fn count_extensions(raw: &[u8]) -> Option<u64>Expand description
Count the extension headers in a raw block, or None if the bytes do not
tile into whole headers.
The block is stored opaque, so the number of headers in it is not something
the value carries - it is a property of the bytes, recovered by walking them
with the same rule skip_extensions reads them by. This is the only draft
that needs it: draft-08 states the field as “Extension Count”, a number of
headers, and every later draft states a byte length that
extensions.len() supplies directly.