[p4, sidecar] fix underlay/external mcast counter ops

dpd-client/tests/integration_tests/common.rs

@@ -45,6 +45,13 @@ pub const ADMIN_LOCAL_MULTICAST_PREFIX: u16 = 0xFF04;
 // packets before notifying us that any are ready.
 const TEST_PCAP_TIMEOUT_MS: i32 = 1;
 
+// Interval and attempt count for polling a counter until it reaches an
+// expected value.
+//
+// Note: counter updates from the model can lag the packet itself.
+const COUNTER_POLL_INTERVAL: Duration = Duration::from_millis(100);
+const COUNTER_POLL_ATTEMPTS: usize = 20;
+
 // Physical port number
 #[derive(Clone, Copy, PartialOrd, Ord, Hash, PartialEq, Eq)]
 pub struct PhysPort(pub u16);
@@ -827,6 +834,35 @@ impl Switch {
     }
 }
 
+pub async fn check_counter_incremented(
+    switch: &Switch,
+    counter_name: &str,
+    baseline: u64,
+    expected_increment: u64,
+    client_name: Option<&str>,
+) -> anyhow::Result<u64> {
+    let expected = baseline + expected_increment;
+    let mut new_value = 0;
+
+    // Poll for the counter value (with timeout)
+    for _i in 0..COUNTER_POLL_ATTEMPTS {
+        thread::sleep(COUNTER_POLL_INTERVAL);
+        new_value =
+            switch.get_counter(counter_name, client_name).await.unwrap();
+
+        if new_value == expected {
+            return Ok(new_value);
+        }
+    }
+
+    // Counter didn't increment as expected
+    Err(anyhow!(
+        "Counter '{counter_name}' expected to increase by \
+         {expected_increment} (from {baseline} to {expected}), but only \
+         reached {new_value}"
+    ))
+}
+
 // Construct a single TCP packet with an optional payload
 pub fn gen_tcp_packet_loaded(
     src: Endpoint,
@@ -1444,5 +1480,6 @@ pub mod prelude {
     pub use super::Switch;
     pub use super::TestPacket;
     pub use super::TestResult;
+    pub use super::check_counter_incremented;
     pub use super::get_switch;
 }