util/ringbuffer: move generic ringbuffer from corp repo

Also add some basic tests for this implementation.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I307ebb6db91d0c172657befb276b38ccb638f828

1 files changed, 55 insertions, 0 deletions

diff --git a/util/ringbuffer/ringbuffer_test.go b/util/ringbuffer/ringbuffer_test.go
new file mode 100644
index 000000000..fae3f5328
--- /dev/null
+++ b/util/ringbuffer/ringbuffer_test.go
@@ -0,0 +1,55 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package ringbuffer
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestRingBuffer(t *testing.T) {
+	const numItems = 10
+	rb := New[int](numItems)
+
+	for i := 0; i < numItems-1; i++ {
+		rb.Add(i)
+	}
+
+	t.Run("NotFull", func(t *testing.T) {
+		if ll := rb.Len(); ll != numItems-1 {
+			t.Fatalf("got len %d; want %d", ll, numItems-1)
+		}
+		all := rb.GetAll()
+		want := []int{0, 1, 2, 3, 4, 5, 6, 7, 8}
+		if !reflect.DeepEqual(all, want) {
+			t.Fatalf("items mismatch\ngot: %v\nwant %v", all, want)
+		}
+	})
+
+	t.Run("Full", func(t *testing.T) {
+		// Append items to evict something
+		rb.Add(98)
+		rb.Add(99)
+
+		if ll := rb.Len(); ll != numItems {
+			t.Fatalf("got len %d; want %d", ll, numItems)
+		}
+		all := rb.GetAll()
+		want := []int{1, 2, 3, 4, 5, 6, 7, 8, 98, 99}
+		if !reflect.DeepEqual(all, want) {
+			t.Fatalf("items mismatch\ngot: %v\nwant %v", all, want)
+		}
+	})
+
+	t.Run("Clear", func(t *testing.T) {
+		rb.Clear()
+		if ll := rb.Len(); ll != 0 {
+			t.Fatalf("got len %d; want 0", ll)
+		}
+		all := rb.GetAll()
+		if len(all) != 0 {
+			t.Fatalf("got non-empty list; want empty")
+		}
+	})
+}