Add `proptest` dependency

3 files changed, 117 insertions, 7 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 070d7c9c1a..cb8c92e08b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -290,6 +290,21 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8c3c1a368f70d6cf7302d78f8f7093da241fb8e8807c05cc9e51a125895a6d5b"
 
 [[package]]
+name = "bit-set"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0700ddab506f33b20a03b13996eccd309a48e5ff77d0d95926aa0210fb4e95f1"
+dependencies = [
+ "bit-vec",
+]
+
+[[package]]
+name = "bit-vec"
+version = "0.6.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "349f9b6a179ed607305526ca489b34ad0a41aed5f7980fa90eb03160b69598fb"
+
+[[package]]
 name = "bitflags"
 version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1636,6 +1651,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "libm"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ec2a862134d2a7d32d7983ddcdd1c4923530833c9f2ea1a44fc5fa473989058"
+
+[[package]]
 name = "linked-hash-map"
 version = "0.5.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2226,6 +2247,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f30b0abd723be7e2ffca1272140fac1a2f084c77ec3e123c192b66af1ee9e6c2"
 dependencies = [
  "autocfg",
+ "libm",
 ]
 
 [[package]]
@@ -2671,6 +2693,26 @@ dependencies = [
 ]
 
 [[package]]
+name = "proptest"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "31b476131c3c86cb68032fdc5cb6d5a1045e3e42d96b69fa599fd77701e1f5bf"
+dependencies = [
+ "bit-set",
+ "bit-vec",
+ "bitflags 2.4.0",
+ "lazy_static",
+ "num-traits",
+ "rand 0.8.5",
+ "rand_chacha 0.3.1",
+ "rand_xorshift",
+ "regex-syntax 0.8.2",
+ "rusty-fork",
+ "tempfile",
+ "unarray",
+]
+
+[[package]]
 name = "prost"
 version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2841,6 +2883,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "rand_xorshift"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d25bf25ec5ae4a3f1b92f929810509a2f53d7dca2f50b794ff57e3face536c8f"
+dependencies = [
+ "rand_core 0.6.4",
+]
+
+[[package]]
 name = "redox_syscall"
 version = "0.2.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -2878,7 +2929,7 @@ dependencies = [
  "aho-corasick",
  "memchr",
  "regex-automata",
- "regex-syntax",
+ "regex-syntax 0.7.5",
 ]
 
 [[package]]
@@ -2889,7 +2940,7 @@ checksum = "c2f401f4955220693b56f8ec66ee9c78abffd8d1c4f23dc41a23839eb88f0795"
 dependencies = [
  "aho-corasick",
  "memchr",
- "regex-syntax",
+ "regex-syntax 0.7.5",
 ]
 
 [[package]]
@@ -2899,6 +2950,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dbb5fb1acd8a1a18b3dd5be62d25485eb770e05afb408a9627d14d451bae12da"
 
 [[package]]
+name = "regex-syntax"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c08c74e62047bb2de4ff487b251e4a92e24f48745648451635cec7d591162d9f"
+
+[[package]]
 name = "resolv-conf"
 version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -3029,6 +3086,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7ffc183a10b4478d04cbbbfc96d0873219d962dd5accaff2ffbd4ceb7df837f4"
 
 [[package]]
+name = "rusty-fork"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb3dcc6e454c328bb824492db107ab7c0ae8fcffe4ad210136ef014458c1bc4f"
+dependencies = [
+ "fnv",
+ "quick-error",
+ "tempfile",
+ "wait-timeout",
+]
+
+[[package]]
 name = "ryu"
 version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -3726,6 +3795,7 @@ dependencies = [
  "nix 0.23.2",
  "once_cell",
  "parking_lot",
+ "proptest",
  "rand 0.8.5",
  "rtnetlink",
  "socket2 0.5.3",
@@ -4223,6 +4293,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "unarray"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eaea85b334db583fe3274d12b4cd1880032beab409c0d774be044d4480ab9a94"
+
+[[package]]
 name = "unicode-bidi"
 version = "0.3.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -4300,6 +4376,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
 
 [[package]]
+name = "wait-timeout"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f200f5b12eb75f8c1ed65abd4b2db8a6e1b138a20de009dacee265a2498f3f6"
+dependencies = [
+ "libc",
+]
+
+[[package]]
 name = "walkdir"
 version = "2.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/talpid-wireguard/Cargo.toml b/talpid-wireguard/Cargo.toml
index c6f3669f8b..d28ccca2ae 100644
--- a/talpid-wireguard/Cargo.toml
+++ b/talpid-wireguard/Cargo.toml
@@ -79,3 +79,6 @@ features = [
     "Win32_UI_Shell",
     "Win32_UI_WindowsAndMessaging",
 ]
+
+[dev-dependencies]
+proptest = "1.4"
diff --git a/talpid-wireguard/src/lib.rs b/talpid-wireguard/src/lib.rs
index 0875ad0a49..09a0fc929a 100644
--- a/talpid-wireguard/src/lib.rs
+++ b/talpid-wireguard/src/lib.rs
@@ -1070,18 +1070,40 @@ async fn auto_mtu_detection(
 /// points.
 #[cfg(target_os = "linux")]
 fn mtu_spacing(mtu_min: u16, mtu_max: u16, step_size: u16) -> Vec<u16> {
-    if mtu_min > mtu_max {
-        panic!("Invalid MTU detection range: `mtu_min`={mtu_min}, `mtu_max`={mtu_max}.");
-    }
-    let second_mtu = mtu_min.next_multiple_of(step_size);
+    assert!(mtu_min < mtu_max);
+    assert!(step_size < mtu_max);
+    assert_ne!(step_size, 0);
+
+    let second_mtu = (mtu_min + 1).next_multiple_of(step_size);
     let in_between = (second_mtu..mtu_max).step_by(step_size as usize);
-    let mut ret = Vec::with_capacity(((mtu_max - second_mtu).div_ceil(step_size) + 2) as usize);
+
+    let mut ret = Vec::with_capacity(in_between.clone().count() + 2);
     ret.push(mtu_min);
     ret.extend(in_between);
     ret.push(mtu_max);
     ret
 }
 
+#[cfg(all(test, target_os = "linux"))]
+mod tests {
+    use crate::mtu_spacing;
+    use proptest::prelude::*;
+
+    proptest! {
+        #[test]
+        fn test_mtu_spacing(mtu_min in 0..800u16, mtu_max in 800..2000u16, step_size in 1..800u16)  {
+            let mtu_spacing = mtu_spacing(mtu_min, mtu_max, step_size);
+
+            prop_assert_eq!(mtu_spacing.iter().filter(|mtu| mtu == &&mtu_min).count(), 1);
+            prop_assert_eq!(mtu_spacing.iter().filter(|mtu| mtu == &&mtu_max).count(), 1);
+            prop_assert_eq!(mtu_spacing.capacity(), mtu_spacing.len());
+            let mut diffs = mtu_spacing.windows(2).map(|win| win[1]-win[0]);
+            prop_assert!(diffs.all(|diff| diff <= step_size));
+
+        }
+    }
+}
+
 #[derive(Debug)]
 enum CloseMsg {
     Stop,