The buffer filter is used to stop filter iteration and wait for a fully buffered complete request. This is useful in different situations including protecting some applications from having to deal with partial requests and high network latency.
If enabled the buffer filter populates content-length header if it is not present in the request already. The behavior can be disabled using the runtime feature envoy.reloadable_features.buffer_filter_populate_content_length.
This filter should be configured with the name envoy.filters.http.buffer.