Struct FlowControlConfig 

pub struct FlowControlConfig {
    pub mode: FlowControlMode,
    pub min_window_size: usize,
    pub max_window_size: usize,
    pub ai_step: usize,
    pub md_factor: f64,
    pub no_honest_deadline: Duration,
    pub persist_stall_parks: u32,
    pub frame_retries: u32,
}

Client-tunable flow-control parameters. Defaults are deliberately conservative (anti-grief-preserving): the window starts at the floor and only grows on proven delivery, and the opt-in robustness knobs are off. This is the clean profile.

Flow control is enabled per-session by providing this config (the transport’s SessionClientConfig::flow_control is an Option — None leaves the session unpaced with today’s behaviour), so there is no separate enabled flag.

Fields

mode: FlowControlMode

Honest-clock mode. Default [FlowControlMode::Reliable].

min_window_size: usize

Minimum in-flight bytes that are always admitted, regardless of delivery feedback or SURB supply. Guarantees the duplex socket never deadlocks (acks/keep-alives can always flow) and is the hard floor a malicious peer can never push the window below — but also never above without honest delivery. Keep small (a few frames). Default 4 KiB.

max_window_size: usize

Hard ceiling on the send window, seeded from the bandwidth-delay product (drain_rate_hint × rtt). The window never opens past this even under sustained delivery. Default 2 MiB.

ai_step: usize

Additive-increase step (bytes added to the window per fully-delivered window) while in congestion avoidance. Default 16 KiB.

md_factor: f64

Multiplicative-decrease factor applied to the window on loss or a soft backoff hint. Must be in (0.0, 1.0). Default 0.5 (classic AIMD).

no_honest_deadline: Duration

In [FlowControlMode::Segmentation] there is no honest delivery signal, so admission may park indefinitely behind a shrinking SURB ceiling. This deadline bounds how long the writer parks before it re-checks the ceiling / makes keep-progress at the floor. Default 250 ms.

persist_stall_parks: u32

Persist probe (opt-in robustness). Consecutive no-progress parks before the writer admits a bounded min_window_size beyond cwnd (still SURB-capped) to break an end-of-stream tail deadlock on a slow/throttled return path. 0 disables it — the default, i.e. the verified clean behaviour. A robust profile (e.g. for deliberately SURB-throttled paths) sets ~8 (≈2 s at the default keep-progress deadline). See the PacedWriter admission logic.

frame_retries: u32

Frame retransmission budget under flow control (opt-in robustness). Applied to the reliable socket’s max_outgoing_frame_retries when flow control is enabled. 2 (the original) is the default; a robust profile raises it (~8) so a merely-delayed ack on a temporarily-starved return path recovers the frame instead of abandoning it (an abandoned frame leaves a gap → stream corruption).

Implementations

impl FlowControlConfig

pub fn robust() -> FlowControlConfig

The robust profile: the clean defaults plus the opt-in tail-tolerance bundle (persist probe + larger retransmission budget) for deliberately SURB-throttled / high-latency return paths. See Self::persist_stall_parks and Self::frame_retries.

pub fn with_bdp( self, drain_rate_bytes_per_sec: u64, rtt: Duration, ) -> FlowControlConfig

Convenience constructor seeding max_window_size from a bandwidth-delay product.

drain_rate_bytes_per_sec is the estimated rate at which the counterparty can drain the return path (for a SURB-capped echo: max_surbs_per_sec / surbs_per_reply_packet × bytes_per_packet). rtt is the round-trip delivery latency.

Trait Implementations

impl Clone for FlowControlConfig

fn clone(&self) -> FlowControlConfig

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FlowControlConfig

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

Formats the value using the given formatter.

impl Default for FlowControlConfig

fn default() -> FlowControlConfig

Return FlowControlConfig { mode: Default::default(), min_window_size: 4 * 1024, max_window_size: 2 * 1024 * 1024, ai_step: 16 * 1024, md_factor: 0.5, no_honest_deadline: Duration::from_millis(250), persist_stall_parks: 0, frame_retries: 2 }

impl PartialEq for FlowControlConfig

fn eq(&self, other: &FlowControlConfig) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for FlowControlConfig

impl StructuralPartialEq for FlowControlConfig