Struct Label 

pub struct Label(/* private fields */);

A domain label: a value that CANNOT be invented.

Why a type where &'static [u8] used to suffice

I-12 requires unique, prefix-free labels, guarded by four probes: uniqueness, prefix-freeness, versioning, and agreement with specification §3.6. All four inspect ALL, the REGISTRY. They never saw call sites: Transcript::new and seal::slot_info accepted arbitrary bytes, and a caller could pass b"CC/v1/lease-cache", a string absent from the registry and extending LEASE. No probe would detect that, because it would check the list rather than the call.

The new type closes exactly this gap: Label values come ONLY from this module’s constants because the constructor is private and the field is not public. The registry’s guarantee becomes a guarantee of every call, checked by the compiler rather than a probe.

Why Debug prints the string itself

A label is not secret: it is plaintext in every file and in the specification. I-11 forbids secrets in Debug, not domain names; hiding the label would blind signature-failure debugging without the slightest benefit.

Implementations

impl Label

pub const fn as_bytes(self) -> &'static [u8]

Label bytes: what enters info, the transcript, and the preimage.

pub const fn len(self) -> usize

Byte length. Needed in const context: the private-metadata AAD layout is computed at build time (aead::META_AAD_LEN).

pub const fn is_empty(self) -> bool

Whether the label is empty. Always false: a label with no bytes cannot separate domains, but without this method clippy::len_without_is_empty is right.

Trait Implementations

impl Clone for Label

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Label

impl Debug for Label

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

Formats the value using the given formatter.

impl Eq for Label

impl Hash for Label

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Label

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for Label

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl PartialOrd for Label

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for Label