tai64n: make the test deterministic

In the presence of preemption, the current test may fail transiently.
This uses static test data instead to ensure consistent behavior.

Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>

diff --git a/tai64n/tai64n.go b/tai64n/tai64n.go
index fb32d0c6c89d8bde2acf0b42bb413f05db1c207d..2838f4fa120bf838a71dd03a3e3d0218476e0250 100644 (file)
--- a/tai64n/tai64n.go
+++ b/tai64n/tai64n.go
@@ -17,16 +17,19 @@ const whitenerMask = uint32(0x1000000 - 1)
 
 type Timestamp [TimestampSize]byte
 
-func Now() Timestamp {
+func stamp(t time.Time) Timestamp {
        var tai64n Timestamp
-       now := time.Now()
-       secs := base + uint64(now.Unix())
-       nano := uint32(now.Nanosecond()) &^ whitenerMask
+       secs := base + uint64(t.Unix())
+       nano := uint32(t.Nanosecond()) &^ whitenerMask
        binary.BigEndian.PutUint64(tai64n[:], secs)
        binary.BigEndian.PutUint32(tai64n[8:], nano)
        return tai64n
 }
 
+func Now() Timestamp {
+       return stamp(time.Now())
+}
+
 func (t1 Timestamp) After(t2 Timestamp) bool {
        return bytes.Compare(t1[:], t2[:]) > 0
 }

diff --git a/tai64n/tai64n_test.go b/tai64n/tai64n_test.go
index 05a9d8fd952578548f903670a2bfd95b0fc1fbf0..6df73671c32e0a0f5f3fd2677473cee99f76fd0e 100644 (file)
--- a/tai64n/tai64n_test.go
+++ b/tai64n/tai64n_test.go
@@ -10,21 +10,31 @@ import (
        "time"
 )
 
-/* Testing the essential property of the timestamp
- * as used by WireGuard.
- */
+// Test that timestamps are monotonic as required by Wireguard and that
+// nanosecond-level information is whitened to prevent side channel attacks.
 func TestMonotonic(t *testing.T) {
-       old := Now()
-       for i := 0; i < 50; i++ {
-               next := Now()
-               if next.After(old) {
-                       t.Error("Whitening insufficient")
-               }
-               time.Sleep(time.Duration(whitenerMask)/time.Nanosecond + 1)
-               next = Now()
-               if !next.After(old) {
-                       t.Error("Not monotonically increasing on whitened nano-second scale")
-               }
-               old = next
+       startTime := time.Unix(0, 123456789) // a nontrivial bit pattern
+       // Whitening should reduce timestamp granularity
+       // to more than 10 but fewer than 20 milliseconds.
+       tests := []struct {
+               name      string
+               t1, t2    time.Time
+               wantAfter bool
+       }{
+               {"after_10_ns", startTime, startTime.Add(10 * time.Nanosecond), false},
+               {"after_10_us", startTime, startTime.Add(10 * time.Microsecond), false},
+               {"after_1_ms", startTime, startTime.Add(time.Millisecond), false},
+               {"after_10_ms", startTime, startTime.Add(10 * time.Millisecond), false},
+               {"after_20_ms", startTime, startTime.Add(20 * time.Millisecond), true},
+       }
+
+       for _, tt := range tests {
+               t.Run(tt.name, func(t *testing.T) {
+                       ts1, ts2 := stamp(tt.t1), stamp(tt.t2)
+                       got := ts2.After(ts1)
+                       if got != tt.wantAfter {
+                               t.Errorf("after = %v; want %v", got, tt.wantAfter)
+                       }
+               })
        }
 }