Function hyper_headers_add 

#[unsafe(no_mangle)]
pub extern "C" fn hyper_headers_add(
    headers: *mut hyper_headers,
    name: *const u8,
    name_len: usize,
    value: *const u8,
    value_len: usize,
) -> hyper_code

Available on hyper_unstable_ffi and crate feature ffi only.

Adds the provided value to the list of the provided name.

If there were already existing values for the name, this will append the new value to the internal list.