bacnet_server/server/

discovery.rs

//! Discovery rate-limiting, duplicate suppression, and directed response handling.
//!
//! Controls response amplification for unconfirmed discovery services (Who-Is
//! and Who-Has) per ASHRAE 135-2020 Clauses 16.9 and 16.10.

use std::collections::HashMap;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, Mutex};
use std::time::{Duration, Instant};

use bytes::BytesMut;

use bacnet_encoding::apdu::{encode_apdu, Apdu, UnconfirmedRequest as UnconfirmedRequestPdu};
use bacnet_encoding::npdu::NpduAddress;
use bacnet_network::layer::{NetworkLayer, ReceivedApdu};
use bacnet_objects::database::ObjectDatabase;
use bacnet_services::who_has::{WhoHasObject, WhoHasRequest};
use bacnet_services::who_is::{DeviceInstanceRange, IAmRequest, WhoIsRequest};
use bacnet_transport::port::TransportPort;
use bacnet_types::enums::{ErrorClass, ErrorCode, NetworkPriority, UnconfirmedServiceChoice};
use bacnet_types::error::Error;
use bacnet_types::primitives::ObjectIdentifier;
use bacnet_types::MacAddr;
use tokio::sync::RwLock;

use super::{BACnetServer, CommState, ServerConfig};

/// Configuration policy for discovery rate limiting and duplicate suppression.
#[derive(Debug, Clone)]
pub struct DiscoveryPolicy {
    /// Maximum discovery responses emitted globally per second (default 64).
    pub max_responses_per_sec_global: u32,
    /// Maximum discovery response bytes emitted globally per second (default 65,536).
    pub max_bytes_per_sec_global: usize,
    /// Maximum discovery responses emitted per source per second (default 16).
    pub max_responses_per_sec_per_source: u32,
    /// Maximum discovery response bytes emitted per source per second (default 16,384).
    pub max_bytes_per_sec_per_source: usize,
    /// Maximum burst capacity for global discovery responses (default 64).
    pub global_burst_capacity: u32,
    /// Maximum burst capacity for per-source discovery responses (default 16).
    pub source_burst_capacity: u32,
    /// Headroom reserved exclusively for configured reserved sources (default 8).
    pub reserved_capacity: u32,
    /// Sources permitted to consume from reserved capacity.
    pub reserved_sources: Vec<MacAddr>,
    /// Coalescing window for duplicate discovery request suppression (default 200ms).
    pub coalesce_window: Duration,
    /// Prefer directed unicast responses over network broadcast (default true).
    pub prefer_directed_responses: bool,
    /// Maximum number of distinct discovery sources tracked concurrently (default 256).
    pub max_tracked_sources: usize,
}

impl Default for DiscoveryPolicy {
    fn default() -> Self {
        Self {
            max_responses_per_sec_global: 64,
            max_bytes_per_sec_global: 65_536,
            max_responses_per_sec_per_source: 16,
            max_bytes_per_sec_per_source: 16_384,
            global_burst_capacity: 64,
            source_burst_capacity: 16,
            reserved_capacity: 8,
            reserved_sources: Vec::new(),
            coalesce_window: Duration::from_millis(200),
            prefer_directed_responses: true,
            max_tracked_sources: 256,
        }
    }
}

impl DiscoveryPolicy {
    /// Create an unlimited discovery policy with all rate limits disabled.
    pub fn unlimited() -> Self {
        Self {
            max_responses_per_sec_global: u32::MAX,
            max_bytes_per_sec_global: usize::MAX,
            max_responses_per_sec_per_source: u32::MAX,
            max_bytes_per_sec_per_source: usize::MAX,
            global_burst_capacity: u32::MAX,
            source_burst_capacity: u32::MAX,
            reserved_capacity: 0,
            coalesce_window: Duration::ZERO,
            prefer_directed_responses: false,
            ..Default::default()
        }
    }

    /// Return a sanitized copy with valid burst and capacity bounds.
    pub fn sanitized(&self) -> Self {
        let mut policy = self.clone();
        if (1..u32::MAX).contains(&policy.max_responses_per_sec_global) {
            policy.global_burst_capacity = policy.global_burst_capacity.max(1);
        }
        if (1..u32::MAX).contains(&policy.max_responses_per_sec_per_source) {
            policy.source_burst_capacity = policy.source_burst_capacity.max(1);
        }
        policy.reserved_capacity = policy.reserved_capacity.min(policy.global_burst_capacity);
        policy.max_tracked_sources = policy.max_tracked_sources.max(1);
        policy
    }
}

/// Operational counters for discovery requests and responses.
///
/// Non-exhaustive, so a counter can be added without breaking callers: read
/// it from [`BACnetServer::discovery_counters`](crate::server::BACnetServer::discovery_counters)
/// and its fields rather than building one.
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
#[non_exhaustive]
pub struct DiscoveryCounters {
    /// Total Who-Is requests received.
    pub who_is_received: u64,
    /// Total Who-Has requests received.
    pub who_has_received: u64,
    /// Total I-Am responses sent.
    pub i_am_sent: u64,
    /// Total I-Have responses sent.
    pub i_have_sent: u64,
    /// Total response bytes sent for discovery.
    pub response_bytes_sent: u64,
    /// Total duplicate or cached requests coalesced without sending responses.
    pub requests_coalesced: u64,
    /// Responses throttled by per-source rate or burst limits.
    pub responses_throttled_source: u64,
    /// Responses throttled by global rate or reserved capacity limits.
    pub responses_throttled_global: u64,
    /// Total directed unicast discovery responses sent.
    pub directed_responses_sent: u64,
    /// Who-Is and Who-Has requests dropped because they didn't decode, such
    /// as one with a single limit or octets after its last member. They are
    /// dropped before any other work and count in neither received total.
    pub malformed_dropped: u64,
}

#[derive(Debug, Default)]
pub(crate) struct AtomicDiscoveryCounters {
    pub(crate) who_is_received: AtomicU64,
    pub(crate) who_has_received: AtomicU64,
    pub(crate) i_am_sent: AtomicU64,
    pub(crate) i_have_sent: AtomicU64,
    pub(crate) response_bytes_sent: AtomicU64,
    pub(crate) requests_coalesced: AtomicU64,
    pub(crate) responses_throttled_source: AtomicU64,
    pub(crate) responses_throttled_global: AtomicU64,
    pub(crate) directed_responses_sent: AtomicU64,
    pub(crate) malformed_dropped: AtomicU64,
}

impl AtomicDiscoveryCounters {
    pub(crate) fn snapshot(&self) -> DiscoveryCounters {
        DiscoveryCounters {
            who_is_received: self.who_is_received.load(Ordering::Relaxed),
            who_has_received: self.who_has_received.load(Ordering::Relaxed),
            i_am_sent: self.i_am_sent.load(Ordering::Relaxed),
            i_have_sent: self.i_have_sent.load(Ordering::Relaxed),
            response_bytes_sent: self.response_bytes_sent.load(Ordering::Relaxed),
            requests_coalesced: self.requests_coalesced.load(Ordering::Relaxed),
            responses_throttled_source: self.responses_throttled_source.load(Ordering::Relaxed),
            responses_throttled_global: self.responses_throttled_global.load(Ordering::Relaxed),
            directed_responses_sent: self.directed_responses_sent.load(Ordering::Relaxed),
            malformed_dropped: self.malformed_dropped.load(Ordering::Relaxed),
        }
    }

    #[inline]
    pub(crate) fn inc(&self, c: &AtomicU64) {
        c.fetch_add(1, Ordering::Relaxed);
    }

    pub(crate) fn record_sent(&self, bytes: usize, directed: bool, is_who_is: bool) {
        if is_who_is {
            self.i_am_sent.fetch_add(1, Ordering::Relaxed);
        } else {
            self.i_have_sent.fetch_add(1, Ordering::Relaxed);
        }
        self.response_bytes_sent
            .fetch_add(bytes as u64, Ordering::Relaxed);
        if directed {
            self.directed_responses_sent.fetch_add(1, Ordering::Relaxed);
        }
    }
}

/// Target of a Who-Has query.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) enum WhoHasTarget {
    Id(ObjectIdentifier),
    Name(String),
}

/// Network-aware identity of a discovery requester.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) struct SourceKey {
    pub(crate) network: u16,
    pub(crate) mac: MacAddr,
}

impl SourceKey {
    pub(crate) fn from_parts(source_mac: &MacAddr, source_network: Option<&NpduAddress>) -> Self {
        if let Some(net) = source_network {
            if (1..=0xFFFE).contains(&net.network) && !net.mac_address.is_empty() {
                return Self {
                    network: net.network,
                    mac: MacAddr::from_slice(&net.mac_address),
                };
            }
        }
        Self {
            network: 0,
            mac: source_mac.clone(),
        }
    }

    pub(crate) fn from_received(received: &ReceivedApdu) -> Self {
        Self::from_parts(&received.source_mac, received.source_network.as_ref())
    }
}

#[derive(Debug)]
struct SourceState {
    tokens: f64,
    byte_tokens: f64,
    last_refill: Instant,
    last_activity: Instant,
    last_who_is: Option<Instant>,
    last_who_has: HashMap<WhoHasTarget, Instant>,
}

fn refill_bucket(
    tokens: &mut f64,
    byte_tokens: &mut f64,
    last_refill: &mut Instant,
    rate: u32,
    byte_rate: usize,
    burst: u32,
    now: Instant,
) {
    let elapsed = now.saturating_duration_since(*last_refill).as_secs_f64();
    if elapsed > 0.0 {
        *tokens = if rate == u32::MAX {
            burst as f64
        } else {
            (*tokens + elapsed * (rate as f64)).min(burst as f64)
        };
        *byte_tokens = if byte_rate == usize::MAX {
            byte_rate as f64
        } else {
            (*byte_tokens + elapsed * (byte_rate as f64)).min(byte_rate as f64)
        };
        *last_refill = now;
    }
}

impl SourceState {
    fn refill(&mut self, policy: &DiscoveryPolicy, now: Instant) {
        refill_bucket(
            &mut self.tokens,
            &mut self.byte_tokens,
            &mut self.last_refill,
            policy.max_responses_per_sec_per_source,
            policy.max_bytes_per_sec_per_source,
            policy.source_burst_capacity,
            now,
        );
    }

    fn has_capacity(&self, policy: &DiscoveryPolicy, bytes: usize) -> bool {
        (policy.max_responses_per_sec_per_source == u32::MAX || self.tokens >= 1.0)
            && (policy.max_bytes_per_sec_per_source == usize::MAX
                || self.byte_tokens >= bytes as f64)
    }

    fn deduct(&mut self, policy: &DiscoveryPolicy, bytes: usize) {
        if policy.max_responses_per_sec_per_source != u32::MAX {
            self.tokens -= 1.0;
        }
        if policy.max_bytes_per_sec_per_source != usize::MAX {
            self.byte_tokens -= bytes as f64;
        }
    }
}

#[derive(Debug)]
struct DiscoveryState {
    global_tokens: f64,
    global_byte_tokens: f64,
    global_last_refill: Instant,
    last_broadcast_who_is: Option<Instant>,
    last_broadcast_who_has: HashMap<WhoHasTarget, Instant>,
    negative_who_has: HashMap<WhoHasTarget, Instant>,
    sources: HashMap<SourceKey, SourceState>,
}

impl DiscoveryState {
    fn refill_global(&mut self, policy: &DiscoveryPolicy, now: Instant) {
        refill_bucket(
            &mut self.global_tokens,
            &mut self.global_byte_tokens,
            &mut self.global_last_refill,
            policy.max_responses_per_sec_global,
            policy.max_bytes_per_sec_global,
            policy.global_burst_capacity,
            now,
        );
    }

    fn has_global_capacity(
        &self,
        policy: &DiscoveryPolicy,
        is_reserved: bool,
        bytes: usize,
    ) -> bool {
        let count_ok = policy.max_responses_per_sec_global == u32::MAX || {
            let req = if is_reserved {
                1.0
            } else {
                1.0 + policy.reserved_capacity as f64
            };
            self.global_tokens >= req
        };
        count_ok
            && (policy.max_bytes_per_sec_global == usize::MAX
                || self.global_byte_tokens >= bytes as f64)
    }

    fn deduct_global(&mut self, policy: &DiscoveryPolicy, bytes: usize) {
        if policy.max_responses_per_sec_global != u32::MAX {
            self.global_tokens -= 1.0;
        }
        if policy.max_bytes_per_sec_global != usize::MAX {
            self.global_byte_tokens -= bytes as f64;
        }
    }

    fn get_or_create_source_mut(
        &mut self,
        policy: &DiscoveryPolicy,
        key: &SourceKey,
        now: Instant,
    ) -> &mut SourceState {
        if !self.sources.contains_key(key) {
            ensure_source_capacity(self, policy, now);
        }
        let src = self
            .sources
            .entry(key.clone())
            .or_insert_with(|| SourceState {
                tokens: policy.source_burst_capacity as f64,
                byte_tokens: policy.max_bytes_per_sec_per_source as f64,
                last_refill: now,
                last_activity: now,
                last_who_is: None,
                last_who_has: HashMap::new(),
            });
        src.refill(policy, now);
        src
    }

    fn is_coalesced_who_has(
        &self,
        policy: &DiscoveryPolicy,
        target: &WhoHasTarget,
        key: &SourceKey,
        is_broadcast: bool,
        now: Instant,
    ) -> bool {
        if policy.coalesce_window.is_zero() {
            return false;
        }
        let is_recent = |ts: &Instant| now.saturating_duration_since(*ts) < policy.coalesce_window;
        self.negative_who_has.get(target).is_some_and(is_recent)
            || (is_broadcast
                && self
                    .last_broadcast_who_has
                    .get(target)
                    .is_some_and(is_recent))
            || self
                .sources
                .get(key)
                .and_then(|s| s.last_who_has.get(target))
                .is_some_and(is_recent)
    }
}

#[derive(Debug)]
struct AtomicDeviceInstance(AtomicU64);

impl AtomicDeviceInstance {
    const PRESENT_BIT: u64 = 0x1_0000_0000;

    fn new(opt: Option<u32>) -> Self {
        Self(AtomicU64::new(
            opt.map_or(0, |i| Self::PRESENT_BIT | (i as u64)),
        ))
    }

    fn load(&self, order: Ordering) -> Option<u32> {
        let val = self.0.load(order);
        (val & Self::PRESENT_BIT != 0).then_some(val as u32)
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum PreCheckDecision {
    Admit,
    OutOfRange,
    Coalesced,
    ThrottledSource,
    ThrottledGlobal,
    DecodeError,
}

/// Thread-safe rate limiter, duplicate coalescer, and negative query cache.
#[derive(Debug)]
pub(crate) struct DiscoveryLimiter {
    policy: DiscoveryPolicy,
    counters: AtomicDiscoveryCounters,
    device_instance: AtomicDeviceInstance,
    state: Mutex<DiscoveryState>,
}

impl DiscoveryLimiter {
    pub(crate) fn new(policy: DiscoveryPolicy, device_instance: Option<u32>) -> Self {
        let now = Instant::now();
        let state = DiscoveryState {
            global_tokens: policy.global_burst_capacity as f64,
            global_byte_tokens: policy.max_bytes_per_sec_global as f64,
            global_last_refill: now,
            last_broadcast_who_is: None,
            last_broadcast_who_has: HashMap::new(),
            negative_who_has: HashMap::new(),
            sources: HashMap::new(),
        };
        Self {
            policy,
            counters: AtomicDiscoveryCounters::default(),
            device_instance: AtomicDeviceInstance::new(device_instance),
            state: Mutex::new(state),
        }
    }

    pub(crate) fn counters(&self) -> DiscoveryCounters {
        self.counters.snapshot()
    }

    #[allow(dead_code)]
    pub(crate) fn policy(&self) -> &DiscoveryPolicy {
        &self.policy
    }

    #[cfg(test)]
    pub(crate) fn negative_who_has_count(&self) -> usize {
        self.state.lock().unwrap().negative_who_has.len()
    }

    #[cfg(test)]
    pub(crate) fn source_byte_tokens(
        &self,
        source_mac: &MacAddr,
        source_network: Option<&NpduAddress>,
    ) -> Option<f64> {
        let key = SourceKey::from_parts(source_mac, source_network);
        self.state
            .lock()
            .unwrap()
            .sources
            .get(&key)
            .map(|s| s.byte_tokens)
    }

    fn check_instance_in_range(&self, range: Option<DeviceInstanceRange>) -> bool {
        self.device_instance
            .load(Ordering::Acquire)
            .is_some_and(|instance| range.is_none_or(|range| range.contains(instance)))
    }

    pub(crate) fn pre_check_who_is(
        &self,
        req_bytes: &[u8],
        received: &ReceivedApdu,
        now: Instant,
    ) -> PreCheckDecision {
        // RB-07 compat mode: provenance threaded here for RB-09, no decision.
        let _ = received.provenance;
        let who_is = match WhoIsRequest::decode(req_bytes) {
            Ok(w) => w,
            Err(_) => {
                self.counters.inc(&self.counters.malformed_dropped);
                return PreCheckDecision::DecodeError;
            }
        };

        self.counters.inc(&self.counters.who_is_received);

        if !self.check_instance_in_range(who_is.range) {
            return PreCheckDecision::OutOfRange;
        }

        let is_broadcast = received.is_group || received.link_layer_group;
        let source_key = SourceKey::from_received(received);
        let mut state = self.state.lock().unwrap();

        // 1. Coalescing check
        if !self.policy.coalesce_window.is_zero() {
            let is_recent =
                |ts: &Instant| now.saturating_duration_since(*ts) < self.policy.coalesce_window;
            let bcast = is_broadcast && state.last_broadcast_who_is.as_ref().is_some_and(is_recent);
            let src = state
                .sources
                .get(&source_key)
                .and_then(|s| s.last_who_is.as_ref())
                .is_some_and(is_recent);
            if bcast || src {
                self.counters.inc(&self.counters.requests_coalesced);
                return PreCheckDecision::Coalesced;
            }
        }

        // 2. Refill & Rate limits
        state.refill_global(&self.policy, now);
        let is_reserved = is_source_reserved(&self.policy, &source_key, received);
        const ESTIMATED_I_AM_BYTES: usize = 64;

        if !state.has_global_capacity(&self.policy, is_reserved, ESTIMATED_I_AM_BYTES) {
            self.counters.inc(&self.counters.responses_throttled_global);
            return PreCheckDecision::ThrottledGlobal;
        }

        let src = state.get_or_create_source_mut(&self.policy, &source_key, now);
        if !src.has_capacity(&self.policy, ESTIMATED_I_AM_BYTES) {
            self.counters.inc(&self.counters.responses_throttled_source);
            return PreCheckDecision::ThrottledSource;
        }

        src.deduct(&self.policy, ESTIMATED_I_AM_BYTES);
        src.last_activity = now;
        src.last_who_is = Some(now);
        state.deduct_global(&self.policy, ESTIMATED_I_AM_BYTES);
        if is_broadcast && !self.policy.prefer_directed_responses {
            state.last_broadcast_who_is = Some(now);
        }

        PreCheckDecision::Admit
    }

    pub(crate) fn record_i_am_sent(
        &self,
        actual_bytes: usize,
        directed: bool,
        source_mac: &MacAddr,
        source_network: Option<&NpduAddress>,
        now: Instant,
    ) {
        self.counters.record_sent(actual_bytes, directed, true);

        const ESTIMATED_I_AM_BYTES: usize = 64;
        let delta = (actual_bytes as f64) - (ESTIMATED_I_AM_BYTES as f64);
        let mut state = self.state.lock().unwrap();
        if delta != 0.0 {
            if self.policy.max_bytes_per_sec_global != usize::MAX {
                state.global_byte_tokens = (state.global_byte_tokens - delta).max(0.0);
            }
            let key = SourceKey::from_parts(source_mac, source_network);
            if let Some(src) = state.sources.get_mut(&key) {
                if self.policy.max_bytes_per_sec_per_source != usize::MAX {
                    src.byte_tokens = (src.byte_tokens - delta).max(0.0);
                }
            }
        }
        if !directed {
            state.last_broadcast_who_is = Some(now);
        }
    }

    pub(crate) fn pre_check_who_has(
        &self,
        req_bytes: &[u8],
        received: &ReceivedApdu,
        now: Instant,
    ) -> PreCheckDecision {
        // RB-07 compat mode: provenance threaded here for RB-09, no decision.
        let _ = received.provenance;
        let who_has = match WhoHasRequest::decode(req_bytes) {
            Ok(w) => w,
            Err(_) => {
                self.counters.inc(&self.counters.malformed_dropped);
                return PreCheckDecision::DecodeError;
            }
        };

        self.counters.inc(&self.counters.who_has_received);

        if !self.check_instance_in_range(who_has.range) {
            return PreCheckDecision::OutOfRange;
        }

        let target = match who_has.object {
            WhoHasObject::Identifier(oid) => WhoHasTarget::Id(oid),
            WhoHasObject::Name(name) => WhoHasTarget::Name(name),
        };

        let is_broadcast = received.is_group || received.link_layer_group;
        let source_key = SourceKey::from_received(received);
        let mut state = self.state.lock().unwrap();

        if state.is_coalesced_who_has(&self.policy, &target, &source_key, is_broadcast, now) {
            self.counters.inc(&self.counters.requests_coalesced);
            return PreCheckDecision::Coalesced;
        }

        state.refill_global(&self.policy, now);
        let is_reserved = is_source_reserved(&self.policy, &source_key, received);
        const ESTIMATED_I_HAVE_BYTES: usize = 64;

        if !state.has_global_capacity(&self.policy, is_reserved, ESTIMATED_I_HAVE_BYTES) {
            self.counters.inc(&self.counters.responses_throttled_global);
            return PreCheckDecision::ThrottledGlobal;
        }

        let src = state.get_or_create_source_mut(&self.policy, &source_key, now);
        if !src.has_capacity(&self.policy, ESTIMATED_I_HAVE_BYTES) {
            self.counters.inc(&self.counters.responses_throttled_source);
            return PreCheckDecision::ThrottledSource;
        }

        src.last_activity = now;
        PreCheckDecision::Admit
    }

    pub(crate) fn is_negative_who_has(&self, target: &WhoHasTarget, now: Instant) -> bool {
        if self.policy.coalesce_window.is_zero() {
            return false;
        }
        let state = self.state.lock().unwrap();
        if let Some(ts) = state.negative_who_has.get(target) {
            now.saturating_duration_since(*ts) < self.policy.coalesce_window
        } else {
            false
        }
    }

    pub(crate) fn record_negative_who_has(&self, target: WhoHasTarget, now: Instant) {
        const MAX_NEGATIVE_WHO_HAS: usize = 512;
        let mut state = self.state.lock().unwrap();
        if state.negative_who_has.len() >= MAX_NEGATIVE_WHO_HAS {
            let window = self.policy.coalesce_window;
            state
                .negative_who_has
                .retain(|_, ts| now.saturating_duration_since(*ts) < window);
        }
        while state.negative_who_has.len() >= MAX_NEGATIVE_WHO_HAS {
            let Some(oldest) = state
                .negative_who_has
                .iter()
                .min_by_key(|(_, ts)| *ts)
                .map(|(k, _)| k.clone())
            else {
                break;
            };
            state.negative_who_has.remove(&oldest);
        }
        state.negative_who_has.insert(target, now);
    }

    pub(crate) fn try_consume_who_has_response(
        &self,
        target: &WhoHasTarget,
        received: &ReceivedApdu,
        response_bytes: usize,
        now: Instant,
    ) -> bool {
        let source_key = SourceKey::from_received(received);
        let mut state = self.state.lock().unwrap();
        let is_broadcast = received.is_group || received.link_layer_group;

        if state.is_coalesced_who_has(&self.policy, target, &source_key, is_broadcast, now) {
            self.counters.inc(&self.counters.requests_coalesced);
            return false;
        }

        state.refill_global(&self.policy, now);
        let is_reserved = is_source_reserved(&self.policy, &source_key, received);

        if !state.has_global_capacity(&self.policy, is_reserved, response_bytes) {
            self.counters.inc(&self.counters.responses_throttled_global);
            return false;
        }

        let src = state.get_or_create_source_mut(&self.policy, &source_key, now);
        if !src.has_capacity(&self.policy, response_bytes) {
            self.counters.inc(&self.counters.responses_throttled_source);
            return false;
        }

        src.deduct(&self.policy, response_bytes);
        src.last_activity = now;
        src.last_who_has.insert(target.clone(), now);
        state.deduct_global(&self.policy, response_bytes);
        if is_broadcast && !self.policy.prefer_directed_responses {
            state.last_broadcast_who_has.insert(target.clone(), now);
        }

        true
    }

    pub(crate) fn record_i_have_sent(
        &self,
        actual_bytes: usize,
        directed: bool,
        target: &WhoHasTarget,
        _source_mac: &MacAddr,
        _source_network: Option<&NpduAddress>,
        now: Instant,
    ) {
        self.counters.record_sent(actual_bytes, directed, false);

        if !directed {
            let mut state = self.state.lock().unwrap();
            state.last_broadcast_who_has.insert(target.clone(), now);
        }
    }
}

fn is_source_reserved(policy: &DiscoveryPolicy, key: &SourceKey, recv: &ReceivedApdu) -> bool {
    policy
        .reserved_sources
        .iter()
        .any(|r| r == &key.mac || r == &recv.source_mac)
}

fn ensure_source_capacity(state: &mut DiscoveryState, policy: &DiscoveryPolicy, now: Instant) {
    if state.sources.len() < policy.max_tracked_sources {
        return;
    }
    state.sources.retain(|_, src| {
        now.saturating_duration_since(src.last_activity) < Duration::from_secs(10)
    });
    while state.sources.len() >= policy.max_tracked_sources {
        let Some(key) = state
            .sources
            .iter()
            .min_by_key(|(_, src)| src.last_activity)
            .map(|(k, _)| k.clone())
        else {
            break;
        };
        state.sources.remove(&key);
    }
}

/// Broadcast this device's I-Am unless DeviceCommunicationControl restricts
/// initiation. Clause 16.1.2 exempts only an I-Am answering a Who-Is, so an
/// announcement made under DISABLE_INITIATION sends nothing and fails with
/// `SERVICES` / `COMMUNICATION_DISABLED`, the code Clause 18.6 keeps for local
/// work that could not initiate a service for that reason.
pub(crate) async fn broadcast_i_am_from<T: TransportPort + 'static>(
    config: &ServerConfig,
    db: &Arc<RwLock<ObjectDatabase>>,
    network: &Arc<NetworkLayer<T>>,
    comm_state: &CommState,
    limiter: Option<&Arc<DiscoveryLimiter>>,
) -> Result<(), Error> {
    let guard = db.read().await;
    let device_oid =
        crate::local_device::validate_apdu_declaration(&guard, config.max_apdu_length)?
            .ok_or_else(|| Error::Encoding("no Device object in database".into()))?;

    // RB-16 alignment: this construction is field-for-field identical to
    // `bacnet-endpoint`'s `DeviceIdentity::iam_request` built from
    // `DeviceIdentity::server_config`. The endpoint session I-Am path encodes
    // the same four fields (object id + max-apdu + segmentation + vendor) so
    // I-Am vs Device ReadProperty vs role limits agree on one identity.
    let mut service_buf = BytesMut::new();
    iam_request_for(device_oid, config).encode(&mut service_buf);

    let mut buf = BytesMut::new();
    encode_apdu(
        &mut buf,
        &Apdu::UnconfirmedRequest(UnconfirmedRequestPdu {
            service_choice: UnconfirmedServiceChoice::I_AM,
            service_request: service_buf.freeze(),
        }),
    )?;

    drop(guard);
    if comm_state.initiation_restricted() {
        return Err(Error::Protocol {
            class: ErrorClass::SERVICES.to_raw() as u32,
            code: ErrorCode::COMMUNICATION_DISABLED.to_raw() as u32,
        });
    }
    if let Some(limiter) = limiter {
        limiter.record_i_am_sent(buf.len(), false, &MacAddr::new(), None, Instant::now());
    }

    network
        .broadcast_apdu(&buf, false, NetworkPriority::NORMAL)
        .await
}

/// RB-16 discovery-alignment helper: single I-Am construction shared with the
/// endpoint identity path.
///
/// `bacnet-endpoint`'s `DeviceIdentity::iam_request` (via
/// `DeviceIdentity::server_config`) builds these same four fields; any drift
/// here breaks the I-Am ≡ ReadProperty ≡ role-capabilities matrix.
#[doc(hidden)]
pub fn iam_request_for(device_oid: ObjectIdentifier, config: &ServerConfig) -> IAmRequest {
    IAmRequest {
        object_identifier: device_oid,
        max_apdu_length: config.max_apdu_length,
        segmentation_supported: config.segmentation_supported,
        vendor_id: config.vendor_id,
    }
}

impl<T: TransportPort + 'static> BACnetServer<T> {
    /// Broadcast I-Am through this server's bounded local-send owner.
    /// Cancelling the waiter leaves admitted work owned until completion or stop.
    /// While DeviceCommunicationControl restricts initiation nothing is sent
    /// and this fails with `SERVICES` / `COMMUNICATION_DISABLED` (Clause 16.1).
    pub async fn broadcast_i_am(&self) -> Result<(), Error> {
        self.broadcaster
            .send(Some(Arc::clone(&self.discovery_limiter)))
            .await
    }
}