Function read_value 

pub(crate) fn read_value<'r, R, T, F, E>(
    reader: &mut R,
    header: Header,
    f: F,
) -> Result<T, E>
where
    R: Reader<'r>,
    E: From<Error>,
    F: FnOnce(&mut R, Header) -> Result<T, E>,

Read a value (i.e. the “V” part of a “TLV” field) using the provided header.

This calls the provided function f with a nested reader created using Reader::read_nested.