Function base_filter 

pub fn base_filter<P: AsRef<str>>(
    path: P,
    max_body_bytes: u32,
) -> BoxedFilter<()>

Returns a boxed warp filter which handles the initial setup.

This includes:

• setting the full path
• setting the method to POST
• ensuring the “content-type” header exists and is set to “application/json”
• ensuring the body has at most max_body_bytes bytes