Function write_advertisement 

pub fn write_advertisement<'a>(
    format: ObjectFormat,
    capabilities: Capabilities,
    refs: impl IntoIterator<Item = (ObjectId, &'a [u8])>,
    output: &mut impl Write,
) -> Result<()>

Write a smart HTTP receive-pack advertisement from a stable, byte-sorted ref projection. Names are raw Git bytes. The host must discard partial output on an invalid ref or sink failure. Only opt into host-backed features.