fix(prometheus): report subsonic error code (#4282)

* fix(prometheus): report subsonic error code

* address feedback

core/metrics/prometheus.go

@@ -20,7 +20,7 @@ import (
 type Metrics interface {
 	WriteInitialMetrics(ctx context.Context)
 	WriteAfterScanMetrics(ctx context.Context, success bool)
-	RecordRequest(ctx context.Context, endpoint, method, client string, status int, elapsed int64)
+	RecordRequest(ctx context.Context, endpoint, method, client string, status int32, elapsed int64)
 	RecordPluginRequest(ctx context.Context, plugin, method string, ok bool, elapsed int64)
 	GetHandler() http.Handler
 }
@@ -56,7 +56,7 @@ func (m *metrics) WriteAfterScanMetrics(ctx context.Context, success bool) {
 	getPrometheusMetrics().mediaScansCounter.With(scanLabels).Inc()
 }
 
-func (m *metrics) RecordRequest(_ context.Context, endpoint, method, client string, status int, elapsed int64) {
+func (m *metrics) RecordRequest(_ context.Context, endpoint, method, client string, status int32, elapsed int64) {
 	httpLabel := prometheus.Labels{
 		"endpoint": endpoint,
 		"method":   method,
@@ -233,7 +233,7 @@ func (n noopMetrics) WriteInitialMetrics(context.Context) {}
 
 func (n noopMetrics) WriteAfterScanMetrics(context.Context, bool) {}
 
-func (n noopMetrics) RecordRequest(context.Context, string, string, string, int, int64) {}
+func (n noopMetrics) RecordRequest(context.Context, string, string, string, int32, int64) {}
 
 func (n noopMetrics) RecordPluginRequest(context.Context, string, string, bool, int64) {}
 

server/subsonic/api.go

@@ -333,6 +333,7 @@ func sendResponse(w http.ResponseWriter, r *http.Request, payload *responses.Sub
 		sendError(w, r, err)
 		return
 	}
+
 	if payload.Status == responses.StatusOK {
 		if log.IsGreaterOrEqualTo(log.LevelTrace) {
 			log.Debug(r.Context(), "API: Successful response", "endpoint", r.URL.Path, "status", "OK", "body", string(response))
@@ -342,6 +343,17 @@ func sendResponse(w http.ResponseWriter, r *http.Request, payload *responses.Sub
 	} else {
 		log.Warn(r.Context(), "API: Failed response", "endpoint", r.URL.Path, "error", payload.Error.Code, "message", payload.Error.Message)
 	}
+
+	statusPointer, ok := r.Context().Value(subsonicErrorPointer).(*int32)
+
+	if ok && statusPointer != nil {
+		if payload.Status == responses.StatusOK {
+			*statusPointer = 0
+		} else {
+			*statusPointer = payload.Error.Code
+		}
+	}
+
 	if _, err := w.Write(response); err != nil {
 		log.Error(r, "Error sending response to client", "endpoint", r.URL.Path, "payload", string(response), err)
 	}

server/subsonic/api_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/navidrome/navidrome/utils/gg"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
+	"golang.org/x/net/context"
 )
 
 var _ = Describe("sendResponse", func() {
@@ -109,4 +110,18 @@ var _ = Describe("sendResponse", func() {
 		})
 	})
 
+	It("updates status pointer when an error occurs", func() {
+		pointer := int32(0)
+
+		ctx := context.WithValue(r.Context(), subsonicErrorPointer, &pointer)
+		r = r.WithContext(ctx)
+
+		payload.Status = responses.StatusFailed
+		payload.Error = &responses.Error{Code: responses.ErrorDataNotFound}
+
+		sendResponse(w, r, payload)
+		Expect(w.Code).To(Equal(http.StatusOK))
+
+		Expect(pointer).To(Equal(responses.ErrorDataNotFound))
+	})
 })

server/subsonic/middlewares.go

@@ -226,21 +226,35 @@ func playerIDCookieName(userName string) string {
 	return cookieName
 }
 
+const subsonicErrorPointer = "subsonicErrorPointer"
+
 func recordStats(metrics metrics.Metrics) func(next http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		fn := func(w http.ResponseWriter, r *http.Request) {
 			ww := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
 
+			status := int32(-1)
+			contextWithStatus := context.WithValue(r.Context(), subsonicErrorPointer, &status)
+
 			start := time.Now()
 			defer func() {
+				elapsed := time.Since(start).Milliseconds()
+
 				// We want to get the client name (even if not present for certain endpoints)
 				p := req.Params(r)
 				client, _ := p.String("c")
 
-				metrics.RecordRequest(r.Context(), strings.Replace(r.URL.Path, ".view", "", 1), r.Method, client, ww.Status(), time.Since(start).Milliseconds())
+				// If there is no Subsonic status (e.g., HTTP 501 not implemented), fallback to HTTP
+				if status == -1 {
+					status = int32(ww.Status())
+				}
+
+				shortPath := strings.Replace(r.URL.Path, ".view", "", 1)
+
+				metrics.RecordRequest(r.Context(), shortPath, r.Method, client, status, elapsed)
 			}()
 
-			next.ServeHTTP(ww, r)
+			next.ServeHTTP(ww, r.WithContext(contextWithStatus))
 		}
 		return http.HandlerFunc(fn)
 	}