fix: Allow nullable ReplayGain and support 0.0 (#4239)

* fix(ui,scanner,subsonic): Allow nullable replaygain and support 0.0

Resolves #4236.

Makes the replaygain columns (track/album gain/peak) nullable.
Converts the type to a pointer, allowing for 0.0 (a valid value) to be returned from Subsonic.
Updates tests for this behavior.

* small refactor

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan <deluan@navidrome.org>

adapters/taglib/end_to_end_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/djherbis/times"
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/model/metadata"
+	"github.com/navidrome/navidrome/utils/gg"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -82,6 +83,29 @@ var _ = Describe("Extractor", func() {
 		e = &extractor{}
 	})
 
+	Describe("ReplayGain", func() {
+		DescribeTable("test replaygain end-to-end", func(file string, trackGain, trackPeak, albumGain, albumPeak *float64) {
+			path := "tests/fixtures/" + file
+			mds, err := e.Parse(path)
+			Expect(err).ToNot(HaveOccurred())
+
+			info := mds[path]
+			fileInfo, _ := os.Stat(path)
+			info.FileInfo = testFileInfo{FileInfo: fileInfo}
+
+			metadata := metadata.New(path, info)
+			mf := metadata.ToMediaFile(1, "folderID")
+
+			Expect(mf.RGTrackGain).To(Equal(trackGain))
+			Expect(mf.RGTrackPeak).To(Equal(trackPeak))
+			Expect(mf.RGAlbumGain).To(Equal(albumGain))
+			Expect(mf.RGAlbumPeak).To(Equal(albumPeak))
+		},
+			Entry("mp3 with no replaygain", "no_replaygain.mp3", nil, nil, nil, nil),
+			Entry("mp3 with no zero replaygain", "zero_replaygain.mp3", gg.P(0.0), gg.P(1.0), gg.P(0.0), gg.P(1.0)),
+		)
+	})
+
 	Describe("Participants", func() {
 		DescribeTable("test tags consistent across formats", func(format string) {
 			path := "tests/fixtures/test." + format

db/migrations/20250701010104_make_replaygain_fields_nullable.go

@@ -0,0 +1,49 @@
+package migrations
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/pressly/goose/v3"
+)
+
+func init() {
+	goose.AddMigrationContext(upMakeReplaygainFieldsNullable, downMakeReplaygainFieldsNullable)
+}
+
+func upMakeReplaygainFieldsNullable(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+ALTER TABLE media_file ADD COLUMN rg_album_gain_new real;
+ALTER TABLE media_file ADD COLUMN rg_album_peak_new real;
+ALTER TABLE media_file ADD COLUMN rg_track_gain_new real;
+ALTER TABLE media_file ADD COLUMN rg_track_peak_new real;
+
+UPDATE media_file SET
+	rg_album_gain_new = rg_album_gain,
+	rg_album_peak_new = rg_album_peak,
+	rg_track_gain_new = rg_track_gain,
+	rg_track_peak_new = rg_track_peak;
+
+ALTER TABLE media_file DROP COLUMN rg_album_gain;
+ALTER TABLE media_file DROP COLUMN rg_album_peak;
+ALTER TABLE media_file DROP COLUMN rg_track_gain;
+ALTER TABLE media_file DROP COLUMN rg_track_peak;
+
+ALTER TABLE media_file RENAME COLUMN rg_album_gain_new TO rg_album_gain;
+ALTER TABLE media_file RENAME COLUMN rg_album_peak_new TO rg_album_peak;
+ALTER TABLE media_file RENAME COLUMN rg_track_gain_new TO rg_track_gain;
+ALTER TABLE media_file RENAME COLUMN rg_track_peak_new TO rg_track_peak;
+	`)
+
+	if err != nil {
+		return err
+	}
+
+	notice(tx, "Fetching replaygain fields properly will require a full scan")
+	return nil
+}
+
+func downMakeReplaygainFieldsNullable(ctx context.Context, tx *sql.Tx) error {
+	// This code is executed when the migration is rolled back.
+	return nil
+}

model/mediafile.go

@@ -36,53 +36,53 @@ type MediaFile struct {
 	Artist        string `structs:"artist" json:"artist"`
 	AlbumArtistID string `structs:"album_artist_id" json:"albumArtistId"` // Deprecated: Use Participants instead
 	// AlbumArtist is the display name used for the album artist.
-	AlbumArtist          string  `structs:"album_artist" json:"albumArtist"`
+	AlbumArtist          string   `structs:"album_artist" json:"albumArtist"`
-	AlbumID              string  `structs:"album_id" json:"albumId"`
+	AlbumID              string   `structs:"album_id" json:"albumId"`
-	HasCoverArt          bool    `structs:"has_cover_art" json:"hasCoverArt"`
+	HasCoverArt          bool     `structs:"has_cover_art" json:"hasCoverArt"`
-	TrackNumber          int     `structs:"track_number" json:"trackNumber"`
+	TrackNumber          int      `structs:"track_number" json:"trackNumber"`
-	DiscNumber           int     `structs:"disc_number" json:"discNumber"`
+	DiscNumber           int      `structs:"disc_number" json:"discNumber"`
-	DiscSubtitle         string  `structs:"disc_subtitle" json:"discSubtitle,omitempty"`
+	DiscSubtitle         string   `structs:"disc_subtitle" json:"discSubtitle,omitempty"`
-	Year                 int     `structs:"year" json:"year"`
+	Year                 int      `structs:"year" json:"year"`
-	Date                 string  `structs:"date" json:"date,omitempty"`
+	Date                 string   `structs:"date" json:"date,omitempty"`
-	OriginalYear         int     `structs:"original_year" json:"originalYear"`
+	OriginalYear         int      `structs:"original_year" json:"originalYear"`
-	OriginalDate         string  `structs:"original_date" json:"originalDate,omitempty"`
+	OriginalDate         string   `structs:"original_date" json:"originalDate,omitempty"`
-	ReleaseYear          int     `structs:"release_year" json:"releaseYear"`
+	ReleaseYear          int      `structs:"release_year" json:"releaseYear"`
-	ReleaseDate          string  `structs:"release_date" json:"releaseDate,omitempty"`
+	ReleaseDate          string   `structs:"release_date" json:"releaseDate,omitempty"`
-	Size                 int64   `structs:"size" json:"size"`
+	Size                 int64    `structs:"size" json:"size"`
-	Suffix               string  `structs:"suffix" json:"suffix"`
+	Suffix               string   `structs:"suffix" json:"suffix"`
-	Duration             float32 `structs:"duration" json:"duration"`
+	Duration             float32  `structs:"duration" json:"duration"`
-	BitRate              int     `structs:"bit_rate" json:"bitRate"`
+	BitRate              int      `structs:"bit_rate" json:"bitRate"`
-	SampleRate           int     `structs:"sample_rate" json:"sampleRate"`
+	SampleRate           int      `structs:"sample_rate" json:"sampleRate"`
-	BitDepth             int     `structs:"bit_depth" json:"bitDepth"`
+	BitDepth             int      `structs:"bit_depth" json:"bitDepth"`
-	Channels             int     `structs:"channels" json:"channels"`
+	Channels             int      `structs:"channels" json:"channels"`
-	Genre                string  `structs:"genre" json:"genre"`
+	Genre                string   `structs:"genre" json:"genre"`
-	Genres               Genres  `structs:"-" json:"genres,omitempty"`
+	Genres               Genres   `structs:"-" json:"genres,omitempty"`
-	SortTitle            string  `structs:"sort_title" json:"sortTitle,omitempty"`
+	SortTitle            string   `structs:"sort_title" json:"sortTitle,omitempty"`
-	SortAlbumName        string  `structs:"sort_album_name" json:"sortAlbumName,omitempty"`
+	SortAlbumName        string   `structs:"sort_album_name" json:"sortAlbumName,omitempty"`
-	SortArtistName       string  `structs:"sort_artist_name" json:"sortArtistName,omitempty"`            // Deprecated: Use Participants instead
+	SortArtistName       string   `structs:"sort_artist_name" json:"sortArtistName,omitempty"`            // Deprecated: Use Participants instead
-	SortAlbumArtistName  string  `structs:"sort_album_artist_name" json:"sortAlbumArtistName,omitempty"` // Deprecated: Use Participants instead
+	SortAlbumArtistName  string   `structs:"sort_album_artist_name" json:"sortAlbumArtistName,omitempty"` // Deprecated: Use Participants instead
-	OrderTitle           string  `structs:"order_title" json:"orderTitle,omitempty"`
+	OrderTitle           string   `structs:"order_title" json:"orderTitle,omitempty"`
-	OrderAlbumName       string  `structs:"order_album_name" json:"orderAlbumName"`
+	OrderAlbumName       string   `structs:"order_album_name" json:"orderAlbumName"`
-	OrderArtistName      string  `structs:"order_artist_name" json:"orderArtistName"`            // Deprecated: Use Participants instead
+	OrderArtistName      string   `structs:"order_artist_name" json:"orderArtistName"`            // Deprecated: Use Participants instead
-	OrderAlbumArtistName string  `structs:"order_album_artist_name" json:"orderAlbumArtistName"` // Deprecated: Use Participants instead
+	OrderAlbumArtistName string   `structs:"order_album_artist_name" json:"orderAlbumArtistName"` // Deprecated: Use Participants instead
-	Compilation          bool    `structs:"compilation" json:"compilation"`
+	Compilation          bool     `structs:"compilation" json:"compilation"`
-	Comment              string  `structs:"comment" json:"comment,omitempty"`
+	Comment              string   `structs:"comment" json:"comment,omitempty"`
-	Lyrics               string  `structs:"lyrics" json:"lyrics"`
+	Lyrics               string   `structs:"lyrics" json:"lyrics"`
-	BPM                  int     `structs:"bpm" json:"bpm,omitempty"`
+	BPM                  int      `structs:"bpm" json:"bpm,omitempty"`
-	ExplicitStatus       string  `structs:"explicit_status" json:"explicitStatus"`
+	ExplicitStatus       string   `structs:"explicit_status" json:"explicitStatus"`
-	CatalogNum           string  `structs:"catalog_num" json:"catalogNum,omitempty"`
+	CatalogNum           string   `structs:"catalog_num" json:"catalogNum,omitempty"`
-	MbzRecordingID       string  `structs:"mbz_recording_id" json:"mbzRecordingID,omitempty"`
+	MbzRecordingID       string   `structs:"mbz_recording_id" json:"mbzRecordingID,omitempty"`
-	MbzReleaseTrackID    string  `structs:"mbz_release_track_id" json:"mbzReleaseTrackId,omitempty"`
+	MbzReleaseTrackID    string   `structs:"mbz_release_track_id" json:"mbzReleaseTrackId,omitempty"`
-	MbzAlbumID           string  `structs:"mbz_album_id" json:"mbzAlbumId,omitempty"`
+	MbzAlbumID           string   `structs:"mbz_album_id" json:"mbzAlbumId,omitempty"`
-	MbzReleaseGroupID    string  `structs:"mbz_release_group_id" json:"mbzReleaseGroupId,omitempty"`
+	MbzReleaseGroupID    string   `structs:"mbz_release_group_id" json:"mbzReleaseGroupId,omitempty"`
-	MbzArtistID          string  `structs:"mbz_artist_id" json:"mbzArtistId,omitempty"`            // Deprecated: Use Participants instead
+	MbzArtistID          string   `structs:"mbz_artist_id" json:"mbzArtistId,omitempty"`            // Deprecated: Use Participants instead
-	MbzAlbumArtistID     string  `structs:"mbz_album_artist_id" json:"mbzAlbumArtistId,omitempty"` // Deprecated: Use Participants instead
+	MbzAlbumArtistID     string   `structs:"mbz_album_artist_id" json:"mbzAlbumArtistId,omitempty"` // Deprecated: Use Participants instead
-	MbzAlbumType         string  `structs:"mbz_album_type" json:"mbzAlbumType,omitempty"`
+	MbzAlbumType         string   `structs:"mbz_album_type" json:"mbzAlbumType,omitempty"`
-	MbzAlbumComment      string  `structs:"mbz_album_comment" json:"mbzAlbumComment,omitempty"`
+	MbzAlbumComment      string   `structs:"mbz_album_comment" json:"mbzAlbumComment,omitempty"`
-	RGAlbumGain          float64 `structs:"rg_album_gain" json:"rgAlbumGain"`
+	RGAlbumGain          *float64 `structs:"rg_album_gain" json:"rgAlbumGain"`
-	RGAlbumPeak          float64 `structs:"rg_album_peak" json:"rgAlbumPeak"`
+	RGAlbumPeak          *float64 `structs:"rg_album_peak" json:"rgAlbumPeak"`
-	RGTrackGain          float64 `structs:"rg_track_gain" json:"rgTrackGain"`
+	RGTrackGain          *float64 `structs:"rg_track_gain" json:"rgTrackGain"`
-	RGTrackPeak          float64 `structs:"rg_track_peak" json:"rgTrackPeak"`
+	RGTrackPeak          *float64 `structs:"rg_track_peak" json:"rgTrackPeak"`
 
 	Tags         Tags         `structs:"tags" json:"tags,omitempty" hash:"ignore"`       // All imported tags from the original file
 	Participants Participants `structs:"participants" json:"participants" hash:"ignore"` // All artists that participated in this track

model/metadata/map_mediafile.go

@@ -53,9 +53,9 @@ func (md Metadata) ToMediaFile(libID int, folderID string) model.MediaFile {
 	mf.MbzAlbumType = md.String(model.TagReleaseType)
 
 	// ReplayGain
-	mf.RGAlbumPeak = md.Float(model.TagReplayGainAlbumPeak, 1)
+	mf.RGAlbumPeak = md.NullableFloat(model.TagReplayGainAlbumPeak)
 	mf.RGAlbumGain = md.mapGain(model.TagReplayGainAlbumGain, model.TagR128AlbumGain)
-	mf.RGTrackPeak = md.Float(model.TagReplayGainTrackPeak, 1)
+	mf.RGTrackPeak = md.NullableFloat(model.TagReplayGainTrackPeak)
 	mf.RGTrackGain = md.mapGain(model.TagReplayGainTrackGain, model.TagR128TrackGain)
 
 	// General properties
@@ -108,23 +108,24 @@ func (md Metadata) AlbumID(mf model.MediaFile, pidConf string) string {
 	return getPID(mf, md, pidConf)
 }
 
-func (md Metadata) mapGain(rg, r128 model.TagName) float64 {
+func (md Metadata) mapGain(rg, r128 model.TagName) *float64 {
 	v := md.Gain(rg)
-	if v != 0 {
+	if v != nil {
 		return v
 	}
 	r128value := md.String(r128)
 	if r128value != "" {
 		var v, err = strconv.Atoi(r128value)
 		if err != nil {
-			return 0
+			return nil
 		}
 		// Convert Q7.8 to float
-		var value = float64(v) / 256.0
+		value := float64(v) / 256.0
 		// Adding 5 dB to normalize with ReplayGain level
-		return value + 5
+		value += 5
+		return &value
 	}
-	return 0
+	return nil
 }
 
 func (md Metadata) mapLyrics() string {

model/metadata/metadata.go

@@ -103,9 +103,11 @@ func (md Metadata) NumAndTotal(key model.TagName) (int, int) { return md.tuple(k
 func (md Metadata) Float(key model.TagName, def ...float64) float64 {
 	return float(md.first(key), def...)
 }
-func (md Metadata) Gain(key model.TagName) float64 {
+func (md Metadata) NullableFloat(key model.TagName) *float64 { return nullableFloat(md.first(key)) }
+
+func (md Metadata) Gain(key model.TagName) *float64 {
 	v := strings.TrimSpace(strings.Replace(md.first(key), "dB", "", 1))
-	return float(v)
+	return nullableFloat(v)
 }
 func (md Metadata) Pairs(key model.TagName) []Pair {
 	values := md.tags[key]
@@ -119,14 +121,22 @@ func (md Metadata) first(key model.TagName) string {
 }
 
 func float(value string, def ...float64) float64 {
+	v := nullableFloat(value)
+	if v != nil {
+		return *v
+	}
+	if len(def) > 0 {
+		return def[0]
+	}
+	return 0
+}
+
+func nullableFloat(value string) *float64 {
 	v, err := strconv.ParseFloat(value, 64)
 	if err != nil || v == math.Inf(-1) || math.IsInf(v, 1) || math.IsNaN(v) {
-		if len(def) > 0 {
+		return nil
-			return def[0]
-		}
-		return 0
 	}
-	return v
+	return &v
 }
 
 // Used for tracks and discs

model/metadata/metadata_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/model/metadata"
 	"github.com/navidrome/navidrome/utils"
+	"github.com/navidrome/navidrome/utils/gg"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -257,38 +258,39 @@ var _ = Describe("Metadata", func() {
 			}
 
 			DescribeTable("Gain",
-				func(tagValue string, expected float64) {
+				func(tagValue string, expected *float64) {
 					mf := createMF("replaygain_track_gain", tagValue)
 					Expect(mf.RGTrackGain).To(Equal(expected))
 				},
-				Entry("0", "0", 0.0),
+				Entry("0", "0", gg.P(0.0)),
-				Entry("1.2dB", "1.2dB", 1.2),
+				Entry("1.2dB", "1.2dB", gg.P(1.2)),
-				Entry("Infinity", "Infinity", 0.0),
+				Entry("Infinity", "Infinity", nil),
-				Entry("Invalid value", "INVALID VALUE", 0.0),
+				Entry("Invalid value", "INVALID VALUE", nil),
-				Entry("NaN", "NaN", 0.0),
+				Entry("NaN", "NaN", nil),
 			)
 			DescribeTable("Peak",
-				func(tagValue string, expected float64) {
+				func(tagValue string, expected *float64) {
 					mf := createMF("replaygain_track_peak", tagValue)
 					Expect(mf.RGTrackPeak).To(Equal(expected))
 				},
-				Entry("0", "0", 0.0),
+				Entry("0", "0", gg.P(0.0)),
-				Entry("0.5", "0.5", 0.5),
+				Entry("1.0", "1.0", gg.P(1.0)),
-				Entry("Invalid dB suffix", "0.7dB", 1.0),
+				Entry("0.5", "0.5", gg.P(0.5)),
-				Entry("Infinity", "Infinity", 1.0),
+				Entry("Invalid dB suffix", "0.7dB", nil),
-				Entry("Invalid value", "INVALID VALUE", 1.0),
+				Entry("Infinity", "Infinity", nil),
-				Entry("NaN", "NaN", 1.0),
+				Entry("Invalid value", "INVALID VALUE", nil),
+				Entry("NaN", "NaN", nil),
 			)
 			DescribeTable("getR128GainValue",
-				func(tagValue string, expected float64) {
+				func(tagValue string, expected *float64) {
 					mf := createMF("r128_track_gain", tagValue)
 					Expect(mf.RGTrackGain).To(Equal(expected))
 
 				},
-				Entry("0", "0", 5.0),
+				Entry("0", "0", gg.P(5.0)),
-				Entry("-3776", "-3776", -9.75),
+				Entry("-3776", "-3776", gg.P(-9.75)),
-				Entry("Infinity", "Infinity", 0.0),
+				Entry("Infinity", "Infinity", nil),
-				Entry("Invalid value", "INVALID VALUE", 0.0),
+				Entry("Invalid value", "INVALID VALUE", nil),
 			)
 		})
 

persistence/mediafile_repository.go

@@ -25,10 +25,10 @@ type dbMediaFile struct {
 	Tags             string `structs:"-" json:"-"`
 	// These are necessary to map the correct names (rg_*) to the correct fields (RG*)
 	// without using `db` struct tags in the model.MediaFile struct
-	RgAlbumGain float64 `structs:"-" json:"-"`
+	RgAlbumGain *float64 `structs:"-" json:"-"`
-	RgAlbumPeak float64 `structs:"-" json:"-"`
+	RgAlbumPeak *float64 `structs:"-" json:"-"`
-	RgTrackGain float64 `structs:"-" json:"-"`
+	RgTrackGain *float64 `structs:"-" json:"-"`
-	RgTrackPeak float64 `structs:"-" json:"-"`
+	RgTrackPeak *float64 `structs:"-" json:"-"`
 }
 
 func (m *dbMediaFile) PostScan() error {

persistence/persistence_suite_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/model/request"
 	"github.com/navidrome/navidrome/tests"
+	"github.com/navidrome/navidrome/utils/gg"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 	"github.com/pocketbase/dbx"
@@ -79,7 +80,7 @@ var (
 	songAntenna       = mf(model.MediaFile{ID: "1004", Title: "Antenna", ArtistID: "2", Artist: "Kraftwerk",
 		AlbumID:     "103",
 		Path:        p("/kraft/radio/antenna.mp3"),
-		RGAlbumGain: 1.0, RGAlbumPeak: 2.0, RGTrackGain: 3.0, RGTrackPeak: 4.0,
+		RGAlbumGain: gg.P(1.0), RGAlbumPeak: gg.P(2.0), RGTrackGain: gg.P(3.0), RGTrackPeak: gg.P(4.0),
 	})
 	songAntennaWithLyrics = mf(model.MediaFile{
 		ID:       "1005",

server/subsonic/api_test.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/navidrome/navidrome/server/subsonic/responses"
+	"github.com/navidrome/navidrome/utils/gg"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -91,7 +92,7 @@ var _ = Describe("sendResponse", func() {
 		It("should return a fail response", func() {
 			payload.Song = &responses.Child{OpenSubsonicChild: &responses.OpenSubsonicChild{}}
 			// An +Inf value will cause an error when marshalling to JSON
-			payload.Song.ReplayGain = responses.ReplayGain{TrackGain: math.Inf(1)}
+			payload.Song.ReplayGain = responses.ReplayGain{TrackGain: gg.P(math.Inf(1))}
 			q := r.URL.Query()
 			q.Add("f", "json")
 			r.URL.RawQuery = q.Encode()

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

@@ -166,6 +166,52 @@
         ],
         "displayComposer": "composer 1 \u0026 composer 2",
         "explicitStatus": "clean"
+      },
+      {
+        "id": "2",
+        "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": 0,
+        "comment": "",
+        "sortName": "",
+        "mediaType": "",
+        "musicBrainzId": "",
+        "isrc": [],
+        "genres": [],
+        "replayGain": {
+          "trackGain": 0,
+          "albumGain": 0,
+          "trackPeak": 0,
+          "albumPeak": 0,
+          "baseGain": 0,
+          "fallbackGain": 0
+        },
+        "channelCount": 0,
+        "samplingRate": 0,
+        "bitDepth": 0,
+        "moods": [],
+        "artists": [],
+        "displayArtist": "",
+        "albumArtists": [],
+        "displayAlbumArtist": "",
+        "contributors": [],
+        "displayComposer": "",
+        "explicitStatus": ""
       }
     ]
   }

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

@@ -33,5 +33,8 @@
         <artist id="2" name="artist2"></artist>
       </contributors>
     </song>
+    <song id="2" 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">
+      <replayGain trackGain="0" albumGain="0" trackPeak="0" albumPeak="0" baseGain="0" fallbackGain="0"></replayGain>
+    </song>
   </album>
 </subsonic-response>

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

@@ -112,6 +112,37 @@
         ],
         "displayComposer": "composer 1 \u0026 composer 2",
         "explicitStatus": "clean"
+      },
+      {
+        "id": "",
+        "isDir": false,
+        "isVideo": false,
+        "bpm": 0,
+        "comment": "",
+        "sortName": "",
+        "mediaType": "",
+        "musicBrainzId": "",
+        "isrc": [],
+        "genres": [],
+        "replayGain": {
+          "trackGain": 0,
+          "albumGain": 0,
+          "trackPeak": 0,
+          "albumPeak": 0,
+          "baseGain": 0,
+          "fallbackGain": 0
+        },
+        "channelCount": 0,
+        "samplingRate": 0,
+        "bitDepth": 0,
+        "moods": [],
+        "artists": [],
+        "displayArtist": "",
+        "albumArtists": [],
+        "displayAlbumArtist": "",
+        "contributors": [],
+        "displayComposer": "",
+        "explicitStatus": ""
       }
     ],
     "id": "1",

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

@@ -25,5 +25,8 @@
         <artist id="4" name="composer2"></artist>
       </contributors>
     </child>
+    <child id="" isDir="false" isVideo="false">
+      <replayGain trackGain="0" albumGain="0" trackPeak="0" albumPeak="0" baseGain="0" fallbackGain="0"></replayGain>
+    </child>
   </directory>
 </subsonic-response>

server/subsonic/responses/responses.go

@@ -546,16 +546,16 @@ type ItemGenre struct {
 }
 
 type ReplayGain struct {
-	TrackGain    float64 `xml:"trackGain,omitempty,attr"    json:"trackGain,omitempty"`
+	TrackGain    *float64 `xml:"trackGain,omitempty,attr"    json:"trackGain,omitempty"`
-	AlbumGain    float64 `xml:"albumGain,omitempty,attr"    json:"albumGain,omitempty"`
+	AlbumGain    *float64 `xml:"albumGain,omitempty,attr"    json:"albumGain,omitempty"`
-	TrackPeak    float64 `xml:"trackPeak,omitempty,attr"    json:"trackPeak,omitempty"`
+	TrackPeak    *float64 `xml:"trackPeak,omitempty,attr"    json:"trackPeak,omitempty"`
-	AlbumPeak    float64 `xml:"albumPeak,omitempty,attr"    json:"albumPeak,omitempty"`
+	AlbumPeak    *float64 `xml:"albumPeak,omitempty,attr"    json:"albumPeak,omitempty"`
-	BaseGain     float64 `xml:"baseGain,omitempty,attr"     json:"baseGain,omitempty"`
+	BaseGain     *float64 `xml:"baseGain,omitempty,attr"     json:"baseGain,omitempty"`
-	FallbackGain float64 `xml:"fallbackGain,omitempty,attr" json:"fallbackGain,omitempty"`
+	FallbackGain *float64 `xml:"fallbackGain,omitempty,attr" json:"fallbackGain,omitempty"`
 }
 
 func (r ReplayGain) MarshalXML(e *xml.Encoder, start xml.StartElement) error {
-	if r.TrackGain == 0 && r.AlbumGain == 0 && r.TrackPeak == 0 && r.AlbumPeak == 0 && r.BaseGain == 0 && r.FallbackGain == 0 {
+	if r.TrackGain == nil && r.AlbumGain == nil && r.TrackPeak == nil && r.AlbumPeak == nil && r.BaseGain == nil && r.FallbackGain == nil {
 		return nil
 	}
 	type replayGain ReplayGain

server/subsonic/responses/responses_test.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/navidrome/navidrome/consts"
 	. "github.com/navidrome/navidrome/server/subsonic/responses"
+	"github.com/navidrome/navidrome/utils/gg"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
@@ -213,7 +214,7 @@ var _ = Describe("Responses", func() {
 		Context("with data", func() {
 			BeforeEach(func() {
 				response.Directory = &Directory{Id: "1", Name: "N"}
-				child := make([]Child, 1)
+				child := make([]Child, 2)
 				t := time.Date(2016, 03, 2, 20, 30, 0, 0, time.UTC)
 				child[0] = Child{
 					Id: "1", IsDir: true, Title: "title", Album: "album", Artist: "artist", Track: 1,
@@ -227,7 +228,7 @@ var _ = Describe("Responses", func() {
 					Isrc: []string{"ISRC-1", "ISRC-2"},
 					BPM:  127, ChannelCount: 2, SamplingRate: 44100, BitDepth: 16,
 					Moods:         []string{"happy", "sad"},
-					ReplayGain:    ReplayGain{TrackGain: 1, AlbumGain: 2, TrackPeak: 3, AlbumPeak: 4, BaseGain: 5, FallbackGain: 6},
+					ReplayGain:    ReplayGain{TrackGain: gg.P(1.0), AlbumGain: gg.P(2.0), TrackPeak: gg.P(3.0), AlbumPeak: gg.P(4.0), BaseGain: gg.P(5.0), FallbackGain: gg.P(6.0)},
 					DisplayArtist: "artist 1 & artist 2",
 					Artists: []ArtistID3Ref{
 						{Id: "1", Name: "artist1"},
@@ -247,6 +248,9 @@ var _ = Describe("Responses", func() {
 					},
 					ExplicitStatus: "clean",
 				}
+				child[1].OpenSubsonicChild = &OpenSubsonicChild{
+					ReplayGain: ReplayGain{TrackGain: gg.P(0.0), AlbumGain: gg.P(0.0), TrackPeak: gg.P(0.0), AlbumPeak: gg.P(0.0), BaseGain: gg.P(0.0), FallbackGain: gg.P(0.0)},
+				}
 				response.Directory.Child = child
 			})
 
@@ -309,13 +313,18 @@ var _ = Describe("Responses", func() {
 					Year: 1985, Genre: "Rock", CoverArt: "1", Size: 8421341, ContentType: "audio/flac",
 					Suffix: "flac", TranscodedContentType: "audio/mpeg", TranscodedSuffix: "mp3",
 					Duration: 146, BitRate: 320, Starred: &t,
+				}, {
+					Id: "2", IsDir: true, Title: "title", Album: "album", Artist: "artist", Track: 1,
+					Year: 1985, Genre: "Rock", CoverArt: "1", Size: 8421341, ContentType: "audio/flac",
+					Suffix: "flac", TranscodedContentType: "audio/mpeg", TranscodedSuffix: "mp3",
+					Duration: 146, BitRate: 320, Starred: &t,
 				}}
 				songs[0].OpenSubsonicChild = &OpenSubsonicChild{
 					Genres:  []ItemGenre{{Name: "rock"}, {Name: "progressive"}},
 					Comment: "a comment", MediaType: MediaTypeSong, MusicBrainzId: "4321", SortName: "sorted song",
 					Isrc:       []string{"ISRC-1"},
 					Moods:      []string{"happy", "sad"},
-					ReplayGain: ReplayGain{TrackGain: 1, AlbumGain: 2, TrackPeak: 3, AlbumPeak: 4, BaseGain: 5, FallbackGain: 6},
+					ReplayGain: ReplayGain{TrackGain: gg.P(1.0), AlbumGain: gg.P(2.0), TrackPeak: gg.P(3.0), AlbumPeak: gg.P(4.0), BaseGain: gg.P(5.0), FallbackGain: gg.P(6.0)},
 					BPM:        127, ChannelCount: 2, SamplingRate: 44100, BitDepth: 16,
 					DisplayArtist: "artist1 & artist2",
 					Artists: []ArtistID3Ref{
@@ -334,6 +343,9 @@ var _ = Describe("Responses", func() {
 					DisplayComposer: "composer 1 & composer 2",
 					ExplicitStatus:  "clean",
 				}
+				songs[1].OpenSubsonicChild = &OpenSubsonicChild{
+					ReplayGain: ReplayGain{TrackGain: gg.P(0.0), AlbumGain: gg.P(0.0), TrackPeak: gg.P(0.0), AlbumPeak: gg.P(0.0), BaseGain: gg.P(0.0), FallbackGain: gg.P(0.0)},
+				}
 				response.AlbumWithSongsID3.AlbumID3 = album
 				response.AlbumWithSongsID3.Song = songs
 			})