feat(backend): added skipped session metric for storage service

backend/internal/storage/storage.go

@@ -95,6 +95,7 @@ func (s *Storage) Upload(msg *messages.SessionEnd) (err error) {
 	if err != nil {
 		if strings.Contains(err.Error(), "big file") {
 			log.Printf("%s, sess: %d", err, msg.SessionID())
+			metrics.IncreaseStorageTotalSkippedSessions()
 			return nil
 		}
 		return err
@@ -110,6 +111,7 @@ func (s *Storage) openSession(filePath string, tp FileType) ([]byte, error) {
 	// Check file size before download into memory
 	info, err := os.Stat(filePath)
 	if err == nil && info.Size() > s.cfg.MaxFileSize {
+		metrics.RecordSkippedSessionSize(float64(info.Size()), tp.String())
 		return nil, fmt.Errorf("big file, size: %d", info.Size())
 	}
 	// Read file into memory

backend/pkg/metrics/storage/metrics.go

@@ -31,6 +31,32 @@ func IncreaseStorageTotalSessions() {
 	storageTotalSessions.Inc()
 }
 
+var storageSkippedSessionSize = prometheus.NewHistogramVec(
+	prometheus.HistogramOpts{
+		Namespace: "storage",
+		Name:      "session_size_bytes",
+		Help:      "A histogram displaying the size of each skipped session file in bytes.",
+		Buckets:   common.DefaultSizeBuckets,
+	},
+	[]string{"file_type"},
+)
+
+func RecordSkippedSessionSize(fileSize float64, fileType string) {
+	storageSkippedSessionSize.WithLabelValues(fileType).Observe(fileSize)
+}
+
+var storageTotalSkippedSessions = prometheus.NewCounter(
+	prometheus.CounterOpts{
+		Namespace: "storage",
+		Name:      "sessions_skipped_total",
+		Help:      "A counter displaying the total number of all skipped sessions because of the size limits.",
+	},
+)
+
+func IncreaseStorageTotalSkippedSessions() {
+	storageTotalSkippedSessions.Inc()
+}
+
 var storageSessionReadDuration = prometheus.NewHistogramVec(
 	prometheus.HistogramOpts{
 		Namespace: "storage",