Enum ConnectionEstablishmentError 

#[non_exhaustive]
pub enum ConnectionEstablishmentError {
    Network(BackendError),
    BrokerRejected {
        code: ConnectReasonCode,
    },
    Timeout {
        timeout_millis: u64,
    },
    BrokerDisconnected {
        reason_code: Option<DisconnectReasonCode>,
    },
}

Errors that can occur during MQTT connection establishment phase.

These errors represent different failure modes when attempting to establish an initial connection to the MQTT broker. They are distinguished from runtime connection errors that occur after a successful initial connection.

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.

Network(BackendError)

Network-level connection failure (DNS, TCP, TLS, I/O, protocol state)

BrokerRejected

MQTT broker rejected the connection attempt

The network connection was successful, but the MQTT broker refused the connection for protocol-level reasons (authentication, protocol version, etc.)

Fields

code: ConnectReasonCode

The specific rejection reason code from the broker

Timeout

Connection establishment exceeded the configured timeout

The connection attempt took longer than the specified timeout period. This can happen due to network latency, broker overload, or network instability.

Fields

timeout_millis: u64

The timeout duration that was exceeded, in milliseconds

BrokerDisconnected

The broker sent a DISCONNECT during the establishment handshake.

Distinct from BrokerRejected (a failed CONNACK): here the broker tore the connection down with a v5 DISCONNECT. Only reachable on MQTT 5, where the reason code is always present (a bare DISCONNECT decodes as NormalDisconnection).

Fields

reason_code: Option<DisconnectReasonCode>

The v5 disconnect reason code.

Trait Implementations

impl Debug for ConnectionEstablishmentError

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

Formats the value using the given formatter.

impl Display for ConnectionEstablishmentError

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

Formats the value using the given formatter.

impl Error for ConnectionEstablishmentError

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<BackendPollError> for ConnectionEstablishmentError

fn from(err: BackendPollError) -> ConnectionEstablishmentError

Classify the poll error, recovering the broker reason code on the ConnectionRefused path.

impl From<ConnectionEstablishmentError> for MqttClientError

fn from(source: ConnectionEstablishmentError) -> MqttClientError

Converts to this type from the input type.