Function cjdns_core::splice::build_label

pub fn build_label<L: LabelBits>(
    path_hops: &[PathHop<'_, L>]
) -> Result<(RoutingLabel<L>, Vec<RoutingLabel<L>>)>

This will construct a label using an array representation of a path (path_hops). If any label along the path needs to be re-encoded, it will be.

Each element in the array represents a hop (node) in the path and each of them has PathHop.label_p and/or PathHop.label_n depending on whether there is a previous and/or next hop. PathHop.label_p is necessary to know the width of the inverse path hop so that the label can be re-encoded if necessary.

let label = build_label(&[
    PathHop::new(l("0000.0000.0000.0000"), l("0000.0000.0000.0015"), &schemes::V358),
    PathHop::new(l("0000.0000.0000.009e"), l("0000.0000.0000.008e"), &schemes::V358),
    PathHop::new(l("0000.0000.0000.0013"), l("0000.0000.0000.00a2"), &schemes::V358),
    PathHop::new(l("0000.0000.0000.001b"), l("0000.0000.0000.001d"), &schemes::V358),
    PathHop::new(l("0000.0000.0000.00ee"), l("0000.0000.0000.001b"), &schemes::V358),
    PathHop::new(l("0000.0000.0000.0019"), l("0000.0000.0000.001b"), &schemes::V358),
    PathHop::new(l("0000.0000.0000.0013"), l("0000.0000.0000.0000"), &schemes::V358),
]);
let expected = (
    l("0000.0003.64b5.10e5"),
    vec![
        l("0000.0000.0000.0015"),
        l("0000.0000.0000.008e"),
        l("0000.0000.0000.00a2"),
        l("0000.0000.0000.001d"),
        l("0000.0000.0000.0092"),
        l("0000.0000.0000.001b"),
    ]
);
assert_eq!(label, Ok(expected));

This function results in a tuple containing 2 elements, label and path. label is the final label for this path. And path is the hops to get there. Notice the second to last hop in the path has been changed from 001b to 0092. This is a re-encoding to ensure that the label remains the right length as the reverse path for this hop is 00ee which is longer than 001b.