From 1d6ac83848c23e5580baefbb927e9d9bb8482d39 Mon Sep 17 00:00:00 2001
From: Ben Schofield <me@benjscho.dev>
Date: Sat, 4 Nov 2023 13:29:26 -0700
Subject: [PATCH] Fix subtraction overflow bug with latency

Previously if you specify a `min_message_latency` greater than the default
`max_message_latency`, the test would fail with a tokio error: `overflow
when subtracting durations`. This change updates the builder to assert
that the min/max latencies are valid on build.
---
 src/builder.rs | 32 ++++++++++++++++++++++----------
 src/top.rs     |  2 ++
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/src/builder.rs b/src/builder.rs
index 70b64e4..6986741 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -64,20 +64,12 @@ impl Builder {
     }
 
     pub fn min_message_latency(&mut self, value: Duration) -> &mut Self {
-        self.link
-            .latency
-            .as_mut()
-            .expect("`Latency` missing")
-            .min_message_latency = value;
+        self.link.latency_mut().min_message_latency = value;
         self
     }
 
     pub fn max_message_latency(&mut self, value: Duration) -> &mut Self {
-        self.link
-            .latency
-            .as_mut()
-            .expect("`MessageLoss` missing")
-            .max_message_latency = value;
+        self.link.latency_mut().max_message_latency = value;
         self
     }
 
@@ -106,7 +98,27 @@ impl Builder {
     }
 
     pub fn build_with_rng<'a>(&self, rng: Box<dyn RngCore>) -> Sim<'a> {
+        if self.link.latency().max_message_latency < self.link.latency().min_message_latency {
+            panic!("Maximum message latency must be greater than minimum.");
+        }
+
         let world = World::new(self.link.clone(), rng, self.ip_version.iter());
         Sim::new(self.config.clone(), world)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use crate::Builder;
+
+    #[test]
+    #[should_panic]
+    fn invalid_latency() {
+        let _sim = Builder::new()
+            .min_message_latency(Duration::from_millis(100))
+            .max_message_latency(Duration::from_millis(50))
+            .build();
+    }
+}
diff --git a/src/top.rs b/src/top.rs
index 4e08b7a..facf2c6 100644
--- a/src/top.rs
+++ b/src/top.rs
@@ -149,6 +149,7 @@ struct Link {
     now: Instant,
 }
 
+/// States that a link between two nodes can be in.
 enum State {
     /// The link is healthy.
     Healthy,
@@ -268,6 +269,7 @@ impl Topology {
     }
 }
 
+/// Represents a message sent between two hosts on the network.
 struct Sent {
     src: SocketAddr,
     dst: SocketAddr,