Struct Cached 

pub struct Cached<T> { /* private fields */ }

A credential that expires and can be obtained again.

A Mutex rather than a lock-free cell: obtaining twice concurrently is harmless but wasteful, and this sits on the once-per-refresh path rather than the once-per-request one. The lock is held across obtaining, so N threads arriving at an expired credential together produce one request rather than N.

Implementations

impl<T> Cached<T>

pub const fn new() -> Self

An empty cache, refreshing within REFRESH_WITHIN of expiry.

pub const fn with_margin(margin: Duration) -> Self

An empty cache with a margin of its own.

For tests, which cannot wait a minute to watch a margin work.

pub fn invalidate(&self)

Drops what is held, so the next get obtains.

The reactive door: a store that has just been told its credential is no longer accepted calls this and tries once more.

impl<T: Clone> Cached<T>

pub fn get( &self, obtain: impl FnOnce(Option<&T>) -> Result<Issued<T>, Error>, ) -> Result<T, Error>

The current credential, obtaining or refreshing it as needed.

obtain is handed the credential it is replacing, if there is one and it has merely gone stale — which is what lets Vault renew a token rather than log in again. It is None on the first call and after invalidate, because there is then nothing to extend.

obtain is a closure rather than a trait method so this module stays free of HTTP: what it decides is when, not how.

Errors

Whatever obtain reports. What was held survives a failed obtain: a credential that is merely close to expiry still works, and throwing it away because a refresh failed would turn a recoverable moment into an outage.

Trait Implementations

impl<T> Debug for Cached<T>

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

Formats the value using the given formatter.

impl<T> Default for Cached<T>

fn default() -> Self

Returns the “default value” for a type.