Function is_valid_node_id 

pub fn is_valid_node_id(node_id: &str) -> bool

The node-id rule a relay enforces at registration, for callers that persist a node-id (such as relay claim) and must not save one the relay refuses. Whether node_id is a routing label a relay will register: non-empty, at most MAX_NODE_ID_LEN bytes, and printable ASCII without spaces.

The relay refuses Register for anything else, so a daemon must not persist a node-id that fails this check: it would save a profile that can never register.