Function build_request_frame 

pub fn build_request_frame(
    opcode: Opcode,
    opaque: u32,
    cas: u64,
    extras: &[u8],
    key: &[u8],
    value: &[u8],
) -> Vec<u8> 

Build a binary-protocol request frame from parts. Useful for tests and for any code that needs to construct wire-format requests.