add flush

handler/meter/meter.go

@@ -92,6 +92,7 @@ func (h *Handler) Metrics(ctx context.Context, req *codecpb.Frame, rsp *codecpb.
 
 	if md, ok := metadata.FromIncomingContext(ctx); gzipAccepted(md) && ok {
 		md.Set(contentEncodingHeader, "gzip")
+		ctx = metadata.NewIncomingContext(ctx, md)
 		gz := gzipPool.Get().(*gzip.Writer)
 		defer gzipPool.Put(gz)
 
@@ -99,6 +100,7 @@ func (h *Handler) Metrics(ctx context.Context, req *codecpb.Frame, rsp *codecpb.
 		defer gz.Close()
 
 		w = gz
+		gz.Flush()
 	}
 
 	if err := h.opts.Meter.Write(w, h.opts.MeterOptions...); err != nil {