Fix getOpenSubsonicExtensions endpoint

Match the current doc: https://opensubsonic.netlify.app/docs/endpoints/getopensubsonicextensions/

openSubsonicExtensions must be an array, not a struct

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

@@ -0,0 +1,16 @@
+{
+  "status": "ok",
+  "version": "1.8.0",
+  "type": "navidrome",
+  "serverVersion": "v0.0.0",
+  "openSubsonic": true,
+  "openSubsonicExtensions": [
+    {
+      "name": "template",
+      "versions": [
+        1,
+        2
+      ]
+    }
+  ]
+}

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

@@ -0,0 +1,6 @@
+<subsonic-response xmlns="http://subsonic.org/restapi" status="ok" version="1.8.0" type="navidrome" serverVersion="v0.0.0" openSubsonic="true">
+  <openSubsonicExtensions name="template">
+    <versions>1</versions>
+    <versions>2</versions>
+  </openSubsonicExtensions>
+</subsonic-response>

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

@@ -0,0 +1,8 @@
+{
+  "status": "ok",
+  "version": "1.8.0",
+  "type": "navidrome",
+  "serverVersion": "v0.0.0",
+  "openSubsonic": true,
+  "openSubsonicExtensions": []
+}

server/subsonic/responses/.snapshots/Responses OpenSubsonicExtensions without data should match .XML

@@ -0,0 +1 @@
+<subsonic-response xmlns="http://subsonic.org/restapi" status="ok" version="1.8.0" type="navidrome" serverVersion="v0.0.0" openSubsonic="true"></subsonic-response>

server/subsonic/responses/responses.go

@@ -424,13 +424,18 @@ type JukeboxPlaylist struct {
 	JukeboxStatus
 	Entry []Child `xml:"entry,omitempty"         json:"entry,omitempty"`
 }
-type OpenSubsonicExtensions struct{}
+type OpenSubsonicExtension struct {
+	Name     string  `xml:"name,attr" json:"name"`
+	Versions []int32 `xml:"versions"  json:"versions"`
+}
+
+type OpenSubsonicExtensions []OpenSubsonicExtension
 
-// OpenSubsonic response type for multi-valued genres list
 type ItemGenre struct {
 	Name string `xml:"name,attr" json:"name"`
 }
 
+// ItemGenres holds a list of genres (OpenSubsonic). If it is null, it must be marshalled as an empty array.
 type ItemGenres []ItemGenre
 
 func (i ItemGenres) MarshalJSON() ([]byte, error) {

server/subsonic/responses/responses_test.go

@@ -725,6 +725,36 @@ var _ = Describe("Responses", func() {
 		})
 	})
 
+	Describe("OpenSubsonicExtensions", func() {
+		BeforeEach(func() {
+			response.OpenSubsonic = true
+			response.OpenSubsonicExtensions = &OpenSubsonicExtensions{}
+		})
+
+		Describe("without data", func() {
+			It("should match .XML", func() {
+				Expect(xml.MarshalIndent(response, "", "  ")).To(MatchSnapshot())
+			})
+			It("should match .JSON", func() {
+				Expect(json.MarshalIndent(response, "", "  ")).To(MatchSnapshot())
+			})
+		})
+
+		Describe("with data", func() {
+			BeforeEach(func() {
+				response.OpenSubsonicExtensions = &OpenSubsonicExtensions{
+					OpenSubsonicExtension{Name: "template", Versions: []int32{1, 2}},
+				}
+			})
+			It("should match .XML", func() {
+				Expect(xml.MarshalIndent(response, "", "  ")).To(MatchSnapshot())
+			})
+			It("should match .JSON", func() {
+				Expect(json.MarshalIndent(response, "", "  ")).To(MatchSnapshot())
+			})
+		})
+	})
+
 	Describe("InternetRadioStations", func() {
 		BeforeEach(func() {
 			response.InternetRadioStations = &InternetRadioStations{}