Enum CapabilityError 

#[non_exhaustive]
pub enum CapabilityError {
    RequiresV5 {
        feature: &'static str,
    },
    RequiresPersistentSession {
        feature: &'static str,
    },
    UnsupportedByBackend {
        feature: &'static str,
    },
}

A requested feature is not available on the negotiated backend/protocol.

Validated early (at config or publish time) so a capability gap surfaces as one typed error rather than a silent no-op or a backend panic.

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.

RequiresV5

The feature requires MQTT 5; connect with ?protocol=5 (or the equivalent config) to use it.

Fields

feature: &'static str

The feature that was requested

RequiresPersistentSession

The feature needs the broker to keep session state across connections; the requested SessionPolicy discards it.

Fields

feature: &'static str

The feature that was requested

UnsupportedByBackend

The feature is not supported by the active backend (reserved for the post-0.4 ack-track backends).

Fields

feature: &'static str

The feature that was requested

Trait Implementations

impl Debug for CapabilityError

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

Formats the value using the given formatter.

impl Display for CapabilityError

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

Formats the value using the given formatter.

impl Error for CapabilityError

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.

impl From<CapabilityError> for MqttClientError

fn from(source: CapabilityError) -> MqttClientError

Converts to this type from the input type.