Enum FetchError 

#[non_exhaustive]
pub enum FetchError {
    AuthorityDenied(String),
    SubjectNotFound(String),
    Throttled(String),
    Other(String),
}

Typed fetch failure. Each variant carries a free-form detail for audit logs; the composer collapses every variant onto super::EpochRevocationError::Transient (fail-closed) so the engine sees a uniform contract regardless of substrate flavor.

0.11.0 BREAKING — widened from pub struct FetchError(pub String) to a typed enum. The variants exist so Fetcher impls (today chat-api’s PgFetcher; a possible future AdminSvFetcher over a PAS per-user readout — design-on-ice in STANDARDS_AUTH_INVALIDATION §5.4.1) can hand the composer a substrate-grained reason that survives into dashboards. The composer still collapses to Transient — fail-closed contract preserved.

#[non_exhaustive] — adding a new variant in a future minor is non-breaking for downstream Fetcher impls (they construct, they don’t match) but requires consumers that DO match to carry a wildcard arm. The composer matches via to_string() / Display-collapse rather than variant-specific arms, so downstream additions don’t ripple.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

AuthorityDenied(String)

Authority denied — the caller credential is rejected by the authoritative substrate (e.g. JWT-signed Admin gRPC client lacks pas.session.read scope, or API-key revoked). Distinct from SubjectNotFound because the substrate refused even to answer the query, not “answered: subject doesn’t exist”.

SubjectNotFound(String)

Subject not found — substrate confirmed the queried sub is absent. For sv-axis this is a “fail closed” signal because admitting a token whose subject the authority can’t confirm would let dangling tokens slip through.

Throttled(String)

Throttled — substrate rate-limit / 429-class response. Surfaces as transient so the caller backs off; not a security signal.

Other(String)

Catch-all for substrate transients (network, deserialization, unspecified 5xx). Replaces 0.10.x’s FetchError(String).

Trait Implementations

impl Debug for FetchError

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

Formats the value using the given formatter.

impl Display for FetchError

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

Formats the value using the given formatter.

impl Error for FetchError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

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

Provides type-based access to context intended for error reports.