feat: implement multi-library support for GetAlbumList and GetAlbumList2 endpoints

- Enhanced selectedMusicFolderIds helper to validate and filter library IDs
- Added ApplyLibraryFilter function in filter/filters.go for library filtering
- Updated getAlbumList to support musicFolderId parameter filtering
- Added comprehensive tests for multi-library functionality
- Supports single and multiple musicFolderId values
- Falls back to all accessible libraries when no musicFolderId provided
- Validates library access permissions for user security

server/subsonic/album_lists.go

@@ -61,6 +61,10 @@ func (api *Router) getAlbumList(r *http.Request) (model.Albums, int64, error) {
 		return nil, 0, newError(responses.ErrorGeneric, "type '%s' not implemented", typ)
 	}
 
+	// Get optional library IDs from musicFolderId parameter
+	musicFolderIds, _ := selectedMusicFolderIds(r, false)
+	opts = filter.ApplyLibraryFilter(opts, musicFolderIds)
+
 	opts.Offset = p.IntOr("offset", 0)
 	opts.Max = min(p.IntOr("size", 10), 500)
 	albums, err := api.ds.Album(r.Context()).GetAll(opts)

server/subsonic/album_lists_test.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/model/request"
 	"github.com/navidrome/navidrome/tests"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -63,6 +64,74 @@ var _ = Describe("Album Lists", func() {
 			errors.As(err, &subErr)
 			Expect(subErr.code).To(Equal(responses.ErrorGeneric))
 		})
+
+		Context("with musicFolderId parameter", func() {
+			var user model.User
+			var ctx context.Context
+
+			BeforeEach(func() {
+				user = model.User{
+					ID: "test-user",
+					Libraries: []model.Library{
+						{ID: 1, Name: "Library 1"},
+						{ID: 2, Name: "Library 2"},
+						{ID: 3, Name: "Library 3"},
+					},
+				}
+				ctx = request.WithUser(context.Background(), user)
+			})
+
+			It("should filter albums by specific library when musicFolderId is provided", func() {
+				r := newGetRequest("type=newest", "musicFolderId=1")
+				r = r.WithContext(ctx)
+				mockRepo.SetData(model.Albums{
+					{ID: "1"}, {ID: "2"},
+				})
+
+				resp, err := router.GetAlbumList(w, r)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(resp.AlbumList.Album).To(HaveLen(2))
+				// Verify that library filter was applied
+				query, args, _ := mockRepo.Options.Filters.ToSql()
+				Expect(query).To(ContainSubstring("library_id IN (?)"))
+				Expect(args).To(ContainElement(1))
+			})
+
+			It("should filter albums by multiple libraries when multiple musicFolderId are provided", func() {
+				r := newGetRequest("type=newest", "musicFolderId=1", "musicFolderId=2")
+				r = r.WithContext(ctx)
+				mockRepo.SetData(model.Albums{
+					{ID: "1"}, {ID: "2"},
+				})
+
+				resp, err := router.GetAlbumList(w, r)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(resp.AlbumList.Album).To(HaveLen(2))
+				// Verify that library filter was applied
+				query, args, _ := mockRepo.Options.Filters.ToSql()
+				Expect(query).To(ContainSubstring("library_id IN (?,?)"))
+				Expect(args).To(ContainElements(1, 2))
+			})
+
+			It("should return all accessible albums when no musicFolderId is provided", func() {
+				r := newGetRequest("type=newest")
+				r = r.WithContext(ctx)
+				mockRepo.SetData(model.Albums{
+					{ID: "1"}, {ID: "2"},
+				})
+
+				resp, err := router.GetAlbumList(w, r)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(resp.AlbumList.Album).To(HaveLen(2))
+				// Verify that library filter was applied
+				query, args, _ := mockRepo.Options.Filters.ToSql()
+				Expect(query).To(ContainSubstring("library_id IN (?,?,?)"))
+				Expect(args).To(ContainElements(1, 2, 3))
+			})
+		})
 	})
 
 	Describe("GetAlbumList2", func() {
@@ -100,5 +169,65 @@ var _ = Describe("Album Lists", func() {
 			errors.As(err, &subErr)
 			Expect(subErr.code).To(Equal(responses.ErrorGeneric))
 		})
+
+		Context("with musicFolderId parameter", func() {
+			var user model.User
+			var ctx context.Context
+
+			BeforeEach(func() {
+				user = model.User{
+					ID: "test-user",
+					Libraries: []model.Library{
+						{ID: 1, Name: "Library 1"},
+						{ID: 2, Name: "Library 2"},
+						{ID: 3, Name: "Library 3"},
+					},
+				}
+				ctx = request.WithUser(context.Background(), user)
+			})
+
+			It("should filter albums by specific library when musicFolderId is provided", func() {
+				r := newGetRequest("type=newest", "musicFolderId=1")
+				r = r.WithContext(ctx)
+				mockRepo.SetData(model.Albums{
+					{ID: "1"}, {ID: "2"},
+				})
+
+				resp, err := router.GetAlbumList2(w, r)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(resp.AlbumList2.Album).To(HaveLen(2))
+				// Verify that library filter was applied
+				Expect(mockRepo.Options.Filters).ToNot(BeNil())
+			})
+
+			It("should filter albums by multiple libraries when multiple musicFolderId are provided", func() {
+				r := newGetRequest("type=newest", "musicFolderId=1", "musicFolderId=2")
+				r = r.WithContext(ctx)
+				mockRepo.SetData(model.Albums{
+					{ID: "1"}, {ID: "2"},
+				})
+
+				resp, err := router.GetAlbumList2(w, r)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(resp.AlbumList2.Album).To(HaveLen(2))
+				// Verify that library filter was applied
+				Expect(mockRepo.Options.Filters).ToNot(BeNil())
+			})
+
+			It("should return all accessible albums when no musicFolderId is provided", func() {
+				r := newGetRequest("type=newest")
+				r = r.WithContext(ctx)
+				mockRepo.SetData(model.Albums{
+					{ID: "1"}, {ID: "2"},
+				})
+
+				resp, err := router.GetAlbumList2(w, r)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(resp.AlbumList2.Album).To(HaveLen(2))
+			})
+		})
 	})
 })

server/subsonic/filter/filters.go

@@ -123,6 +123,21 @@ func SongsByArtistTitleWithLyricsFirst(artist, title string) Options {
 	})
 }
 
+func ApplyLibraryFilter(opts Options, musicFolderIds []int) Options {
+	if len(musicFolderIds) == 0 {
+		return opts
+	}
+
+	libraryFilter := Eq{"library_id": musicFolderIds}
+	if opts.Filters == nil {
+		opts.Filters = libraryFilter
+	} else {
+		opts.Filters = And{opts.Filters, libraryFilter}
+	}
+
+	return opts
+}
+
 func ByGenre(genre string) Options {
 	return addDefaultFilters(Options{
 		Sort:    "name",