Struct PathMtuState 

pub struct PathMtuState { /* private fields */ }

Path MTU tracking for a single session.

Destination side: observes path_mtu from incoming SessionDatagram envelopes and generates PathMtuNotification messages back to the source.

Source side: applies received PathMtuNotification to limit outbound datagram size. Decrease is immediate; increase requires 3 consecutive notifications.

Implementations

impl PathMtuState

pub fn new() -> Self

Create path MTU state with no initial measurement.

pub fn current_mtu(&self) -> u16

Current effective path MTU (source-side, for sending).

pub fn last_observed_mtu(&self) -> u16

Last observed incoming path MTU (destination-side).

pub fn update_interval_from_srtt(&mut self, srtt_ms: f64)

Update notification interval from SRTT: max(10s, 5 * SRTT).

pub fn seed_source_mtu(&mut self, outbound_mtu: u16)

Seed source-side current_mtu from outbound transport MTU.

Called on each send. Only decreases (never increases) the current_mtu so the destination’s PathMtuNotification can still raise it later. Ensures current_mtu doesn’t stay at u16::MAX before any notification arrives from the destination.

pub fn observe_incoming_mtu(&mut self, path_mtu: u16)

Observe the path_mtu from an incoming SessionDatagram envelope.

Called on the destination (receiver) side for every session message.

pub fn should_send_notification(&self, now: Instant) -> bool

Check if a PathMtuNotification should be sent.

Send on first measurement, on decrease (immediate), or periodic confirmation at the notification interval.

pub fn build_notification(&mut self, now: Instant) -> Option<u16>

Build a PathMtuNotification from current state.

Returns the path_mtu value to send. Caller handles encoding.

pub fn apply_notification(&mut self, reported_mtu: u16, now: Instant) -> bool

Apply a received PathMtuNotification.

• Decrease: immediate (take the lower value).
• Increase: require 3 consecutive notifications with the same higher value, spanning at least 2 * notification_interval.

Returns true if the effective MTU changed.

Trait Implementations

impl Default for PathMtuState

fn default() -> Self

Returns the “default value” for a type.