Spring ShallowEtagHeaderFilter setWriteWeakETag causes content-length header to be removed due to GZIP kicking in (Spring 3.2.2, Tomcat+Jetty)

Problem: Setting setWriteWeakETag to true causes the content-length header to be removed from the response headers. Without this flag, it sends content-length along normally.

If this is desired, this "side effect" should be documented, because content-length is important for frontend applications to show progress (among other things).

Why it matters: Combining GZIP compression with ETag only works with weak ETags, otherwise GZIP compression won't work.

Configuration:

    @Bean
    public ShallowEtagHeaderFilter shallowEtagHeaderFilter() {
        ShallowEtagHeaderFilter filter = new ShallowEtagHeaderFilter();
        filter.setWriteWeakETag(true);
        return filter;
    }

Documentation: here and here make no mention of this.

Comment From: bclozel

As far as I know this filter does not remove the "Content-Length" header at all. Is it possible that the Servlet container removes the content-length header because it compresses the response on the fly and doesn't know the actual length before writing the resource?

In this case, I would argue that this should be documented by the Servlet container.

Comment From: mdmm13

As far as I know this filter does not remove the "Content-Length" header at all. Is it possible that the Servlet container removes the content-length header because it compresses the response on the fly and doesn't know the actual length before writing the resource?

In this case, I would argue that this should be documented by the Servlet container.

Indeed, so this is caused by content compression, which only works with this flag, so I had it backwards. Might be worth documenting the link between setWriteWeakETag and GZIP. Will close as this belongs elsewhere.