1 files changed, 75 insertions, 0 deletions
diff --git a/third_party/rust/neqo-transport/tests/sim/drop.rs b/third_party/rust/neqo-transport/tests/sim/drop.rs
new file mode 100644
index 0000000000..629fbf48d3
--- /dev/null
+++ b/third_party/rust/neqo-transport/tests/sim/drop.rs
@@ -0,0 +1,75 @@
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![allow(clippy::module_name_repetitions)]
+
+use std::{
+    fmt::{self, Debug},
+    time::Instant,
+};
+
+use neqo_common::{qtrace, Datagram};
+use neqo_transport::Output;
+
+use super::{Node, Rng};
+
+/// A random dropper.
+pub struct Drop {
+    threshold: u64,
+    max: u64,
+    rng: Option<Rng>,
+}
+
+impl Drop {
+    /// Make a new random drop generator.  Each `drop` is called, this generates a
+    /// random value between 0 and `max` (exclusive).  If this value is less than
+    /// `threshold` a value of `true` is returned.
+    pub fn new(threshold: u64, max: u64) -> Self {
+        Self {
+            threshold,
+            max,
+            rng: None,
+        }
+    }
+
+    /// Generate random drops with the given percentage.
+    pub fn percentage(pct: u8) -> Self {
+        // Multiply by 10 so that the random number generator works more efficiently.
+        Self::new(u64::from(pct) * 10, 1000)
+    }
+
+    pub fn drop(&mut self) -> bool {
+        let mut rng = self.rng.as_ref().unwrap().borrow_mut();
+        let r = rng.random_from(0..self.max);
+        r < self.threshold
+    }
+}
+
+impl Node for Drop {
+    fn init(&mut self, rng: Rng, _now: Instant) {
+        self.rng = Some(rng);
+    }
+
+    // Pass any datagram provided directly out, but drop some of them.
+    fn process(&mut self, d: Option<Datagram>, _now: Instant) -> Output {
+        if let Some(dgram) = d {
+            if self.drop() {
+                qtrace!("drop {}", dgram.len());
+                Output::None
+            } else {
+                Output::Datagram(dgram)
+            }
+        } else {
+            Output::None
+        }
+    }
+}
+
+impl Debug for Drop {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("drop")
+    }
+}