fix(server): ensure that similar artists retrieved from provider are no more than limit (#4267)

* fix(provider): ensure that similar artists retreived from provider are no more than limit

* add overlimit multiplier

core/agents/agents.go

@@ -258,6 +258,8 @@ func (a *Agents) GetArtistBiography(ctx context.Context, id, name, mbid string)
 	return "", ErrNotFound
 }
 
+// GetSimilarArtists returns similar artists by id, name, and/or mbid. Because some artists returned from an enabled
+// agent may not exist in the database, return at most limit * conf.Server.DevExternalArtistFetchMultiplier items.
 func (a *Agents) GetSimilarArtists(ctx context.Context, id, name, mbid string, limit int) ([]Artist, error) {
 	switch id {
 	case consts.UnknownArtistID:
@@ -265,6 +267,9 @@ func (a *Agents) GetSimilarArtists(ctx context.Context, id, name, mbid string, l
 	case consts.VariousArtistsID:
 		return nil, nil
 	}
+
+	overLimit := int(float64(limit) * conf.Server.DevExternalArtistFetchMultiplier)
+
 	start := time.Now()
 	for _, agentName := range a.getEnabledAgentNames() {
 		ag := a.getAgent(agentName)
@@ -278,7 +283,7 @@ func (a *Agents) GetSimilarArtists(ctx context.Context, id, name, mbid string, l
 		if !ok {
 			continue
 		}
-		similar, err := retriever.GetSimilarArtists(ctx, id, name, mbid, limit)
+		similar, err := retriever.GetSimilarArtists(ctx, id, name, mbid, overLimit)
 		if len(similar) > 0 && err == nil {
 			if log.IsGreaterOrEqualTo(log.LevelTrace) {
 				log.Debug(ctx, "Got Similar Artists", "agent", ag.AgentName(), "artist", name, "similar", similar, "elapsed", time.Since(start))
@@ -320,6 +325,8 @@ func (a *Agents) GetArtistImages(ctx context.Context, id, name, mbid string) ([]
 	return nil, ErrNotFound
 }
 
+// GetArtistTopSongs returns top songs by id, name, and/or mbid. Because some songs returned from an enabled
+// agent may not exist in the database, return at most limit * conf.Server.DevExternalArtistFetchMultiplier items.
 func (a *Agents) GetArtistTopSongs(ctx context.Context, id, artistName, mbid string, count int) ([]Song, error) {
 	switch id {
 	case consts.UnknownArtistID:
@@ -327,6 +334,9 @@ func (a *Agents) GetArtistTopSongs(ctx context.Context, id, artistName, mbid str
 	case consts.VariousArtistsID:
 		return nil, nil
 	}
+
+	overLimit := int(float64(count) * conf.Server.DevExternalArtistFetchMultiplier)
+
 	start := time.Now()
 	for _, agentName := range a.getEnabledAgentNames() {
 		ag := a.getAgent(agentName)
@@ -340,7 +350,7 @@ func (a *Agents) GetArtistTopSongs(ctx context.Context, id, artistName, mbid str
 		if !ok {
 			continue
 		}
-		songs, err := retriever.GetArtistTopSongs(ctx, id, artistName, mbid, count)
+		songs, err := retriever.GetArtistTopSongs(ctx, id, artistName, mbid, overLimit)
 		if len(songs) > 0 && err == nil {
 			log.Debug(ctx, "Got Top Songs", "agent", ag.AgentName(), "artist", artistName, "songs", songs, "elapsed", time.Since(start))
 			return songs, nil

core/agents/agents_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 
+	"github.com/navidrome/navidrome/conf/configtest"
 	"github.com/navidrome/navidrome/consts"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/tests"
@@ -19,6 +20,7 @@ var _ = Describe("Agents", func() {
 	var ds model.DataStore
 	var mfRepo *tests.MockMediaFileRepo
 	BeforeEach(func() {
+		DeferCleanup(configtest.SetupConfig())
 		ctx, cancel = context.WithCancel(context.Background())
 		mfRepo = tests.CreateMockMediaFileRepo()
 		ds = &tests.MockDataStore{MockedMediaFile: mfRepo}
@@ -240,6 +242,7 @@ var _ = Describe("Agents", func() {
 
 		Describe("GetArtistTopSongs", func() {
 			It("returns on first match", func() {
+				conf.Server.DevExternalArtistFetchMultiplier = 1
 				Expect(ag.GetArtistTopSongs(ctx, "123", "test", "mb123", 2)).To(Equal([]Song{{
 					Name: "A Song",
 					MBID: "mbid444",
@@ -247,6 +250,7 @@ var _ = Describe("Agents", func() {
 				Expect(mock.Args).To(HaveExactElements("123", "test", "mb123", 2))
 			})
 			It("skips the agent if it returns an error", func() {
+				conf.Server.DevExternalArtistFetchMultiplier = 1
 				mock.Err = errors.New("error")
 				_, err := ag.GetArtistTopSongs(ctx, "123", "test", "mb123", 2)
 				Expect(err).To(MatchError(ErrNotFound))
@@ -258,6 +262,14 @@ var _ = Describe("Agents", func() {
 				Expect(err).To(MatchError(ErrNotFound))
 				Expect(mock.Args).To(BeEmpty())
 			})
+			It("fetches with multiplier", func() {
+				conf.Server.DevExternalArtistFetchMultiplier = 2
+				Expect(ag.GetArtistTopSongs(ctx, "123", "test", "mb123", 2)).To(Equal([]Song{{
+					Name: "A Song",
+					MBID: "mbid444",
+				}}))
+				Expect(mock.Args).To(HaveExactElements("123", "test", "mb123", 4))
+			})
 		})
 
 		Describe("GetAlbumInfo", func() {