Function send_known 

fn send_known(
    client: &Client,
    kind: Kind,
    dir: &Path,
    listed: &Listed,
    item: &ItemState,
    refetch: &mut BTreeSet<String>,
    report: &mut Report,
) -> Result<Sent, SyncError>

One item known to the server, sent if it changed here, deleted there if deleted here. A file whose size and time are as noted is not read.