) {
+	return marshalJSONArray(d)
+}
+
+// marshalJSONArray marshals a slice of any type to JSON. If the slice is empty, it is marshalled as an
+// empty array instead of null.
+func marshalJSONArray[T any](v []T) ([]byte, error) {
+	if len(v) == 0 {
+		return json.Marshal([]T{})
+	}
+	a := v
+	return json.Marshal(a)
+}

server/subsonic/responses/responses_test.go

@@ -176,6 +176,7 @@ var _ = Describe("Responses", func() {
 					Id: "1", Name: "album", Artist: "artist", Genre: "rock",
 					Genres:        []ItemGenre{{Name: "rock"}, {Name: "progressive"}},
 					MusicBrainzId: "1234", IsCompilation: true, SortName: "sorted album",
+					DiscTitles: DiscTitles{{Disc: 1, Title: "disc 1"}, {Disc: 2, Title: "disc 2"}},
 				}
 				t := time.Date(2016, 03, 2, 20, 30, 0, 0, time.UTC)
 				songs := []Child{{