fix

internal/server/server.go

@@ -289,7 +289,8 @@ func (s *Server) HandleUpload(w http.ResponseWriter, r *http.Request) {
 
 	timestamp := time.Now().Format("2006-01-02_15:04:05")
 
-	if client.StorageType == "s3" {
+	// Check if S3 backend is available for S3 storage type
+	if client.StorageType == "s3" && s.s3Backend != nil {
 		// S3 upload
 		storageKey := fmt.Sprintf("%s/%s_%s.zfs", req.ClientID, req.DatasetName, timestamp)
 		if req.Compressed {
@@ -303,6 +304,12 @@ func (s *Server) HandleUpload(w http.ResponseWriter, r *http.Request) {
 			StorageKey:   storageKey,
 			UploadURL:    fmt.Sprintf("/upload-stream/%s", req.ClientID),
 		})
+	} else if client.StorageType == "s3" && s.s3Backend == nil {
+		// S3 requested but not configured
+		respondJSON(w, http.StatusInternalServerError, UploadResponse{
+			Success: false,
+			Message: "S3 storage requested but S3 backend is not configured on server",
+		})
 	} else {
 		// Local ZFS receive
 		snapshotName := fmt.Sprintf("%s@%s_%s", client.Dataset, req.ClientID, timestamp)
@@ -346,9 +353,17 @@ func (s *Server) HandleUploadStream(w http.ResponseWriter, r *http.Request) {
 	ctx := context.Background()
 
 	// Upload to S3
+	// When using chunked transfer (io.Pipe), ContentLength is -1
+	// MinIO requires -1 for unknown size to use streaming upload
 	size := r.ContentLength
 	if size < 0 {
-		size = 0
+		size = -1 // Use streaming upload for unknown size
+	}
+
+	if s.s3Backend == nil {
+		log.Printf("Error: S3 backend not initialized")
+		http.Error(w, "S3 backend not configured", http.StatusInternalServerError)
+		return
 	}
 
 	if err := s.s3Backend.Upload(ctx, storageKey, r.Body, size); err != nil {