Enum NarResidency 

pub enum NarResidency {
    Streaming,
    Capped(usize),
    WholeValue,
}

What a backend’s NAR path costs in resident memory.

Every StorageBackend implementor must state this — it has no default. That is the mechanism, not decoration: the streaming verbs (get_nar_stream / put_nar_stream) do carry a buffering fallback so a test double stays a few lines, and without a required declaration a new production backend could silently inherit it and reintroduce the OOM. Making the declaration mandatory means adding a backend without deciding is a compile error, and shipping a production backend that declares WholeValue is caught by [every_production_backend_bounds_its_nar_path] in CI.

Tier-honest: this is parse-time-rejected (you cannot omit the decision) plus CI-gate-caught (you cannot ship the wrong one from the factory). It is not truly-unrepresentable — the buffering code path still exists and a hand-constructed backend may use it.

Variants

Streaming

O(chunk). The backend never holds more than NAR_CHUNK_BYTES of a NAR, whatever the NAR’s size.

Capped(usize)

O(min(nar, cap)). Bounded by a configured cap; a NAR past the cap is refused (StoreError::TooLarge), never buffered. The hot-tier shape: a cap is a real bound because the durable tiers below still take the write.

WholeValue

O(nar). The whole NAR is materialized. Legal only for in-memory test doubles and small-value stores — never for a tier that serves real builds.

Implementations

impl NarResidency

pub const fn is_bounded(self) -> bool

Whether the peak is bounded independently of NAR size.

pub fn weaker(self, other: NarResidency) -> NarResidency

The weaker of two residencies — the honest answer for a composite backend, whose real cost is its worst tier’s.

Order: Streaming (best) < Capped < WholeValue (worst); two Cappeds compose to the larger cap, because either one may be the one that holds the bytes.

Trait Implementations

impl Clone for NarResidency

fn clone(&self) -> NarResidency

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for NarResidency

impl Debug for NarResidency

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

Formats the value using the given formatter.

impl Eq for NarResidency

impl PartialEq for NarResidency

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for NarResidency