Struct SubnetPolicy 

pub struct SubnetPolicy { /* private fields */ }

Policy for assigning nodes to subnets based on capability tags.

Rules are evaluated in order. Each rule maps a tag prefix to a hierarchy level and provides a value map for the tag’s value.

Example: a node with tags ["region:us-west", "fleet:alpha"] and rules:

• SubnetRule { tag_prefix: "region:", level: 0, values: {"us-west": 1} }
• SubnetRule { tag_prefix: "fleet:", level: 1, values: {"alpha": 2} }

Would get SubnetId::new(&[1, 2]).

Semantics (rule precedence and matching contract)

Pinned by unit tests in this module — changes here are behavioral breaks for operators configuring subnets:

1. Rule order is declaration order. assign() walks rules in the order passed to add_rule(). Two rules targeting the same level with overlapping values resolve as later-rule-wins: the earlier rule may write the level byte first, but a subsequent match at the same level overwrites it.
2. First tag wins per rule. Inside one rule, the first capability tag whose stripped suffix is present in values wins — subsequent tags matching the same rule are ignored.
3. No partial-prefix match on values. tag_prefix is stripped by str::strip_prefix; the remaining value is then looked up by exact string equality against values. A rule region: matching on "us" will not match the tag region:us:extra (the stripped suffix "us:extra" is not in the values map).
4. Unmatched levels stay zero. Levels with no rule (or a rule that failed to match) remain 0, which SubnetId interprets as “no restriction at this level”.

Implementations

impl SubnetPolicy

pub fn new() -> Self

Create an empty policy (all nodes get SubnetId::GLOBAL).

pub fn add_rule(self, rule: SubnetRule) -> Self

Add a rule to the policy.

Panics

Panics if the rule’s level is >= 4. For untrusted input (config files, FFI, JSON) prefer Self::try_add_rule, which returns a SubnetError instead of panicking.

pub fn try_add_rule(self, rule: SubnetRule) -> Result<Self, SubnetError>

Fallible variant of Self::add_rule.

Pre-existing add_rule panics on rule.level >= 4. Subnet policies typically come from config / FFI / JSON and a malformed entry should surface as a recoverable error rather than crashing the daemon loader.

pub fn assign(&self, caps: &CapabilitySet) -> SubnetId

Assign a subnet ID to a node based on its capability tags.

Evaluates all rules against the node’s tags. Unmatched levels remain zero (meaning “no restriction at that level”).

Trait Implementations

impl Clone for SubnetPolicy

fn clone(&self) -> SubnetPolicy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SubnetPolicy

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for SubnetPolicy

fn default() -> Self

Returns the “default value” for a type.