Weighted Fairness + 3-Leveled Pressure Model

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

src/transport/middle_proxy/tests/fairness_security_tests.rs

@@ -2,6 +2,7 @@ use std::time::{Duration, Instant};
 
 use bytes::Bytes;
 
+use crate::protocol::constants::RPC_FLAG_QUICKACK;
 use crate::transport::middle_proxy::fairness::{
     AdmissionDecision, DispatchAction, DispatchFeedback, PressureState, SchedulerDecision,
     WorkerFairnessConfig, WorkerFairnessState,
@@ -114,6 +115,62 @@ fn fairness_keeps_fast_flow_progress_under_slow_neighbor() {
     assert!(snapshot.total_queued_bytes <= 64 * 1024);
 }
 
+#[test]
+fn fairness_prioritizes_quickack_flow_when_weights_enabled() {
+    let mut now = Instant::now();
+    let mut fairness = WorkerFairnessState::new(
+        WorkerFairnessConfig {
+            max_total_queued_bytes: 256 * 1024,
+            max_flow_queued_bytes: 64 * 1024,
+            base_quantum_bytes: 8 * 1024,
+            pressured_quantum_bytes: 8 * 1024,
+            penalized_quantum_bytes: 8 * 1024,
+            default_flow_weight: 1,
+            quickack_flow_weight: 4,
+            ..WorkerFairnessConfig::default()
+        },
+        now,
+    );
+
+    for _ in 0..8 {
+        assert_eq!(
+            fairness.enqueue_data(10, RPC_FLAG_QUICKACK, enqueue_payload(16 * 1024), now),
+            AdmissionDecision::Admit
+        );
+        assert_eq!(
+            fairness.enqueue_data(20, 0, enqueue_payload(16 * 1024), now),
+            AdmissionDecision::Admit
+        );
+    }
+
+    let mut quickack_dispatched = 0u64;
+    let mut bulk_dispatched = 0u64;
+    for _ in 0..64 {
+        now += Duration::from_millis(1);
+        let SchedulerDecision::Dispatch(candidate) = fairness.next_decision(now) else {
+            break;
+        };
+
+        if candidate.frame.conn_id == 10 {
+            quickack_dispatched = quickack_dispatched.saturating_add(1);
+        } else if candidate.frame.conn_id == 20 {
+            bulk_dispatched = bulk_dispatched.saturating_add(1);
+        }
+
+        let _ = fairness.apply_dispatch_feedback(
+            candidate.frame.conn_id,
+            candidate,
+            DispatchFeedback::Routed,
+            now,
+        );
+    }
+
+    assert!(
+        quickack_dispatched > bulk_dispatched,
+        "quickack flow must receive higher dispatch rate with larger weight"
+    );
+}
+
 #[test]
 fn fairness_pressure_hysteresis_prevents_instant_flapping() {
     let mut now = Instant::now();