fix

internal/client/client.go

@@ -134,9 +134,11 @@ func (c *Client) streamToS3(snapshot *zfs.Dataset, uploadURL, storageKey string)
 		gzWriter := gzip.NewWriter(pw)
 
 		go func() {
-			defer pw.Close()
-			defer gzWriter.Close()
+			// Copy zfs output to gzip writer
 			io.Copy(gzWriter, zfsOut)
+			// Close gzip writer first to flush footer, then close pipe
+			gzWriter.Close()
+			pw.Close()
 		}()
 
 		reader = pr

internal/client/snapshot.go

@@ -222,9 +222,11 @@ func (c *Client) streamIncrementalToS3(snapshot *zfs.Dataset, base, uploadURL, s
 		gzWriter := gzip.NewWriter(pw)
 
 		go func() {
-			defer pw.Close()
-			defer gzWriter.Close()
+			// Copy zfs output to gzip writer
 			io.Copy(gzWriter, zfsOut)
+			// Close gzip writer first to flush footer, then close pipe
+			gzWriter.Close()
+			pw.Close()
 		}()
 
 		reader = pr

internal/server/server.go

@@ -346,9 +346,11 @@ 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 err := s.s3Backend.Upload(ctx, storageKey, r.Body, size); err != nil {