The Rack::Chunked middleware conflict with the Rack::Sendfile middleware / approach.

The Rack::Chunked doesn't test if the 'X-Sendfile' header family is set, adding the chunked transfer encoding header.

This results in two possible approaches:

1. The server ignores any headers set by the application (losing any cookie data or other custom headers).

2. The encoding header remains intact*, causing the response to fail.

Both approaches result in loss of data (either the cookie data or a failed response).

The best way to fix the issue might be to add tests to the Rack::Chunked middleware, testing for the 'X-Sendfile' header family.

* Consider that the header might have been Transfer-Encoding: gzip and the file X-sendfile: style.css.gz, which means that the header should have remained intact.

This issue originated here.