utils

const (
	DefaultFileMod           os.FileMode = 0o644
	DefaultExecutableFileMod os.FileMode = 0o755
	DefaultDirMod            os.FileMode = 0o755
)

const DefaultMqttConnectTimeout time.Duration = 30 * time.Second

DefaultMqttConnectTimeout bounds a single MQTT connect attempt.

This is intentionally decoupled from InitialReconnectInterval. An earlier design capped the connect timeout at the shortest reconnect backoff slot (1.5 * InitialReconnectInterval, i.e. ~1s) so a connect attempt could never outlive the next backoff slot. In practice that cap was far too aggressive: the TCP + TLS + MQTT CONNACK handshake to Azure IoT Hub routinely takes longer than a second on slow, high-latency, or lossy links (satellite, congested VPN, poor cellular, distant regions), so every attempt timed out before it could complete and the device never came online.

The connect timeout and the reconnect backoff schedule serve different purposes and are now sized independently: the backoff (ReconnectTimeout Generator) governs how long to wait *between* attempts, while this value governs how long a single attempt is allowed to run. A slow-but-successful handshake is now allowed to complete rather than being aborted prematurely; the reconnect loop still backs off and retries when an attempt genuinely fails. 30s comfortably accommodates a slow TLS handshake while still bounding a truly stuck attempt. Endpoints that need even more can raise it per-device via the device config (mqtt_connect_timeout_seconds).

const DefaultMqttKeepAlive time.Duration = 30 * time.Second

DefaultMqttKeepAlive is the interval at which the client sends MQTT PING requests to the broker while otherwise idle. It is configured explicitly rather than relying on paho's implicit default so the liveness behavior of a marginal connection is predictable. Together with DefaultMqttPingTimeout it bounds how quickly a silently-dropped connection is detected: the client declares the connection lost (triggering the reconnect loop) within roughly DefaultMqttKeepAlive + DefaultMqttPingTimeout.

const DefaultMqttPingTimeout time.Duration = 10 * time.Second

DefaultMqttPingTimeout is how long the client waits for a PINGRESP after sending a PING before considering the connection dead. Set explicitly for the same predictability reason as DefaultMqttKeepAlive.

const InitialReconnectInterval time.Duration = time.Second

InitialReconnectInterval is the base interval the reconnect backoff seeds from. The first reconnect slot produced by ReconnectTimeoutGenerator is therefore ~2x this value (doubled) with up to ±25% jitter, i.e. it is never shorter than 1.5 * InitialReconnectInterval.