Function receive 

fn receive(
    how: &Receiving<'_>,
    store: &Store,
    file: &str,
    path: &Path,
    value: Option<&str>,
    current: Option<&str>,
    seen: &dyn Fn(&str) -> bool,
    known: Option<&Known>,
    gathered: Option<&Stat>,
    damaged: &mut BTreeMap<String, (u64, u64, u64)>,
) -> Result<Received, Fault>

Another device’s change to a file sealed apart, written here: its content opened from the folder beside the file and checked, then put in its place, the file as it was kept first (history: by reference when a record named that content, else copied). A file here that is neither what that change replaced nor a content the others’ records name (seen) changed here too: it is kept beside, under a name that says so (its path in the folder returned), never lost. A file changed here since it was looked at (gathered) is not written over. Nothing is written without room for it, for the copy kept, and some left (disk::kept_free).