Function fastly_sys::fastly_http_req::header_value_get

pub unsafe extern "C" fn header_value_get(
    req_handle: RequestHandle, 
    name: *const u8, 
    name_len: usize, 
    value: *mut u8, 
    value_max_len: usize, 
    nwritten: *mut usize
) -> FastlyStatus